Class 10 Disaster Management All Chapters Summary / Short Summary

Disaster Management

A disaster is a destructive event that occurs suddenly and involves loss of life and property. Disasters can be of two types, natural and man-made.

Earthquakes, volcanic activity, tsunamis, floods, cyclones, landslides, avalanches and droughts are natural disasters. Some of the man-made disasters are: bomb explosions, terrorism, war or civil war, leakage of poisonous chemicals, breach in dams, air or water pollution, industrial accidents and epidemics.

Disaster Management refers to the measures taken for the safety and protection of life and property from natural or man-made disasters.

This means being prepared for disasters, fighting disasters effectively, ensuring the safety of life during disasters and helping in rebuilding society after the disaster.

Earthquakes

An earthquake is a sudden tremor or movement of the earth's crust, originating at or below the surface. The outer layer of the earth is solid and is divided into many sections known as plates on which all the continents stand.

The plates float over the molten magma flowing beneath the earth’s crust, moving slowly. Sometimes, during the course of their movements, these plates move against each other. Earthquakes occur on the edges of these plates along fault lines where the plates collide or try to slide past each other.

Earthquakes are also caused by explosive volcanic eruptions. There are other man-made causes of earthquakes like vibrations caused by big rocks falling down hills because of erosion, hollow parts of mines falling down due to dissolution of minerals by water and due to nuclear explosions.

The point of origin of the earthquake within the crust or mantle is called the seismic focus. The location of the earthquake is referred to as the point on the surface of the earth, vertically above the seismic focus called the epicentre.

The extent of damage that an earthquake can cause depends on its magnitude. Earthquakes can be measured with a device called the seismometer; a device which also records is known as a seismograph.

The magnitude of the earthquake is measured through an instrument called ‘Richter Scale’.
The under-sea earthquakes, give rise to giant waves called the tsunami, which cause great deal of destruction along the coasts.

Two thirds of all the earthquakes occur in the ‘Ring of Fire’ in the Pacific Ocean. Kashmir, western Himalayas, middle Himalayas, northeast India, the plains of the Ganga and Indus, Rajasthan, Gujarat, Lakshadweep, Andaman and Nicobar Islands are the earthquake- prone regions in India.

Measures for preparing against earthquakes:

In absence of an early warning system, the information about earthquakes and their intensity should be shared with the public through radio, television and newspapers.

Buildings must be based on earthquake-resistant techniques and all under-construction houses should be made to follow the building guidelines.

Buildings to be constructed over concrete and iron pillars built deep in the ground.

In emergency, water, ration, first-aid kits, radios, flash lights, battery, blankets, jackets and fire extinguishers should be stored in safe places.

To do things when an earthquake strikes:

Remain calm

Take cover under a solid surface like a table, or stand in the doorway if inside building or house

Move to an open space away from trees, electric poles and buildings if outside

Switch off the gas and electric supply in the house during a quake and don not use elevators.

After the quake the affected people should be given immediate medical help and vaccinated to stop

epidemics from spreading.

Transport and communication facilities should be restored as soon as possible so that rescue teams can reach the earthquake-hit area.

Police and paramilitary forces should be deployed to protect properties which had to be abandoned from theft.

Volcanoes, Tsunamis and Cyclones

Volcano eruptions happen when the molten rocks or lava in the earth’s crust come out along with gases and steam flow on the earth’s surface.

There are three types of volcanoes: active, dormant and extinct. The active volcanoes erupt from time to time. The dormant volcanoes were active in the past, though they have not shown any activities for a long time. The extinct volcanoes do not have any recorded history of being active. Most of the volcanoes are found in the Ring of Fire in the Pacific Ocean.

Earthquakes and volcanic eruptions cause a sudden disturbance at the base of the ocean, causing abrupt displacement of water. Such activities produce very high waves which are called Tsunamis. Even though tsunamis or big earthquakes cannot be precisely predicted, there are automated early warning systems that can provide warnings immediately after an earthquake in time to save lives.

A cyclone is an egg-shaped air formation that moves in the form of swirling winds. It has low air pressure at its centre but very high pressure at the surface. Since air moves from a region of high pressure to a region of low pressure, cyclones cause high winds and heavy rainfall.

Some precautions from cyclone are:

Using early warning system. The Indian Meteorological Department issues cyclone warnings in India.

Cyclone proof structures should be built in coastal areas.

Planting trees also help in fighting cyclones

All about Floods

Floods occur when land gets submerged under water due to various causes like excessive rain, overflowing rivers, increase in water in reservoirs, cyclones, tsunami, sea tides and melting of glaciers. Floods caused by cloud bursts, bursting of dams, or tsunamis are called flash floods.

Flooding damages crops and this leads to a shortage of food. Shortage of drinking water also arises as the sources of fresh water get contaminated by the flood water, causing epidemics.

Any flood is preceded by a threat period known as the Probability Period. This allows the authorities to issue warnings and plan evacuation. In India, the Central Water Commission has 132 forecasting stations covering all inter-state flood prone rivers.

Steps to be taken before floods to reduce the damage:

Mapping of major rivers, their flood plains and basins

Construction of artificial embankments like dikes and levees to divert flood water

Stream behaviour should also be studied for charting of rivers and other water bodies

Artificial reservoirs with sluice gates and sand bags to be built to block the flow of water

Low grounds or viaducts can be created to carry water in a certain direction or underground

Trees should be planted in the catchment areas to stop soil erosion

In case of an impending flood, all attention should be paid towards the safety of dams. Encroachments of human settlements on river banks should also be prevented.

Precautions in case of floods:

Rush to high and safe places and ensure to have clean drinking water

Do not drive if water levels are rising in an area

Keep away from rivers, dams and bridges during floods

Clean and disinfect the houses

Get medical help in case of water borne disease

Injured or sick animals should be treated by veterinarians

Plant more trees to prevent floods

Droughts

Droughts are severe when rainfall in an area is below 50% of the average rainfall. When an area receives rainfall that is 25% less than the average rainfall, it is termed as a General Drought. Droughts are divided into three types: Seasonal Drought, Water Drought and Agricultural Drought.

Seasonal Drought occurs when there’s little rain for a prolonged period. Lack of water in water resources such as rivers, lakes and ponds is called a Water Drought and lack of crops is called an Agricultural Drought.

Factors for occurrence of drought:

Scarce rain or no rain at all

Destruction of forests

Over use of agricultural land. Less vegetation also leads to droughts

Depleting ground water level accompanied by the absence of rain

Coping with drought:

Store rain water to prevent droughts. Dig ponds to collect the rain water and build dams to collect excess rain water.

Plant more trees to avoid droughts, around 35% of land should be earmarked as green belts

Regions that receive excess rainfall may share the extra water with the parched and dry regions

Water supply to the agricultural fields in the parched regions can be increased by rainwater harvesting, canal irrigation and building contour bunds

Farmers can insure their crop to prevent financial losses.

Atomic, Biological and Chemical Disasters

Weapons are created by man, so the disasters linked to it are called man-made disasters. Human disasters are man-made and involve elements of human intent, negligence, or the failure of a man-made system.

Atomic disasters are extremely damaging and are mostly caused through weapons of mass destruction. Apart from nuclear bombs, traditional bombs, often used by terrorists, also cause severe destruction.

Government plays important role in making people aware of such disasters like:

Warnings forbidding the people to touch unclaimed substances put up everywhere especially on public transport

In case of an attack, people are advised to stay calm and try to help the wounded

Biological disaster is another type of man-made disaster. Such disasters are caused by microorganisms that cause epidemics and have spread due to man-made conditions. Most of these have been infectious diseases such as malaria, plague, diphtheria, tuberculosis and influenza. These viruses affect birds and animals too.

Chemical disaster is another man-made disaster. Leakages of radioactive material result of human error and result in far reaching damages.

General Human Disasters - 1

Fires disasters are mostly man-made and caused due to negligence and lack of maintenance.

Causes of sire:

Household fires are quite common and are caused mostly of carelessness

Electrical wiring should be checked regularly to prevent house fires caused by short circuits

Defective gas cylinder with leaks may explode on lighting the stove

Military ammunition depots are also prone to accidental fires. Forests are also prone to man-made fires which occur due to the carelessness of man. Fire can occur indoors as well as outdoors.

Fire preventive measures:

Keep inflammable matter at home and a fire extinguisher handy

Remember to switch off all the electrical gadgets and the gas before going outside

Keep match boxes out of reach of children and restrain smoking in the house

For quick getaway in case of fire, ensure that all exits like doors are easily accessible

Call the fire brigade immediately without wasting a single moment

Try to crawl because smoke is always less near the floor

The government has its own share of do’s and don’ts. It contributes to the safety of its people through stringent checks against violation of safety norms.

Disasters Involving Modes of Transport

Human disasters include accidents that occur while traveling by road, rail and air. Speeding, drunk driving and inadequate use of helmets, seat belts and child restraints in vehicles are the main reasons for road accidents in India.

Measure to prevent road accidents:

Follow traffic rules

Legal age to start driving is 18. Start only when you are competent and legally allowed to drive

Strictly follow the rules.

No talking on cell phones while driving, following the speed limit and using helmets when riding bikes.

A number of accidents occur on the highways generally involving trucks. Truck drivers in India need to be educated about traffic rules and the authorities need to be strict about enforcing these. Train accidents are usually caused by derailment, signal failure or fires caused by inflammable material.

Rules to prevent train accidents:

Avoid smoking in trains and never carry an inflammable material

Pay attention to signals, and look out while crossing unmanned level crossings

Air travel has gained popularity in recent years due to the introduction of low cost carriers. Plane accidents occur due to human error as well as extreme climactic conditions. Some human-made air disasters can be caused by poor maintenance of the aircraft, fire outbreaks and tired or inexperienced pilots. There are also eventualities like hijacking.

Rules to prevent air accidents:

On boarding, listen carefully to the instructions given in the plane

Look out for the nearest emergency exits and understand how they work

Disasters involving road, rail and air are usually caused by human errors and can be easily avoided by following rules and regulations.

Stages of Disaster Management

Disaster management prepares us to deal with such situations by preventing any calamity, minimising the effects, and taking timely action for normalising the situation. Disaster Management is a chain of activities carried out before, during and after the disaster occurs.

Disaster management has 4 important stages:

These are advance preparation,

Relief to the victims,

Restoration of normalcy and

Prevention plan for the future.

Role of Administration

On national level, the role of the administration is to initiate rescue and relief operations depending on the gravity of the disaster. At the Central level, the Government has nominated nodal ministries to manage various types of disasters which help in streamlining rescue operations.

The National calamity management committee is controlled by the Cabinet Secretary. The calamity management group also is responsible for disaster management and functions under the Central Aid Commissioner.

Technical support is provided by organizations like the Central Weather Science Department (for cyclone and earthquake), Defence Research and Development Organisation and the Civil Defence General Director.

At the State Level, a committee under the Chief Minister or the Chief Secretary views and takes care of relief operations. At the district level, the District Magistrate and the District Administration are responsible for executing relief operations.

The Block Development Officer manages the operations at the block level in case of any disaster. At the village level, the Sarpanch of a village heads the disaster management committee and assists the various organizations working in the field.

The various institutions involved in disaster management at different levels throughout the country are the United Nations Disaster Management Team (UNDMT), Indian Armed Forces, National Cadet Corps (NCC), Civil Defence, National Service Scheme (NSS), Nehru Youth Centre, Home Guards along with some volunteers from the private sector and media.

To increase awareness among people, a course for disaster management has been introduced in schools, technical colleges, training and higher academic courses. The government passed the National Disaster Management Act (DM Act) in 2005 having a holistic approach to disasters that cover -prevention, mitigation, capacity-building, preparedness, assessment and rehabilitation.

Class 10 Science All Chapters Summary / Short Summary

Chemical Reactions and Equations

Chemical Reactions and Equations

Chemical reaction:
The process of combination of different atoms to form different products is known as chemical reaction. Chemical reaction involves a change in the physical and chemical properties like:

• Change in the colour of the substance
• Change in the state of the substance
• Change in heat energy - Absorption of energy or release of energy
• Release of gas
• Evolution of light and sound

Example:
Burning of coal: During the burning coal, the solid state coal burns with release of heat and gas.


Chemical equation:
A chemical equation is a symbolic representation of the reactants and the products using their chemical formulae.
A chemical equation contains:
       •  Reactants
       •  Products
       •  An arrow separates  the reactants and products
Reactants are the substances which take parts in the chemical reaction.
Products are the substances which produced during chemical reaction.
C + O₂       →  CO₂
Reactants               Product
Representation of physical states of reactants and products:
       •  For  solids it is "(s)".
       •  For  liquids it is "(l)".
       •  For  gases it is "(g)".
       •  For aqueous solutions it is  "(aq)".
       •  For gas produced in the reaction it is "(↑)".
       •  For precipitate formed in the reaction it is  "(↓)".
       •  Direction of reaction is indicated by "(→)".

Example:



Zn _(s) + dil.H₂SO_{4 (aq)} → ZnSO_{4 (aq)} + H_2 (g) (↑)
  (Reactants)                               (Products)

A chemical equation is helpful to understand a chemical reaction in a easy way.
In a chemical equation the masses of reactants and products may or may not be equal. But according to law of conservation of mass "the total mass of the reactants and the products should be equal".
So in order maintain the law true it is necessary to balance a chemical equation.



Steps involved in balancing of chemical equation:
       •  Determining the reactants and products in a reaction.
       •  Counting the number of atoms of each element on both sides of the equation.
       •  Selecting the elements that occur for the least number of times in the equation.
       •  Balance atoms of each element on both sides of the reaction.
       •  Always leave hydrogen and oxygen for last to balance.
       •  Balance the hydrogen atoms lastly followed by balancing of oxygen atoms.

Example:
Formation of Ammonia:
         N₂ + H₂ → NH₃   (Un-balanced equation)
Step 1: 2-Nitrogen atoms, 2-Hydrogen atoms → 1 –Nitrogen atom, 3-Hydrogen atoms

Step 2: In the above equation number of Nitrogen atoms on both sides are not equal, multiply with suitable integer to balance the Nitrogen atoms on both sides.
So, multiply with "2" on the product side.
        N₂ + H₂ → 2NH₃

In the above equation the number of Nitrogen atoms were balanced.
Step 3: Hydrogen atoms on both sides were not balanced. So, multiply with suitable integer.
Multiply with "3" to Hydrogen on reactant side.
         N₂ + 3H₂ → 2NH₃

Now the above equation is balanced.
Reaction of potassium hydroxide with sulphuric acid:
Write down the equation
KOH + H₂SO₄ → K₂SO₄ + H₂O (This is not balanced equation)

Check the number of atoms of each element on both sides
Potassium (K) Atoms on both sides are not equal, balance the Potassium atoms by multiplying with suitable integer.
2KOH + H₂SO₄ → K₂SO₄ + H₂O
Now Potassium  atoms on both sides are balanced.

Number of Hydrogen atoms on both sides is not equal, balance hydrogen atoms by multiplying with suitable integer.
2KOH + H₂SO₄ → K₂SO₄ + 2H₂O

Now Hydrogen atoms on both sides are balanced. And Oxygen atoms on both sides get balanced.
This is balanced equation as atoms of all elements on both sides are balanced
2KOH + H₂SO₄ → K₂SO₄ + 2H₂O

Types of Chemical Reactions

In general chemical reactions are classified into:

•    Combination reactions
•    Decomposition reactions
•    Single displacement reactions
•    Double displacement reactions

Combination reactions:
A combination reaction is one in which two or more reactants combine to form a single product. Combination reactions are again of three types.
They are:
Combination reactions between elements.
Combination reactions between compounds.
Combination reactions between elements and compounds.
Combination reactions between elements:
In these reactions elements were combined to form a product.

Examples :
Formation of calcium oxide by the combination elements calcium and oxygen.
2Ca + O₂ → 2CaO
Formation of ammonia by the combination of elements nitrogen and hydrogen.
N₂ + 3H₂ → 2NH₃

Combination reactions between compounds:
In these reactions compounds were combined to form product.
Example:
Reaction of calcium oxide in water to form calcium hydroxide
CaO + H₂O  → Ca(OH)₂
Combination reactions between elements and compounds:
In these reactions elements and compounds combined to form product.
Example:
Formation of sulphur trioxide by the combination of sulphur dioxide and oxygen.
2SO₂ + O₂ →  2SO₃

Decomposition reaction:
Decomposition reactions are those in which a substance splits into two or more simpler substances. Decomposition reactions are the opposite of combination reactions.  Decomposition reactions are of three types:

•    Thermal decomposition
•    Electrolysis
•    Photolysis
  Decomposition by the application of heat on a substance is called thermal decomposition.
  Example:
  Thermal decomposition of calcium carbonate.
  CaCO₃ + Δ (Heating) → CaO + CO₂
  Decomposition of any substance by passing current through it is called electrolysis.
  Example:
  Electrolysis of water 

2H₂O → 2H₂ + O₂

The decomposition reaction resulting from action of light energy is called photolysis.
Example:
Photolysis of silver chloride
2AgCl  → 2Ag + Cl₂

Single displacement reaction:
Single displacement reaction is the one in which one element substitutes or displaces another element in a compound to give new compound. Generally in a single displacement reaction,  less active metal is displaced by a more active metal.

It is important to note that in a single displacement reaction, one of the reactants is always an element.
Example:
The reaction of magnesium with copper chloride
Mg + CuCl₂ →  MgCl₂ + Cu

Double displacement reaction:
The reactions which involves exchange of ions (cations and anions) between the reactants are called double displacement reactions.
AB + CD → AC + BD
Example:


Double displacement reactions classified into different types. They are: 

• Neutralization reactions
• Precipitation reactions
• Gas forming reactions

Neutralization reaction:
Reaction in which hydrogen ions of an acid react with hydroxide ions of a base to form water is an neutralization reaction.

Example : The reaction of hydrochloric acid with sodium hydroxide.
H⁺Cl^–  + Na⁺OH^– → Na⁺Cl^– + H₂O

Precipitation reaction:
Reactions which proceeds through the formation of precipitation are called precipitation reactions.
Example:
In the reaction of barium chloride with sodium sulphate produces precipitate of barium sulphate along with formation of sodium chloride.
BaCl_2 (aq) + Na₂SO_4 (aq) → BaSO_4 (s) + NaCl _(aq)

Gas forming reaction:
In these reactions gas is produces as one of the product during reaction.



Example:
Na₂CO_3 (s) + 2HCl _(aq) → 2NaCl _(aq) + H₂O _(l) + CO_2 (g)

Based on energy differeneces between reactants and products the chemical reactions are classified into two types. They are exothermic reaction and endothermic reaction.

Exothermic reaction:
Chemical reactions in which heat energy released are known as exothermic reactions.
Burning of methane gas in air produces heat energy.
CH_4 (g) + 2O₂ (g) → CO₂ (g) +  2H₂O (l)+ heat
All combustion reactions are exothermic reactions.

Endothermic reaction:
Reactions which involves absorption of energy are known as endothermic reactions.
Example:
Formation of nitric oxide from nitrogen and oxygen.
N_2 (g)+ O_2 (g) + Heat → 2NO

Combustion reaction:
Burning of a substance in the presence of oxygen which resulting release of energy is called combustion.
Example:
Combustion of ethylene gas.
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O

Oxidation reaction:
Oxidation reaction involves the addition of oxygen or the removal of hydrogen from a substance.
Example:
Rusting of iron
Rusting of iron:
Iron when reacted with both water and oxygen are present (moist air), corrodes. Its silvery colour changes to a reddish-brown, because hydrated oxides are formed which is commonly called as rust.
Reaction showing the formation of rust when reacted with water in presence of oxygen (atmosphere).                       
4Fe + 3O₂+ XH₂O → 2Fe₂O₃.XH₂O

Reduction reaction:
The reaction which involves addition of hydrogen or removal of oxygen from a substance is called reduction reaction.
Example:
Photosynthesis is a reduction reaction.

Redox reaction:
The reactions in which both oxidation and reduction occurring together are known as redox reactions.
Example:
CuO + H₂ → Cu + H₂O


The above is a redox reaction as copper is reduced and hydrogen is oxidised.

Acids Base and Salt

Acids

The word "acid" comes from the Latin word "acidus" which means sour.
According to Arrhenius theory an acid is a substance which ionizes and gives hydrogen ions when dissolved in water
Example: Hydrochloric acid in water releases H⁺ ions.
HCl + H₂O → H⁺ _(aq) + Cl^–_(aq)

A hydrogen ion cannot exist on its own, so it combines with a water molecule to form a hydronium ion. 
Example: Hydrochloric acid when dissolved in water liberates a hydrogen ion and a chloride ion. The hydrogen ion combines with water to form a hydronium ion.
HCl + H₂O → H₃O⁺ _(aq) + Cl^–_(aq)

Classification of acids:
Classification of acids based on source:
Based on the source the acids were classified into two types. They are organic acids and in-organic acids.

Organic acids:
Acids obtained from food like curd, lemons, grapes, raw mango, citrus fruits and gooseberry are called organic acids.

In-organic acids:
Acids which are synthesised in the laboratory are called as in-organic acids or mineral acids
Following table is the list of some acids which are used in the laboratory.

Name of the acid	Chemical formula
Sulphuric acid	H2SO4
Nitric acid	HNO3
Hydrochloric acid	HCl
Acetic acid	CH3COOH

Classification of acids based on concentration:
The word concentration indicates the quantity of acid in relative to the quinatity of water in the aqueous solution of that acid.
Highly concentrated acid contains high percentage of acid in comparision with water in that solution.
Low concentrated acid contains low percentage of acid in comparision with water in that solution.
Dilution of acid:
Mixing an acid with water reduces the concentration of hydronium ions of the acid per unit volume. This is called dilution of acid. The action of acids with water is exothermic as heat is generated on dilution.
Classification of acids based on strength:
Based on ionisation, the acids were classified into strong acids and weak acids.
Strong acids: Acids which ionises complely into its ions are called strong acids.
Example: HCl, H₂SO₄, HNO₃...etc
Weak acids: Acids which ionises partially into its ions are called weak acids.
Example: CH₃COOH, H₂CO₃...etc

Classification of acids based on basicity of acids:
Based on basicity acids were classified into different types. They are
Mono-basic acids
Di-basic acids
Tri-basic acids
Mono-basic acids:
Acids which on ionisation produces on hydronium ion in water are termed as mono-basic acids.
Example: HCl
Di-basic acids:
Acids which on ionisation produces two hydronium ions are called as di-basic acids.
Example: H₂SO₄, H₂CO₃..etc
Tri-basic acids:
Acids which on ionisation produces three hydronium ions are called astri-basic acids.
Example: H₃PO₄, H₃PO₃..etc

Properties of acids:
Acids have corrosive action on skin.
Acids are good conductors of electricity.
Acids neutralizes bases to form salt and water.

Chemical properties of acids:
Reaction of acids with active metals:
Acids reacts with metals to form metal salts. In this reaction, hydrogen gas is liberated.
Example: In the reaction of hydrochloric acid reacts with zinc produces hydrogen gas and zinc chloride.
 2HCl + Zn → ZnCl₂ + H₂

Reaction of acids with metal carbonates:
Acids reacts with metal carbonates to form corresponding salts, carbon dioxide and water.
Example: Hydrochloric acid on reaction with sodium carbonate forms sodium chloride, carbon dioxide and water.
 2HCl + Na₂CO₃ → 2NaCl +  CO₂ + H₂O

Reaction of acids with metal hydrogen carbonates:
Acids reacts with metal hydrogen carbonates and form corresponding salts, carbon dioxide and water.
Example: Hydrochloric acid on reaction with sodium bicarbonate forms sodium chloride, carbon dioxide and water.
 HCl + NaHCO₃ → NaCl + CO₂ + H₂O

Reaction of acids with metal oxides:
Acids reacts with metal oxide to form salt and water.
Example:
Sulphuric acid on reaction with cupric oxide forms copper sulphate and water.
CuO + H₂SO₄ → CuSO₄ + H₂O

Indicators:
An acid base indicator is a substance which exhibits different colour in acids and bases.
Red cabbage is a visual indicator used to detect acids.
Onions are called olfactory indicators. They change their odour with change in the nature of solution.
Litmus is a natural indicator and is extracted from lichens.
Apart from natural indicators there are a few synthetic indicators, such as methyl orange and phenolphthalein.
Following table gives colours of the indicators in presence of acids and bases.

Indicator	Acid	Base
Methyl orange	Red	Yellow
Phenolphthalein	Colourless	Pink
Blue litmus paper	Red colour	No Change
Red litmus paper	No change	Blue colour

Universal indicator is a mixture of different number of indicators which shows different colours in different solutions.

Uses of acids:

• Sulphuric acid is used in the manufacture of fertilisers, paints, dyes, chemicals , plastics  and synthetic fibres.
• Sulphuric acid is also used in car batteries.
• Nitric acid is used in the manufacture of fertilizers, explosives like TNT, dyes and drugs.
• Hydrochloric acid is used before galvanizing, to remove oxide film from steel and also as a descaling agent for boilers. It is also used in the textile, leather and food industry.
• Hydrochloric acid used in the manufacture of glucose from corn starch.
• Ethanoic acid (CH₃COOH) is used for coagulating latex to prepare rubber from it. It is also used in the preparation of perfumes.
• Boric acid (H₃BO₃) is useful as an antiseptic and insecticide.
• Boric acid is useful as a flame retardent.
• Carbonic acid (H₂CO₃) is useful in the form of carbonated drinks

Bases

According Arrhenius theory any substance that can produce hydroxide ions when dissolved in water is called as a base.
        Substance + Water → Metal ion + OH^–
Example:
        NaOH (aq)  → Na⁺ _(aq) + OH^– (aq)

A base is said to be an alkali if it is soluble in water. In general hydroxides of alkali metals and alkaline earthmetals are considered as alkalies.
Example:
        KOH  (aq) → K⁺(aq) + OH^– (aq)
        Ca(OH)₂(aq) → Ca⁺² (aq) + OH^– (aq)

It is not a necessary that a base should contain hydroxide ion.
There are some bases even they does not contain hydroxide ion, can be considered as bases.
Example: Ammonia (NH₃)
Ammonia when dissoled in water forms ammonium hydroxide which is a weak base.
NH₃ + H₂O → NH₄OH (aq)

Oxides of alkali metals and alkaline earthmetals are also considered as basic in nature.
Example: CaO, MgO, Na₂O, K₂O...etc

Classification of bases:
Classification based on the strength:
Based on the extent of ionisation bases are classified into strong bases and weak bases.

Strong bases:
The bases which undergoes complete ionisation in aquesous solution are called as strong bases.
Example: NaOH, KOH...etc

Weak bases:
The bases which undergoes partial ionisation in aqueous solution are called weak bases.
Example: NH₄OH, NH₃...etc

Classification of based on acidity:
Based on acidity bases can be classified into different types. They are:
Mono acidic base
Di acidic base
Tri acidic base
Mono acidic bases:
Bases which produces only one hydroxide (OH^-) ion in aqueous solutions are called mono acidic bases.
Example: NaOH, KOH...etc
Di acidic bases:
Bases which produces two hydroxide ions in aqueous solutions are called di acidic bases.
Example: Ca(OH)₂, Mg(OH)₂...etc
Tri acidic bases:
Bases which produces three hydroxide ions in aqueous solutions are called tri acidic bases.
Example: Al(OH)₃, Fe(OH)₃...etc

Physical properties of bases:
        • Bases are bitter to taste, soapy to touch.
        • Bases are good conductors of electricity in aqueous solution. In aqueous solution, they release ions, which conduct electricity.
        • Bases liberates heat on dilution.

Indicators in pressence of bases:
Bases turns red litmus to blue.
Phenolphthalein turns pink in pressence of bases.
Methyl orange turns to yellow in pressence of bases.

Chemical properties:
Reaction with active metals:
Bases react with metals to liberate hydrogen gas
Example: Sodium hydroxide react with zinc and liberate hydrogen and sodium zincate.

           NaOH + Zn → Na₂ZnO₂ + H₂

Reaction with non-metal oxides:
Bases react with non-metallic oxides to form salt and water. This is similar to a neutralization reaction between an acid and a base.          
Example: Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water

              Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
From this reaction, it can be concluded that non-metallic oxides are acidic in nature.
Reaction with acids:
Bases reacts with acids to form salts and water.
Example:
Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water.
KOH + HCl → KCl + H₂O
Uses of Bases:
        •  Mild bases neutralise the acidity in the stomach.
        • Sodium hydroxide is used in the manufacture of soaps, paper and synthetic fibres like rayon.
        • Calcium hydroxide is used in the manufacture of bleaching powder. Bleaching powder is used as a disinfectant.
        • Magnesium hydroxide is used as an antacid to neutralize the acid in the stomach.
        • Ammonium hydroxide is used in the preparation of fertilizers like ammonium phosphate and ammonium sulphate.

