SCIENCE

Science is a systematic and organised attempt to acquire knowledge about the surroundings through observations, experiments and verifications.

SCIENTIFIC METHOD

  • Several inter-related steps are involved in the scientific method. Some of the most significant steps are as follows:
  • The systematic observations
    (i) Reasoning
    (ii) Mathematical modelling
    (iii) Theoretical prediction

PHYSICS

  • Physics is a fundamental science concerned with understanding the natural phenomena that occur in our universe.It has many branches such as :
    Mechanics,
    Electromagnetism,
    Thermodynamics,
    Modern Physics, etc.
  • Between 1600 and 1900, three broad areas were developed, which together are called Classical Physics.
  • These three areas of study are classical mechanics, thermodynamics and electromagnetism.
  • But by 1905 it became apparent that classical ideas failed to explain several phenomena.
  • Then some new theories were developed in what is called Modem Physics such as Special Relativity, Quantum Mechanics, etc.

SCOPE AND EXCITEMENT OF PHYSICS

  • The scope of Physics is very broad and covers a wide range of magnitudes of physical quantities such as length, mass, time, energy, etc.
  • It deals with the macroscopic world like galaxies and the universe as well as the microscopic world like the nucleus of an atom and fundamental particles like electrons, protons, neutrons etc.
  • Immense excitement is involved in the study of physics since it explains every naturally occuring phenomena with a set of rules, so that clear understanding can be achieved.
  • The challenge to carry out imaginative new experiments to unlock the secrets of nature, to verify or refute theories, is really exciting.

PHYSICS IN RELATION TO OTHER SCIENCES

Physics is a very significant branch of science which plays a crucial role in understanding the developments pertaining to the other branches of science such as Chemistry, Biology etc.

(i) Physics in relation to Mathematics:

Study of physical variables led to the idea of differentiation, integration and differential equations. Meaningful interpretation of Mathematics becomes Physics.

(ii) Physics in relation to Chemistry:

The concept of X-ray diffraction and radioactivity has helped to distinguish between the various solids and to modify the periodic table. Understanding the bonding and the chemical structure of substances is easy with the help of the concept of interactions between various particles.

(iii) Physics in relation to Astronomy:

Optical telescopes of reflecting and refracting type enabled man to explore the space around. Discoveries like radio telescopes have revolutionised the study of Astronomy.

(iv) Physics in relation to Biology:

The conceptual study of pressure and its measurement has helped us to know blood pressure and hence the functioning of the heart. Invention of X-rays developed the field of diagnosis. Electron and optical microscopic designs have revolutionised the study of medical science.

(v) Physics in relation to Meteorology:

The discoveries regarding the study of pressure variations help us to forecast the weather. Various other inventions of physics have opened new vistas of study in the field of sciences and social sciences.

PHYSICS IN RELATION TO TECHNOLOGY AND SOCEITY

  • Advancement in physics has led to new technologies and vice-versa.
  • Sometimes technology gives rise to new dimensions of physics; at other times physics generates new technology.
  • In fact, technological development is closely related to the application of science and physics in particular.
    Physics has a dominant influence on society. It has helped the human being to develop its ideas.
  • Development of digital communication systems, rapid mass transport systems, lasers making bloodless surgeries, etc., has made human life easy and pleasant.
  • There are four fundamental forces in nature that govern the diverse phenomena of the microscopic and macroscopic world.
  • These are ;
    the ‘gravitational force’,
    the ‘electromagnetic force’;
    the ‘strong nuclear force’, and
    the ‘weak nuclear force’.
  • Unification of forces is a basic quest in physics. The electromagnetic and the weak nuclear forces have now been unified and are seen as aspects of a single ‘electro-weak’ force.
  • Attempts are being made to unify electro-weak and strong forces.
  • Conservation of energy, momentum, angular momentum, charge, etc., are considered to be the fundamental laws in physics.
  • Conservation laws have a deep connection with the symmetries of nature.
  • Symmetries of space and time, and other types of symmetries play a central role in modern theories of fundamental forces in nature.

IMPORTANT TABLES

  • Everything that surrounds us is the environment. It includes both living (biotic) and non- living (abiotic) components.
  • Interaction between these biotic and abiotic components form an ecosystem.
  • In an ecosystem living components depend on each other for their food which give rise to food chains and food webs in nature.
  • Human activities lead to environmental problems such as depletion of ozone layer and production of huge amounts of garbage.