Strength of Acids and Bases

Neutralization is a chemical reaction in which an acid reacts with a base to form salt and water. In this process, a hydrogen ion of the acid combines with a hydroxide ion of the base to form a water molecule. The anion of the acid combines with the cation of the base to form a salt.

For example when hydrochloric acid reacts with sodium hydroxide the chlorine of hydrochloric acid combines with sodium of sodium hydroxide to form sodium chloride. The hydrogen of hydrochloric acid combines with the hydroxyl part of the sodium hydroxide and forms water.
 HCl + NaOH → NaCl + H₂O

Strength of acids or bases:
Based on extent of ionization acids and bases are classified into strong acids, weak acids and strong bases, weak bases.

Strong acids or strong bases ionizes completly (100%) to form ions in the aqueous solution.
Example:
Hydrochloric acid ionizes completly to form ions.
HCl (aq) → H⁺(aq) + Cl^–(aq)
Sodium hydroxide ionizes completly to form ions.
NaOH (aq) → Na⁺ (aq) + OH^– (aq)

Weak acids or weak bases ionizes partially (<100%) to form ions in the aqueous solution.
Example:
Acetic acid ionizes partially in aqueous solution to form ions.
CH₃COOH (aq) ⇔ H⁺(aq) + CH₃COO^– _(aq)
Ammonium hydroxide ionizes partially in aqueous solution to form ions.
NH₄OH ⇔ NH₄⁺ + OH^– (aq)
An acid or base is considered as strong or weak depending on the concentration of hydrogen and hydroxide ions within it.
This concentration or the power of hydrogen differs from substance to substance and can be measured using a scale, called the pH scale.
A solution that has a pH value of less than 7 is acidic and a solution with a pH value of more than 7 is basic. A neutral solution is indicated by a pH value of 7 on the scale.
Strong acids will posses pH values between 0-2 and weak acids posses pH values more than 3.
Strong bases will posses pH values between 12-14 and weak bases posses pH values less than 12.



pH of some of the acids and bases:

Acid/Base	pH
Hydrochloric acid	0.1 - 1.0
Sulphuric acid	1.0 - 1.2
Phosphoric acid	1.3 -1.5
Acetic acid (Vineger)	2.9 - 3.0
Carbonic acid	3.8 - 4.0
water	6.9 - 7.0
Ammonia	10.8 - 11.2
Sodium hydroxide	13 - 14

Applications of neutralization concept in daily life: 

• Antacids like Milk of Magnesia are mild bases that neutralize the acids in the stomach and aid digestion.
• If the pH lowers, the acidity in the mouth increases and leads to tooth decay.  Toothpastes are basic in nature and they counteract the acid in the mouth.
• Hydrangea produces pink flowers when the soil has a pH value of 6.8 or higher and blue flowers when the pH value is 6.0 or less.
• If the soil is acidic, then the applied pesticides, herbicides and fungicides will not be absorbed by the soil. In order to neutralize the soil, suitable bases are used. Generally, salts of calcium or magnesium, which are basic are used to neutralize soil acidity.
• When a bee stings, formic acid is released. That is what makes the skin burn. Baking soda, which is a base, neutralizes the formic acid and provides relief from the pain.

Salts and their Properties

The compounds formed by the reaction between an acids and a bases are known as a salts.
                                Acid + Base → Salt + Water

Salts are ionic compounds which contain positively charged cations and negatively charged anions. During salt formation cation is coming from base and anion is coming from acid.
Example: In Sodium chloride (NaCl) formation cation sodium is coming from sodium hydroxide and anion chlorine is coming from hydrochloric acid.

Classification of salts:
Based on nature the salts have been classified into different types. They are:
Normal salts
Acidic salts
Basic salts
Double salts
Complex salts
Normal salts:
These salts are formed by the complete replacement of hydrogen in acids by other metal cations from the bases.
NaCl is normal salt formed by the reaction of HCl with NaOH.
HCl + NaOH → NaCl + H₂O

Acidic salts:
Salts which are formed by the partial replacement of hydrogens atoms of acids are called acidic salts.
Example:
NaHSO4 is formed when partial replacement of hydrogen atoms by the sodium atoms of base.
H₂SO₄ + NaOH → NaHSO₄ + H₂O
In general these salts formed when the reacted base is not sufficient for the neutralisation of acid.
Basic salts:
Salts which are formed by the partial replacement of hydroxyl group are called basic salts.
Example:
Ca(OH)Cl is formed by the partial replacement of hydroxide group from Ca(OH)2 by chloride ions of acid.
Ca(OH)₂ + HCl → Ca(OH)Cl + H₂O
In general these salts formed when the reacted acid is not sufficient for the neutralisation of base.
Table below giving neutral, acidic and basic salts.

Type of Salt	Type of Acid	Type of Base	Example
Neutral         pH = 7	Strong Acids   Examples:   HCl   H2SO4	Strong Bases   Examples:   NaOH   KOH	NaCl   K2SO4
Acidic        pH < 7	Strong Acids   Examples:   HCl   HNO3	Strong Bases   Examples:   NH4OH   Mg(OH)2	NH4Cl   Mg(NO3)2
Basic         pH > 7	Weak Acids   Examples:   H2CO3   CH3COOH	Strong Bases  Examples:   NaOH   KOH	Na2CO3   CH3COOK

Double salts:
Salts that are formed by mixing of two simple salts which are obtained crystallisation.
Example:
Potash alum - K₂SO₄ Al₂ (SO₄)₃ .24H₂O
Dolomite - CaCO₃.MgCO₃

Complex salts:
The salts which contains different types of metal atoms which on hydrolysis produces complex ions along with simple ions are called complex salts.
Example:
[Ag(NH₃)₂]Cl  ⇄  [Ag ( NH₃ )₂ ]⁺ + Cl^-

Salts in our daily life:
Baking soda
Chemical name: Sodium hydrogen carbonate
Molecular formula: NaHCO₃
Sodium hydrogen carbonate is commenly called as baking soda.
Sodium hydrogen carbonate is used in the baking industry.
It is used in preparation of soda acid.
It is also used in foam type fire extinguishers.

Washing soda:
Molecular formula:  Na₂CO₃.10H₂O
Chemical formula: Sodium carbonate.decahydrate
Adding water to sodium carbonate and this allowing this mixture to cool to forms decahydrated sodium carbonate. This is commenly called as washing soda.
Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
In general sodium carbonate is prepared by passing CO₂ gas through concentrated NaOH.
2NaOH + CO₂ → Na₂CO₃ + H₂O

Properties:
It is a white crystalline solid. It exists as decahydrate of sodium carbonate.
When exposed to dry air and heating it loses water molecules to change into anhydrous form.
Na₂CO₃.10H₂O + Exposure to open dry air → Na₂CO₃.H₂O + 9H₂O
Na₂CO₃.H₂O + Heating → Na₂CO₃
It is soluble in water and during dilution heat will releases out.
On reaction with acids sodium carbonate releases carbon dioxide along with the formation of sodium salts and water.
Na₂CO₃ + HCl → 2NaCl + H₂O + CO₂
Sodium carbonate is used to manufacture of glass, cleansing agents, soap, glass and paper.
Bleaching powder (CaOCl₂):
Bleaching powder chemically known as calcium oxy chloride.
It is prepared by the reaction between chlorine and slaked lime at about 40 ⁰C.
Ca(OH)₂ + Cl₂ → Ca(OCl)Cl + H₂O + Cl₂
Ca(OH)₂ + H₂SO₄ → CaSO₄ + H₂O + Cl₂

It acts a strong oxidising agent to bleach substances.
CaOCl₂ + KNO₂ → CaCl₂ + KNO₃
CaOCl₂ + H₂S → CaCl₂ + H₂O + S
It is used to bleach cotton, linen textiles and wood pulp.
Coloured matter + Bleaching powder → Colourless product
It is also used to disinfect drinking water.
Hydrated salts:
The molecules of salts which contain fixed number of water molecules in them are called hydrated salts.
In general they exists as dry in pure form.
These salts on heating loses water molecules in them and forms anhydrous salts.

Example:
Ferrous sulphate heptahydrate (FeSO₄.7H₂O) on heating loses water molecules in it.
          FeSO₄.7H₂O (on heating) → FeSO₄ + 7H₂O

Some of the hydrated salts along with their chemical formula.

Name of the salt	Chemical formula
Sodium carbonate decahydrate	Na2CO3.10 H2O
Zinc Sulphate heptahydrate or White vitriol	ZnSO4.7H2O
Magnesium sulphate heptahydrate or Epsom salt	MgSO4.7H2O
Potash alum	K2SO4 Al2 (SO4)3 .24H2O
Copper (II) sulphate pentahydrate or Blue vitriol	CuSO4.5H2O
Calcium sulphate dihydrate or Gypsum	CaSO4.2H2O

Plaster of paris (CaSO₄. 1 2 H₂O):
Plaster of paris which is chemically called calcium sulphate hemihydrate.
Since it is brought to use from paris, called as "plaster of paris".
It is prepared by heating of gypsum at 373K.

CaSO₄.2H₂O    373 K →      CaSO₄  1 2 H₂O      +    1 1 2 H₂O  
  Gypsum                         Plaster of Paris            Water        

Uses:
It is used as a bandage, proofing material, sealing agent.
It is used for making statues, toys and decorative articles.
It is also used for smoothening wall surfaces.

Metals and Non-metals

Metals and Non-metals

Metals:
In general metals can be defined as the elements which have a tendency to lose electrons and form positively charged ions or cations.
Example: sodium has an electronic configuration of 2,8,1. During a chemical reaction, sodium can lose an electron to a non-metal like chlorine to form a sodium ion that has an electronic configuration of 2,8.

Physical properties of metals:
Physical state:
All metals are solids at room temperature.
Example: Iron and copper.
The one exception is mercury, which is a liquid.

Lustrous nature:
All metals are lustrous. Metal surfaces shine when they are freshly cut.
Example: Gold and silver are popularly used for making jewellery because of their lustrous nature.
Density:
Metals have high densities and, therefore, tend to sink in water.
Example: Tin and lead sink in water.
Exceptions to this rule are lithium, sodium and potassium. The density of these elements is lower than that of water and hence they do not sink.
Malleability:
Metals are highly malleable, and can be beaten into thin sheets.
Example: Aluminium and zinc can be rolled into thin sheets. This property makes them suitable for use in various industries like construction and manufacturing.
Ductility:
Metals are highly ductile and can be drawn into wires.
Example: Copper and silver can be drawn into thin wires.
Conductivity:
Metals are good conductors of heat and electricity. Copper wires are commonly used in electric cables because of this property.
Melting point:
Metals have high melting points.


Example: Tungsten has a high melting point, due to which it is used in bulb filaments.
Mercury is an exception to this property, since it has a low melting point.

Chemical properties of Metals:
Metals react with non-metals to form ionic compounds.
Example: Sodium reacts with chlorine to form sodium chloride.
            2Na + Cl₂  → 2NaCl

Reaction of metals with oxygen:
Most of the metals combine with Oxygen to form basic metal oxides.
Example: When magnesium burns in oxygen it forms magnesium oxide.
             2Mg + O₂ → 2MgO

Metal oxides of alkali metals soluble in water to form hydroxide solutions, called alkalies.
Example: Sodiumoxide soluble in water to form sodium hydroxide.
             2Na₂O + H₂O →2 NaOH

Reaction of metals with water:
Sodium, potassium reacts vigorously even with cold water.
             2Na + 2H₂O → 2NaOH + H₂
             2K + 2H₂O → 2KOH + H₂

Calcium reacts slowly with cold water. And can react vigorously with hot water.
             Ca + 2H₂O → Ca(OH)₂ + H₂

Magnesium does not reacts with cold water. It reacts very slowly with hot water but reacts vigorously with steam.
             Mg + 2H₂O → Mg(OH)₂ + H₂

Iron and zinc do not react either with cold or hot water but react with steam.
             Zn + H₂O → ZnO + H₂
             Fe + H₂O → FeO + Fe₂O₃ + H₂

Aluminum do not reacts either with cold water, hot water and even steam because of its protective oxide layer.
Metals like Lead, Copper, Gold and Silver do not show any reaction with water.

Non-metals:
Non-metals are elements that have a tendency to accept electrons to form negatively charged ions or anions.
Example: Chlorine has an electronic configuration of 2,8,7. During a chemical reaction, chlorine can accept an electron from a metal like sodium to form a chloride ion. A chloride ion has an electronic configuration of 2,8,8.

Physical properties of non-metals: 
Physical state:
Non-metals exist as solids, liquids and gases.
Example: Silicon and carbon are solids; bromine is a liquid; chlorine, fluorine and oxygen are gases.
Lustrous nature:
Non-metals are non-lustrous and have a dull appearance in nature.
Density:
Most of the non-metals have very low density.
Example: Oxygen and nitrogen are lighter than air.
Exception is diamond, a form of carbon. Diamond is one of the strongest known substances.
Non-metals are not malleable. 
Non-metals are bad conductors of heat and electricity.
Exception is graphite, a form of carbon which is a good conductor of electricity.
Non-metals have low melting and boiling points.
Example: Sulphur and Phosphorus have low melting and boiling points.
Chemical properties of non-metals:
Formation of covalent compounds:
Reaction between non-metals produces covalent compounds.
Example: Hydrogen and chlorine reacts with each other form hydrogen chloride      
         H₂ + Cl₂ → 2HCl
Reaction of non-metals with oxygen:
Non-metals reacts with oxygen to form oxides which are either acidic or neutral in nature.
Example:
Sulphur reacts with oxygen to form sulphur dioxide which is acidic in nature
     S + O₂ → SO₂
Nitrogen reacts with limited supply oxygen to form nitric oxide which is a neutral oxide in nature.
    N₂ + O₂ → 2NO
Non-metal oxides dissolves in water to form acidic solutions.
Example:
Sulphur dioxide dissolves in water to form sulphurous acid.
     SO₂ + H₂O → H₂SO₃
Non-metals are good oxidizing agents.
Example: Sulphur in hydrogen sulphide undergoes oxidation when hydrogen sulphide reacts with chlorine.
     H₂S + Cl₂ → 2HCl + S
Metals and non-metals are separated through electrolysis

Activity Series

The arrangement of metals in the decreasing order of their reactivity is known as activity series. In the activity series highly reactive metals placed at the top and least reactive metals placed at the bottom.
Gold placed at bottom of the series is the least reactive among the metals and potassium placed at the top is the highly reactive metal.  Hydrogen is the non-metal included iin order to compare the reactivity of metals.
The metal placed higher in the series can displace the other metal from its salt solution. Thus potassium can displace all other metals from their salt solutions.
Example: Potassium can displace hydrogen from the acids.
        2K + 2HCl →2KCl + H₂


Metals of low reactivity cannot displace high reactive metals from their salts. For this reason oxides of highly reactive metals like magnesium and aluminium are not reduced easily either by hydrogen, carbon or carbon monoxide.
Metals that are placed below copper do not rust easily because of their low reactivity.

Reactivity towards oxygen:
On moving down in the reactivity series the reactivity with oxygen decreases.
Metals like potassium, sodium, calcium, magnesium and aluminium can react with oxygen at room temperatures.

Potassium can react with oxygen to form its super oxide in addition to oxide.
K + O₂ → KO₂
4K + O₂ →  2K₂O

Sodium on reaction with oxygen forms metal oxide as well as metal peroxide.
4Na + O₂ → 2Na₂O
2Na + O₂ →  Na₂O₂

Calcium, magnesium and aluminum on reaction with oxygen forms their metal oxides.
2Ca + O₂ → 2CaO
2Mg + O₂ → 2MgO
4Al + 3O₂ → 2Al₂O₃

Reactivity towards water:
While moving down in the activity series the reactivity towards water decreases.
Potassium, sodium and calcium can reacts vigorously even with cold water with the liberation of hydrogen gas.
K + H₂O → KOH + H₂
Na + H₂O → NaOH + H₂
Ca + H₂O → Ca(OH)₂ + H₂
Magnesium reacts very slowly with cold water but can reacts vigorously with hot water to produce hydrogen gas
Mg + H₂O → MgO + H₂

Metals like aluminium, zinc and iron does not reacts with cold water or warm water but can reacts with hot steam.
2Al + H₂O → Al₂O₃ + H₂
Zn + H₂O → ZnO + H₂
3Fe + H₂O → Fe₃O₄ + H₂

Reactivity towards mineral acids:
The metals which are present above hydrogen in the reactivity series can reduce hydrogen ions from the acids like HCl and H₂SO₄. Reactivity decreases on moving down the group in the series.
Potassium, sodium reacts vigorously with dilute acids to liberate hydrogen gas.
K + 2HCl → 2KCl + H2
Na + 2HCl → 2NaCl + H2

Calcium, magnesium also reacts vigorously but slowly with acids libearating hydrogen gas.
Ca + 2HCl → CaCl₂ + H₂
Mg + 2HCl → MgCl₂ + H₂

Metals below to hydrogen in the series does not liberate hydrogen on reaction with concentrated or diluted acids.

Ore:
Metals are available in the form of their ores.
Ore is a mineral which contains high percentage of metal from which a metal can be extracted most economically.


Methods of extraction of metals from ore  are based on the reactivity of metals.

Methods of extraction:
        •  Reduction
        •  Electrolysis

Reduction is the process of removal of oxygen for extraction of metals from their oxide ores. The common reducing agents used for reduction of metal oxides are:
        •  Carbon monoxide
        •  Carbon
        • Hydrogen

Examples:
During the extraction of iron from its oxide:
Iron oxide is reduced to iron by carbon monoxide.
      FeO + CO → Fe + CO₂

Iron oxide is reduced to iron using carbon as the reducing agent.
      FeO + C → Fe + CO

During the extraction of copper from its oxide:
Copper oxide is reduced to copper using carbon as the reducing agent.
      CuO + C → Cu + CO

Copper oxide is reduced to copper using hydrogen as the reducing agent.
      CuO + H₂ → Cu + H₂O

But oxides of potassium, sodium, lithium, barium,calcium, magnesium and aluminum cannot be reduced by using carbon, carbon monoxide and hydrogen because of their high affinity for oxygen.

Important ores of Aluminium:
        •  Bauxite: Chemial formula is:  Al₂O_3.2H₂0
        •  Bauxite is the principal ore of aluminium.
        •  Corundum: Chemial formula is: Al₂O₃
        •  Cryolite: Chemial formula is: Na₃AlF₆.
The extraction of aluminium from bauxite involves three steps:
        •  The purification of bauxite using Bayer’s process.
        •  The electrolytic reduction of anhydrous Al₂O₃ by Hall and Herault’s process.
        •  The last step is the purification of impure aluminium by Hoope’s process 

Aluminium is used in:
        •  Manufacture of automobile components
        •  Construction process
        •  Manufacture of electric wires
        •  Packing medicines and pharmaceutical products
        •  Manufacture of soft drink cans and espresso coffee makers
        •  Manufacture of utensils

Alloy:
An alloy is a homogeneous mixture of solid solution of two or more metals or metals with non-metals.

Duralumin is a light and tensile alloy of aluminium. Duralumin is used in the making of air craft frames, pressure cookers.
Magnalium is an alloy of aluminium and magnesium. Magnalium is used in the making of balances because of its high structural strength and resistance to corrosion. It is also used in the making of optical instruments like cameras and microscopes due to its light weight and resistant to corrosion.

Some important alloys:

Name of  the Alloy	Composition	Properties	Uses
Brass	Cu: 80% Zn: 20%	It is generally strong resistant to corrosion and easily moulded into different shapes.	In making of utensils, pipes and radiator statues etc
Bronze	Cu: 90% Sn: 10%	It is very strong in nature and also posses good resistance property.	In making of coins, ornaments, utensils and statues
Stainless steel	Fe: 82% (Ni + Cr): 18	Resistant to water, air and alkalies.	In making of surgical instruments, watches and utensils etc
Magnalium	Al: 95% Mg: 5%	Very light in weight and very hard in nature.	In making light articles and physical balance etc
Duralumin	Al: 95% Cu: 4% Mn: 0.5%	It is very strong in nature and very light in weight. And is resistant to corrrosion.	In making parts of aeroplane and ship etc

Forms of Carbon

Forms of Carbon

Allotropy:
Allotropy is the property of an element to exist in more than one physical forms having similar chemical properties but different physical properties.
Carbon exists both in crystalline and amorphous allotropic forms.

Crystalline allotropes of carbon:
Diamond
Graphite
Fullerene

Amorphous  allotropes of carbon:
Coal
Coke
Charcoal
Lampblack
Gas carbon
Coke

Diamond:
Diamond is a rigid, compact, three dimensional structure.
Diamond is very hard to break.
Diamond is bad conductor of heat and electricity. Because in diamond each carbon is bonded to four other carbon atoms. There are no free electrons present in it.
Diamond are not attacked by acids, bases and other reagents but it can reacts with fluorine to form carbon tetrafluoride at about 1023 K temperature.
           C + 2F₂  → CF4
Diamond burns in air at about 1173 K to produce carbon dioxide gas.
In diamond carbon atoms are in  tetrahedral arrangement.

Uses:
Diamonds are used in glass cuttings and in making drills.
Diamond is widely valued in jewellary is used as an abrasive in sharpening tools.
Diamond is also useful in die-making and in the manufacture of tungsten filaments for light bulbs.
Because of reflection property it is used as gem  in jewellery.

Graphite:
Graphite contains carbon atoms in hexagonal rings, which are joined to form layers.
The layers of carbon can slide over each other.Graphite is a good conductor of heat and electricity. Since graphite contains free electrons, it is a good conductor of heat and electricity.
Graphite burns in air at about 973 K to produce carbon dioxide gas.



Uses:
Since graphite is a good conductor of electricity it is used as electrode.
Graphite is used as moderator in nuclear reactors.
It is also used as solid lubricant in machines.

Fullerenes :
Fullerene was discovered in the year 1985.
C₆₀ is the very popular and stable form of the known fullerenes. This consists of 60 carbon atoms arranged in pentagons and hexagons, like in a standard football.
Fullerenes are also called Buckminsterfullerenes as they are shaped like the geodesic dome designed and built by the US architect Buckminster fuller.
Fullerenes are prepared from graphite at higher temperatures.
There exists other members of fullerenes like C₇₀, C₈₄...etc

Bonding in Carbon

In general carbon involves in covalent bonding.

Covalent bond:
A bond formed by the sharing of valence electrons between atoms of similar electronegativity is called covalent bond.

Properties of covalent compounds:
Covalent compounds have low melting and boiling points.
Covalent compounds are non conductors of electricity this is due to the absence of free ions.

Classification of covalent bonds:
Based on the number electrons shared between the atoms, the covalent bond is classified into three types. They are:
       • Single covalent bond
       • Double covalent bond
       • Triple covalent bond

Single Covalent Bond: 
Single covalent bond is formed by sharing a single pair of electrons.
Example: H₂ (H - H)

Hydrogen has one electron and it requires one more electron to attain the nearest inert gas configuration. To achieve this each hydrogen atom contributes an electron to form a single bond. Thus, a single covalent bond is formed between the two atoms of the hydrogen molecule.

Double Covalent Bond: 
Double bond is formed by the sharing of two pairs of electrons of the valence shell.
Example: Oxygen molecule (O = O)
The atomic number of oxygen is 8. It requires two electrons to achieve the nearest stable inert gas configuration, which is neon. To achieve this, two oxygen atoms contribute two unpaired electrons to produce two bond pairs. Thus, they share these two electron pairs to form a double bond




Triple Covalent Bond: 
Triple bond is formed by sharing of  three pairs of electrons of the valence shell.
Example : Nitrogen molecule (N ≡ N).
The atomic number of nitrogen is 7. It requires 3 more electrons for attaining the nearest inert gas (neon) configuration. Thus, 2 nitrogen atoms combine together and produce 3 bond pairs and share the three bond pairs between them.



Representation of a Bond:
Bond formation can be represented using Lewis structures. The Lewis dot structures provide a picture of the bonding in molecules in terms of the shared pairs of electrons and the octet rule.
Example: Lewis dot structures of CCl₄ and CH_4.



Bond Formation in Carbon:
From the electronic configuration of carbon, it is clear that it has to either gain or lose four electrons, to attain noble gas configuration.
If carbon gains four electrons it would form a c^-4 ion. It is unable to hold four extra electrons. It would be difficult for the six protons to hold the ten electrons.

Formation of C⁺⁴ is difficult as it requires high amount of energy which leaves six protons in the nucleus and holding only two electrons.
Thus formation of both C^-4 and C⁺⁴ forms is difficult.

Carbon overcomes this difficulty by sharing its electrons with other atoms of carbon or with atoms of other elements. sharing of electrons results in a covalent bond and the shared electrons belong to either of the atoms, this sharing helps in achieving noble gas configuration.

Covalent Bond Formation in Methane:
During the formation of a methane molecule carbon atom share its four valence electrons with four hydrogen atoms. Thus in methane molecule there exists four single bonds between carbon and four hydrogen atoms.

 

Double bond formation of Carbon:
Carbon can involve in double bonding either with it self or with other atoms like Oxygen.
Example:
Formation of CO₂: Carbon shares its four valence electrons with two oxygen atoms. Thus carbon forms two double bonds with two oxygen atoms.


Triple bond formation of Carbon:
Carbon can involve in triple bonding either with it self or with other atoms like Nitrogen.
Example:
Formation of HCN: Carbon shares three of its valence electrons with one nitrogen atom to form triple bond with it. And shares one electron with one hydrogen to form single bond with it.

Hydrocarbons

he existence of such a large number of organic compounds is due to the unique properties of carbon.
The unique properties of carbon are:
        → Tetra valency
        → Catenation
        → Formation of multiple bonds

Tetravalency:
Carbon shares its four valence electrons with other atoms and forms four single covalent bonds to get nearest noble gas formation. This is known as tetravalency.



Catenation:
The property of self linkage among identical atoms to form long chain compounds is known as catenation.
Carbon exhibits maximum catenation, when compared to elements like sulphur and silicon, due to strong carbon-carbon bonds and tetra valency. Due to this catenation, carbon atoms can form various types of straight chains, branched chains and ring structures.



Formation of multiple bonds:
Carbon atoms are capable of forming multiple bonds with other carbon atoms.

Hydrocarbons:
All the carbon compounds which contain just carbon and hydrogen are called hydrocarbons.

Classification of hydrocarbons:
Hydrocarbons are broadly divided into two groups.
        •  Open chain hydrocarbons
        •  Cyclic or closed chain hydrocarbons

Open chain hydrocarbons:
Open chain hydrocarbons contain carbon-carbon straight chains. They are further classified into two types.
        •  Saturated hydrocarbons
        •  Unsaturated hydrocarbons.

Saturated hydrocarbons or Alkanes:
Saturated hydrocarbons are straight chain compounds containing only single covalent bonds. These are also known as alkanes.
General formula of alkanes is C_nH_2n+2.
Example: Methane, ethane, propane, butane... etc.



Unsaturated hydrocarbons:
Unsaturated hydrocarbons are the straight chain compounds containing double or triple covalent bonds.
Unsaturated hydrocarbons are classified into two types. They are alkenes and alkynes.

Alkenes:
Hydrocarbons with a double bond between carbon atoms are known as alkenes.
General formula of alkenes is C_nH_2n.
Example: Ethene, propene, butene...etc




Alkynes:
Hydrocarbons with triple bonds between carbon atoms are known as alkynes.
General formula of alkynes is C_nH_2n-2.
Example: Ethyne, propyne...etc


Cyclic or closed chain hydrocarbons:
The compounds of carbon which contain a closed ring of carbon atoms are called as cyclic hydrocarbons. They are of two types.
        •  Alicyclic hydrocarbons
        •  Aromatic hydrocarbons

Alicyclic Hydrocarbons:
Alicyclic hydrocarbons are in the form of a carbon cycle. They contain three or more carbon atoms.
Example: Cyclopropane, Cyclo butane.



Alicyclic compounds does not follow Huckel's rule.

Aromatic Hydrocarbons:
The cyclic compounds which contain a single and a double bond at alternate positions and exhibit special properties are known as aromatic compounds.
Huckel's rule (4n+2 rule): According to Huckel’s rule the hydrocarbons which contains 4n+2 (where n = 0,1,2,3,…etc) number of delocalized pi electrons which are present in a ring structure are called aromatic compounds.
Example:
Benzene: Benzene (C₆H₆) containing a six membered carbon ring with alternate single and double bonds is an aromatic compound.




Homologous Series:
A series of organic compounds with the same general formula but differ from adjacent members by "-CH₂-" group are referred to as homologous series of compounds.
And successive members of homologous series differ from one another in their mass by 14 units.

Example:
Homologous series of alkanes:
General formula of homologous series of alkanes is C_nH_2n+2.

Number of carbon atoms	Molecular formula	Structure of the               molecule	Name of the alkane	Molecular mass
n =1	CH4	CH3-H	Methane	16
n =2	C2H6	CH3-CH2-H	Ethane	30 (16+14)
n =3	C3H8	CH3-CH2-CH2-H	Propane	44 (30+14)
n=4	C4H10	CH3-CH2-CH2-CH2-H	Butane	58 (44+14)
n=5	C5H12	CH3-CH2-CH2-CH2-CH2-H	Pentane	72 (58+14)
n =6	C6H14	CH3-CH2-CH2-CH2-CH2-CH2-H	Hexane	86 (72+14)
n = 7	C7H16	CH3-CH2-CH2-CH2-CH2-CH2-CH2-H	Heptane	100 (86+14)

Homologous series of alcohols:
CH₃ - OH : Methanol
CH₃-CH₂-OH : Ethanol
CH₃-CH₂-CH₂-OH : Propanol
CH₃-CH₂-CH₂-CH₂-OH : Butanol



The difference between methanol and ethanol, the difference between ethanol and propanol is by a 'CH₂'group.
Similarly the homologous series of alkanes:
CH_4, C₂H₆, C₃H₈, C₄H₁₀......

Nomenclature of Hydrocarbons

The system of assigning a name to a compound is known as nomenclature. There are two systems for naming organic compounds

·         Common or trivial system 

·         IUPAC system

The trivial names are given on the basis of the source and certain properties of organic compounds.
Ex: Citric acid is named, as it is found in citrus fruits.

In the year 1947 the IUPAC that is the International Union of Pure and Applied Chemistry system of naming compounds was first developed.

The IUPAC system is a systematic nomenclature in which the name of a compound correlates to its molecular structure.

The IUPAC nomenclature system is a set of logical rules devised and used to write a unique name for every distinct compound. According to the IUPAC system of nomenclature, the name of an organic compound consists of a root word, a suffix and a prefix.



Root Word:
The root word indicates the number of carbon atoms in the basic skeleton.

Number of carbon atoms	Root word
C	Meth
C-C	Eth
C-C-C	Prop
C-C-C-C	But
C-C-C-C-C	Pent
C-C-C-C-C-C	Hex
C-C-C-C-C-C-C	Hept
C-C-C-C-C-C-C-C	Oct
C-C-C-C-C-C-C-C-C	Non
C-C-C-C-C-C-C-C-C-C	Dec

Example: C-C-C-C-C
Root word in the above system is ‘Pent’ (as it contains five carbon atoms).

Suffix:
A suffix designate the  functional groups that may be present in the compound. The suffix is again divided into primary and secondary.

Primary suffix:
Primary suffix  indicates the degree of saturation or unsaturation in the basic skeleton and is added immediately after the root word.
Primary suffix + Root word → Saturated or unsaturated carbon chain

Nomenclature of Alkanes:
For saturated hydrocarbons, the primary suffix “ane” should be added.
Example: The IUPAC name of a molecule which contains single bond between carbon atoms.
CH₃-CH₃ : Eth + ane : Ethane
CH₃-CH₂-CH₃ : Prop + ane : Propane

Nomenclature of Alkenes:
Hydrocarbons containing double bonds are known as alkenes.  For such hydrocarbons, the primary suffix “ene” should be added to the root word.
Example: The IUPAC name of a molecule which contains double bond between carbon atoms.
CH₂=CH₂: Eth + ene:  Ethene
CH₃-CH=CH₂: Prop + ene:  Propene
In writting nomeclature of alkenes according to IUPAC, it is important to mention the position of double for the molecules which contain more than three carbon atoms.
Example:
CH₂=CH-CH₂-CH₃:
Root word: But
Prefix: 1-ene
Root word + prefix: 1-Butene

CH₃-CH=CH-CH₃:
Root word: But
Prefix: 2-ene
Root word + prefix: 2-Butene

Nomenclature of Alkynes:
Hydrocarbons that contain a triple bond between carbon atoms are known as alkynes and for naming such hydrocarbons the primary suffix “yne “should be added.
Example: The IUPAC name of a molecule which contains triple bond between carbon atoms.
CH≡CH: Eth + yne:  Ethyne
CH₃-C≡CH: Prop + yne:  Propyne
In writting nomeclature of alkynes according to IUPAC, it is important to mention the position of triple bond for the molecules which contain more than three carbon atoms.
Example:
CH≡C-CH₂-CH₂-CH₃:
Root word: Pent
Prefix: 1-yne
Root word + prefix: 1-Pentyne

CH₃-C≡C-CH₂-CH₃:
Root word: Pent
Prefix: 2-yne
Root word + prefix: 2-Pentyne

Secondary Suffix:
A secondary suffix indicates the functional group present in the carbon compound. Functional groups are defined as  specific atoms, group of atoms or ions which are part of a larger hydrocarbon chain and impart characteristic properties to the compounds.

Nomenclature of a molecules with functinal group:

Organic Compound	Functional Group	Secondary Suffix to be used
Alcohols	-OH	-ol
Aldehydes	-CHO	-al
Ketones	>CO	-one
Carboxylic acid	-COOH	-oic aid
Acid amides	-CONH2	-amide
Acid chlorides	-COCl	-oyl chloride
Esters	-COOR	-alkyl...oate
Cyanides	-CN	-nitrile
Thioalcohols	-SH	-thiol
Amines	-NH2	-amine

Example: 
A molecule of ethyl alcohol contains two carbon atoms, so the root word should be “eth”.
It is saturated so the primary suffix should be “ane” but as there is a functional group (alcohol) "–OH" in the molecule, remove the “e” from the name of the molecule and add the secondary suffix “ol”.
Therefore, the IUPAC name of ethyl alcohol is “ethanol”.

CH₃-CH₂-OH : Eth + an+ol : Ethanol

Similarly:
The IUPAC  name of the propanaldehyde molecule can be written as Propanal,
CH₃-CH₂-CHO :
Root word:Prop
Primary suffix: an
Secondary suffix: al
Root word + Primary suffix + Secondary suffix: Propanal

The IUPAC name of acetone can be written as propanone.
CH₃-CO-CH₃:
Root word:Prop
Primary suffix: an
Secondary suffix: one
Root word + Primary suffix + Secondary suffix: Propanone

And IUPAC name of acetic acid can be written as ethanoic acid
CH₃-COOH :
Root word:Eth
Primary suffix: an
Secondary suffix: oic acid
Root word + Primary suffix + Secondary suffix: Ethanoic acid

Prefix:
The parts of the name that precede the root word are called prefixes. For example, in the compound, cyclobutane, “cyclo” is the prefix that indicates the alicyclic nature of the compounds.

A primary prefix is used to differentiate acyclic and cyclic compounds. But the rules for using these are slightly different.

Ex: In cyclic compounds, the prefix cyclo is added before the word root.

Functional groups with halogen as the hetero atom are,

Functional group	Formula	Prefix to be used
Flourine	-F	Flouro
Chlorine	-Cl	Chloro
Bromine	-Br	Bromo
Iodine	-I	Iodo

Nomenclature of molecule with halogen as functinal group:
IUPAC nomenclature of molecule of ethyl chloride.
CH₃-CH₂-Cl
Root word: Eth
Primary suffix: ane
Prefix: Chloro
Prefix + Root word + primary suffix: Chloro ethane

In case molecules with more than three carbon atoms, it is important to specify the position of halogen.
Example:
CH₃-CH₂-CH₂-Cl
Root word: Prop
Primary suffix: ane
Prefix:: 1-Chloro
Prefix + Root word + primary suffix: 1-Chloro propane

CH₃-CH(Cl)-CH₃
Root word: Prop
Primary suffix: ane
Prefix: 2-Chloro
Prefix + Root word + primary suffix: 2-Chloro propane

Chemical Properties of Carbon Compounds

arbon compounds undergo different types of chemical reactions.

•Substitution
•Addition
•Polymerisation
•Combustion
•Thermal cracking.

Combustion:
All carbon compounds react with oxygen to produce heat and light along with carbon dioxide and water. This reaction of carbon with oxygen is called combustion.

Carbon Compound + Oxygen → Carbon dioxide + water + heat and light
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat and light.
        •  Aliphatic compounds on combustion produce a non-sooty flame.
        •  Aromatic compounds on combustion produce sooty flame.

Oxidation:
Alcohols undergo oxidation in presence of oxidising agents like alkaline potassium permanganate
or acidified potassium dichromate to form carboxylic acids.
Example:
Ethyl alcohol on oxidation with alkaline potassium permanganate or acidified potassium dichromate gives acetic acid.
             CH₃-CH₂-OH    Alkaline KMnO 4 or Acidified K 2 Cr 2 O 7 →   CH₃-COOH

Addition reaction:
A chemical reaction is said to be an  addition reaction if two substances combine and form a third substance. In general unsaturated hydrocarbons like alkenes and alkynes prefers to undergo addition reactions.
In addition reactions molecules add across double bond or triple bond.
Hydrogenation reaction involves the addition of hydrogen to unsaturated hydrocarbons in presence of catalyst like nickel or platinum to form saturated hydrocarbons.
Example:
Addition of hydrogen to ethene



Addition of hydrogen ethyne.
 CH ≡ CH + 2H₂         Ni or Pt →          CH₃-CH₃

Addition of halogens to alkenes.
CH₂ = CH₂ + X₂ → CH₂X - CH₂X

Similar to alkenes, addition reactions are also characteristic of alkynes.
Example:
Ethyne reacts readily with hydrogen in the presence of a suitable catalyst to form ethene, an intermediate and then adds another hydrogen molecule to give ethane.
                 CHΞCH + H₂ + (Catalyst) → CH₂=CH₂ + H₂ → CH₃-CH₃

Halogens, especially chlorine, react readily with alkynes to produce tetra-halogen derivatives.

The addition of one molecule of chlorine to ethyne produces 1,2-dichloroethene. The product obtained contains a carbon-carbon double bond and can further add one molecule of chlorine thus yielding a tetra halogen derivative, 1,1,2,2-tetrachloroethane.
CHΞCH + Cl₂ → CH(Cl)=CH(Cl) + Cl₂ → CH(Cl₂)-CH(Cl₂)


Addition of unsymmetrical reagents:
When unsymmetrical reagents like HCl, HBr or H₂O across the double bond in such a way that one part of the molecule attaches itself to one carbon of the double bond, while the other part of the molecule attaches itself to the other carbon of the double bond.

Example:
Ethene on reaction with HCl, produces chloroethane.
                     CH₂=CH₂ + HCl → CH₃-CH₂Cl

The addition product of ethene and HBr is bromoethane.
                    CH₂=CH₂ + HBr → CH₃-CH₂Br


Substitution reaction:
A reaction in which an atom or group of atoms replaces another atom or group of atoms is called substitution reaction. Alkanes undergo substitution reactions.
Example:
Chlorination of methane in presence of sunlight gives a mixture of products like methyl chloride,
methylene chloride, chloroform and carbon tetrachloride.

CH₄ + Cl₂      Sunlight →       CH₃Cl + HCl
CH₃Cl+Cl2         Sunlight →        CH₂Cl₂ + HCl
CH₂Cl₂+Cl₂       Sunlight →        CHCl₃+HCl
CHCl₃+Cl₂       Sunlight →         CCl₄+HCl

Polymerization reaction:
Alkenes and alkynes at higher temperatures under polymerization to form bigger molecules called as polymers.
Example:
Ethene at 400 °C undergoes polymerization to form polyehene.

nCH₂ = CH₂ → [-CH₂ -CH₂ - CH₂ - CH₂-]_n

The polymer is usually named by adding the word “poly” to the name of the monomer. Thus, the polymer of ethene is named polyethene or polythene.

A variety of industrially important polymers are obtained by using substituted ethenes in place of ethene.
Propene gives polypropene on polymerisation.

Chloroethene, commonly known as vinyl chloride, yields poly vinyl chloride or PVC, on polymerisation.
(Teflon) Tetra fluoro ethene, on polymerisation, yields poly tetra fluoro ethene, commonly known as Teflon.

Applications of polymers:
Polythene, polypropene and PVC are common plastics widely used to make plastic bags, bottles, electrical insulation, pipes and many more things.
Teflon is used in the manufacture of non-stick cookware.


_Cracking:
When hydrocarbons of high molecular masses are heated to high temperatures under high pressures, they decompose, forming hydrocarbons of lower molecular masses. This breaking up of large hydrocarbon molecules into smaller at high temperatures is known as thermal cracking. The hydrocarbon molecules are broken up in a fairly random way to produce mixtures of smaller hydrocarbons.

The products of thermal cracking depend upon the nature of the hydrocarbon, temperature, pressure, and the catalyst used. Thermal cracking of decane gives hexane and butene.
_Example:
              C₁₀H₂₂           Cracking at 600 - 700 ℃ →          C₆H₁₄  +  C₄H₈

Important Carbon Compounds

The two important carbon compounds are Ethanol and Ethanoic acid

Alcohol:
Molecules in which hydroxy group attached to alkyl groups are the alcohols.
The formula of alochols can be written by replacing hydrogen ("H") from alkanes with hydroxy group ("OH").
R - H + OH → R - OH
Alcohols can be named by replacing "e" from alkanes with "ol".
Alkan -e + ol → Alkanol

Some of the important alcohols are:

Name of the alcohol	Chemical formula of alcohol
Methanol	CH3-OH
Ethanol	CH3-CH2-OH
Propanol	CH3-CH2-CH2-OH
Butanol	CH3-CH2-CH2-CH2-OH
Pentanol	CH3-CH2-CH2-CH2-CH2-OH

Ethanol:
Ethanol is considered as one of the important organic compound.
The molecular formula of ethanol is C₂H₅OH. It is also called as ethyl alcohol.

Preparation of Ethanol:
Ethanol can be manufactured through fermentation of molasses.
The process involves slow decomposition of a complex organic compound like molasses into simpler compounds including ethanol, by means of microorganisms like yeast.

Physical Properties of ethyl alcohol:
     •  It is a colourless inflammable and sweet smelling liquid
     •  Is miscible with water
     •  It is a good solvent that dissolves most known substances.
     •  Ethanol can cause drunkenness on consumption, even in small quantities of dilute ethanol.
     •  Extremely poisonous when consumed in pure form (absolute alcohol)

Chemical properties of Ethanol:
It involves in different chemical reactions due to the presence of hydroxy group (-OH).

Reaction of ethanol with sodium:
Ethanol readily reacts with sodium to form sodium ethoxide and hydrogen gas.
2Na + 2CH₃CH₂OH → 2CH₃CH₂O^–Na⁺ + H₂        

Reaction with concentrated sulphuric acid:
Ethanol on heating to a temperature of 443 K with excess concentrated sulphuric acid, gives ethene.

CH₃-CH₂-OH        Hot Conc. H ₂ SO ₄ →         CH₂=CH₂+H₂O

Oxidatation:
Ethanol undergoes oxidation in presence of Potassium dichromate to form intially ethanal and finally formsfurther oxidised ethanoic acid.

CH₃-CH₂-OH + K₂Cr₂O₇ → CH₃-CHO → CH₃-COOH

Esterification:
Reaction of ethanol with carboxylic acids is called esterification reaction. The product formed in this reaction is an ester along with water.
Esters are sweet smelling substances which are used in making perfumes and as flavoring agents.
Example:
CH₃-CH₂-OH + CH₃-COOH → CH₃-COOC₂H₅ + H₂O

Uses of Ethanol:
     •  Ethanol is used in pharmaceutical preparations like tincture of iodine, cough syrups, and tonics.
     •  Ethanol is used in the manufacture of organic compounds like acetaldehyde, acetic acid and chloroform.
     •  Ethanol is used as a preservative for biological specimen.



Acetic acid:
The molecular formula of acetic acid is CH₃COOH.
5-8% solution of acetic acid in water is called vinegar.

Preparation of Ethanoic acid:
Ethanoic acid is prepared by the oxidation of ethanol in the presence of oxidising agents like Alkaline KMnO₄  or acidified K₂Cr₂O_7.

CH₃-CH₂-OH    Alkaline   KMnO 4   or Acidified   K 2 Cr 2 O 7 →          CH₃-COOH

Physical Properties of Ethanoic acid:
     •  Ethanoic acid is a colourless corrosive liquid with a pungent odour.
     •  The melting point of pure ethanoic acid is 17 ⁰C.
     •  Ethanoic acid freezes during the winter and is known as glacial acetic acid.
     •  Miscible with water, ether and ethyl alcohol.

Chemical Properties of Ethanoic acid:
Reaction with sodium carbonate:
Ethanoic acid reacts with sodium carbonate to give sodium acetate ,carbon dioxide and water

                    2CH₃-COOH + Na₂CO₃ → 2CH₃COO^-Na⁺ + CO₂ + H₂O

Reaction with sodium hydrogen carbonate:
Ethanoic acid reacts with sodium hydrogen carbonate to give sodium acetate ,carbon dioxide and water.
                    CH₃-COOH + NaHCO₃ → CH₃COO^-Na⁺ + CO₂ + H₂O

Reaction with base:
Ethanoic acid reacts with bases to give salt and water.
Example:
Reaction of ethanoic acid with sodium hydroxide to form sodium acetate and water.
                         CH₃-COOH + NaOH → CH₃COONa + H₂O

Reaction with sodium hydrogen carbonate, sodiumhydrogen carbonate and with bases are the acidic properties of ethanoic acid.

Saponification:
Esters react in the presence of an acid or a base to give back the alcohol and carboxylic acid. This is called saponification reaction. This is reverse reaction of esterification reaction.

CH₃COOC₂H₅       Sodium Hydroxide →      CH₃-COOH + CH₃-CH₂-OH

Reaction with active metals:
Ethanoic acid reacts with active metals to form metal ethanoate and hydrogen gas.
Example:
                      2CH₃COOH + 2Na → 2CH₃COONa + H₂ 
                     2CH₃COOH + Ca → (CH₃COO)₂Ca + H₂ 

Reduction:
Ethanoic acid is reduced to ethanol in presence of reducing reagnets like LiAlH₄ (Lithium aluminum hydrate), NaBH₄(Sodium borohydrate).
CH₃COOH + LiAlH₄ → CH₃-OH

Uses of Ethanoic acid:
     •  Preserve food items
     •  Manufacture of artificial fibres
     •  Ethanoic acid is used for coagulating latex to prepare rubber from it.
     •  It is used as a reagent in the laboratory.
     •  It is used in the preparation of perfumes.

Soaps and Detergents

Soaps:
Soapnut powder has been in use for almost 3,000 years. And still in many parts of India, soap nut powder is using as a natural soap to remove oil.

Soap is a sodium salt or potassium salt of long chain fatty acids having cleansing action in water. They are using as cleansing agents to remove dirt, oil from the skin and clothes.
Examples:
Sodium stearate, sodium oliate and sodium palmitate formed using stearic acid oleic acid and palmitic acid.

Preparation of soap in laboratory:
Animal fat or vegetable oil act as glyceride or glyceryl ester. And sodium hydroxide and potassium hydroxide act as bases.

Take about 30 ml of vegetable oil in a beaker. Then add 60 ml of 20% sodium hydroxide solution to it.
This mixture is heated slowly till it boils. After the mixture has boiled for five to ten minutes add 5grams of sodium chloride in order to separate soap from the solution. Allow the solution to cool. The creamy layer floating on top of the solution is the soap.
Thus soap is prepared by hydrolysing fat or oil with bases such as sodium hydroxide or potassium hydroxide. This process of soap preparation is known as saponification

Generally soaps are prepared by heating animal fat or oil with alkalies like sodium hydroxide or potassium hydroxide. This is saponification reaction.
Fat or Oil + Alkali → Soap + Glycerol


Commercial preparation of soap:
It involves mixture of oil or fat and a strong solution of sodium hydroxide is boiled in an iron tank which leads to the formation of a sodium salt of fatty acid or soap and glycerol.
Once the soap is formed, it is separated with the help of sodium chloride. Sodium chloride also reduces the solubility of soap. Since the soap is lighter, it floats like cream on the solution.
It is separated from the solution, suitable chemicals are added for colour and odour and then it is cast into moulds.
When the soap cools and solidifies, it is cut out into desired shapes and packed.Glycerol, which exists in a dissolved state in the solution, is separated with the help of distillation.
It is possible to prepare different types of soaps from different salts of fatty acids.




Glycerol is by -product formed in the saponification reaction. This is used in the preparation of cosmetics, paints and even explosives.

The Soap molecule has two ends with different properties. They are hydrophillic end and hydrophobic end.
Hydrophillic end :
Hydrophillic end dissolves in water.

Hydrophobic end:
Hydrophobic which dissolves in hydrocarbons.



Cleaning action of soap:
The cleaning action of soap is due to micelle formation and emulsion formation. Inside water a unique orientation forms clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends on the surface of cluster. This results in the formation of micelle.

Soap in the form of micelle cleans the dirt as the dirt will be collected at the centre of micelle.
This property of soap makes it an emulsifier. The dirt suspended in micelles is easily rinsed away. This is known as cleaning action of soap.



Scum:
In hard water soap don't give lather .Hard water contains calcium and magnesium salts, which combine with soap molecules to form insoluble precipitates known as scum.

Detergents:
Detergents have almost the same properties as soaps but they are more effective in hard water. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in water.

History of Periodic Table

History of Periodic Table

he earliest classification categorized elements into metals and non-metals. It was difficult to classify the elements, such as boron, which exhibited the properties of both metals as well as non-metals. After further research a German scientist, Dobereiner arrived at a hypothesis in the year 1829.



According to Dobereiner, all elements occurred in groups of three, when arranged in increasing order of atomic masses. He referred to these groups as triads. In a traid the elements had similar chemical properties.

Traids of the Dobereiners classification:
Traid1:

Element	Atomic mass
Lithium  (Li)	7
Sodium (Na)	23
Potassium (K)	39

Traid2:

Element	Atomic mass
Chlorine (Cl)	35.5
Bromine (Br)	80
Iodine (I)	127

Traid3:

Element	Atomic mass
Calcium (Ca)	40
Strontium (Sr)	88
Barium (Ba)	137

Dobereiner’s law of triads states that, the atomic mass of the middle element of a triad is the arithmetic mean of the atomic masses of the other two elements.

Example:
In the triad of lithium, sodium and potassium. The atomic mass of lithium is 7 and  the atomic mass of potassium is 39. The average of masses of lithium and potassium gives atomic mass of sodium 23.

Drawbacks:
All the known elements could not be arranged in the form of triads.
This law did not hold good for elements with very low or very high atomic mass.
Example: The arithmetic mean of the atomic masses of fluorine 19 and bromine 80, which comes to 49.5, varies significantly from the atomic mass of chlorine, which is 35.5.

Since Dobereiner’s law could not successfully group elements, the attempts at classification continued. The next attempt came in 1864, when an English chemist, John Newlands, stated his observations in the form of Newlands Law of Octaves.

Newlands Law of Octaves:



When Newlands arranged elements in according to their atomic weights then there was similarity of every eighth element. Newland described it as "law of octaves".
According to this law every eighth element is similar to that of the first element, similar to the first and the eighth notes in the musical scale.

Newlands classification of elements:

Li	Be	B	C	N	O	F
Na	Mg	Al	Si	P	S	Cl
K	Ca

Example: When starting from lithium, the eighth element is sodium. Similarly, the eighth element from sodium is potassium. Lithium, sodium and potassium show similar properties.

Drawbacks:

• Not valid for elements having atomic masses higher than calcium.
• Newly discovered elements could not find a place in Newlands table.

Mendeleev's periodic table:



Mendeleev based his work on the research by Newlands and took it further. He felt that effective grouping of elements and prediction of properties could be based on two parameters:

• Atomic mass 
• Chemical reactivity

Mendeleev’s periodic law states that "the physical and chemical properties of all elements are the periodic function of their atomic masses".

Row	Group I	Group II	Group III	Group IV	Group V	Group VI	Group VII	Group VIII
1  2  3	H = 1 Li = 7 Na = 23	Be = 9 Mg = 24	B = 11 Al = 27	C = 12 Si = 28	N = 14 P = 31	O = 16 S = 32	F = 19 Cl = 35.5
4  5	K = 39 Cu = 63	Ca = 40 Zn = 65		Ti = 48	V = 51 As = 75	Cr = 52 Se = 79	Mn = 35 Br = 80	Fe = 56 Co = 58.94 Ni = 58.68
6  7	Rb = 85 Ag = 108	Sr = 87 Cd = 112	Y = 89 In = 113	Zr = 90 Sn = 118	Nb = 94 Sb = 120	Mo = 96 Te = 128	I = 127	Ru = 103 Rh = 104 Pd = 106
8  9	Cs = 133	Ba = 137	La = 138	Ce = 140
10  11	Au = 198	Hg = 200	Yb = 173 Tl = 204	Pb = 206	Ta = 182 Bi = 208	W = 184		Os = 191 Ir =193 Pt = 196
12				Th = 232		U = 240

The main features of Mendeleev’s periodic table:

• The known 63 elements were classified into groups and periods.
• The table had 8 vertical columns called groups and 12 horizontal rows called periods.
• In every group, a gradation of physical and chemical properties of elements was observed.
• The table provided gaps for undiscovered elements.
• The table helped to predict the properties of three unknown elements of that time. These elements were named eka-boron, eka-aluminium and eka-silicon. When these elements were discovered, they were named scandium, gallium and germanium. The properties of these elements were very close to those predicted by Mendeleev.

Merits:
The table helped in the correction of atomic mass for many elements. It predicted the existence of some elements that have not been discovered at the time the table was created.

Demerits:
The atomic weights of two pairs of elements were reversed.
Alkali metals and coinage metals were placed in the same group.
Lanthanides and actinides were not given proper place in the periodic table.
Isotopes were not placed in the periodic table.
The position of hydrogen was not clearly discussed

Modern Periodic Table

The systematic arrangement of elements into groups and periods is called periodic table.
In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.



So Mendeleev’s Periodic law was modified and atomic number was adopted as the basis of the Modern Periodic Table.

The Modern Periodic Law is stated as: "Properties of elements are a periodic functions of their atomic number". Atomic number is the basis for modern periodic table.
Atomic number is the number of protons in the nucleus, it is also equal to the number of electrons in the atom.
Example: In Carbon



The main features of modern periodic table:



        •  Elements are arranged in the increasing order of atomic numbers.
        •  Horizontal rows in the periodic table are called periods and vertical columns in the table are called groups.
        •  Elements in the modern periodic table are arranged in 7 periods and 18 groups.

Filled orbitals and number of elements in different periods:

Period	Nature of period	Filled orbitals	Number of electrons accomdated	Strating -Last element	Number of elements
1	Shortest period	1s	2	Hydrogen - Helium	2
2	Short period	2s 2p	2 + 6	Lithium - Neon	8
3	Short period	3s 3p	2 + 6	Sodium - Argon	8
4	Long period	4s 3d 4p	2 + 10 + 6	Potassium - Krypton	18
5	Long period	5s 4d 5p	2 + 10 + 6	Rubidium - Xenon	18
6	Longest period	6s 5d 4f     5d 7p	2 + 1 + 14 + 9 + 6	Cesium - Radon	32
7	Longest period	7s 6d 5f 6d 7p	2 + 1 + 14 + 9 + 6	Francium - Uuo	32

Elements were classified into groups based on the number of valence electrons.
According to IUPAC nomenclature the 18 groups in modern periodic table are numbered as 1 to 18.

Types of elements:
The elements in the modern periodic table were classified into four types. They are
Representative elements
Transition elements
Inner transition elements
Noble gases





Representative elements:
The elements of group -1, group-2 and group-13 to group-17 are the representative elements.

Group-1:
Lithium, Sodium, Potassium, Rubidium, Cesium and Francium are the elements of this group. Their general electronic configuration is ns¹.
These elements have one electron in their valence shell.
This group elements are also known as alkali metals as the hydroxides of these group elements are basic in nature and soluble in water.