ECOSYSTEM

All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. E.g., forest, pond etc.

TYPES OF ECOSYSTEM

(i) Natural ecosystem:

The ecosystem which exists in nature on its own. Example: forest, lake, ocean.

(ii) Artificial ecosystem:

Man-made ecosystems are called artificial ecosystems. Example: crop field, aquarium, garden.

COMPONENTS OF ECOSYSTEM

(i) Abiotic Components:

All the non- living components such as air, water, land, light, temperature etc. form the abiotic components.

(ii) Biotic Components:

All the living components such as plants, animals, bacteria, fungi etc. form the biotic components.
On the basis of nutrition biotic components are further divided into:
  • Producers: All green plants and blue-green algae can produce their own food using abiotic components (photosynthesis), hence called producers.
  • Consumers: Include all animals which depend on producers directly or indirectly for their food.
  • Decomposers: Include organisms which decompose the dead plants and animals. Example: bacteria, fungi. These help in the replenishment of natural resources.
Division of Consumers:

(i) Herbivores: Plant eaters. Example: goat, deer. 
(ii) Carnivores: Flash eaters. Example: tiger, crocodile. 
(iii) Omnivores: Eats both plants and animals. Example: human. 
(iv) Parasites: Live on the body of the host and take food from it. Example: lice, cascuta. 

FOOD CHAIN

  • Food chain is a series of organisms in which one organism eats another organism as food. For example: Grass → Deer → Lion
  • In a food chain various steps where transfer of energy takes place is called a trophic level.

FLOW OF ENERGY BETWEEN TROPHIC LEVELS

  • Flow of energy in a food chain is unidirectional.
  • Green plants capture 1% of sunlight and convert it into food energy.
  • 10 percent law : Only 10% of energy is transferred to the next trophic level. The remaining 90% energy is used in life processes (digestion, growth, reproduction etc.) by present trophic level.
  • Due to this gradual decrease in energy, food chains contain 3-4 trophic levels.

TROPHIC LEVELS

  • Decrease in energy
  • 1 kJ ↣ 10 kJ ↣ 100 kJ ↣ 1000 kJ

BIOLOGICAL MAGNIFICATION

  • The concentration of harmful chemicals increases with every next trophic level in a food chain. This is called biological magnification.
  • Maximum concentration of such chemicals accumulates in human bodies as humans occupy the top level in any food chain.

FOOD WEB

In nature large numbers of food chains are interconnected forming a food web.

ENVIRONMENTAL PROBLEMS

Changes in the environment affect us and our activities change the environment around us. Human activities lead to pollution, deforestation etc.

OZONE LAYER

  • Ozone layer is a protective blanket around the earth which absorbs most of the harmful UV (ultraviolet) radiations of the sunlight, thus protecting living beings from many health hazards such as skin cancer, cataract, destruction of plants etc.
  • Ozone (O3) layer is present at higher levels of the atmosphere (i.e. stratosphere). It is a deadly poison at ground level.

Formation of ozone molecule

  • The high energy UV radiations break down the O2 molecules into free oxygen (O) atoms. O (UV) O + O (atoms)
  • These oxygen atoms then combine with oxygen (O2) molecules to form the ozone molecule. O2 + O → O3 (ozone)

Depletion of ozone layer

  • The decrease in the thickness of the ozone layer over Antarctica was first observed in 1985 and was termed an ozone hole.
  • This decrease was linked to excessive use of synthetic chemicals like chlorofluorocarbons (CFCs) which are used in refrigerators, ACs, fire- extinguishers, aerosols, sprays etc.
  • United Nations Environment Programme (UNEP) succeeded in forging an agreement to stop CFC production at 1986 levels (KYOTO PROTOCOL) by all countries.

GARBAGE DISPOSAL

Improvements in lifestyle have resulted in accumulation of large amounts of waste materials.

Types of materials in Garbage

  • Biodegradable: Substances which can be decomposed by the action of micro- organisms are called biodegradable wastes. Example: fruit and vegetable peels, cotton, jute, dung, paper, etc.
  • Non-biodegradable wastes: Substances which cannot be decomposed by the action of micro-organisms are called non-biodegradable wastes. Example: plastic, polythenes, metals, synthetic fibres, radioactive wastes, pesticides etc. Micro-organisms release enzymes which decompose the materials but these enzymes are specific in their action that’s why enzymes cannot decompose all the materials.