Group-2:
Beryllium, Magnesium, Calcium, Strontium, Barium and Radium are the elements of this group. Their general electronic configuration is ns².
These elements have two electrons in their valence shell.
The hydroxides of these group elements are basic in nature and soluble in water. These elements obtained from earth crust because of these reasons these elements are called as alkaline earth metals.

Group-13:
Boron, Aluminium, Gallium, Indium and Thallium are the elements of this group. Their general electronic configuration is ns²np¹.
These elements have three electrons in their valence shell.
These group elements mostly form covalent compounds.

Group-14:
Carbon, Silicon, Germanium and Tin are the elements of this group. Their general electronic configuration is ns²np².
These elements have four electrons in their valence shell.

Group-15:
Nitrogen, Phosphorous, Arsenic, Antimony and Bismuth are the elements of this group. Their general electronic configuration is ns²np³.
These elements have five electrons in their valence shell.
These group elements are also called as pnictogens.

Group-16:
Oxygen, Sulphur, Selenium, Tellurium and Polonium are the elements of this group. Their general electronic configuration is ns²np⁴.
These elements have six electrons in their valence shell.
This group elements are also known as chalcogens.

Group-17:
Fluorine, Chlorine, Bromine, Iodine and Astatine are the elements of this group. Their general electronic configuration is ns²np⁵.
These elements have seven electrons in their valence shell.
This group elements are also called as halogens.

Group-18:
Helium, Neon, Argon, Krypton, Radon and Xenon are elements of this. This group also referred as zero group. Their general electronic configuration is ns²np⁶.
These elements have eight electrons (octet configuration) in their valence shell.
This group elements are also known as inert gas elements.

Transition elements:
Elements which contains incomplete penultimate ((n-1):d -sub shell) shell with electrons are called transition elements. Elements present between the group -2 and group-13 in the modern periodic table are the transition elements. In transition elements the valency electrons goes to d - sub shell.
General electronic configuration of transition elements is ns² (n-1)d ^1-10.
^{Transition elements are classified into four series of elements.}

They are 3d- series (1^st transition series), 4d –series (2^nd transition series), 5d - Series (3^rd transition series) & 6d – series (4^th transition series).



Lanthanides and actinides:
Elements which kept kept separately under the table in two seperate rows in the Modern periodic table are called lanthanides and actindes.
Theses elements contains incomplete anti-penultimate shells ((n-2): f -sub shells). So these elements are also called as inner transition elements.
General electronic configuration lanathanides and actindies is (n-2) f^1-14 (n-1)d^0-1 ns².

Position of Hydrogen in the periodic table:
There is an anomaly when it comes to the position of Hydrogen in the periodic table as it can be placed either in group I or 17 group of the first period.

Reasons for abnormality regarding the position of hydrogen:
Hydrogen can show properties similar to alkali metals and it has one electron in it valence shell just similar to alkalimetals.
Just similar to alkali metals it loses one electron to form cation.
Similar to alkali metals it combines with Oxygen, Sulphur and Halogens to form similar compounds. 

Hydrogen shows similar properties to halogens.
It exists as a diatomic molecule (H₂). Just similar to halogens which exists as X₂ (X =F, Cl, Br, I).
Hydrogen combines with metals and non metals to form covalent compounds.
Example:
Hydrogen combines with metals to form metal hydrides just similar to halogens which forms halides with metals.
H₂ + 2Na → 2NaH
Cl₂ + 2Na →2NaCl

Because of the above reasons their is uncertainity regarding the position of hydrogen.

Periodic Properties

The term periodic properties in elements, refers to the properties that recur at regular intervals. The trend of recurrence of properties is called periodicity. Important periodic properties are:
        •  Atomic radius
        •  Ionization energy
        •  Electron affinity
        •  Electronegativity
        •  Metallic and non-metallic character

Atomic radius:
Atomic radius is the distance from the centre of the nucleus to the valence electron in an energy level. Atomic radius is expressed in angstrom units.

Trend in atomic radius:
The atomic radius decreases across a period due to increase in nuclear charge.
Example:
The graph below shows decreasing order of atomic radius in period:
         Li > Be > B > N > O



Atomic radius increases down the group due to addition of new shell.
Example:
Following graph shows increasing order of atomic radius in group:
         Li < Na < K < Rb



Ionization energy:
Ionization Energy is the minimum energy required to remove the outermost electron from a gaseous neutral atom to form a cation.
The unit for ionization energy is electron volts or kilo joules per mole.

Trend in Ionization energy:
Ionization energy increases across a period due to increase in the nuclear charge.
The following depicts the increase of IE in period.



Ionization energy decreases down the group due increase due to increase in the atomic size (addition of new shell).
The following graph gives decrease of IE in group-1.



Helium has the highest ionization energy in the periodic table while cesium has the lowest ionization energy.

Electron affinity:
The energy released when an electron is added to a neutral gaseous atom is known as electron affinity. The unit for electron affinity is kilo joules per mole.
It depends mainly on two factors. They are atomic size and nuclear charge.
Atomic size: As the atomic size increases the nucler attraction force on the valence shell decreases. Thus electron affinity will be more for smaller atomic size elements.
Nuclear charge:
Electron affinity increases with increase in the nuclear charge. With the increase in nucler attraction force the electron in the valence shell binds strongly to the atom.

Trend in electron affinity:
The electron affinity increases across a period while it decreases down a group.
The zero group elements have the lowest electron affinity values. Halogens posses highest electron affinity in the periodic table. In halogens chlorine posses highest electron affinity in the periodic table.

Electronegativity:
The tendency of an atom to attract the shared pair of electrons towards itself is known as electronegativity.

Trend in electronegativity:
Electronegativity increases across a period.
Example:
In second period electronegativity increases from lithium to fluorine.

Electronegativity decreases while moving down the group.
Example:
In group-1 electronegativity decreases while moving from top to bottom.
In the periodic table, halogens have high electronegativity. Among halogens Fluorine has the highest electronegativity of 4.0 than Chlorine, Bromine and Iodine.
In the periodic table alkali metals possess very low electronegativity values. Among alkali metals Cesium has the lowest value of 0.7.

Metallic character:
The tendency of an atom to lose electrons is known as metallic character.
Metallic character decreases across a period and increases down the group.
Metals are highly electropositive in nature.

Non-metallic character:
The tendency of an atom to gain electrons is known as non-metallic character.
 Non-metallic character increases across a period and decreases down the group.
Non-metals are more electronegative in nature.

In the periodic table:
        •  Metals are placed on the left side of the periodic table.
        •  Non-metals are placed on the right side of the periodic table.
        •  Metalloids are placed between the metals and the non-metals.

Life Processes

Photosynthesis

Life processes
The processes performed by living organisms in order to maintain and continue life are called as life processes.  Life processes include nutrition, respiration, circulation or transport, excretion, and reproduction.

Nutrition
It is the process by which organisms can assimilate and utilise food for their basic needs. Nutrition is of two different types, namely, autotrophic and heterotrophic.

Photosynthesis:
Photosynthesis is an autotrophic mode of nutrition by plants and some bacteria. Photosynthesis is the physico-chemical process by which plants can convert light energy into chemical energy, in the form of carbohydrate from simple inorganic substances like atmospheric carbon dioxide and water.

Basic raw materials for photosynthesis
Photosynthesis requires carbon dioxide, sunlight, water and chlorophyll as its basic raw materials.



Sites of photosynthesis

• Leaves are considered to be the sites of photosynthesis. Hence, they are called as food factories of the plant.
• Leaves possess small pores called as stomata on both their surfaces. Stomata are the structures which help in the exchange of gases. Opening and closing of the stomata are brought about by the guard cells present in them.
• Leaves are rich in plastids. Green coloured plastids are chloroplasts rich in chlorophyll pigment. Chlorophyll  is responsible for trapping the energy from sunlight.

Overall reaction of photosynthesis

                                 Light Energy
6CO₂ + 12H₂O     Chlorophyll →       C₆H₁₂O₆ + 6O₂ + 6H₂O

Photosynthesis involves two types of reactions namely, light reactions and dark reactions.

a) Light reactions: Light reactions are light dependent reactions. These reactions happen only in the presence of sunlight. The photosynthetic pigments trap the energy from the sunlight. PS-I and PS-II collectively bring in the cyclic photophosphorylation and non-cyclic photophosphorylation reactions. As a result of these reactions energy rich molecules like ATP and NADPH₂ are synthesised. Photolysis of water molecules results in the release of oxygen as a by-product.
          H2O → 2H⁺ + 2e^- + ½O₂

b) Dark reactions: Dark reactions are independent of light. Energy rich molecules like ATP andNADPH2 are utilised in these reactions. Dark reactions involve Calvin cycle during which carbon dioxide is reduced to carbohydrate.
C3 pathway is also known as Calvin cycle.C3 pathway involves set of carbon reactions which are catalysed by the enzyme Rubisco to synthesise 3 carbon compound, 3-phosphoglycerate from 5-carbon compound, Ribulose bisphosphate.

• Ribulose bisphosphate is the primary acceptor of CO₂.
• Chloroplasts present are only of one type.
• Anatomy of leaves does not resemble Kranz anatomy.
• Phosphoglyceric acid is synthesised as the product.
• Mesophyll cells exhibit Calvin cycle.
• Photorespiration is observed.
• Optimum temperature required for photosynthesis is between 20 degree celsius to 25 degree celsius.
• This cycle is less efficient in utilising CO₂.

LIGHT REACTIONS	DARK REACTIONS
These are light dependent reactions.	These are light independent reactions.
Splitting of water molecules releases oxygen as a by-product.	Carbon dioxide is reduced to carbohydrates.
Grana of chloroplasts are the sites of these reactions.	Stroma of chloroplasts are the sites of these reactions.
ATP and NADPH2 are the energy rich compunds synthesised in these reactions.	Energy rich compounds are utilised in the synthesis of carbohydrates.

Events in photosynthesis
Photosynthesis can be split into three basic events.
 
                                 

Factors affecting photosynthesis
Rate of photosynthesis depends on many factors like light, carbon dioxide, water and chlorophyll.



a) Light: Visible spectrum of the sunlight ranges from 380 to 750 nanometres in wavelength.

• Quality of the light also influences the rate of photosynthesis. Photosynthetic rate is higher in red and blue light. It is very poor in green light.
• Intensity of light also determines the rate of photosynthesis.
• Day-length of plants is also an important factor for photosynthesis to be effective. 
• Essentiality of sunlight and chlorophyll are demonstrated using starch test.
• Essentiality of carbon dioxide is demonstrated by bell jar experiment.
• Plants obtain water from the soil by the process of absorption performed by roots.

b) Carbon dioxide: Carbon dioxide occupies 0.04% of the total atmosphere.

• Carbon dioxide plays an important role in providing carbon for the process of photosynthesis.
• Increased concentration of carbon dioxide content enhances the rate of photosynthesis.
• But too much of its concentration proves to be toxic to the plants.
• Carbon dioxide is reduced to carbohydrate in the dark reaction.

c) Water: Water being a universal solvent, almost all the minerals present in the soil dissolve in it.

• It plays a vital role in the process of photosynthesis.
• Water along with minerals is absorbed by roots and is carried to the sites of photosynthesis through xylem tissue.
• 1% of absorbed water is utilized and the remaining water is released during photosynthesis.
• Water serves as a source for oxygen which is released as a by-product. 

d) Chlorophyll: Chlorophyll, green coloured pigment, present in the chloroplasts plays a vital role in the process of photosynthesis.

• Chlorophyll absorbs blue light effectively and then the red light, but proves to be a poor absorber of green light.
• It traps the solar energy and converts into chemical energy which is utilised in the dark reaction of photosynthesis to form glucose.
• Chlorophyll a and chlorophyll b are most prominent forms of chlorophyll found in plants.

Digestion

Heterotrophic nutrition
Heterotrophic nutrition is the mode of nutrition exhibited by heterotrophs. Heterotrophs are the organisms that depend on plants or other organisms for their food.  Heterotrophic mode of nutrition is of different types – saprophytic as in fungi, parasitic as in leeches and symbiotic as in hermit crab.

Unicellular organisms exhibit holozoic type of nutrition. e.g. Amoeba and Paramecium. This type of nutrition involves ingestion of liquid or solid organic material, digestion, absorption and assimilation to utilise it. e.g.Food in the food vacuoles of the amoeba and paramecium is digested by lytic enzymes.

Multicellular organisms exhibit a complex process in obtaining their nourishment.

Digestion:  The process of breaking down complex food substances into simple molecules is called as digestion.

Digestive system in human beings consists of alimentary canal and digestive glands.

• Alimentary canal is made up of mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum and anus.
• The digestive glands are the salivary glands, the gastric glands, the liver, the pancreas and the intestinal glands.

Digestion in buccal cavity is brought about by three pairs of salivary glands opening into the oral cavity.

• Salivary glands include submaxillary, sublingual and parotid glands.
• Amylase, a digestive enzyme in saliva, breaks down the starch in food into simpler sugar.
• Saliva also prevents tooth decay due to the presence of amylase, lysozyme and minerals.

Peristalsis includes a series of muscular contractions in the oesophagus that push the food forward to the stomach.

The stomach is divided into three compartments namely cardiac, fundus and pylorus.  The junction of oesophagus and stomach is guarded by valve which does not allow the food to travel in backward direction.
        •  In the stomach, food is mixed with the gastric juices secreted by the gastric glands.
        •  Gastric juice is a combination of hydrochloric acid, enzymes like pepsin, lipase and mucous. Gastric glands secrete HCL, pepsinogen, mucous.Gastric juice is a secretion of gastric glands located in the lining of the stomach. It is mainly made up of electrolytes, mucus, enzymes, hydrochloric acid, intrinsic factor etc. HCl secreted by parietal cells provides acidic medium for many enzymes to get activated. Neck cells secrete mucus which lubricated the passage of the food. Chief cells secrete pepsinogen which helps in the digestion of proteins after getting activated into pepsin by HCl. Enzymes of the gastric juice bring about digestion of different components of the food. Gastric lipase helps in emulsification of lipids in the stomach. Partially digested food in the stomach is called as chyme and this passes on into small intestine

        •  Partially digested food in the stomach becomes acidic and is known as chyme.

Liver is the largest gland in our body. The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder. Bile plays an important role in the digestion of fats.   Bile is sent into duodenum through a narrow tube-like structure called the bile duct. Bile breaks the larger fat molecules into tiny droplets, thereby increasing their surface area, which helps in the digestion of fats easily. Bile is a dark green alkaline fluid secreted by liver. It comprises of water, bile salts, bile pigments, fats and inorganic salts. Bile comprises of yellow pigment bilirubin which oxidizes to form green pigment biliverdin only when it enters the intestine.

        •  Bile makes the food alkaline for the action of pancreatic and intestinal enzymes in the small intestine.

        •  Bile brings about emulsification of fats which are later digested by intestinal lipases.

Pancreas is the mixed gland. It acts as a both endocrine and exocrine gland. The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the lipids into fatty acids and glycerol. 

The exocrine part of pancreas secretes pancreatic juice which includes trypsin and lipase that help break down proteins and fats. Trypsin and chymotrypsin help in the digestion of proteins.

Liver and pancreas open into intestine through hepato-pancreatic duct to throw their secretions for further digestion of food.

Small intestine is made up of three regions namely duodenum, jejunum and ileum. Acidic chyme from the stomach is received by the duodenum for further digestion. 

• Duodenum receives bile form the liver.  Bile provides an alkaline environment for many enzymes to get active. It also reduces the acidity of chyme. Bile plays an important role in the digestion of fats.  
• Duodenum also receives pancreatic secretions which help in the digestion of food. Pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats.  
• Duodenum also secretes some enzymes on its own. Cells lining the inner lining of intestine secrete enzyme rich intestinal juice. Intestinal juice comprises of many enzymes like enterokinase, invertase, maltase and lipase. The intestinal enzymes act upon partially digested proteins, carbohydrates and fats.
• All these substances bring about digestion of food in the duodenum. The inner walls of small intestine are thrown into many folds which have millions of small finger like projections called villi.
• Intestinal glands are present in the inner lining of small intestine. These secrete various enzymes which aid in the process of digestion of all the components of food. Maltase, sucrase and lactase bring about digestion of carbohydrates. Peptidases help in digestion of proteins. Enterokinase helps in the activation of other enzymes.
• Proteins, carbohydrates and fats are simplified into amino acids, glucose, fatty acids and glycerol in a liquid medium known as chyle.
•  Specific structures called as villi in the small intestine increase its surface area to ensure efficient and rapid absorption of nutrients. Villi increase the surface area for digestion as well as absorption of digested food by eight times.  Blood capillaries in the villi absorb nutrients and transport the food to all the cells in the body.

The large intestine comprises caecum, appendix, colon, rectum and anus. The large intestine absorbs water from undigested food and forms solid waste.
        •  The rectum stores the solid excreta until it is ready to be excreted from the digestive system through anus.
        •  The appendix is a small, hollow, finger-like pouch, which hangs at the end of the cecum. It does not have any function in the digestive system of humans. However, it is functional in herbivores such as cows.

Respiration

Respiration
 It is the process by which chemical energy stored in the food is released in the form of ATP along with carbon dioxide and water.

Respiration begins with breathing, a combined process of inhaling oxygen and exhaling carbon dioxide.

Types of respiration
 Respiration can be of two types – Aerobic and Anaerobic.  Both of these respirations take place inside the cell.

• Aerobic respiration involves breakdown of glucose into carbon dioxide and water in the presence of oxygen. In aerobic organisms, the pyruvate molecule is further broken down in the mitochondria of a cell. The pyruvate molecule that contains three carbon atoms is broken down into three molecules of carbon dioxide and three molecules of water by the action of mitochondrial enzymes.
• Anaerobic respiration involves the breakdown of food into alcohol and carbon dioxide in the absence of oxygen.   The breakdown of glucose to release energy from the cells in anaerobic conditions is fermentation. Under anaerobic conditions prevailing in our muscle cells, the insufficiency of oxygen converts the pyruvate molecules into lactic acid and energy.   Accumulation of lactic acid in our muscle cells causes cramps.

Process of respiration 

During respiration, a glucose molecule that contains six carbon atoms is broken down into pyruvate. Pyruvate is a molecule that contains three carbon atoms.

1) In aerobic organisms, the pyruvate molecule is further broken down in the mitochondria of a cell. The pyruvate molecule that contains three carbon atoms is broken down into three molecules of carbon dioxide and three molecules of water by the action of mitochondrial enzymes.

• Glycolysis is the process which involves breakdown of glucose molecule to release two molecules of pyruvate. It is  multi-step procedure occurring in the cytoplasm of the cells. The process is same for plant cells and animal cells. This process results in the formation of pyruvate molecules along with some ATP molecules. Pyruvate molecules act as substrate molecules for the Krebs cycle which occurs in the mitochondria of both animal and plant cells. Krebs cycle also finally releases ATP molecules, energy coins of the cell.Glycolysis is made up of preparatory phase and pay-off phase. The net gain of glycolysis is 2 ATP and 2 NADH2. Pyruvate can be utilised in Kreb's cycle, lactic acid or alcohol fermentation, based on the availability of oxygen. 
• Krebs' cycle involves a set of enzymatic reactions taking part in mitochondria in the presence of oxygen to yield energy rich molecules. It is also called as Tricarboxylic acid cycle. The net gain of aerobic respiration at the end of Krebs' cycle is 2 ATP molecules, 8 molecules of NADH+H+  and 2 molecules of FADH2. As we know, ATP is the energy rich coin of the cell utilised for different purposes.
• Electron Transport Chain is a step wise process which generates energy in the form of ATP molecule from NADH and FADH2 produced during glycolysis, Krebs cycle and other catabolic processes. Electron Transport Chain is an important step of cellular respiration. The mechanism by which Electron Transport Chain generates ATP is called as chemiosmotic phosphorylation. Electron Transport Chain is made up of different complexes and enzymes which participate in ATP synthesis. ETS comprises of several energy carriers which include NADH dehydrogenase complex (Complex I), Ubiquinone (Complex Q), Succinate dehydrogenase complex (complex II), Cytochrome bc1 complex (Complex III), Cytochrome c, Cytochrome c oxidase (Complex IV)

2) Under anaerobic conditions prevailing in our muscle cells, the insufficiency of oxygen converts the pyruvate molecules into lactic acid and energy.  Accumulation of lactic acid in our muscle cells causes cramps. Fermentation is an anaerobic process which takes place in the absence of oxygen. It converts sugar substrates into alcohol and carbon dioxide. Fermentation process also releases certain amount of energy

Both aerobic and anaerobic respiration release energy in the form of ATP.  The energy released in the aerobic process is 19 times greater than the energy released in anaerobic process. The energy in the form of ATP is used for many activities such as the contraction of muscles, protein synthesis and conduction of nervous impulses etc.

Respiration in plants
Respiration in plants is just opposite to that of photosynthesis. Exchange of gases takes place in plants through special structures called as stomata. Stomata are small pores present on the surface of leaves and green parts of plant. Opening and closing of stomata are controlled by guard cells.

• Dark respiration taking place in plants is independent of the presence of light. Plant cells after synthesizing sugar molecules through photosynthesis, undergo cellular respiration to break down food molecules to obtain energy in the form of ATP molecules. Dark respiration is a form of respiration where carbon dioxide is released without the aid of sunlight.
• Light phase or photorespiration is an inevitable process which occurs in C3 plants. There is a decreased output of photosynthesis. ATP is not synthesized in photorespiration and carbon is released in the form of carbon dioxide. Nitrogen is also released in the form of ammonia.

Respiration in aquatic forms
The rate of breathing in aquatic organisms is much faster than in terrestrial organisms. Respiration in aquatic animals is performed by diffusion through body surface and special respiratory organs called as gills.
Fish are the aquatic vertebrates which respire through structures called as gills. This is called as branchial respiration.

• Gills are present on either side of the head and are supplied by rich blood vessels. Fish obtain oxygen dissolved in water.
• During respiration, water enters the body through mouth, passes through gills and comes out of the operculum.
• Exchange of gases takes place in the gills of fish supplied by numerous blood vessels. They accept oxygen into the body and expel out carbon dioxide.

Respiration in terrestrial forms
Terrestrial animals have special organs for taking in oxygen from the atmosphere. For instance, cockroaches respire through the trachea, and scorpions through the book lungs. Breathing is the physical act of inhaling and exhaling. Breathing involves taking in oxygen from the environment and removal of carbon dioxide from the body. The diaphragm is a thin thin sheet of muscle separating the thorax and the abdomen, and helps in respiration.

Path taken by air
Air enters a human body through the nostrils. It passes through nasal cavity and  then enters trachea. From the trachea, air enters the bronchi and then goes into the lungs. The bronchi form a network of bronchioles. Each bronchiole has alveoli at the end in the lungs. The thin membranes of alveoli allow the exchange of gases. Alveoli are richly supplied with blood vessels.

• Haemoglobin present in RBCs is a metallo-globulin which is made up of 2 alpha chains and 2 beta chains. The respiratory pigment, haemoglobin present in blood absorbs oxygen from the lungs and carries it to tissues all over the body. In return it carries carbon dioxide from the tissues to the lungs.

Transportation in Animals

Circulatory system
The system which pumps the fluid tissue to transport it throughout the body is called the circulatory system. Human circulatory system comprises of heart, blood and a network of blood vessels. The system transports oxygenated blood from lungs and the heart throughout the body via arteries. The oxygenated blood is supplied to all the organs by arteries branching out as capillaries. The deoxygenated blood is returned to veins through capillaries. These veins carry deoxygenated blood to the heart and the lungs.

Human heart

The heart is the central organ for pumping the blood throughout the body.  Heart is made up of strong cardiac muscles. It is located in the chest cavity with its lower part pointing towards the left. Its size is that of the person’s fist. It pumps blood rich in carbon dioxide to the lungs and oxygen-rich blood to other parts of the body. 

• The heart consists of four chambers namely auricles and ventricles. The two upper chambers of the heart are known as the auricles.
• The two lower chambers of the heart are the ventricles. Left and right parts of the heart are separated by a muscular partition called as septum.
• Heart has number of valves which allow the blood to flow in one direction. These prevent the oxygenated blood mixing with de-oxygenated blood. 
• SA node, the natural and primary pace maker of the heart is located in the upper wall of the right atrium in the heart.
• AV node, the secondary pace maker is located in the bundles of tissues on the border between right atrium and right ventricle of the heart.

Blood vessels
Blood vessels are tube like structures which form an intricate network to transport blood to various parts of the body. They are classified as arteries, veins and capillaries.
a) Arteries are the blood vessels which carry pure oxygenated blood from the heart to different tissues in the body. Arteries are with thick walls as the heart pumps blood with greater pressure into the arteries. Inturn arteries also offer some pressure on the blood. This is called as peripheral resistance. Pulmonary artery carries impure blood to the lungs from heart 

b) Veins arise from the bodily tissues. Thus deoxygenated blood is carried by veins and is returned to heart. All the veins carry impure blood to the heart except for pulmonary veins which carry pure blood from lungs to the heart. Veins have wider inner diameters and valves to prevent the back flow of blood. Blood is just allowed to go towards the heart and not in any other way. The walls of veins are thinner when compared to the walls of the artery.  Pulmonary veins carry pure blood from lungs to the heart. Pulmonary veins need not have thicker walls as such as blood is not pumped by the heart in to these veins. They carry pure blood from lungs. They have valves in them so as to prevent backward flow of the blood. There are totally four pulmonary veins and all of them are connected to left atrium of our heart.

c) Blood capillaries are the structures which branch out form arteries on entering the tissues. Blood capillaries supply pure blood to inner parts of the tissue. These capillaries in turn collectively form a single vein from the tissue. The heart pumps deoxygenated blood into the lungs through pulmonary arteries.
Pulmonary artery carries impure blood to the lungs from heart . Blood gets purified in the lungs.  Pulmonary veins carry pure oxygenated blood from lungs to the heart.

Functions of the heart

• All parts of our body require oxygen to carry out life processes. We take in oxygen by the process of respiration. But this oxygen should be carried over to all parts of the body.The oxygen in the lungs binds to  hemoglobin present in the blood. This oxygenated blood is taken to heart. This oxygen carrying blood should be transported to all the parts of our body. To pump this blood with pressure we need a central pumping organ called as heart. This is the reason why our heart pumps continuously.  
• It is a central pumping organ of the circulatory system which pumps oxygenated (pure) blood into the blood vessels to be carried over to different parts of the body.
• It receives deoxygenated (impure) blood from different parts of the body and sends it to the lungs for purification.

Blood
Blood and lymph are the important modes of transport in the circulatory system. Blood is a fluid tissue made from plasma and formed elements.

• Plasma is a pale yellowish fluid that contains albumin (the chief protein constituent), fibrinogen (responsible, in part, for the clotting of blood) and globulins (including antibodies). Plasma is obtained by separating the liquid portion of blood from the cells. Plasma serves a variety of functions like maintaining a satisfactory blood pressure and volume, serving as the medium for exchange of vital minerals, maintaining a proper pH in the body. It also helps in transporting gases, nutrients and nitrogenous waste.
• Red blood cells in the blood are flattened disc like structures responsible of transporting oxygen and carbon dioxide gases. Red blood cells consist of red iron-containing pigment called as haemoglobin. Haemoglobin is a respiratory pigment that carries oxygen through red blood cells. Oxygenated blood is carried to tissues. 
• White blood cells are otherwise known as leukocytes. WBCs help the body in fighting against the diseases. Different types of WBCs are Granulocytes, Monocytes and Lymphocytes. Granulocytes are further divided into Neutrophils, Eosinophils and Basophils. Monocytes can transform themselves into two types of cells namely, Dendritic cells and Macrophages. Lymphocytes can be of two types namely B-lymphocytes and T-lymphocytes.
•  Platelets are the non nucleated, irregular cells which bring about clotting of the blood.These are also called as thrombocytes as they release thromboplastin which plays an important role in clotting of blood. Platelets immediately come to the place of injury and lyse themselves to release thromboplastin. The remnants aggregate in large amounts to form a plug on the injury preventing the blood loss.

Functions of blood
Blood plays a vital role in transporting many substances to all parts of the body.

• As the blood contains RBCs, it transports oxygen from lungs to cells and in turn carries carbon dioxide in the opposite direction.
• Urea , the main excretory product formed in the liver is carried away by the blood to kidneys.
• Blood transports soluble digested food materials which are absorbed in the small intestine.
• Blood provides a medium of transport for the hormones secreted by different endocrine glands to reach their   target organs.
• Blood also transports water required by the cells to perform various biochemical reactions.

Lymph
Lymph is a clear fluid sometimes white in colour comprises of white blood cells mainly lymphocytes. Lymph is a colourless fluid that contains less protein than plasma, and lacks RBC. These cells also attack bacteria entering the cells. Lymph also contains the fluid from the intestine containing proteins and fats.  Lymph helps in carrying absorbed fat molecules from the intestine to different parts of the body.The composition of lymph varies with that of blood plasma.  When the lymph is produced from the intestine, it is thick milky white solution rich in triglycerides.   

Types of circulation
The two types of circulation are single circulation and double circulation. 

• Single circulation is the type of circulation in which blood passes through the heart only once through the heart. For example, it is seen in fishes. Fish is a lower vertebrate with a two chambered heart. Fish has a two chambered heart comprising of one atrium and one ventricle. Gills help in purifying the deoxygenated blood. This two chambered heart exhibits single mode of circulation. Impure blood is pumped to gills for oxygenation. This oxygenated blood from gills is supplied directly to the body tissues without sending to the heart. 
• Incomplete double circulation is observed in amphibians and reptiles which have three-chambered hearts with two atria and one ventricle. 
• Double circulation is the type of circulation during which blood passes twice through the heart. Higher vertebrates like birds and mammals exhibit double circulation. 

Blood pressure

Blood pressure is the pressure exerted by the blood on the walls of the arteries.

• The pressure can be systolic pressure during contraction and diastolic pressure at relaxed state.
• The pressure exerted by blood against the wall of an artery during ventricular contraction or systole is called systolic pressure, and that exerted during ventricular expansion or diastole is called diastolic pressure. 
• Normal blood pressure is 120/80mmHg. If the blood pressure is less than 100/50 then it is termed to be low blood pressure or hypotension. If it exceeds 140/90, it is termed to be high blood pressure or hypertension.
• An instrument called the sphygmomanometer is used to measure blood pressure. The normal systolic pressure is about 120 mm of Hg, and diastolic pressure is 80 mm of Hg.

Transport of gases
We take in oxygen during inhalation and it reaches lungs through respiratory tract. Hemoglobin, an intracellular protein is the primary vehicle for transporting 97% of oxygen in the blood. 3% of Oxygen is carried by plasma. Hemoglobin is contained in erythrocytes. 

• The amount of oxygen bound to the hemoglobin at any time is related to the partial pressure of oxygen to which the hemoglobin is exposed. In the lungs, at the alveolar-capillary interface, the partial pressure of oxygen is high, and therefore the oxygen binds readily to hemoglobin. As the blood circulates to other body tissue in which the partial pressure of oxygen is less, the hemoglobin releases the oxygen into the tissue because the hemoglobin cannot maintain its full bound capacity of oxygen in the presence of lower oxygen partial pressures.
• Red blood cells in the blood are flattened disc like structures responsible of transporting oxygen and carbon dioxide gases. Red blood cells consist of red iron-containing pigment called as haemoglobin. Haemoglobin is a respiratory pigment that carries oxygen through red blood cells. Oxygenated blood is carried to tissues. 
• The exchange of gases at tissue level is called as peripheral gas exchange. The capillaries of circulatory system deliver the oxygen rich blood to the tissues of the body. This oxygen diffuses across the walls of the capillaries into tissues. In turn carbon dioxide diffuses into the blood from tissues. The carbon dioxide diffused into the blood binds to haemoglobin present in the blood to form carboxyhaemoglobin. This de-oxygenated blood is carried to lungs for purification. In the lungs, carbon dioxide from carboxyhaemoglobin dissociates leaving behind haemoglobin. The cycle continues to cary oxygen from lungs to tissues and carbon dioxide from tissues to lungs by haemoglobin. 

Transportation in Plants

Plants obtain minerals from soil, water and fertilisers. Need for transportation in plants is to distribute water and nutrients to various parts. Transportation in a plant is a method of circulation of water and minerals from soil throughout the body of a plant.

Vascular tissues in transport
Vascular tissues like the xylem and phloem help in the conduction of water, minerals and nutrients throughout a plant’s body.

a) Xylem is the vascular tissue extending from top to bottom of the plant.

• Xylem tissue is present in the roots, stems and leaves. 
• It helps in the transport of water molecules and dissolved substances from the root hairs to aerial parts of the plant.
• Xylem mainly comprises of tracheids, vessels, xylem parenchyma and xylem sclerenchyma.
• The transport in xylem is unidirectional.
• Xylem mostly occupies the centre of the vascular bundle.
• The xylem transports water and minerals from the roots to the leaves.
• Tracheids and vessels are interconnected to form a continuous system of water-conducting channels that reach all parts of a plant.
• Cells in the roots take up ions to create a high ion concentration. This causes water to move into the roots.   

b) Phloem is the vascular tissue which transports food molecules to the place of necessity in the plant.

• The elements in the phloem are sieve elements, fibres, phloem parenchyma and companion cells.
• The transport in the phloem tissue is bidirectional.
• It forms vascular bundles in association with xylem.
• Phloem occupies the edges of the vascular bundle. 

Transpiration

Transpiration is the evaporation of water from the leaves in the form of water vapour. Transpiration occurs in leaves through special structures present on them called as stomata.Transpiration is the process which helps the plant in many ways.

• Transpiration always occurs against the gravity. 
• Transpiration involves mainly the xylem cells which become active during absorption process by the roots.
• Excess water is removed from the cells of the plant to prevent plant decay.
• Osmotic balance of the cell is maintained by the process of transpiration.
• Transpiration is the process which helps all the parts of the plant to cool them.
• Transpiration helps in the distribution of dissolved substances to all parts of the plant.

Translocation

Translocation is the process of the movement of synthesised products from the leaves to the roots and other parts of a plant’s body through the phloem. 

• The phloem is a conducting tissue for nutrients from the leaves to the other parts of a plant’s body. Translocation does not always occur against gravity. 
• Translocation involves both xylem and phloem cells to carry the synthesized food materials within the plant. 
• As sugar is synthesised in the leaves by the process of photosynthesis, a high concentration of organic substance inside the phloem cells of the leaf creates a diffusion gradient by which more water is sucked into the cells.
• Translocation takes place in the sieve tubes, with the help of adjacent companion cells.

Types of transport
a) Passive transport can be explained by diffusion. Diffusion is the movement of molecules in a random manner that is from a region of higher concentration to a region of lower concentration. Diffusion involves no expenditure of energy as it does not involve any semi-permeable mebrane.Diffusion is a process which can occur in all media which involve solid, liquid and gaseous molecules. Diffusion is a passive process which occurs in the transportation of substances in plants.

b) Active transport involves the movement of ions against concentration gradient through membranes. It is carried out with expenditure of energy. Active transport requires carriers for transport across the cell membrane. Active transport is involved in translocation os minerals in the plant body and accumulation in the plant cells. e.g Glucose molecules in the leaves are transferred to the phloem tissue using energy from ATP.

c) Osmosis is the process of diffusion of solvent particles from the region of less solute concentration to a region of high solute concentration through semi-permeable membrane. Osmosis can be observed in human beings in the phenomenon of membrane transport.  Cells possess cell membranes. These cell membranes are selectively permeable and many molecules move in and out of the cell by the process of osmosis.

Types of solutions
Osmosis can occur in hypertonic solutions, hypotonic solutions and isotonic solutions. Sometimes cell can even undergo the phenomenon called as plasmolysis.

• Hypotonic solutions are the ones which have a lower concentration of solute than the cell. Water diffuses into the cell to balance the solute concentration on either side (outside and inside) equal. Here the cell swells up due to entry of water.
• Hypertonic solutions are the ones which have higher solute concentration than the cell. Water moves out of the cell through cell membrane to balance the concentration of the solute on either side. It results in cell shrinking .This may also lead to desiccation of the cell.
• Isotonic solutions have the same concentration of the solute as the cell. Water moves in and out of the cell with no net change. 

Excretion

Excretion
Excretion is the process of removing harmful metabolic wastes such as urea, uric acid and salts from the body.

Excretion in organisms

• Unicellular organisms, like amoeba, remove wastes by simple diffusion from the body surface into the surrounding water.
• Lower multi-cellular organisms like flat worms use flame cells while earthworms use nephridia for excretion.
• Higher multi-cellular organisms like fish, frogs, lizards, birds and humans use kidneys for excretion. Homeostasis is the tendency of the physiological system of higher animals to maintain internal stability of the body.

Excretory system in humans
The excretory system in human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. This is also known as the urinary system.

1) Kidney
Kidney is an excretory organ present in the human body. Kidneys act as excretory organs and also control the balance of water and mineral ions in the body. Kidney is divided into two parts namely, external region and internal region.

• External region is made up of a thick layer followed by a layer of fat. Fat acts as a shock absorber.
• Inner region comprises of renal cortex and renal medulla. The medulla is composed of conical masses of tissue that lead to pelvis. The cortex has a random arrangement of tiny tubules called nephrons which are the functional units of the kidney.

Nephrons are the microscopic basic filtration units of the kidney. Nephrons carry out an important process of urine formation in the kidney. Ultra-filtration is the first step in the urine formation in which nephrons filter minerals, waste and water but retain red cells, proteins and large molecules. A single nephron is made up of renal corpuscle and a renal tubule.

a) Renal corpuscle is made up of tangled clusters of tiny blood capillaries called glomerulus and Bowman’s capsule. 

• Glomerulus is called the filtration unit. 
• Bowman's capsule surrounds the glomerulus.

b) Renal tubule is made up of proximal convoluted tubule, Henle’s loop and distal convoluted tubule. 

• Renal tubule leads away from Bowman's capsule and becomes highly coiled to form the proximal convoluted tubule.  
• The tubule makes a hairpin loop, called the loop of Henle. It joins the distal convoluted tubule.
• The distal convoluted tubule opens into a collecting duct, which passes into the renal medulla.

2) Ureter
Each ureter is a tubular structure which arises on from each kidney and join to form a single tube which opens From each kidney, a ureter arises which opens into the urinary bladder.

3) Urinary bladder
It is a muscular sac situated at the lower part of the abdomen which receives urine from the kidney through ureters. It stores this urine until it becomes full. Urinary bladder opens out through urethra. Urethra passes urine to the outside of the body. The urethra emerges through the penis in males and close to the vagina in females.

Excretory pathway in kidney – Blood is carried by the renal artery to the nephron from there to renal pyramid leading to pelvis to the ureter, then to the urinary bladder and finally to the urethra which passes it to outside.

Other organs of excretion
a) Skin

• Sweat glands in the skin allow evaporation of excess water along with some salts which have to be excreted out of the body. Sweating is a vital function of your body. Sweating helps in thermoregulation of the body. Sweat glands secrete fluids that will cool your body in cases of extreme heat. 
• Sebaceous glands in the skin excrete excess oil outside in the form of sebum.

b) Lungs
Lungs are the respiratory organs in human beings. Pulmonary artery carries impure blood to the lungs from the heart.The alveolar cells of the lungs help in exchange of oxygen with carbon dioxide  to provide the former to the bodily tissues. Lungs excretel carbon dioxide out of the body.

c) Anus
Anus is the opening of the alimentary canal to the exterior. Undigested waste is stored in the rectum for defecation. Anus helps in the excretion of faeces by the process of egestion.

Excretory pathway in kidney – Blood is carried by the renal artery to the nephron from there to renal pyramid leading to pelvis, to the ureter, then to the urinary bladder and finally to the urethra which passes it to outside.

Steps in urine formation
The kidney performs three functions as steps involved in urine formation - ultra-filtration, selective re-absorption and tubular secretion.

• Ultra-filtration is the process in which nephrons filter minerals, waste and water but retain red cells, proteins and large molecules.  
• Selective re-absorption involves reabsorption of some substances of the initial filtrate, such as glucose, amino acids, salts, and a major amount of water. Urine is allowed to flow along the tube.
• Tubular secretion involves the secretion of substances not required by the body into the filtrate by the cells of the distal convoluted tubule before it leaves the kidney.  

Excretory substances
Excretory sunstances can be ammonia, urea and uric acid.

a) Ammonia is generated as a result of oxidative deamination reactions occurring in the body. Ammonia is a toxic nitrogeneous waste and need to be eliminated. It is very toxic to the body and requires more amount of water to excrete it. Aquatic organisms excrete ammonia as they have water around them. Terrestrial animals either convert ammonia into urea or uric acid. Ammonia reaches the liver, the key site which converts this ammonia into urea. 

b) Urea is the excretory waste of human beings. As a result of amino acid metabolism, many nitrogeneous wastes like ammonia.   As ammonia is toxic to human body when retained, it is coverted into urea by the liver.   Urea is also called as carbamide. Urea , the main excretory product formed in the liver is carried away by the blood to kidneys.

c) Uric acid is a bicyclic, heterocyclic compound made by the combination of carbon, hydrogen, oxygen and nitrogen. It is formed in the body during protein metabolism. Animals that excrete their waste in the form of nucleic acid form shelled eggs which are permeable to soluble gases. Most of the terrestrial organisms which do not have much access to water excrete uric acid as their excretory product. e.g.Reptiles, Birds. In human beings, it is formed as a result of metabolism of food mainly containing purines. Uric acid formed dissolves in the blood and taken to kidneys for excretion. It is very concentrated and requires very less amount of water to be excreted along with it. Excess of uric acid in the blood causes the disease called as gout.

Dialysis:
Dialysis is the process which involves separation of nitrogeneous wastes from the blood artificially. Dialysis is performed using a device which removes nitrogenous wastes from blood in case of kidney failure.

• An artificial kidney contains a number of tubes with a semi-permeable lining suspended in a tank filled with dialysing fluid.
• The patient’s blood is passed through these tubes.
• During this passage, waste products from the blood diffuse into the dialysing fluid.
• The purified blood is pumped back into the patient.

Excretion is also observed in plants. Plants get rid of excess water by the process of transpiration. Resins, gums and dead leaves are some excretory products of plants.

How do organism reproduce

Reproduction and Its Significance

Reproduction
Reproduction is the biological process by which existing organisms give rise to their offspring. Reproduction is carried out by different living organisms to perpetuate their species. Reproduction can be of two types – Sexual mode and Asexual mode.

• Reproduction prevents all kinds of organisms from becoming extinct.
• Reproduction is not necessary for carrying out life processes of an individual but helps in increasing the individuals in a population.
• Reproduction is essential in creating variations in species through genetic recombination. 
• Reproduction is necessary in the process of evolution by carrying favourable variations from one generation to another generation. 

Evolution
It is a long, drawn out process with gradual changes that take place over millions of years.  Evolution operates on different factors like variations, natural selection and adaptation. Evolution results in group of organisms living together in a well-defined environment.  Organisms living in this specific environment reproduce the offspring which are adapted to that specific environment. e.g. Over generations, giraffes developed long necks to eat leaves growing high up on trees.

Evolution occurs by stages
Evolution is a step by step process, it does not happen in few years. It takes generations by generations to exhibit variations over a large range. Organisms get adapted to their habitat by bring about certain changes in their structure. These changes are called as adaptations which bring about variations in the evolution. These variations are carried on to successive generations by natural selection.

• A classic example which supports the statement 'Evolution by stages' is the evolution of eye.
• In lower organisms like planaria, optic sensory structures are present  as patches which act as eye spots.
• In organisms like cockroaches, compound eyes are present which help them to see around their body.
• In organisms like octopus, eye is remarkable having  iris, circular lens, vitreous cavity, retina with photoreceptor cells. They lack a cornea. The lens in octopus does not change its shape but focusses through movement.
• In vertebrates, eye is a well-developed sensory structure with iris, ciliary muscles, pupil, cornea and a lens. The size of the pupil can be regulated. Shape of the lens can be adjusted in order to focus the image on the retina.

Evolution cannot be equated with progress

• Evolution is not exactly taking place from lower organisms to higher organisms but it can be related to the fact that higher and complex body forms evolved even when the low and simple forms are still existing. An individual also plays an important role in the evolutionary process. An individual contributes its specific genes into the gene pool of the population during transferring its genetic variations to its offspring. 
• These variations are carried on to successive generations by natural selection.
• If these genetic variations get accumulated over a period of time, alter the individuals of the subgroup and later give rise to new species.

Variations
These are the changes caused in the genetic material thereby bringing about changes in the offspring.

• Deoxyribonucleic acid is a genetic material present in chromosomes. 
• It carries information from parents to children.
• DNA replication is the process of creating similar copies of DNA during reproduction.
• Mutation leads to variation in DNA.
• Variations accumulated over a period of time are carried on to successive generations by natural selection. These genetic variations alter the individuals of the subgroup and later give rise to new species.
• Variations in species bring about diversity.

Variations caused by mutations can be beneficial or detrimental.

• Some variations might cause new born cells to die or survive. The surviving cells are similar to or different from each other.
• Variations can help species to evolve and survive in adverse conditions. e.g. Adaptation of giraffes, snakes and bacteria to the changing environment.
• Only advantageous variations occurring in an individual are able to exist in population. This is because variations which are detrimental cause the death of the individual. Hence, there is no chance for the detrimental variations to be carried to the next generation.

Varations are advantageous to species and not individuals

• Variations are advantageous to species as the changes which are acquired by variations are inherited by the offspring and certain alterations occur over many generations to make the changes acquired by variations perfect.
• Variations may prove to be advantageous or disadvantageous to the individual as the life span of the individual is so small. Variations acquired by the individual are not easily acceptable. Individual with variations is not easily accepted into the group.

Adverse changes in the environment can kill a species

Reproduction in Unicellular and Multicellular Organisms

Reproduction
Reproduction is the phenomenon which involves the production of an offspring by particular individual or individuals to propagate their species. Reproduction is done during reproductive phase.

Reproduction based on the number
Unicellular organisms are single celled forms whereas multicellular organisms are made up of many cells. Depending upon the complexity of the body, reproduction in unicellular organisms is different from that of multicellular organisms. 

• Unicellular organisms reproduce by asexual means. This asexual mode of reproduction involves single parent to produce their offspring. Different asexual modes of reproduction include binary fission, multiple fission, fragmentation, budding etc.
• Multicellular organisms can chose both asexual and sexual modes to reproduce their offspring. The mode of reproduction by organisms depends upon the favourable and unfvourable conditions prevailing.

Types of reproduction 
Reproduction can be of two different types, namely, asexual reproduction and sexual reproduction.

• Asexual mode of reproduction: It is a mode of reproduction in which a single individual is responsible for creating a new generation of species. Reproductive structures are not involved. Vegetative parts of individuls are used for the process of reproduction. Gametes are not formed. Single parent cell gives rise to daughter cell. Offspring formed are exact individuals of the parents
• Sexual mode of reproduction: It involves the union of two opposite sex cells by the process of fertilisation to give rise to zygote, the single cell. This type of reproduction involves two organisms, the male and the female. Reproductive organs in humans produce gametes - eggs and sperms. Egg is the female gamete produced by female reproductive organ. Sperms are male gametes produced by male reproductive organ. A zygote is the future individual formed by the fusion of an egg and a sperm.

Types of asexual reproduction
Different asexual modes of reproduction by which offspring can be produced are binary fission, budding, fragmentation, regeneration, vegetative propagation, spore formation etc.

1) Binary fission: It involves the longitudinal or transverse splitting of an organism into two equal halves which develop into two separate individuals.

• Binary fission is generally seen in unicellular organisms such as amoeba and paramecium falling into the category of protozoa.
• Amoeba is a simple, unicellular organism which reproduces by transverse binary fission. The division begins with the division of nucleus.
• Binary fission can also be observed in multicellular animals like sea anemones and planarians. 
• Binary fission observed in Leishmania is longitudinal binary fission. Longitudinal binary fission is the division occurring in a definite orientation in relation to the whip-like structures located at one end of the cell. 

2) Multiple fission: Multiple fiision is the process by which organisms reproduce under unfavourable conditions. Under unfavourable conditions, organism does not stop reproducing but divides rapidly inside a cyst and forms many individuals inside the cyst, when favourable conditions prevail, organism releases multiple individuals at the same time which are formed by multiple fission

• Plasmodium is a malarial parasite which reproduces both inside a mosquito and also in human being.
• It chooses multiple fission, asexual mode of reproduction for producing the cells. 
• Multiple fission is the division of mother cell into many daughter cells simultaneously. 
• A multinucleate mass is formed with rich cytoplasm which does not undergo division until certain amount of time. 
• The specific reason behind the organism reproducing by multiple fission is that, it can divide itself into many cells at the same time inside the cyst during unfavourable conditions in the host.

3) Budding: This is a form of asexual reproduction which involves development of small mass of cells as protuberances on the parental body to give rise to new structures called as buds.

• These buds separate out from the parental body and develop into new individuals.
• Two types of budding are external budding and internal budding. 
• Yeast reproduces by beans of buds. Buds grow in chains or detach from the parent and fall on the substratum. When buds are on the substratum, they grow as new individuals.  

4) Fragmentation: It involves breaking of parent organism into two or many fragments. Each fragment develops into an individual organism. Fragmentation is seen in sea stars which accidentally break their body into fragments. Fragmentation is also observed in annelids, turbellarians and some of poriferans.  Spirogyra reproduces through fragmentation during which each fragment grows into a new individual.  

5) Regeneration:  If the organism is cut up, its pieces can grow into separate individuals.  It occurs in some fully differentiated organisms. Regeneration is also called morphallaxis. e.g.  Hydra, Planaria. Regeneration is referred to tissue repair to normal state. It is restoration of normal structure and function of the organ. It is actually replacement of damaged tissue with same type of cells. Some organisms like lizards have the power of regenerating their tail. 

6) Spore formation:  Spore formation is one form of asexual reproduction. Spore formation is the method of developing new individuals by forming reproductive structures called spores.

• A spore is a small spherical or oval structure which protects the future individual in a thick protective covering.
• Spore germinates on a substratum under favourable conditions.
• Some organisms like ferns, some groups of fungi reproduce by spore formation.
•  Fungus reproduces by means of spores. Fungus like bread mould produce spores which germinate on moist organic surfaces. The cottony white mass on bread formed by fungus after spore germination is called a mould. Spores can survive in extreme conditions because of the protective hard coat.

7) Vegetative propagation:  Vegetative propagation is one mode of asexual reproduction in plants.

• Vegetative propagation  is the production of new plants from the vegetative parts of the plant.
• Roots, stems and leaves are called the vegetative parts of a plant. Any of these parts serve as vegetative propagules.
• Vegetative propagation takes place by different methods like Grafting, Leaf propagation, Root propagation, underground stem propagation etc.       
• Though vegetative reproduction results in the production of varieties of plants, offspring propagated through vegetative propagation are more uniform to parents.

Vegetative propagules
Vegetative propagules are the structures used to raise new plants. These are the vegetative structures from the plant which are used to develop new individuals. These can be like rhizome (ginger), runner(grass), bulbs(onion), tuber (potato), leaves(bryophyllum).

Advantages of vegetative propagation

• Vegetative propagation is an easier method than growing plants from seeds. 
• Vegetative propagation is used in plants which do not produce seeds.
• Plants propagated through vegetative propagation require less time to grow.
• Plants propagated through vegetative propagation are more uniform to parents.
• Vegetative propagation helps in producing varieties in the plants.

Disadvantages of vegetative propagation

• Plants produced by asexual reproduction are short lived than the plants produced by sexual reproduction.
• The wood of vegetatively produced plants are small in size hence is not costly.
• Vegetatively propagated plants cannot be cultivated on a large scale.
• There os a reduction in plant vigour.
• Parent plants with diseases transfer their diseases to the offspring.

Natural methods of vegetative propagation
a) Leaf propagation: Bryophyllum propagates vegetatively by the formation of leaf buds on the margins of a leaf. When the buds come in contact with moist soil, each bud is capable of growing into a new plant.
b) Root propagation: Sweet potato and Dhalia are capable of producing young ones from their roots.
c) Stem propagation: Potato giving rise to new plants is an example of stem propagation. 

Artificial methods of vegetative propagation
Many artificial methods are developed to propagate plants vegetatively. Layering and grafting are some artificial methods of vegetative propagation.

a) Layering: This involves bending of a young stem towards the ground and burying it under the soil for development of roots . After a period of time, as the roots develop, the bent stem is cut off from the parent plant. This acts as a new plant. e.g. Jasmine. 

b) Cutting: It involves planting a young cutting of the stem with buds into moist soil. This develops roots which absorb nutrition from the soil and help in the growth of new plant. e.g. Bougainvellia.

c) Grafting: It involves fusion of tissues of one plant with those of another plant. Grafting is a vegetative method of propagation for apples and roses.
     
8)Tissue culture:  Plant tissue culture is a method used to propagate exact copies of plants under hygienic conditions. Tissue culture is the process of culturing single line cells under sterile, controlled conditions, in vitro by exposing them to nutrients, hormones and specific amount of sunlight. There are different steps involved in the tissue culture process. 

• Step 1: Material is selected and sterilized for propagation of cells, in vitro initiating the process of culturing the cells.
• Step 2: The plant material is re-divided and placed in separate plates with medium rich in plant growth regulators. These growth regulators induce shoot formation. This process can be repeated till the desired number of plants is obtained.
• Step 3: The hormones which induce the formation of root are introduced into the medium. Now, complete plantlets are formed.   These plantlets are transferred from lab into the green house for further growth.

9) Cloning
It is a type of asexual reproduction which involves the creation of an exact copy of a biological entity.

• Cloning involves the process of forming a cell or a complete individual from a body cell. 
• A clone is created by inserting the complete genetic material of a regular body cell from a donor into a recipient. 
• Cloning is done in many animals including sheep, cattle, pigs etc. But for the first time cloning of sheep was successful in producing a clone of the parent sheep. 

·         Reproduction in Animals

Reproductive phase is the phase in the life of every individual which makes the individual capable of reproducing the offspring. In the early reproductive phase, individuals acquire changes in the body which result in the formation of germ cells. Sperms are male germ cells and eggs are female germ cells. Reproductive phase involves the changes in appearance and size of the bodily organs.

Puberty: It is the time during which there occur sexual and physical changes which allow the transition of a child to an adult. Puberty starts at the beginning of adolescence. The onset of puberty starts much earlier in girls, between 8 and 13 years of age lasts 2 to 4 years. The onset of puberty is marked by physical changes. A child becomes an adolescent. 

• Different changes in boys include change in the voice, active functioning of sweat and sebaceous glands, growth of facial and body hair, enlargement of penis etc.
• Different changes in girls include growth of pubic hair, active functioning of sweat and sebaceous glands, menstrual cycle, enlargement of breasts.

Adolescence: It is the period of life between the onset of puberty and reaching adulthood, that is, the period that leads to reproductive maturity. Adolescent is a general term for teenagers of both sexes. Adolescence is the period of life that leads to reproductive maturity, making a person capable of reproduction.

Male reproductive system:  This system includes a pair of testis, vas deferens and a muscular organ, the penis.

a) Testes: Testis is the main reproductive organ in males. A pair of testis is placed in a structure called as scrotum which is located outside the abdominal cavity. At lower temperature maintained by the scrotum, testes produce sperms by the process of spermatogenesis. Sperms are the male gametes possessing a head, body and a tail. Testes also secrete male sex hormones like testosterone to regulate the development of sperms and the secondary sexual characteristicsleading to puberty.

b) Vas deferens: Sperm duct is also known as vas deferens. They are two in number, each one arising from testis placed on either side. They transport sperms into penis. They also collect fluids secreted by different glands. These secretions are rich in proteins to enrich the sperms. Sperms along with these secretions form thick substance called as semen. Semen is conveyed to urethra through which it is discharged outside. Prostate gland and seminal vesicles secrete semen to make the movement of sperms easier.

c) Urethra: Urethra forms a common passage for both the sperm and urine as it is just one tube that connects both the glands – urinary bladder and vas deferens.
d) Penis: It is a part of male reproductive system. Penis is a muscular organ which transfers semen into female reproductive tract. Penis receives both urinary tube and sperm duct and serves as a common transporting organ for urine and semen. It opens out through a small tube called as urethra. Penis is underlined by thin blood vessels which give it continuous supply of blood.

Testes are placed in a structure called as scrotum which is located outside the abdominal cavity. Scrotum helps in keeping the testes at lower temperatures. Testes produce the male gametes known as sperms. Sperms are the male gametes possessing a head, body and a tail. Testosterone is the male sex hormone secreted by the testes. It regulates the development of sperms and the secondary sexual characteristics leading to puberty.