Methods of waste disposal

(i) Biogas plant: Biodegradable waste can be used in biogas plants to produce biogas and manure. 
(ii) Sewage treatment plant: The drain water can be cleaned in sewage treatment plants before adding it to rivers. 
(iii) Land fillings: The wastes are buried in low lying areas and are compacted by rolling with bulldozers. 
(iv) Composting: Organic wastes are filled in a compost pit and covered with a layer of soil, after about three months garbage changes to manure. 
(v) Recycling: Non-biodegradable wastes are recycled to make new items. 
(vi) Reuse: It is a conventional technique to use an item again. Example: newspaper for making envelopes. 

  • Energy comes in different forms and one form can be converted into another. 
  • A source of energy is one which provides an adequate amount of energy in a convenient form over a long period of time.
    Need of energy

NEED FOR ENERGY

  • For making food
  • For lightning
  • For transport
  • For running machines
  • For industrial activities and agricultural work

QUALITIES OF A GOOD SOURCE OF ENERGY

  • Which would do a large amount of work per unit mass.
  • Cheap and easily available.
  • Easy to store and transport.
  • Safe to handle and use.
  • Does not cause environmental pollution.

FUELS

The materials which are burnt to produce heat energy are known as fuels. Example: wood, coal, LPG, kerosene.

CHARACTERISTICS OF A GOOD FUEL

  • High calorific value (give more heat per unit mass).
  • Burn without giving out any smoke or harmful gases.
  • Proper ignition temperature.
  • Cheap and easily available.
  • Easy to handle, safe to transport.
  • Convenient to store.
  • Burn smoothly.

SOURCES OF ENERGY

CONVENTIONAL SOURCES OF ENERGY

Sources of energy which are known to most people. Example: fossil fuels, biomass etc. 

  • Fossil fuels (Coal, Petroleum)
  • Thermal power plant
  • Hydro power plants
  • Geothermal energy 

1. FOSSIL FUELS

  • Fuels developed from the fossils e.g., coal, petroleum.
  • Take millions of years to form.
  • Available in a very limited amount.
  • These are non-renewable sources of energy.
  • India has about 6% share in the world reserved coal, that may last 250 years more at the present rate of consumption.
Pollution Caused by Fossil Fuels
  • Released oxides of carbon, nitrogen and sulphur (acidic in nature) which causes acid rain that damages trees, plants, and reduces fertility of soil.
  • Produces large amounts of CO2 in the atmosphere which causes a greenhouse effect leading to excessive heating of the earth.
Controlling Pollution Caused by Fossil Fuels
  • Increasing the efficiency of the combustion process.
  • Using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

2. THERMAL POWER PLANTS

  • A power plant which uses heat energy to generate electricity.
  • Burning of fossil fuels produces steam to run turbines.
  • Set up (power plants) near the coal and oil fields to minimize the cost of transportation and production.
  • Transmission of electricity is more efficient.

3. HYDRO POWER PLANTS

  • Convert the potential energy of falling water into electricity.
  • Hydro power plants are associated with Dams.
  • Around 25% of our country’s energy requirement is met by Hydro Power plants.
Advantages of Hydro power plants
  • No environmental pollution.
  • Flowing water is a renewable source of electric energy.
  • Construction of dams prevents flooding of rivers, provide water for irrigation.
Disdvantages of Hydro power plants
  • Large areas of agricultural land, a vast variety of flora and fauna, human settlements get submerged in the water of the reservoir formed by the dam.
  • Large ecosystems are destroyed.
  • Vegetation that is submerged under water rots under anaerobic conditions and produces a large amount of methane which is a greenhouse gas.
  • Creates the problems of satisfactory rehabilitation of displaced people.

4. GEOTHERMAL ENERGY

  • ‘Geo’ means ‘earth’ and ‘thermal’ means ‘heat’.
  • Geothermal energy is the heat energy from hot rocks present inside the earth.
  • When underground water comes in contact with a ‘hotspot’, steam is generated. Steam trapped in rocks is routed through pipes to a turbine and used to generate electricity. Advantages of Geothermal energy
  • Economical to use geothermal energy.
  • Does not cause any pollution.
Limitations of Geothermal Energy
  • Geothermal energy is not available everywhere.
  • Deep drilling in the earth to obtain geothermal energy is very difficult and expensive.
  • In New Zealand and the USA, there are no power plants based on geothermal energy that are operational.

NON-CONVENTIONAL SOURCES OF ENERGY

Day by day, our demand for energy increases, so there is a need for another source of energy.