Female reproductive system:  This system includes a pair of ovaries, a pair of oviducts, uterus and vagina opening out through urethra.

a) Ovary: A pair of ovaries forms the gonads in female. Ovaries are the female sex organs that lie one on either side of the abdominal cavity. Ovaries by the process of oogenesis form eggs or ova which are released as one per month. Ovaries produce two hormones, namely, estrogen and progesterone.Estrogen controls the changes that occur during puberty, like feminine voice, soft skin and development of mammary glands, growth of pubic hair and controls the release of mature eggs.Progesterone controls the uterine changes during menstrual cycle, and helps in the maintenance of pregnancy.

b) Oviducts: A tube like structure arising from each ovary on either side is called as an oviduct. This is also called as fallopian tube. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube.The two oviducts combine and open into an elastic bag-like structureknown as the uterus.

c) Uterus: Uterus is a hollow muscular organ which has the capacity to bear the child. It is otherwise called as womb. Zygote formed after fertilisation in the fallopian tube travels downward by dividing itself continuously to form an embryo. Embryo as it reaches the uterus gets implanted into the wall of the uterus. After fertilisation, female reproductive hormones bring in many changes to the uterus, so as to bear the growing embryo. As the embryo grows, it transforms into foetus. Uterus is the organ which bears the foetus.

d) Vagina: It is the reproductive part situated at the end of the uterus in female reproductive tract. It connects uterus to the outside world. Vagina secretes mucous to keep the tract wet. It opens out through vulva.

Eggs, the female gametes develop inside the ovaries.  One mature egg is released by either of the ovaries per month. Ovaries secrete two hormones namely estrogen and progesterone which bring about secondary sexual characters in females. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube. The two oviducts combine and open into an elastic bag-like structure known as the uterus. The uterus opens into vagina through cervix. The uterus helps in the development of the foetus.

Fertilisation: Fertilisation is the fusion of male and female gametes to give rise to a single cell – zygote. Fertilisation can be external fertilisation or internal fertilisation.

• When male and female gametes unite outside the body, it is called external fertilisation
• When fertilisation takes place inside the body, it is called internal fertilisation.
• When fertilisation takes place in a test tube, the offspring are called test tube babies.
• Fertilisation that takes place outside the human body is in vitro fertilisation.

Zygote:  It is the super cell formed by the fusion of pronuclei of male and female gametes. It  divides repeatedly to form an embryo.

Embryo: It is transformed zygote with a three layers of cells. This  gets embedded in the wall of uterus, part of the female reproductive system.The development of the embryo takes place in the mother’s uterine wall.All parts of the body start developing in an embryo which finally transforms itself into foetus.

Implantation:   Embryo gets implanted in the lining of the uterus for further development. The placenta is a connective tissue established between foetus and the mother.  It provides a large surface area for the nutrients and oxygen to pass from mother to the embryo. It also helps in transporting excretory wastes from embryo to mother.

Menstruation:  The monthly cycle of changes in the ovaries and the lining of uterus resulting in periodic discharge of blood, mucous and cellular debris through vagina in the absence of fertilisation.  This cycle takes place roughly every month and is controlled by ovarian hormones. Menses lasts for two to eight days.

Contraceptive devices:  These are the devices which block the entry of sperm into oviducts thereby preventing the egg from being fertilized. 

• Condom is a barrier method falling under the category of contraceptive methods. Condoms are available for both males and females. These structures act as barriers which prevent sperm from meeting the ovum. Condoms are made up of thin rubber or latex sheath.
• The Copper T is a simple intra-uterine device (IUD) made of a flexible, "T" shaped piece of plastic wrapped with a thin copper containing wire. It is a contraceptive device which prevents from getting pregnant. Copper ions prevent pregnancy by inhibiting the movement of sperm as they are toxic to sperm. 
• Other than this copper T cannot inhibit the action or kill bacteria or viruses which cause different STDs.
• Vasectomy is the surgical method executed for permanent birth control in males. It is the sterilisation technique by which vas deferens from the testis is cut or tied to prevent the mixing of sperm with the semen ejaculated from the penis. Semen of vasectomised males will not have sperms in them. As semen is devoid of sperms, there occurs no fertilisation of ovum produced by females.
• Tubectomy is a surgical method performed in females as a birth control method. It is a permanent contraceptive method. Fallopian tubes emerging out of the ovaries on either side are cut and tied. This is a permanent contraceptive method as there occurs no fertilisation in the fallopian tube. Ovum cannot reach the fallopian tube and wait there for the sperm coming to fertilise it.  

·        
Reproductive health: It is a state of physical, emotional, mental and social well-being in relation to sexuality. Reproductive health requires positive approach to sexuality and healthiness of the individuals participating in mating. Reproductive health also refers to the capability of satisfying the partner. It also specifies the ability and freedom to reproduce.

Sexually transmitted diseases:  STD stands for Sexually Transmitted Diseases. These are the diseases which are transmitted from one person to another during the sexual act between two individuals. STDs can be caused by different microorganisms like bacteria, fungi, virus, protozoans etc. STDs can mostly be prevented from transmission from one individual to another by using protective or contraceptive devices. Gonorrhea, Syphillis, AIDS etc are some of the examples of STDs. 

·         Sexual Reproduction in Plants

·         Sexual reproduction:  
This type of reproduction involves two organisms, the male and the female in the process of producing the offspring.  Sexual reproduction provides greater variations in the DNA thereby making the offspring adapted for better survival. Sexual reproduction ensures a mixing of the gene pool of the species. Due to genetic recombination, variations occur in the process of sexual reproduction.

Sexual reproduction in plants:
Plants reproduce sexually by producing male gametes in the form of pollen and the female gametes in the form of eggs.

Flower:
It is the main reproductive structure of a plant. A flower comprises sepals, petals, stamens and carpels.

       • Sepals and petals are considered to be the accessory whorls of the flower as they do not take part in the process of reproduction.
       • Stamens and carpels are the reproductive parts of a flower comprising germ cells. Germ cells help in the process of reproduction.
       • A unisexual flower contains either stamens or carpels. For example, papaya and watermelon are unisexual flowers.
       • A bisexual flower contains stamens as well as carpels. For example, hibiscus and mustard flowers are bisexual.
       • The stamen is the male reproductive organ that consists of filament and anther. The anther produces male gametes in the form of pollen grains.
       • The carpel is the female reproductive organ located at the centre of a flower. It consists of the ovary, style and stigma. The ovary is the swollen part at the bottom of the carpel. Ovary contains the female gametes in the form of eggs or ovules.

Pollination:
This is the transfer of pollen grains from the anther to the stigma of the carpel.

       • Different agents of pollination are wind, water, animals, birds, insects, human beings etc.
       • Petals attract insect or bird pollinators by their colour, scent, and nectar, which may be secreted in some part of the flower.
       • Two types of pollination are self-pollination and cross-pollination. Self-pollination involves the transfer of pollen grains from anther to the stigma of the same flower. Cross-pollination involves the transfer of pollen grains from anther of one flower to the stigma of another flower.
       • Pollen grains are trapped by sticky stigma during the process of pollination.
       • Pollen grains germinate on the stigma to give rise to pollen tube which aids in the process of fertilisation.

Fertilisation:
This involves the fusion of male germ cell with the female germ cell resulting in the formation of a single cell, the zygote. This process is also called as syngamy.

       • There occur many changes after fertilisation.  After fertilisation, the zygote divides repeatedly to form an embryo which resides inside the seed.
       • The ovule develops into a seed.
       • The ovary ripens to form a fruit.
       • Seed inside the fruit encloses the embryo, the future plant.

Germination:
It is the growth of an embryonic plant residing inside the seed under favourable conditions.  It results in the formation of a new seedling which further grows into a new plant. The factors essential for germination are nutrients, water and proper temperature. Seed has an embryo protected by reserved food materials in the form of cotyledons and also an outer covering called as seed coat.

 

                  Heredity and Evolution

Heredity and Variations

Trait is any characteristic that is transferred from parent to offspring. e.g. height and colour.

The process of passing traits from parent to offspring is called heredity.

Variations are the minor differences between offspring and the parent.

Mendel and his contributions
Gregor Johann Mendel was a pioneer among geneticists who put forward the concept of inheritance of characteristics or traits from parent to offspring.

Mendel proposed the principle of inheritance and is known as the “Father of Genetics”.

Mendel has chosen pea plants for his experimentation and found variations among them.

Gene is a structural and functional unit of heredity and variations.

Gene is a DNA segment on the chromosome. Genes control the expression of characteristics. Mendel called the genes to be factors.

Alleles are a pair of alternative forms of a gene.  Each gene is present in two alternative forms, each called an allele. Each allele controls a single trait.

Traits can be either dominant or recessive. Tallness in a plant is a dominant trait, controlled by a dominant allele and is represented by “T” (capital). Shortness in a plant is a recessive trait, controlled by a recessive allele and is represented by “t” (small).

         • Homozygous is a condition in which a gene possesses a pair of the same alleles (TT or tt) for a single characteristic.
         • Heterozygous is a condition in which a gene possesses a pair of different alleles (Tt) for a single characteristic.

Phenotype is a morphological expression of a single character. For example, tallness or shortness represents the phenotype of the plant.

Genotype is the genetic make-up of a cell, an organism, or an individual (i.e. the specific allele make-up of the individual), usually with reference to a specific characteristic under consideration. Alleles combine to make a genotype, such as TT or Tt or tt.

Punnett square is a statistical method that was used by Mendel to predict the possible genotypes and phenotypes of the offspring.

Monohybrid inheritance
It is the inheritance of a single characteristic controlled by different alleles of the same gene.

         • F₁ generation is the first filial generation offspring produced by crossing two parental strains.  All the progeny of F₁ generation were tall i.e. the traits of only one parent were visible.

         • F₂ generation is the second filial generation offspring produced by crossing F₁’s. The F₂ progeny were not all tall. Instead, one quarter of them was short indicating both the traits – that of tallness and shortness were inherited in the F₂ plants.

         • Genotypic ratio – 1:2:1, Phenotypic ratio – 3:1.

Dihybrid inheritance
It is the simultaneous inheritance of two characters.

         • Dihybrid inheritance is the experimentation of two characteristics with their four contrasting traits.
         • For instance, dihybrid inheritance involves a plant producing round and yellow seeds (RR and YY) crossing with a plant producing wrinkled green seeds (rr and yy).
         • F₁ progeny produces round and yellow seeds (R and r, and Y and y) in which round and yellow are dominant traits.
         • F₂ progeny were similar to their parents and produced round yellow seeds, while some of them produced wrinkled green seeds. However, some plants of the F₂ progeny even showed new combinations, like round-green seeds and wrinkled-yellow seeds.

Sex determination
It is a mechanism which determines the individual to be a male or a female based on the sex chromosomes present in it.  X and Y are the sex chromosomes inherited one from each parent, determine the offspring to be a male.  X and X are the sex chromosomes inherited one from each parent, determine the offspring to be a female.  A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him

Evolutionary Relationships I

All the life on Earth has descended from a common ancestor.

Evolution: It is the sequence of gradual changes over millions of years in which new species are produced.

Charles Robert Darwin was an English naturalist who observed various species of life on the earth and put forward the idea of “evolution of species by natural selection.” He said that a species inherits its characters from its ancestors.

Variations: These are the differences among individuals of a species caused by genetic and environmental factors.

Mutation: It is the change in the sequence of the nitrogen base pairs in DNA. e.g. A mutation in the gene for green colouration in green beetles leads to offspring with brown colouration.

Gene flow: It is the transfer of genes from one population to another due to migration. Breeding between the brown and green beetles introduces new gene combinations into the population.

Natural selection: It explains that organisms that are physiologically or behaviourally better adapted for the environment are selected. Selected organisms can survive and reproduce.

Genetic drift: It is the genetic variation in small populations caused by a specific environmental factor.

Species: It can be defined as a group of individuals of the same kind that can interbreed and produce fertile progeny.

Speciation: It is an event that splits a population into two independent species which cannot reproduce among them.
         • Process of speciation-Genetic drift: It occurs due to changes in the frequencies of particular genes by chance alone. e.g. If a hurricane strikes the mainland, and bananas with beetle eggs on them are washed away to an island. This is called a genetic drift.
         • Process of speciation - natural selection: These are the variations caused in individuals due to natural selection which lead to the formation of a new species. e.g. If the ecological conditions are slightly different on the island as compared to the mainland, it leads to a change in the morphology and food preferences in the organisms over the course of generations.
         • Process of speciation - splitting of population: A population splits into different sub-populations due to geographical isolation that leads to the formation of a new species.

Evolutionary Relationships II

Characteristics
These are the hereditary traits transmitted from parent organisms to their offspring.

Characteristics are of two types namely, homologous characteristics or analogous characteristics

         • Homologous characteristics are organs that have the same basic structure and origin, but different functions. For example, mammals, birds, reptiles and amphibians have four limbs with the same basic limb layout because they have inherited the limbs from a common ancestor. These limbs have been modified to perform different functions.

         • Analogous characteristics are organs that have different structures and are of different origin, but perform same functions. For example, the design of the wings of bats and the wings of birds look similar because they have a common purpose – to fly.

Fossils
Fossils are the remains or traces of a plant or animal that existed in a past geological age, and that has been excavated from the soil.

Fossilisation is the process in which an organism is converted into a fossil.

Biological convergence
This is a phenomenon by which two unrelated organisms become quite alike after a period of time through few generations, if it is assumed that they have a common ancestor. The eyes of the octopus and the eyes of vertebrates have evolved independently. These similarities of structure, despite of different origins provide a classic example of biological convergence.
Adaptation
A characteristic of a particular animal may, post-evolution be useful for performing a totally different function.
For example, long feathers were considered to provide insulation in cold weather. Some reptiles like the dinosaur had feathers but very few were adapted for flying. In the present day, birds use feathers for flight, which is an example of adaptation.

Artificial selection
This is the usage of plants with desirable characteristics to produce new varieties.
Broccoli, kohlrabi and kale are produced from its ancestor wild cabbage by artificial selection.
The tools used to trace evolutionary relationships are excavation, time-dating, studying fossils, and determining DNA sequences. These have been used for studying human evolution.

LIGHT  - REFLECTION AND RAREFACTION

Reflection

Light 

Light is the form of energy, which enables us to interact with our surroundings in a most effective way. Light causes the  sensation of vision. There are two major phenomena of light that takes place in the process of “seeing”. They are “reflection” and “refraction”.

In general reflection is the process where the incident light on an object is bounced back into the same medium.


Mirror

Most of all the objects reflect the light incident on them to different extent. Some of the objects which have a smooth surface reflect the incident light to the maximum extent. An object that reflects 100% of the incident light is called a “mirror”. If the surface of the mirror is plane, it is referred to as a plane mirror. Other types of mirrors are curved mirrors.

We find our images in proper proportions in plane mirrors due to regular reflection.

We cannot observe our images formed by plane mirrors on a screen as they are virtual images unlike those which are formed on a screen and termed as real images. The reflection that takes place on other surfaces other than plane mirrors is  irregular reflection. Irrespective of the type of reflection, the light ray (which is the path of light) follows two laws of reflection.


Laws of Reflection

The first law of reflection states that the angle of incidence (i.e., the angle between the incident ray and the normal at the point of incidence) is equal to the angle of reflection (i.e., the angle between the normal and the reflected ray). The second law of reflection states that the incident ray, reflected ray and the corresponding normal, all lie in the same plane.


Rear View Mirror

The  rear view mirror in a car is a plane mirror as it helps us to estimate the distances of the vehicles that are behind our car in motion. In a plane mirror, the object distance is equal to the image distance.

If we stand at any distance in front of one whose length is half your height we can observe our full size image in a plane mirror.

If we rotate a plane mirror maintaining the object position, through certain angle we find that the reflected ray rotates twice the angle.

Regular and Diffuse Reflection

The phenomenon of bouncing back of light after falling on the surfaces of the objects is called reflection of light.

The reflection of light is of of two types, they are

1. Regular reflection or Specular reflection
2. Diffused or irregular reflection.

In general, reflection is the process where the light incident on an object bounces back into the same medium. This happens when light is incident on a translucent or an opaque medium. When light is incident on a transparent medium, all the incident light passes through the medium, and reflection does not take place. In the case of translucent medium, a part of the incident light is reflected, and the rest is transmitted through the medium.

We get light from a luminous object, which we refer to as a source of light. If the size of the source of light is very small, then we call it a point source of light. If the size of the source of light is considerable, then we say it is an extended source of light. Light rays from a point source of light travel in all directions, moving away with time. Such a beam of light is called a divergent beam of light.

If the light source is an extended source, then we get a parallel beam of light from it. Consider a parallel beam of light from an extended source, incident on a plane surface like a plane mirror. As the beam of light is parallel, and the surface on which the beam is incident is a plane surface, the angle made by each ray with the normal at the point of incidence on the surface is equal, which implies that the angle of incidence of all the rays is equal.

Each ray of light follows the laws of reflection irrespective of whether it is from a parallel beam or not. According to the laws of reflection, the angle of reflection is equal to the angle of incidence.

Thus, for every ray of light incident on the mirror, the angle of reflection is equal to its angle of incidence.

Regular Reflection

As the angles of incidence of a parallel beam of t all the ligh rays are equal for a smooth plane like a plane mirror,the angles of reflection of all the rays equal. This implies that all the reflected rays are parallel. When all the reflected rays, reflected from a given surface, are parallel then it is called regular reflection.

Diffuse Reflection

If the surface is not a plane surface, then the reflected rays are not parallel to each other. In such a case, the reflection is called diffused reflection.


The diffused reflection occurs at the rough or un polished or the slightly polished non smooth or rough surfaces.

Figure above represents the light falling over the rough surface.

As the rays of light falls on a rough surface at any angle of incidence then the angle of reflection is equal to the angle of incidence.

Note:

Laws of reflection are valid for both regular and irregular reflections of liht.

Spherical Mirrors 

Terms Associated with Spherical Mirrors

• Centre of curvature (C) is the centre of the sphere, of which the mirror is a part.
• Radius of curvature (R) is the radius of the sphere, of which the mirror is a part.
• Pole (P) is the geometric centre of the spherical mirror.
• Principal axis is the line joining the pole and the centre of curvature.
• Principal focus (F) is the point on the principal axis, where a parallel beam of light, parallel to the principal axis after reflection converges in the case of a concave mirror and appears to diverge from in the case of a convex mirror.
• Focal length (f) is the distance of the principal focus from the pole of the mirror.

                            

There are two types of images: real and virtual. Real images are those that can be caught on a screen while virtual images are those that cannot be caught on a screen.


Concave Mirror

If a part of a hollow glass sphere is cut and the cut part of the sphere is coated outside with silver or similar material, then its inner surface reflects the entire light incident on it, and thus, forms a mirror. Since the inner surface is a concave surface, the mirror so formed is called a concave mirror.

Concave mirrors converge the light incident on them and hence are called converging mirrors. We can observe ourselves magnified when the mirror is placed close to our face. This is due the position of the object between the focus and the pole. As the object moves away from the mirror, the size of its image reduces along with its distance from the mirror. If an object is placed close to a concave mirror such that the distance between the mirror and the object is less than its focal length, then a magnified and virtual image is formed. Due to this property, concave mirrors are used as shaving mirrors, and by dentists to view clearly the inner parts of the mouth.


Convex Mirror

If the cut part of the glass sphere is coated from inside with silver or a similar material, then its outer surface reflects the entire light incident on it, and thus forms a mirror. Since the outer surface is a convex surface, the mirror so formed is called a convex mirror.

Convex mirrors diverge the light incident on them and hence they are called the diverging mirrors. Due to this they always form diminished, virtual and erect images irrespective of the position of the object in front of them. Thus, the magnification produced by these mirrors is always less than one. The field of view for a convex mirror is greater than that for a plane mirror, the aperture being the same. Hence, convex mirrors are used as rear-view mirrors in vehicles. It is also installed behind automated teller machines as a security measure.

Rules for Construction of Ray Diagrams for Spherical Mirrors

Rule 1: A light ray incident parallel to the principal axis, after reflection, either actually passes through the principal focus or appears to pass through the principal focus.
Rule 2: A light ray which first passes through the principal focus or appears to pass through the principal focus, after reflection, will travell parallel to the principal axis. 
Rule 3: A light ray which first passes through the centre of curvature or appears to pass through the centre of curvature, after reflection, retraces its initial path.

Image Formation by Concave Mirror

Depending on the position of the object in front of the concave mirror, the position, size and the nature of the image varies.

1. Object at infinity:  A real, inverted, highly diminished image is formed at the focal point F, in front of the concave mirror.



2. Object beyond C: A real, inverted, diminished image is formed between C and F, in front of the concave mirror.




3. Object at C: A real, inverted, same sized image is formed at C, in front of the concave mirror.




4. Object between C and F: A real, inverted, enlarged image is formed beyond C, in front of the concave mirror.



5. Object at F: A real, inverted, highly enlarged image is formed at infinity, in front of the concave mirror.




6. Object between F and P: A virtual, erect and enlarged image is formed behind the concave mirror.





Image Formation by Convex Mirror

Irrespective of the position of the object, a virtual, erect and diminished image is formed between F and P, behind the convex mirror.





Mirror Formula and Sign Conventions 

The relation between the focal length (f), object distance (u) and the image distance (v) is given by 1/f = 1/v + 1/u. This is called the mirror formula. All the distances are measured from the pole of the mirror. If we measure the distances in the direction of the incident light, then they are taken positive or else they are taken negative. These constitute the sign conventions.

Uses of Concave Mirrors 

• Concave mirrors are used as shaving mirrors to see a larger image of the face.
• Dentists use concave mirrors to view the back of the tooth.
• ENT doctors use them for examining the internal parts of the ear, nose and throat.
• They are used as reflectors in the headlights of vehicles, search lights and in torch lights to produce a strong parallel beam of light.
• Huge concave mirrors are used to focus sunlight to produce heat in solar furnaces.

Uses of Convex Mirrors

• Used as rear view mirrors in automobiles as it covers wide area behind the driver.

Spherical Mirrors

Mirrors are the basic means of viewing our own beauty. Generally we can classify the mirrors into the following two types as

i.  Plane mirrors
ii. Curved mirrors.

Generally mirrors refer to plane mirrors. But if the surface of a mirror is curved it is said to be a curved mirror. If the curved mirror is a part of a huge sphere, then the mirror is a spherical mirror.

Terms Associated with Spherical Mirrors

• Centre of curvature (C) is the centre of the sphere, of which the mirror is a part.
• Radius of curvature (R) is the radius of the sphere, of which the mirror is a part.
• Pole (P) is the geometric centre of the spherical mirror.
• Principal axis is the line joining the pole and the centre of curvature.
• Principal focus (F) is the point on the principal axis, where a parallel beam of light, parallel to the principal axis after reflection converges in the case of a concave mirror and appears to diverge from in the case of a convex mirror.
• Focal length (f) is the distance of the principal focus from the pole of the mirror.                    

Spherical mirrors can be further classified into the following two types as

i.  Concave mirrors
ii . Convex mirrors.

The images formed by the mirrors are of two types they are

i.  Real images
ii. Virtual Images

Real images are those that can be caught on a screen while virtual images are those that cannot be caught on a screen.

Formation of Images by Spherical Mirrors
The image formed by a convex mirror is always erect, virtual, and diminished in size. The location of the object does not affect the characteristics of the image. Thus, as the object approaches the mirror, the image approaches the mirror too but not proportionately. This is why, the rear view mirrors of the cars and bikes are made of convex mirrors.

Hence, we have the caution “Objects seen in the mirror are closer than they appear” printed on the outside rear view mirrors of vehicles.

Unlike in a convex mirror, the nature and size of the image in a concave mirror depends on the distance of the object from the mirror.

Concave Mirror



If a part of a hollow glass sphere is cut and the cut part of the sphere is coated outside with silver or similar material, then its inner surface reflects the entire light incident on it, and thus, forms a mirror. Since the inner surface is a concave surface, the mirror so formed is called a concave mirror.

• The geometric centre of a concave mirror is called its pole. 
• The centre of the sphere from which concave mirror was cut is called the centre of curvature of the concave mirror. 
• The distance from any point on the concave mirror to its centre of curvature is called the radius of curvature of the concave mirror. 
• An imaginary line passing through the centre of curvature and the pole of the concave mirror is called principal axis of the concave mirror. 
• The area of a concave mirror that is exposed to incident light is called the aperture of the concave mirror.
• The length along the principal axis from the pole to the principal focus is called the focal length of the concave mirror.

If an object is placed close to a concave mirror such that the distance between the mirror and the object is less than its focal length, then a magnified and virtual image is formed. Due to this property, concave mirrors are used in many applications. A concave mirror can be used as a shaving mirror, and by dentists to view clearly the inner parts of the mouth.

Concave mirrors converge the light incident on them and hence are called converging mirrors. We can observe ourselves magnified when the mirror is placed close to our face. This is due the position of the object between the focus and the pole. As the object moves away from the mirror, the size of its image reduces along with its distance from the mirror. If an object is placed close to a concave mirror such that the distance between the mirror and the object is less than its focal length, then a magnified and virtual image is formed. Due to this property, concave mirrors are used as shaving mirrors, and by dentists to view clearly the inner parts of the mouth.

Reflection by Concave Mirrors

Incident Ray	Reflected Ray
Parallel to principal axis	Passes through focus
Passes through C	Retraces its path
Passes through focus	parallel to principal axis
Strikes the pole at an angle eith principal axis	Makes the same angle with principal axis

Image Formation by Concave Mirror

Depending on the position of the object in front of the concave mirror, the position, size and the nature of the image varies.

Object at infinity
A real, inverted, highly diminished image is formed at the focal point F, in front of the concave mirror.




Object beyond C
A real, inverted, diminished image is formed between C and F, in front of the concave mirror.




Object at C
A real, inverted, same sized image is formed at C, in front of the concave mirror.




Object between C and F 
A real, inverted, enlarged image is formed beyond C, in front of the concave mirror.




Object at F
A real, inverted, highly enlarged image is formed at infinity, in front of the concave mirror.




Object between F and P
A virtual, erect and enlarged image is formed behind the concave mirror.

Image Formation by a Concave Mirror

Object Location	Image Location	Nature of Image
Infinity	At F	• Real • Inverted • Highly Diminished
Beyond C	Beyond F and C	• Real • Inverted • Diminished
At C	At C	• Real • Inverted • Equal to size of object
Between C and F	Beyond C	• Real • Inverted • Magnified
At F	Infinity	• Real • Inverted • Highly Magnified
Between F and P	Behind the mirror	• Virtual • Erect • Magnified

Uses of Concave Mirrors

• Concave mirrors are used as shaving mirrors to see a larger image of the face.

·         Dentists use concave mirrors to view a magnified view of the interior parts of the mouth are concave.

• ENT doctors use them for examining the internal parts of the ear, nose and throat.
• They are used as reflectors in the headlights of vehicles, search lights and in torch lights to produce a strong parallel beam of light.
• Huge concave mirrors are used to focus sunlight to produce heat in solar furnaces.

Convex Mirror

If the cut part of the glass sphere is coated from inside with silver or a similar material, then its outer surface reflects the entire light incident on it, and thus forms a mirror. Since the outer surface is a convex surface, the mirror so formed is called a convex mirror.

• The geometric centre of a convex mirror is called its pole. 
• The centre of the sphere from which the mirror was cut is called the centre of curvature of the mirror. 
• The distance from any point on the convex mirror to its centre of curvature is called the radius of curvature. 
• An imaginary line passing through the centre of curvature and the pole of the mirror is called its principal axis.
• The reflected rays, when projected backwards, appear to meet at a point on the principal axis. This point is called the principal focus. The length along the principal axis from the pole to the principal focus is called the focal length. 
• The area of a convex mirror that is exposed to incident light is called the aperture. If the aperture of a convex mirror is small, then its focal length is equal to half its radius of curvature.

Convex mirrors diverge the light incident on them and hence they are called the diverging mirrors. Due to this they always form diminished, virtual and erect images irrespective of the position of the object in front of them. Thus, the magnification produced by these mirrors is always less than one. The field of view for a convex mirror is greater than that for a plane mirror, the aperture being the same. Hence, convex mirrors are used as rear-view mirrors in vehicles. It is also installed behind automated teller machines as a security measure.

The field of view for a convex mirror is greater than that for a plane mirror, the aperture being the same. Hence, convex mirrors are used as rear-view mirrors in vehicles. It is also installed behind automated teller machines as a security measure. The images formed by convex mirrors are always diminished, virtual and erect, irrespective of the position of the object.

Reflection by Convex Mirror

Incident Ray	Reflected Ray
Parallel to principal axis	Appears to pass through focus
Directed towards the focus	Appears to pass parallel to principal axis
Strikes the pole at an angle eith principal axis	Makes the same angle with principal axis

Image Formation by Convex Mirror

Irrespective of the position of the object, a virtual, erect and diminished image is formed between F and P, behind the convex mirror.




Uses of Convex Mirrors

• Used as rear view mirrors in automobiles as it covers wide area behind the driver.
• Used as reflectors for street light bulbs as it diverges light rays over a wide area.
• Used as Rear view mirrors of vehicles and the ones used in ATM centres.

Sign Convention for Spherical Mirrors

·         Object is always considered at the left of mirror

·         Distances measured along y-axis above the principal axis are taken as positive and that measured along y-axis below the principal axis are taken as negative.

·         Distances measured in the direction of the incident ray are taken as positive and the distances measured in the direction opposite to that of the incident rays are taken as negative.

·         All distances are measured from the pole of the mirror.

Table Showing the Sign Convention

Types of Mirror	u	v		f	R	Height of the Object	Height of the Image
		Real	Virtual				Real	Virtual
Concave mirror	–	–	+	–	–	+	–	+
Convex mirror	–	No real image	+	+	+	+	No real image	+

Rules for Construction of Ray Diagrams for Spherical Mirrors

Rule 1: A light ray incident parallel to the principal axis, after reflection, either actually passes through the principal focus or appears to pass through the principal focus.
Rule 2: A light ray which first passes through the principal focus or appears to pass through the principal focus, after reflection, will travell parallel to the principal axis. 
Rule 3: A light ray which first passes through the centre of curvature or appears to pass through the centre of curvature, after reflection, retraces its initial path.


Mirror Formula
The relation between the focal length (f), object distance (u) and the image distance (v) is given by

1 f =  1 v +   1 u  


Magnification

The ratio of the height of the image in a spherical mirror, to the height of the object is called magnification (m)

Magnification (M) =  Heigth of the Image (H_i) Height of the Object (H_o) =  Image Distance (v) Object  distance(u)


The distance from the principal focus to the pole of the mirror is the focal length of the mirror and is equal to half the radius of curvature, which is the distance between the centre of curvature and the pole.

For a real image object distance (u) and the image distance (v) are negative and the magnification is negative. If the  magnification of an image is negative it does mean that the image is real and inverted.
On the other hand for a virtual image object distance (u) is negative and image distance (v) is positive and hence the magnification is positive, i.e., the image is erect. If the  magnification of an image is positive it does mean that the image is virtual and erected.

If the magnification is less than 1 The image formed is diminished in size.
If the magnification is more than 1 The image formed is magnified in size.
If the magnification is equal to 1 The image formed is  equal to the object in size.


Differences Between Convex Mirror and Concave Mirror

Convex Mirror

Concave Mirror

1. Convex mirror is curved outwards. 2. The focal point of convex mirror is behind the mirror. 3. In convex mirror the image is always virtual, upright and smaller than the object. 4. Convex mirrors are used in cars (as passenger-side mirror since they provide upright and wide view), they are also used in camera phones, for safety measures there are also used in roads and driveways. Besides these convex mirrors are found in many hospitals, schools etc. as hallway safety mirror. 5. It has a virtual focus.

1. Concave mirror is curved inwards. 2. The focal point of concave mirror is in front of the mirror. 3. In case of concave mirror different types of images are formed on different location of the object. The image is upside down (inverted) and far away but if we bring the object close to the mirror then image will be larger and upright. 4. Concave mirrors are used in telescope. These are also used as make up and shaving mirrors since these provide larger images. Besides these concave mirrors are used by dentists and also used in headlights of cars, solar devices, satellite dishes etc. 5. It has a real focus.

·         Refraction Basics

• Light bends while travelling from one medium to another as its velocity differs from one medium to another. The change in the directionof the path of light, when it passes from one transparent medium to the another transparent medium is called refraction of light.The refraction is a surface phenomenon.
  
  The speed of light in optically rarer medium is larger compared to that in optically denser medium. Hence, while travelling from one medium to another, light bends. Light ray passing from rarer to denser medium bends towards the normal. This makes the angle of incidence (angle between the incident ray and the normal at the point of incidence) larger than that of the angle of refraction (angle between the normal and the refracted ray). The incident ray, the normal and the refracted ray, all lie in a plane. If the light ray retraces its path while travelling from denser to rarer, the angle of incidence is lesser than that of the refraction. This is the principle of reversibility.
  
  The extent to which a light ray bends depends on the refrangibility of the ray with respect to the medium. The ratio of velocity of light in vacuum to that in a medium, which is the absolute refractive index (m) of the medium, is the measure of the ability of light to get bend in the given medium. Measuring speed of light is difficult. Hence, Snell’s law helps to determine the refractive index. According to Snell’s law,
  µ =  Sin i Sin r                      
  
  When a light ray, incident at an angle, passes through a glass slab, the emergent ray is shifted laterally. The lateral shift depends on the thickness and refractive index of the glass slab.
  
  When a light ray bends from denser to rarer medium, it bends away from the normal. If the angle of incidence gradually increases, the angle of refraction too increases. At a particular angle of incidence in the denser medium, the refracted ray emerges along the surface. That particular angle is the critical angle. If the angle of incidence is greater than the critical angle, the ray undergoes total internal reflection. It is due to this phenomenon we observe mirages in deserts.
  
  The bottom of a water glass appears to rise upwards when viewed normally. This is due to the vertical shift of the bottom of the glass, which takes place because of refraction.
  
  Terms Used for Lens
  Centre of Curvature: The centre of the imaginary glass sphere of which the lens is a part, is called centre of curvature.
  
  Principal Axis: An imaginary line joining the centres of curvature of the two spheres, of which lens is a part, is called Principal Axis.
  
  Optical Centre: A point within the lens, where a line drawn through the diameter of lens meets principal axis, is called optical centre.
  
  Principal Focus for Convex Lens: It is a point on the principal axis of a convex lens,  where parallel beam of light rays, travelling parallel to principal axis, after passing through the lens actually meet.
  
  Principal Focus for Concave Lens: It is a point on the principal axis of a concave lens, from where parallel beam of light rays, travelling parallel to principal axis, after passing through the lens, appears to come.
  
  Focal Length: The distance between principal focus and optical centre is called focal length.
  Aperture: The effective diameter of the lens through which refration takes place is called aperture of lens.
  
  Optic centre is a point on the axis of a lens such that any light ray passing through this point emerges without refraction.
        •  Principal focus is a point on the axis of a lens.
        •  Principal focus is also known as the focal point

·         Refraction by Spherical Lenses

Lenses are the most used things in optical devices like microscopes and telescopes. Bi-convex and bi-concave lenses are the most popular ones in use among school labs. Lenses use the phenomenon of refraction of light to form images.

Concave lens diverge the light incident on it. Hence, called the diverging lens. Due to this these lenses always form diminished, virtual and erect images irrespective of the position of the object in front of them. Thus, the magnification produced by these lenses is always less than one.

Convex lenses converge the light and hence are called the converging lenses. You can observe the magnified image of your palm when the lens is placed close to your palm. This is due the position of the object between the focus and the optic centre. As the object moves away from the lens, the size of its image reduces along with its distance from the lens. Convex lenses form erect, virtual, magnified images or inverted, real, diminished/magnified images depending on the position of the object.

Lens
A lens is a piece of transparent optical material with one or two curved surfaces to refract light rays.
It may converge or diverge light rays to form an image.

A bi-convex lens is one with a surface that is bulged outwards on both the sides. It is generally referred to as a convex lens.

Another type of a lens is a bi-concave lens that has two inward bent surfaces. It is generally referred to as a concave lens. 

A Plano-convex lens has a convex surface on one side and a plane surface on the other.

A Plano-concave lens is the one that has a concave surface on one side and a plane surface on the other.

A concavo-convex lens has a concave surface on one side and a convex surface on the other.

Convex and concave lenses are important as they are more commonly used than the other types of lenses.

Terms Used for Lens
Centre of Curvature: The centre of the imaginary glass sphere of which the lens is a part, is called centre of curvature.

Principal Axis: An imaginary line joining the centres of curvature of the two spheres, of which lens is a part, is called Principal Axis.

Optical Centre: A point within the lens, where a line drawn through the diameter of lens meets principal axis, is called optical centre.

Principal Focus for Convex Lens: It is a point on the principal axis of a concex lens,  where parallel beam of light rays, travelling parallel to principal axis, after passing through the lens actually meet.

Principal Focus for Concave Lens: It is a point on the principal axis of a concave lens, from where parallel beam of light rays, travelling parallel to principal axis, after passing through the lens, appears to come.

Focal Length: The distance between principal focus and optical centre is called focal length.
Aperture: The effective diameter of the lens through which refration takes place is called aperture of lens.

Optic centre is a point on the axis of a lens such that any light ray passing through this point emerges without refraction.
      •  Principal focus is a point on the axis of a lens.
      •  Principal focus is also known as the focal point. 

Convex Lens:
      •  A lens in which both the surfaces are convex, is known as convex lens
      •  Light rays incident on a convex lens get converged at its focus
      •  Used by palmists and fingerprint experts
      •  If an incident ray passes through a focus and its emergent ray passes parallel to the principal axis, then that focus is called the first principal focus.
      •  If an incident ray passes parallel to the principal axis, and its emergent ray converges at a focus, then that focus is called the second principal focus.
      •  The distance between the optic centre and the focal point is called the focal length. 

Behaviour of Light Rays Propagating Through a Convex Lens

Incident Ray	Emergent Ray
Is parallel to principal axis	Passes through focus
Passes through optic centre	Passes with out deviation
passes through focus	Passes parallel to principal axis

Location and Characteristics of Images Formed by a Convex Lens
 

Object Location	Image Location	Nature of Image
Infinity	At F2	Real Inverted Highly Diminished
Beyond 2F1	Between F2 and 2F2	Real Inverted Diminished
At 2F1	At 2F2	Real Inverted Equal in size to that of the object
Between 2F1 and F1	Beyond 2F2	Real Inverted Magnified
At F1	Infinity	Real Inverted Highly Magnified
Between F1 and O	On the same side of lens as the object	Virtual Erect Magnified

Concave Lens 
A lens, in which both the surfaces are concave, is known as a concave lens.

An image formed by a concave lens is always diminished due to the divergence of rays. This is why concave lenses are widely used to correct eye defects such as myopia.

A concave lens is also known as a diverging, reducing, negative and myopic or minus lens.

Behaviour of Light Rays Propagating Through a Concave Lens  

Incident Ray	Emergent Ray
Is parallel to principal axis	Appears to pass through focus
Passes through optic centre	Passes without deviation
Is directed towards focus	Passes parallel to principal axis

The lens formula defines the relationship between the focal length of the lens (f), the distance of the object from the optic centre (u) and the distance of the image from the optic centre (v):
  1 f   = 1 v - 1 u 
Where,
     f = focal length
    u = object distance
     v = image distance

Location and Characteristic of the Images Formed by a Concave Lens  

Object Location	Image Location	Nature of Image
Infinity	As a point at F1	Virtual Erect Highly Diminished
Beyond 2F1	Between F1 and O	Virtual Erect Diminished

Sign convention for spherical lenses:

·         All distances measured above the principal axis are taken as positive. Thus, height of an object and that of an erect image are positive and all distances measured below the principal axis are taken as negative.

·         The distances measured in the direction of incident rays are taken as positive and all the distances measured in the direction opposite to that of the incident rays are taken as negative.

·         All distances on the principal axis are measured from the optic center.

Lens Formula and Sign Conventions

1 f = 1 v - 1 u 
Where, 
     f = focal length
    u = object distance
     v = image distance

All the distances are to be measured from the optic centre of the lens:

The distances measured in the direction of the incident light are taken as positive (+).
The distances measured in the direction opposite to that of the incident light are taken as negative (-).

Magnification (m)
Magnification is the ratio of the image size to the object size. It is also measured as the ratio of image distance to object distance.

 m = (Size of the image / Size of Object ) Or m = (Image distance / Object distance)

If m = 1;  image size = object size
If m > 1:  image size > object size
If m < 1:  image size < object size

Power of Lens (P)
      •  The converging or diverging capacity of a lens is ascertained by its power
      •  Power of a lens is the reciprocal of its focal length expressed in metre. P =  1 f  ( measured in meters).
      •  SI Unit of power of a lens is dioptre (D).
      •  Power of a convex lens is positive and that of a concave lens is negative.

Differences Between Convex Lens and Concave Lens

Convex Lens	Concave Lens
1.  It is thick in the middle and thin at the edges. 2.  It converges the incident rays towards the principal axis. 3. It has a real focus.	1.  It is thin in the middle and thick at the edges. 2. It diverges the incident rays away from the principal axis. 3. It has a virtual focus.

• HUMAN EYE AND COLOURFUL WORLD

Human Eye

Human eye is the most important organ of our body which is an optical device that serves as our organ of sight. It consists of a tough fibrous membrane called sclera that protects the internal parts of the eye.

Cornea is the membrane covering the front of the eye that is bulged out and is responsible for the maximum refraction of the light that enters the eye.

Aqueous humour lies behind cornea that enables the eye to cope up with the atmospheric changes.

Iris forms the coloured part of the eye. It adjusts the size of the pupil, thereby controls the amount of light entering the eye.

the crystalline lens, lies behind Iris a biconvex structure that helps in fine adjustment to the refracted light so that it is focused on the screen of the eye, which is referred to as retina.

Ciliary muscle helps in adjusting the focal length of the lens by contraction or relaxing. Vitreous humour lies behind the lens which is a dense, clear, jelly like fluid which helps to maintain the shape of the eye and focus the image clearly on the retina.

Retina is actually a canopy of the nerve endings of the optical nerve through which images are converted into electrical impulses and transferred to the brain for realization of the image.

The eye can focus near objects as well distant objects and this is accommodation of the eye. The minimum distance of the object at which an eye can focus clearly is the near point the maximum is called the far point.

If an eye is unable to focus the nearby objects and is able to view clearly the far off objects, the defect is called hypermetropia or long sightedness and can be corrected by a suitable convex lens.

On the other hand if a person is able to view the nearby objects clearly and unable to view the distant objects the defect is myopia or short sightedness and can be corrected by a suitable concave lens.

The power of the corrective lens is calculated by using lens formula and is measured in dioptre. The major parts of the human eye and their functions are as the following:

Functions of the Parts of Human Eye

Sclera
Protects and contains internal parts

Cornea
Cornea is responsible for maximum refraction of incident light

Aqueous Humour
Prevents collapse of the eye due to atmospheric pressure changes

Iris
Iris controls the light entering the eye by  adjusting the size of pupil

Crystalline Lens
Focuses the light reflected by objects on the retina.

Ciliary Muscles
Alter focal length of the crystalline lens

Retina
Receives optical image and converts it to electrical impulses

Vitreous Humour
Maintains the shape of the eye

Optic Nerve
Carries electrical impulses to the brain. Brain interprets these impulses and produces the sense of vision.

The functioning of a camera is similar to that of the eye.

Accommodation
The ability of the eye to change the focus between objects at different distances by altering the curvature of the lens is called accommodation.

        •  To form a clear image of different objects at different distances from the eye, the focal length of the eye lens has to be changed.
        •  The contraction and relaxation of ciliary muscles helps to alter the curvature of the lens.
        •  Far point is the maximum distance from the eye at which the eye can obtain a focused image of an object without straining.

Far point
The farthest point upto which a shortt sighted eye can see clearlyis called the farpoint of the eye. For a normal human eye, the far point is infinity.

Near Point
Near point is the minimum distance at which the eye can obtain a focused image of an object without straining. For a normal human eye, of an adultthe near point is about25 cm from the eye.

Least Distance of Distinct Vision
The minimum distance required between the object and the eye to view the object comfortably is called the least distance of distinct vision.
      
        •  Long exposure of the eyes to ultraviolet light, effects of diabetes, hypertension and old age can result in a condition called cataract.
        •  Cataract results in a cloudy translucent eye lens. This cloudiness affects the ability of the eye to accommodate.
        •  The horizontal field of view for a single eye is 150^o.
        •  Stereovision position of the eyes, help us to see the maximum possible number of objects around us.

Factors causing irregularities in vision

        •  Irregularities on the surface of the cornea
        •  Development of cataract
        •  Weakening of ciliary muscles
        •  Change in the size of the eyeball

These irregularities lead to the following three major types of defective vision.

        •  Myopia
        •  Hypermetropia
        •  Presbyopia

Myopia
Myopia, also known as short sightedness or near sightedness, is a defect in which a human eye can see nearby objects clearly but distant objects appear blurred and unclear.

Myopia can be corrected by placing a suitable concave lens in the line of sight.

Hypermetropia
Hypermetropia also known as long sightedness is a defect of vision in which a human eye has problems seeing objects located nearby, clearly.

        •  A person suffering from hypermetropia can see distant objects clearly.
        •  Hypermetropia occurs when the converging power of the eye lens is less than normal.
        •  Hypermetropia can be corrected by placing a suitable convex lens in the line of sight.

Presbyopia
Presbyopia is a condition in which the crystalline lens of an eye loses its flexibility.

Persons suffering from presbyopia are unable to read or see clearly even at the least distance of distinct vision, which is 25 centimetre. To correct presbyopia, a bifocal lens is used.


Correction of Hypermetropia and Myopia

To correct the short sightedness i.e. Myopia a concave lens whose focal length is equal to the distance of the far poin tof the myopic eye is to be placed in front of the the myopic eye.

To correct the Longt sightedness i.e. Myopia a converging i.e. convex lens of suitable focal length is used. When it is placed before the eye lens, the final image is focussed on to the retina.


Calculation of focal length of the corrective lens of  Longt sightedness (Myopia)


The Focal length of the creective lens is calculated as the following.

If x is the distance of the near point of the defective eye and D is the least distance of distict vision, the
u = - D,v  = -x, where u = Object distance and x = Distance of the near point of the defective eye
⇒(1/f) = [(1/v) -(1/u)]
⇒(1/f) = [-(1/x) =(1/D)]
⇒(1/f) = [(x D)/(x - D)]
⇒(1/f) = xD/(x - D)
Since x>D, the focal lenth is posive.



whose focal length is equal to the distance of the far poin tof the myopic eye is to be placed in front of the the myopic eye.

Dispersion and Scattering of Light

Rainbow is the natural phenomenon in which dispersion takes place. The cause of dispersion is that sun light consists of seven constituents (colours namely violet, indigo, blue, green, yellow, orange and red popularly referred to as VIBGYOR) that have different refractive index with respect to a medium. The wavelength of each colour is different that causes the difference in velocity of the corresponding light when passing from one medium to another.

This phenomenon can be observed in a lab environment using a triangular glass prism. It is a solid structure having three rectangular and two triangular surfaces. Any two rectangular faces are the refracting surfaces and the third one is the base. The angle between two refracting surfaces of a triangular glass prism is denoted by A, called the angle of the prism or the refracting angle.

 

The ray that deviates at the point of incidence due to a change in the medium is the refracted ray.

The angle formed between the incident ray and the normal at the point of incidence is known as the angle of incidence.

The angle between the normal and the refracted ray is known as the angle of refraction.

The angle between the directions of the incident ray and that of the emergent ray is called the angle of deviation and is represented by Greek letter δ or q_d.

        •  The splitting of white light into its constituent colours is called dispersion of light.
        •  Light disperses and creates a rainbow effect, when it propagates and refracts in a prism.
        •  Light disperses and creates a rainbow effect, when it propagates and refracts in a prism.

The order of colours in a rainbow is popularly identified using the acronym, VIBGYOR, each letter standing for a colour in order.

Atmospheric refraction refers to the apparent random wavering or flickering of objects due to inconsistency in the physical conditions of the refracting media such as air.

In scientific terms, the twinkling of stars is termed as astronomical scintillation. When the sun is just below the horizon, its rays enter earth’s atmosphere and are refracted towards the earth. The refracted rays reach the earth making it appear as if the sun has already risen above the horizon. This is apparent sunrise.

Apparent sunset occurs slightly later than the actual sunset, since the light from the sun is already below the horizon, it refracts through the atmosphere, enabling us to see the apparent sunset, even after the sun has already set.

Scattering of light is the deviation of light rays from its straight path. As light propagates through the atmosphere, it travels in a straight path until it is obstructed by bits of dust or gas molecules.

During sunrise and sunset, the sun is at the horizon and refractive index of the atmosphere of the earth decrease with height. Due to this, light reaching the earth's atmosphere from different parts of the vertical diameter of the sun enters at different heights in earth's atmosphere and so travels in media of different refractive indices at the same instant and hence, bend unequally. Due to this unequal bending of of light from the vertical diameter, the image of the sun gets destored and it apppears oval and larger. However, at noon when the sun is overhead, then due to normal incidence of light there is no bending of light and hence, the sun appears circular.

The sky appears blue because out of the seven colours of light, blue has the shortest wavelength, and therefore it experiences more scattering than other colours.

Scattering of light gives rise to many amazing and spectacular phenomena such as the Tyndall effect and the reddening of the sun at sunrise and sunset.

The Tyndall effect is the scattering of light by colloidal particles.

Sun Appears red at Sunrise and Sunset
The sun appears white at noon becuase the light from the sun overhead would travel relatively shorter distance. As only a little of the blue and violetcolours are scattered.

the light from the sun, near the horizon, passes through the thicker layers of air and covers a large distance in the earth's atmosphere before reaching our eyes.

Near the horizon, most of the blue light and other shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelengths. This gives rise to the reddish appearance of the sun.


Clouds are White

Clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths the component colours of white light(i.e red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light.

            CHAPTER  -   ELECTRICITY

             Current Electricity Basics

Electricity is one of the oldest branches of science without which we cannot just imagine ourselves in the current world. The current flow from a high potential area to a low potential area is termed the conventional current whereas the flow of electrons constitute the electron current and is in a direction opposite to that of the conventional current.

Flowing water constitutes water current in rivers. Similarly, if the electric charge flows through a conductor we say that there is an electric current in the conductor. A continuous and closed path of an electric current is called an electric circuit.

In a torch light, the cells provide flow of charges or an electric current through the torch bulb to glow. The torch gives light only when its switch is on. If the circuit is broken anywhere (or the witch of the torch is turned off), the current stops flowing and the bulb does not glow.

In circuits using metallic wires, electrons constitute the flow of charges. As the electrons ere not known (not discovered) at the time of the observation of the electric phenomenon. So, electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current.

Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges. Electric current is the rate of flow of charges.

If a net charge Q flows across any cross-section of a conductor in time t, then the current I through the cross-section is I =  Q t .

The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 10¹⁸electrons. (We know that an electron possesses a negative charge of 1.6 × 10^–19 C.) The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836). One ampere is constituted by the flow of one coulomb of charge per second, i.e., 1 A = 1 C/1 s. The SI unit of electric current is ampere.

Small quantities of current are expressed in milliampere (1 mA = 10^–3 A) or in microampere (1 μA = 10^–6 A). An instrument called ammeter measures electric current in a circuit.

An ammeter is always connected in series in a circuit through which the current is to be measured. In a typical electric circuit comprising a cell, an electric bulb, an ammeter and a plug key, the electric current flows from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter.

Charges do not flow in a copper wire by themselves, just as water in a perfectly horizontal tube does not flow. Water flows in a tube only if there is a pressure difference between the two ends of a tube. Similarly electrons move along the conductor only if there is a difference of electric pressure, known as the potential difference.

For flow of charges in a conducting metallic wire, the gravity, of course, has no role to play.

The difference of potential may be produced by a battery, consisting of one or more electric cells. The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it. When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it.

The electric potential difference between two points in an electric circuit carrying some current is the work done to move a unit positive charge from one point to the other: Potential difference (V) between two points = Work done (W)/Charge (Q),
i.e.,  V =  W Q 

The SI unit of electric potential difference is volt (V), named after the Italian physicist Alessandro Volta. One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other. 1 volt = 1 joule/1 coulomb; 1 V = 1 J/ C.

The potential difference is measured using a voltmeter. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured.

A schematic diagram in which different components of the circuit are represented by symbols is called aelectric circuit diagram.

A closed loop through which charge can continuously move is referred to as a closed circuit. If the loop is not complete then charge stops flowing and such a circuit is called an open circuit.

In 1827, a German physicist Georg Simon Ohm (1787–1854) found out the relationship between the current I, flowing in a metallic wire and the potential difference across its terminals. He stated that the electric current flowing through a metallic wire is directly proportional to the potential difference V, across its ends provided its temperature remains the same. This is called Ohm’s law. In other words, V/I = constant = R, or V = IR, where R is a constant for the given metallic wire at a given temperature and is called its resistance.

As per electricity, we have two categories of materials, namely conductors and insulators. All of the conductors do not conduct electricity the same way. Some of them offer a restriction to the flow of charge and are referred to as resistors. The restriction to the flow of charge is electrical resistance and depends on the physical dimensions and temperature of the conductor.

The resistance (R) of a conductor varies directly with its length (l) and inversely with its area of cross-section (A). The mathematical expression is   R = ρl/A,  where ‘r’ is the constant called resistivity or specific resistance of the material which depends on the nature and temperature of the material. Resistivity is measured in ohm-metre.

At a given temperature, the current through a conductor is directly proportional to the potential difference across its ends and is known as Ohm’s law.

Ohmic Conductors	Non-Ohmic Conductors
1. Conductors that obey Ohm’s Law are called Ohmic conductors. 2. In Ohmic conductors, current is proportional to voltage. 3. Magnitude of current remains unchanged when current or voltage is reversed in Ohmic conductors. 4. In Ohmic conductors, temperature affects current and resistance.	1. Conductors which do not obey Ohm’s Law are called Non-Ohmic conductors. 2. In Non-Ohmic conductors, current is not proportional to voltage. 3. Magnitude of current changes when current or voltage is reversed in Non-Ohmic conductors. 4. In Non-Ohmic conductors, different factors affect current and resistance.

Factors affecting the resistance of a conductor :
(1) The material of wire : The resistance of a wire depends on the number of collisions which the electrons moving through it suffer with the other electrons and with the fixed positive ions of the wire. In different materials, the concentration of electrons and the arrangement of atoms are different, therefore, the resistance of wires of same length, same area of cross section, but of different materials differ depending on their material. Good conductors having higher concentration of free electrons (such as metals) offer less resistance.
(2) The length of wire : The number of collisions suffered by the moving electrons will be more if they have to travel a longer distance in wire, therefore, a long wire offers more resistance than a short wire (i.e, resistance ∝ length of wire)
(3) The area of cross section of wire : In a thick wire, electrons get a larger area of cross section to flow as compared to a thin wire, therefore, a thick wire offers a less resistance ((i.e, resistance ∝ 1/area of cross section)
(4)The temperature of wire: If the temperature of wire increases, ions in it vibrate more violently. As a result, the number of collisions increases and hence the resistance of wire increases with the increase in its temperature.

Current Electricity Circuits

An electric circuit is a closed path for flow of electricity through which electricity can be converted into different forms of energy. An electric circuit basically contains a source of electricity, a load resistance, a switch or a key for making the circuit on or off at ones convenience (which makes or breaks the circuit correspondingly).

The diagrammatic representation of an electric circuit is called the circuit diagram. Each electric component in a circuit has a unique symbol through which it is represented in a circuit diagram. If a circuit is switched off, it is called an open circuit and if the circuit is switched on it is called a closed circuit.

The reciprocal of the net resistance of a number of resistors connected in parallel is the sum of the reciprocals of the individual resistances.

The resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc. Tungsten is used almost exclusively for filaments of electric bulbs, whereas copper and aluminium are generally used for electrical transmission lines.

In various electrical gadgets, we often use resistors in various combinations. There are two methods of joining the resistors together.

Series Combination of Resistors
If a number of resistors are joined end to end in an electric circuit, the resistors are said to be connected in series.

In a series combination of resistors the current is the same in every part of the circuit or the same current flows through each resistor, i.e., there is only one path for the flow of current.