  • Solar energy (example: solar cooker, solar cell panel)
  • Energy from the sea (tidal wave)
  • Biomass-biogas plant and Wind energy
  • Nuclear energy

REASONS FOR ALTERNATE SOURCES OF ENERGY

  • The fossil fuel reserves in the earth are limited which may get exhausted soon if we use them at the current rate.
  • Reduce the pressure on fossil fuels making them last for a much longer time.
  • To reduce the pollution level and to save the environment.

1. SOLAR ENERGY

  • Sun is the ultimate source of energy.
  • Energy obtained from the sun is called solar energy. Solar constant = 1.4 KJ/s/m2
  • Outer edge of the earth receives solar energy equal to 1.4 KJ/s/m2 or 1.4 KW/m2 [… 1 KJ/s = 1 KW]
Solar energy devices

(i) Solar cooker 
(ii) Solar water heater 
(iii) Solar cells 

2. WIND ENERGY

Unequal heating of the landmass and water bodies by solar radiations generates air movement and causes wind to blow.
Uses of Kinetic Energy generated by Wind Energy
  • To generate electricity by turning the rotor of the turbine.
  • To lift water from the well.
  • To run the flour mills.
  • The output of a single wind mill is quite small so a number of windmills are erected over a large area called wind energy farm.
  • The minimum wind speed for a mill to serve as a source of energy is 15-20 KmPH.
Advantages of Wind Energy
  • Eco-friendly.
  • Efficient source of renewable energy.
  • No recurring expenses for production of electricity.
Disadvantages of Wind Energy
  • Wind energy farms need a large area of land.
  • Difficulty in getting a regular wind speed of 15-20 KmPH.
  • Initial cost of establishing a wind energy farm is very high.
  • High level of maintenance of blades of wind mill.
  • Denmark is called the ‘Country of Winds’.
  • India is ranked 5 th in harnessing wind energy for the production of electricity.
  • India ‘s largest wind energy farm has been established near Kanyakumari in Tamil Nadu and it generates 380 MW of electricity.

3. BIOMASS

The dead parts of plants and trees and the waste materials of animals and man are called Biomass.
(i) Wood
It is a biomass and used as a fuel for a long time.
Disadvantages of Using Wood as Fuel
  • Produces a lot of smoke on burning.
  • Do not produce much heat.
  • Thus by improvement in technology we can improve the efficiency of traditional sources of energy. For example: wood can be converted into much better fuel called charcoal.
(ii) Charcoal
  • When wood is burnt in a limited supply of air, then water and other volatile materials get removed and charcoal is formed.
  • Wood on limited supply of Oxygen gas gets converted into Charcoal.
  • Charcoal is better fuel than wood because:
  • It has higher calorific value than wood.
  • Does not produce smoke while burning.
  • It is a compact fuel, easy to handle and convenient to use.
(iii) Cowdung
  • It is biomass but it is not good to burn cow dung directly as fuel because :
    → produces a lot of smoke.
    → cowdung does not burn completely, producing a lot of ash as residue.
    → low calorific value.
    → by making biogas (or gobar gas) from cow dung, we get a smokeless fuel.
(iv) Biogas
  • It is produced in a biogas plant.
  • Anaerobic microorganisms decompose the complex compound of the cow dung+water slurry.
  • It takes a few days for the decomposition process to generate gases like methane, CO2, hydrogen and hydrogen sulphide.
  • Bio gas is stored in the gas tank above the digester from which they are drawn through pipes for use.
Advantages of Biogas
  • It is an excellent fuel as it contains upto 75% methane (CH4 ).
  • It burns without smoke.
  • Leaves no residue like ash in wood & coal burning.
  • Heating capacity is high.
  • It is also used for lighting.
  • Slurry left behind is used as excellent manure rich in nitrogen and phosphorus.
  • Safe and efficient method of waste disposal.