Let us consider a circuit in which three resistors R₁, R₂ and R₃ are connected in series with a battery of potential difference V. The potential difference V is equal to the sum of potential differences V₁, V₂, and V₃. That is the total potential difference across a combination of resistors in series is equal to the sum of potential difference across the individual resistors. That is,
V = V₁ + V₂ + V₃ ------------ (i)

Let I be the current through the circuit. The current through each resistor is also I. It is possible to replace the three resistors joined in series by an equivalent single resistor of resistance R_s, such that the potential difference V across it, and the current I through the circuit remains the same.

Applying the Ohm’s law to the entire circuit,
V = I R_s. ------------------- (ii)

On applying Ohm’s law to the three resistors separately,
V₁ = I R₁;    V₂ = I R₂;   and V₃ = I R₃.  ------------------- (iii)
From the eaquations (i),(ii) and (iii)
I R_s = I R₁ + I R₂ + I R₃ implies that
R_s = R₁ +R₂ + R₃.

When several resistors are joined in series, the resultant resistance of the combination Rs equals the sum of their individual resistances, R₁, R₂, R₃.

Note: Rs is greater than any individual resistance.

Parallel Combination of resistors
In a parallel circuit each resistor is placed in its own separate branch.  A parallel circuit provides multiple paths for the current to flow.

Consider the arrangement of three resistors joined in parallel with a  battery.  It is observed that the total current I, is equal to the sum of the separate currents through each branch of the combination.
I = I₁ + I₂ + I₃ --------------- (i)

The potential difference across each resistor is the same and is equal to the voltage of the battery.

Let R_p be the equivalent resistance of the parallel combination of resistors. By applying Ohm’s law to the parallel combination of resistors,
I =  V R p     --------------- (ii)

On applying Ohm’s law to each resistor,
I₁ =   V R 1   ; I₂ =    V R 2     ; and I₃ =   V R 3   --------------- (iii)

From the equations (i), (ii) and (iii)

   V R p     =   V R 1   +   V R 2 +    V R 3    

or    1 R p   =    1 R 1   +   1 R 2 +   1 R 3   .

The reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances.

Note:  The effective resistance in a parallel circuit is always less than the lowest resistance in the circuit.

In a series circuit the current is constant throughout the electric circuit. Thus it is obviously impracticable to connect an electric bulb and an electric heater in series, because they need currents of widely different values to operate properly. Another major disadvantage of a series circuit is that when one component fails the circuit is broken and none of the components works. For example, the electrician has to spend lot of time in trouble-locating and replacing the ‘dead’ bulb in a series of decorative bulbs– each has to be tested to find which has fused or gone.

On the other hand, a parallel circuit divides the current through the electrical gadgets. The total resistance in a parallel circuit is decreased. This is helpful particularly when each gadget has different resistance and requires different current to operate properly.

Ohmic Conductors	Non-Ohmic Conductors
1. Conductors that obey Ohm’s Law are called Ohmic conductors. 2. In Ohmic conductors, current is proportional to voltage. 3. Magnitude of current remains unchanged when current or voltage is reversed in Ohmic conductors. 4. In Ohmic conductors, temperature affects current and resistance.	1. Conductors which do not obey Ohm’s Law are called Non-Ohmic conductors. 2. In Non-Ohmic conductors, current is not proportional to voltage. 3. Magnitude of current changes when current or voltage is reversed in Non-Ohmic conductors. 4. In Non-Ohmic conductors, different factors affect current and resistance.

Laws of Electric Resistance
1. The resistance (R) of a conductor of a given material is directly
Proportional to its length (l)
Rα l ----------------- (i)

2. The resistance (R) of a conductor of a given material is inversely
Proportional to its area of cross section (A)
Rα  1 A     ----------------- (ii)

From the equations (i) and (ii)
R =  ρl A    , where ρ is called the resistivity of the material of unit length and unit cross-sectional area.

It is measured in ohm-meter. It is independent of the length or cross-sectional area of the conductor.

Heating Effect of Electric Current

Heating effect of electricity is one of the widely used effects in the world. When electric current is passed through a conductor, it generates heat due to the resistance it offers to the current flow. The work done in overcoming the resistance is generated as heat.

This is studied by James Prescott Joule and he enunciated various factors that affect the heat generated. The heat produced by a heating element is directly proportional to the square of the electric current (I) passing through the conductor, directly proportional to the resistance (R) of the conductor, time (t) for which current passes through the conductor. It is given by the expression
H = I²Rt and is well known as Joule’s Law.

Applications of the heating effect of electric current include appliances like electric immersion water heater, electric iron box, etc. All of these have a heating element in it. Heating elements are generally made of specific alloys like, nichrome, manganin, constantan etc.

A good heating element has high resistivity and high melting point. An electric fuse is an example for the application of heating effect of electric current. The rating of 3 A of an electric fuse implies the maximum current it can sustain is three ampere.

The chemical reaction within the cell generates the potential difference between its two terminals that sets the electrons in motion to flow the current through a resistor or a system of resistors connected to the battery. To maintain the current, the source has to keep expending its energy.

A part of the source energy in maintaining the current may be consumed into useful work (like in rotating the blades of an electric fan). Rest of the source energy may be expended in heat to raise the temperature of gadget. For example, an electric fan becomes warm if used continuously for longer time, etc.

If the electric circuit is purely resistive, that is, a configuration of resistors only connected to a battery, the source energy continually gets dissipated entirely in the form of heat. This is known as the heating effect of electric current. When  a conductor offers resistance to the flow of current the work done by the electric current in overcoming this resistance is converted into heat energy.

The generation of heat in a conductor is an inevitable consequence of electric current. In many cases, it is undesirable as it converts useful electrical energy into heat. In electric circuits, the unavoidable heating can increase the temperature of the components and alter their properties.

The electric heating is also used to produce light, as in an electric bulb. Here, the filament must retain as much of the heat generated as is possible, so that it gets very hot and emits light. It must not melt at such high temperature. A strong metal with high melting point such as tungsten (melting point 3380°C) is used for making the filaments of the bulb. The filament should be thermally isolated as much as possible, using insulating support, etc. The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of filament. Most of the power consumed by the filament appears as heat, but a small part of it is in the form of light radiated.

Devices which work on the heating effect of electric current have a heating element or filament. Good heating elements have high resistivity, high melting point and negligible variation in resistance due to temperature changes.

The three metal alloys most commonly used as heating elements are: Nichrome (80% Ni + 20% Cr); Manganin (86% Cu + 12% Mn + 2% Ni); Constantan (60% Cu + 40% Ni).

Joule's law
The Joule's law states that the quantity of heat produced in a resistor is directly proportional to: (i)the square of current for a given resistance, (ii) the resistance for a given current, and (iii) the time for which the current flows through the resistor, i.e., H = I²Rt.

Consider a current I flowing through a resistor of resistance R.
Let the potential difference across it be V.
Let t be the time during which a charge Q flows across.

The work done in moving the charge Q through a potential difference, V =VQ.
⇒ The source must supply energy equal to VQ in time t.
⇒  The power input to the circuit by the source is
P =   VQ t     = VI.
Or the energy supplied to the circuit by the source in time t
⇒H= P × t,
⇒ H = VIt
This energy gets dissipated in the resistor as heat.
Thus for a steady current I, the amount of heat H produced in time t is H = VIt.
Applying Ohm’s law,  H = I² Rt.

In practical situations, when an electric appliance is connected to a known voltage source, current can be calculated using the relation I =   V R   . Using this value in H = I²Rt, the heat produced can be calculated.

One of the common applications of Joule’s heating is the fuse used in electric circuits. An electric fuse is a safety device used to protect circuits and appliances by stopping the flow of any unduly high electric current. It works on the heating effect of electric current.

Electric Fuse
The fuse is placed in series with the device. An electric fuse consists of a piece of wire made of a metal or an alloy of appropriate melting point, for example aluminum, copper, iron, lead, etc. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit. The fuse wire is usually encased in a cartridge of porcelain or similar material with metal ends.

The fuses used for domestic purposes are rated as 1 A, 2 A, 3 A, 5 A, 10 A, etc. For an electric iron which consumes 1 kW electric power when operated at 220 V, a current of (1000/220) A, that is, 4.54 A will flow in the circuit. In this case, a 5 A
fuse must be used.

Electric energy and power
The rate of doing work is called power. This is also the rate of consumption of energy.

The equation H = I² Rt gives the rate at which electric energy is dissipated
or consumed in an electric circuit. This is also termed as electric power. The power P is given by P = VI. Or P = I²R =  V 2 R   .
 The SI unit of electric power is watt (W).
It is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V.

1 W = 1 volt × 1 ampere = 1 V A.

The unit ‘watt’ is very small. Therefore, in actual practice we use a much larger unit called ‘kilowatt’. It is equal to 1000 watts.

Since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (W h). One watt hour is the energy consumed when
                   1 watt of power is used for 1 hour.

The commercial unit of electric energy is kilowatt hour (kW h), commonly known as ‘unit’. 1 kW h = 1000 watt × 3600 second = 3.6 × 10⁶ watt second = 3.6 × 10⁶ joule (J).

We pay the electricity board or electric company to provide energy to move electrons through the electric gadgets like electric bulb, fan and engines. We pay for the energy that we use and not for the electrons. Electrons are not consumed in a circuit, as many people think.

MAGNETIC EFFECTS OF ELECTRIC CURRENTS

Magnetic Effects of Electric Current

Magnetic effect of electric current is one of the major effects of electric current in use, without the applications of which we cannot have motors in the existing world. A current carrying conductor creates a magnetic field around it, which can be comprehended by using magnetic lines of force or magnetic field lines. The nature of the magnetic field lines around a straight current carrying conductor is concentric circles with centre at the axis of the conductor.

The direction of the magnetic field lines of force around a conductor is given by the Maxwell’s right hand grip rule or the right handed cork screw rule.

The strength of the magnetic field created depends on the current through the conductor. If the conductor is in the form of a circular loop, the loop behaves like a magnet.

Clock-S rule
Cloak-S rule is rule which helps us to find the formation of magnetic South Pole due to electromagnetic induction in a current carrying conducting coil.

According to clocks rule if one face of a current carrying conducting coil is placed such that one face of the coil is faced to us and current is moving in the clockwise direction with respect to us then the face of the coil which is faced to us becomes as a magnetic south pole and the other face behaves as the north magnetic pole.

A current carrying conductor in the form of a rectangular loop behaves like a magnet and when suspended in an external magnetic field experiences force.

SNOW Rule
SNOW rule states that if the current is flowing in an electric circuit from South to North direction and a magnetic compass is placed Over the conducting wire, the needle of the compass deflects in the direction of west.

Right hand thumb rule 


Right hand thumb rule states that if we hold the conductor in the right hand such that the thumb points in the direction of electric current, then the direction in which the fingers curl gives the direction of the magnetic field

If we point thumb down wards in the direction of the current, the magnetic field would be represented by the curled fingers as the circles around the conductor.So, if it is viewed from the above plane this field lines will be clockwise circles, but the direction of the magnetic field at any point on this circular magnetic lines is in the direction of the tangent drawn to the circular magnetic lines at the desired points.

Maxwell’s cork-screw rule:


Maxwell' cork screw rule is also known as maxwell's right hand thumb ruleIf the head of a cork-Screw is rotated such that the tip of the screw advances in the direction of electric current, then the direction of rotation of the head of the screw represents the direction of the magnetic field aroundthe conductor.

A magnetic field caused by a current-carrying conductor consists of sets of concentric lines of force. The direction of the magnetic field lines depends on the direction of the current passed through the conductor.

Electromagnet
An electromagnet is a magnet made up of a coil of insulated wire wrapped around a soft iron core that is magnetised only when current flows through the wire.

Solenoid
The solenoid is an electro magnet which is a long cylindrical coil of wire consisting of a large number of turns bound together very tightly.

Note:  The length of the coil should be longer than its diameter. (Or)
Solenoid is a coil of a number of turns of insulated copper wire closely wrapped in shape of a cylinder. Magnetic field around a current carrying solenoid is as shown in the figure.


Theses appear to be similar to that of a bar magnet. One end of the solenoid behaves like North Pole and the other end behaves like the South Pole. Magnetic field lines inside the solenoid are in the form of parallel straight lines. This means that the field is same at all the points inside the solenoid.

When soft iron rod is placed inside the solenoid, it behaves like an electro magnet. The use of soft iron as core in the solenoid produces the strongest magnetism.

A solenoid consists of an insulated conducting wire wound on a cylindrical tube made of plastic or cardboard.

Fleming’s left hand rule



If the forefinger, middle finger and thumb of the left hand are stretched such that they are at right angles to each other, then:The forefinger gives the direction of the magnetic field.

       •  The middle finger points in the direction of the current.
       •  The thumb gives the direction of the force acting on the current-carrying conductor placed in the external magnetic field.
       •  An electric motor converts electrical energy into mechanical energy using the magnetic effect of electricity.

Electric motor
The direction of the force is given by Fleming’s left hand rule. This gives the basis for an electric motor. An electric motor essentially consists of a coil as an armature, a split ring commutator for changing the direction of the current in the coil. There are two brushes linked with the split rings that maintain the contact with the armature for the current flow. Electric motor converts electrical energy to mechanical energy.

A number of such loops form a coil and the coil is termed solenoid. If there is a soft iron core in the solenoid, it behaves like a magnet as long as there is current through the coil. Thus it is an electromagnet.

When an electric current passes through a conductor, a magnetic field is created around the conductor. This phenomenon is known as the magnetic effect of electricity.

A magnetic field is the extent of space surrounding a magnet where the magnet’s effect can be felt.
Magnetic field lines represent the lines of action of the force acting on a unit North Pole placed in a magnetic field.

Electromagnetic Induction

Electromagnetism created a revolution by leading to the devices called motors which convert electrical energy to mechanical energy. Experiments by scientists like Oersted and Faraday made a long leap by converting mechanical energy to electrical energy.

When a straight conductor is moved in a magnetic field an electric current is induced in it and the phenomenon is electromagnetic induction. The emf caused is the induced emf and the current is induced current.

Oersted found the same by relative motion of a magnet with respect to a coil. Faraday's experiment proved that the strength of the induced current depends on several factors like the strength of the magnet, the speed of motion of the magnet, its orientation, the number of turns in the coil and the diameter of the coil. The induced current can be detected by a galvanometer.

Fleming’s right hand rule gives the direction of the induced current in a conductor when it is moved in amagnetic field. Transformers are based on this principle, which consist of a primary coil and a secondary coil. The number of turns in the coils is selected based on the type of the transformer to be made, namely, step-up or step-down.

Electric generators work on the same principle. They have an armature which is free to rotate in a magnetic field. Its terminals are connected to two slip rings, which are further connected to two brushes and they are connected across a load resistance through which the generated electricity can be trapped. The rotation of the armature in the magnetic field changes the magnetic flux in the coil of the armature and an electric current is induced. As the direction of the induced current changes for every half rotation, it is called alternating current.

The current at the power plants is distributed through transmission lines at a high voltage and hence the lines are referred to as high tension power lines. At the substations these are stepped down to a lower voltage and supplied to houses at a low voltage.

A domestic electric circuit essentially contains mains, a fuse, live or line, neutral and earth wires. From the poles supply cables bring the current to the mains. Within the house, all the equipment is connected in parallel combination.

Electromagnetic induction (EMI) is the process of generating an electromotive force by moving a conductor through a magnetic field.

The electromotive force generated due to electromagnetic induction is called induced emf. The current due to induced emf is called induced current.

Fleming’s right hand rule



Fleming’s right hand rule states that if the index finger points in the direction of the magnetic field and the thumb indicates the direction of the motion of the conductor, then the middle finger indicates the direction of the induced current flow in the conductor.

An electric generator is used to convert mechanical energy into electrical energy, using electromagnetic induction.

Alternating current (AC) is the current induced by an AC generator. AC current changes direction periodically. Direct current (DC) always flows in one direction, but its voltage may increase or decrease.

Electrical components and wires fitted in a household to supply electricity to various appliances form a domestic electric circuit. The main supply cable has two wires: Live wire and neutral wire. Domestic electric circuits have earth wires to save users from severe electric shocks. An electric fuse is a safety device used to protect an electric circuit against excessive current.

Electricity and magnetism are inter-related and are also inter-convertible. In this setup an electric current passing through a conductor produces a magnetic field which can be observed through the deflection of a magnetic compass needle placed near the conductor. This proves that moving electric charges produce magnetic fields. Electric motors work on this principle. Electromagnetic Induction.

However, in this setup we see that an electric current is induced in a closed coil when subjected to a changing magnetic field. The phenomenon in which an electric current is generated by varying magnetic fields is called electromagnetic induction.

Electric generators work on this principle. We will now discuss and learn about three experiments
by Faraday and Henry, relating to electromagnetism. In the first experimental setup, a coil is connected to a Galvanometer.

When a bar magnet with its north pole facing the coil, is moved towards or away from the coil, the
Galvanometer needle deflects to the right and left side of zero reading respectively, showing
the presence of a current in the coil.

Let us see what happens if the south pole of the magnet faces the coil. The Galvanometer needle deflects to the left side of zero reading as the magnet approaches the coil and deflects to the right when the magnet moves away from the coil, showing the presence of a current in the coil.
The Galvanometer needle deflects only as long as the bar magnet is in motion. Once the bar magnet comes to rest the galvanometer needle settles down at “0” reading indicating that there is no current in the coil.

From all these observations we can conclude that whenever there is relative motion between a bar
magnet and a coil, an electric current is induced in the coil. In the second experimental setup, there are two coils:

Coil 1 connected to a Galvanometer, Coil 2 connected to a battery Due to the steady current in coil 2, a steady magnetic field is set up around the coil 2 and this magnetic field is also linked to the coil 1.
When coil 2 is kept stationary and coil 1 is moved towards coil 2, a current is induced in coil 1 and
the galvanometer needle deflects to the left of “0”. When coil 2 is kept stationary and coil 1 is moved away from coil 2, a current is induced in coil 1 and the galvanometer needle deflects to the
right of “0”. If we keep coil 1 stationary and move coil 2 towards coil 1, a current is induced in coil 1 and a deflection is observed in the galvanometer needle to the left of “0”.

Now if we keep coil 1 stationary and move coil 2 away from coil 1, a current is induced in coil 1 and a deflection is observed in the galvanometer needle to the right of “0”. From all these observations we can conclude that whenever there is relative motion between a current carrying coil and a closed coil in which a galvanometer is connected a current is induced in the closed coil.

In the third experiment a tap key is provided in the coil 2 circuit. Here we can observe the
deflection of the galvanometer needle even when the two coils are stationary. This deflection is observed only at those instants when the tap key is either switched on or off. This happens because of the change in magnetic field during switching on and off.

When a ferromagnetic material like an iron rod is placed co axially along the two coils, the effect
of the magnetic field linked to the coil 2 increases due to the nature of the ferromagnetic material as it allows more number of magnetic lines of force to link within the area of the coil. Hence the deflection of the galvanometer needle increases indicating an increase in the induced current.

Electricity and magnetism are inter-related and the energies linked with them are also inter-convertible. Whenever there is relative motion between the magnet and a coil, an electric current is induced in the coil.

              SOURCES OF ENERGY  

Sources of Energy

We cannot imagine the world without energy. The source of energy is important as well. There are various sources of energy available today to the mankind. On a broad sense, sources of energy can be categorized into non-renewable and renewable. Wood, coal, oil, natural gas are some of the non-renewable sources as they cannot be renewable. These are also called the conventional sources of energy. Nuclear fuels like uranium produce energy by fission process. Nuclear energy from sun is obtained by nuclear fusion process.

Conventional fuels and sources of energy cause a lot of pollution to mankind and hence there is a need for looking towards alternate sources of energy, which are most likely to be renewable. Solar energy, energy from wind, hydro energy, geothermal energy and energy from biomass are some of the alternate sources of energy. Wind energy can be harnessed by using wind mills that can be erected at suitable locations. Hydroelectric plants make use of hydro energy. In most of the rural areas biomass is utilized.


Characteristics of a Good Source of Energy

       •  Enables us to do a large amount of work per unit volume or mass.
       •  Is easily accessible.
       •  Is easy to store and transport.
       •  Is economical.

Burning coal or petroleum products causes acidic oxides to be released. Thermoelectric production of electricity involves turbines. In thermal power stations, fossil fuels are burned to produce steam, basically a form of heat energy. This steam runs a turbine, which rotates a generator to produce electricity.

In hydroelectric power stations, the kinetic energy of flowing water, which is actually the potential energy of water stored at a height, is converted into electricity. Plant and animal products, wood and cow-dung cakes, are used as fuels. The source of these fuels is called bio-mass.

Burning a given mass of charcoal generates more heat than burning an equal mass of wood. Cow-dung, crop residue, garbage and sewage are decomposed in the absence of oxygen to produce bio-gas.

Advantages of Bio-Gas:
       •  It is an excellent fuel with 75% methane.
       •  It burns without smoke.
       •  It has a high heating capacity.
       •  It is also used for lighting.

Wind is another freely available resource that is used for generating energy.

Alternative or Non-Nonventional Sources of Energy:
       •  Energy from the sun
       •  Energy from the sea
       •  Geothermal energy
       •  Nuclear energy

Black surfaces absorb more heat when compared to white under identical conditions.

Three Types Energy From the Sea:
       •  Tidal energy
       •  Wave energy
       •  Ocean thermal energy

Molten rock in the earth’s crust is pushed upward and trapped in certain regions called hot spots.

Nuclear energy is produced either by nuclear fission or nuclear fusion. Exploiting various sources of energy causes dist

                  OUR ENVIRONMENT

Our Environment

Balance in nature is maintained by the interaction between biotic components with that of abiotic components.

The ecosystem is a community of organisms and their physical environment interacting with each other as an ecological unit, involving the flow of energy.

       •  An ecosystem consists of biotic components including living organisms and abiotic components, the physical factors like temperature, rainfall, wind, soil and minerals.
       •  An ecosystem can be natural or artificial. Organisms in the ecosystem can be categorised into producers, consumers and decomposers.

Producers are the organisms that produce their own food without the help of any other organism.

       •  They are also known as autotrophs.
       •  They make their food from inorganic substances through a process called photosynthesis.
       •  Autotrophs are green plants, phytoplankton and blue green algae.

Consumers are the organisms which cannot produce food but depend on producers for the same.

       •  These are also called as called heterotrophs.
       •  Heterotrophs are the animals can be classified into herbivores, omnivores, carnivores and parasites based on their food pattern.

Decomposers are the organisms which feed on dead and decaying matter.

       •  Decomposers break down the complex organic compounds present in dead animals and plants, which are then used by other members of the ecosystem.
       •  Decomposers like bacteria and fungi are known as saprobes.

Food chains describe the feeding relationship between the organisms of an ecosystem.

       •  The flow of energy from one species to another at various biotic levels forms a food chain.
       •  The successive levels in the food chains of a community are called as trophic levels.
       •  Various trophic levels in a food chain include producers, primary consumers, secondary consumers and tertiary consumers.
       •  A web of cross-linked food chains is called a food web.

Biological magnification is a phenomenon by which toxic substances accumulate from one trophic level to another. As human beings occupy the top level in any food chain, the maximum concentration of these toxic chemicals gets accumulated in your body which becomes toxic to us.

Ozone is molecule formed by the combination of three oxygen atoms. There is a layer of ozone in the stratosphere. It acts as a natural sun-block and shields us from the UV radiations of the sun which are dangerous to living organisms.Ozone depletion is the sharp reduction of ozone in the stratosphere due to chlorofluorocarbons (CFC’s) used as refrigerants and in fire extinguishers.

Increased use of non-biodegradable items have left the environment polluted with them.

MANAGEMENT OF NATURAL RESOURCES

Management of Forest Resources

Natural resources are the materials provided by nature. They include forests, water, coal and petroleum reserves. Day-by-day we are exploiting our natural resources.

River Ganga features an example for the exploitation of natural resources.
       •  The river Ganga runs its course of over 2500 kilometres from Gangotri in the Himalayas to the Bay of Bengal, through Uttar Pradesh, Bihar and West Bengal.
       •  Pollution of the river Ganga is due to activities like bathing, washing clothes, immersion of the ashes of the dead, industrial effluents and release of untreated sewage.
       •  The coliform bacteria are usually found in the human intestine whose presence in the Ganga water indicates contamination by faeces and disease-causing micro-organisms.
       •  The Ganga Action Plan project was launched in 1985 to clean the Ganga and make its water free from pollution.

Forests are 'biodiversity hotspots' due to the sheer number as well as the variety of species of flora and fauna that live in them.
       •  Stake holders are people who live in and around forest, the forest department of the government, industrialists, forest and wildlife activists etc.
       •  We have to conserve forests which are of greater use to the environment.
       •  The Chipko Andolan ('Hug the Trees Movement') originated in the 1970's, in a village called Reni in Garhwal high up in the Himalayas. It was to save trees from being cut down.
       •  The conservation of forests by the Bishnoi community in Rajasthan became well known because of Amrita Devi Bishnoi, who sacrificed her life in 1731 for the protection of the Khejri trees in village Khejrali.
       •  The role of the government in forest conservation includes owning of forest land, controlling industries, framing rules to ensure that local people benefit and to control illegal activities.
       •  Biodiversity should be conserved. This happens by protecting flora and fauna of the place.
       •  The ways to conserve our resources are judicious use, long-term perspective, and equitable distribution.
       •  Pollution should be controlled.

The 3R's in conserving resources are Reduce, Recycle and Reuse.

Sustainable development is not only about the resources we use but also ensures that they are equally distributed. Stake holders together help in sustainable management.

Government should control the industries in using raw materials. It should ensure that local people should not be marginalised. Government should also control illegal activities. Industries should play an important role in the management of natural resources.

Management of Water and Coal Resources

Water
Water is an essential form of life. Water is useful in agriculture, industries, cooking and various domestic activities.Most of us depend on rainfall for water.

The rainfall pattern in India differs in different geographical regions. Tropical regions receive more rainfall as compared to desert regions.

The passage of water from water bodies to the atmosphere and back to the earth is called water cycle.
During water cycle, water from aquatic bodies evaporates into the atmosphere due to sunlight and condenses into clouds. Due to air currents, the clouds turn into rains and reach water bodies and the ground.

Forms of water
       •  Around 97.5 percent of water in the oceans is salty.  About 1.75 percent of fresh water remains frozen in glaciers and polar ice caps while the remaining 0.75 percent exists as groundwater.
       •  The advantages of groundwater are that it does not evaporate, it recharges wells and it is protected from contamination by human and animal waste.

Dams
Dams are the structures constructed to divide and retain river water in a particular area.

       •  Some famous dams in India are the Bhakra Nangal Dam, the Sardar Sarovar Dam and the Tehri Dam.
       •  Dams provide water which is used to generate hydroelectric power.
       •  Dams are also used to supply water for agriculture, for domestic purposes and as drinking water in cities. Water from dams is distributed through canal systems that transport stored water to great distances.
       •  The Indira Gandhi Canal is one of the biggest canal projects in India which provides water for Rajasthan.
       •  The disadvantages of dams are deforestation, sedimentation, erosion of river beds, and disruption of animal and plant life.

Watershed management
Watershed management is an integrated multi resource management of land and water.
       •  Watershed management aims at water conservation to increase biomass production.
       •  Water harvesting is an age old concept in India.
       •  Water harvesting techniques are named differently at different places, but the use remains the same. For example, Khadins and Nadis in Rajasthan, Bandharas and Tals in Maharashtra, Bundhis in Madhya Pradesh and Uttar Pradesh, Ahars and Pynes in Bihar, and Eris in Tamil Nadu.
       •  Kulhs in Himachal Pradesh, Kattas in Kerala, Trenches in Karnataka help in recharging water resources.

Fossil fuels
Coal, petroleum and natural gas are the fossil fuels which provide us energy in many activities of our life. These are non-renewable sources of energy.
       •  Coal was formed hundreds of million years ago as a result of the action of heat and pressure on decaying, buried plants in the swampy areas of the earth. It is a continuous process taking place under the earth.
       •  Coal helps in the production of thermal electricity. About 37 percent of the world’s electricity is produced using coal.
       •  Coal is a non-renewable but cheaper resource than other fuels like petroleum and gas.
       •  The disadvantages of fossil fuels are that they release carbon dioxide, oxides of nitrogen and oxides of sulphur on combustion. Carbon dioxide causes global warming.

Some alternative sources of energy are wind, solar, thermal and hydroelectric energy. These are all viable options since they are more environment-friendly.

Energy conservation can be done by recycling and reusing plastic bags, switching off lights, and also by using CFL bulbs.