4.NUCLEAR ENERGY

  • The energy released during a nuclear reaction is called nuclear energy.
  • It can be obtained by two types of nuclear reactions :
    (i) Nuclear fission
    (ii) Nuclear fusion
(i) Nuclear Fission
  • ‘Fission’ means split up.
  • The process in which the heavy nucleus of a radioactive atom (such as uranium, plutonium or thorium) splits up into smaller nuclei when bombarded with low energy neutrons, is called nuclear fission.
  • A tremendous amount of energy is produced.
  • U-235 is used as a fuel in nuclear reactors in the form of uranium rods.
Working of Nuclear Fission
In a nuclear reactor self sustaining chain reaction releases energy at a controlled rate, which is used to produce steam and further generate electricity.
Major Nuclear Power Plants

(i) Tarapur (Maharashtra) 
(ii) Rana Pratap Sagar (Rajasthan) 
(iii) Kalpakkam (Tamil Nadu) 
(iv) Narora (U. P.) 
(v) Kakrapar (Gujrat) 
(vi) Kaiga (Karnataka) 

(ii) Nuclear Fusion
  • When two nuclei of light elements (like hydrogen) combine to form a heavy nucleus (like helium) and a tremendous amount of energy is released is called nuclear fusion.
  • Very-very high temperature and pressure is needed for fusion.
  • Hydrogen bomb is based on this phenomenon.
  • Nuclear fusion is the source of energy in the sun and other stars.
Advantage of Nuclear Fusion
  • Production of large amounts of useful energy from a very small amount of nuclear fuel.
  • Does not produce greenhouse gases like CO2.
Limitations of Nuclear Fusion
  • Environmental contamination due to improper nuclear waste storage and its disposal.
  • Risk of accidental leakage of harmful radiations.
  • High cost of installation.
  • Limited availability of nuclear fuel.

ENVIRONMENTAL CONSEQUENCES

  • Exploiting any source of energy disturbs the environment in some way or the other.
  • The source we would choose depends upon following the factors:
    (i) Ease of extracting energy from the source.
    (ii) Cost of extracting energy from the source.
    (iii) Efficiency of technology available to extract energy.
    (iv) The environmental damage caused by using that source.
  • In other words, no source of energy is said to be pollution free. Some sources are cleaner than the others.
  • For example, solar cells may be pollution free but the assembly of the device would have cause some environmental damage.

NON-RENEWABLE SOURCES OF ENERGY

Sources that will get depleted some day. For example : Fossil fuel

RENEWABLE SOURCES OF ENERGY

Energy sources that can be regenerated and that will last forever. For example : Wind energy, water energy.
  • Magnet is any substance that attracts iron or iron-like substances.
  • An electric current-carrying wire behaves like a magnet.
  • Electromagnets and electric motors involve the magnetic effect of electric current, and electric generators involve the electric effect of moving magnets.
  • Compass needles get deflected on passing an electric current through a metallic conductor.

PROPERTIES OF MAGNET

(i) Every magnet has two poles i.e. North and South. 
(ii) Like poles repel each other. 
(iii) Unlike poles attract each other. 
(iv) A freely suspended bar magnet aligns itself in nearly north-south direction, with its north pole towards north direction. 

CHARACTERISTICS OF FIELD LINES

  • Field lines arise from the North pole and end into the South pole of the magnet.
  • Field lines are closed curves.
  • Field lines are closer in stronger magnetic fields.
  • Field lines never intersect each other as for two lines to intersect, there must be two north directions at a point, which is not possible.
  • Direction of field lines inside a magnet is from South to North.
  • The relative strength of the magnetic field is shown by the degree of closeness of field lines.

MAGNETIC FIELD OF A BAR MAGNET

H. C. Oersted was the first person to state that electric current has a magnetic field.

RIGHT HAND THUMB RULE

  • Imagine you are holding a current carrying a straight conductor in your right hand such that the thumb is pointing towards the direction of current.
  • Then the fingers wrapped around the conductor give the direction of the magnetic field.

MAGNETIC FIELD DUE TO CURRENT THROUGH A STRAIGHT CONDUCTOR

  • It can be represented by concentric circles at every point on the conductor.
  • Direction can be given by right hand thumb rule or compass.
  • Circles are closer near the conductor.
  • Magnetic field ∝ Strength of current.
  • Magnetic field ∝ 1/Distance from conductor

MAGNETIC FIELD DUE TO CURRENT THROUGH A CIRCULAR LOOP

  • It can be represented by concentric
    circle at every point.
  • Circles become larger and larger as we move away.
  • Every point on wire carrying current would give rise to a magnetic field appearing as a straight line at the centre of the loop.
  • The direction of the magnetic field inside the loop is the same.

FACTORS AFFECTING MAGNETIC FIELD OF A CIRCULAR CURRENT CARRYING CONDUCTOR

  • Magnetic field ∝ Current passing through the conductor
  • Magnetic ∝ 1/Distance from conductor
  • Magnetic field ∝ No. of turns in the coil
  • Magnetic field is additive in nature i.e., the magnetic field of one loop adds up to the magnetic field of another loop. This is because the current in each circular turn
    has some direction.

SOLENOID

  • A coil of many circular turns of insulated copper wire wrapped closely in a cylindrical form.
  • Magnetic field of a solenoid is similar to that of a bar magnet.
  • Magnetic field is uniform inside the solenoid and represented by parallel field lines.

DIRECTION OF MAGNETIC FIELD

(i) Outside the solenoid: North to South 
(ii) Inside the solenoid: South to North 
Solenoid can be used to magnetise a magnetic material like soft iron.

ELECTROMAGNET

  • It is a temporary magnet, so, can be easily demagnetised.
  • Strength can be varied.
  • Polarity can be reversed.
  • Generally strong magnet.

PERMANENT MAGNET

  • Cannot be easily demagnetised.
  • Strength is fixed.
  • Polarity cannot be reversed.
  • Generally weak magnet.

FORCE ON A CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD

  • Andre Marie Ampere suggested that the magnet also exerts an equal and opposite force on a current carrying conductor.
  • The displacement in the conductor is the maximum when the direction of current is at right angle to the direction of magnetic field.
  • Direction of force is reversed by reversing the direction of current.

FLEMING'S LEFT HAND RULE

  • Stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular.
  • If the forefinger points in the direction of the magnetic field, the middle finger in the direction of the current , then the thumb will point in the direction of motion or force.
  • Heart and brain in the human body have a significant magnetic field.

MRI (Magnetic Resonance Imaging):

Image of internal organs of body can be obtained using magnetic field of the organ.

GALVANOMETER

Instrument that can detect the presence of current in a circuit. It also detects the direction of current.

ELECTRIC METER

An electric motor is a rotating device that converts electrical energy to mechanical energy.

COMMUTATOR

A device that reverses the direction of flow of current through a circuit is called a commutator.

ARMATURE

The soft iron core, on which the coil is wound including the coils is called armature. It enhances the power of the motor.

COMMERCIAL USE OF MOTORS

(i) an electromagnet in place of permanent magnet 
(ii) large number of turns of the conducting wire in the current-carrying coil 
(iii) a soft iron core on which the coil is wound. 

ELECTROMAGNETIC INDUCTION

  • When a conductor is placed in a changing magnetic field, some current is induced in it.
  • Such current is called induced current and the phenomenon is called electromagnetic induction.

FLEMING'S RIGHT HAND RULE

→ When a conductor is placed in a changing magnetic field, some current is induced in it.
→ Such current is called induced current and the phenomenon is called electromagnetic induction.

ELECTRIC GENERATOR

An electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity. Working principle of electric generator.
Used to find direction of induced current. 

ALTERNATE CURRENT(A.C)

  • The current which reverses its direction periodically.
  • In India, A. C. reverses its direction every 1/100 second.
  • Time period = 1/100 + 1/100 = 1/50 s
  • Frequency = 1/time period = 1/50 = 50 Hz

ADVANTAGE OF A.C

A. C. can be transmitted over long distances without much loss of energy.

DISADVANTAGE OF A.C

A. C. cannot be stored.

DIRECT CURRENT(A.C)

  • The current which does not reverse its direction.
  • D. C. can be stored.
  • Loss of energy during transmission over long distances is high.
  • Sources of D. C.: Cell, Battery, Storage cells.

DOMESTIC ELECTRIC CIRCUITS

  • There are three kinds of wires used:
    (i) Live wire (positive) with red insulation cover.
    (ii) Neutral wire (negative) with black insulation cover.
    (iii)Earth wire with green insulation cover.
  • The potential difference between live and neutral wire in India is 220 V.
  • Pole ⇒ Main supply ⇒ Fuse ⇒ Electricity meter ⇒ Distribution box ⇒ To separate circuits
  • Earth Wire: Protects us from electric shock in case of leakage of current especially in metallic body appliances. It provides a low resistance path for current in case of leakage of current.
  • Short Circuit: When live wire comes in direct contact with neutral wire accidentally. The resistance of the circuit becomes low which can result in overloading.
  • Overloading: When current drawn is more than current carrying capacity of a conductor, it results in overloading. Causes of overloading:
    (i) Accidental hike in voltage supply.
    (ii) Use of more than one appliance in a single socket.
  • Safety devices:
    (i) Electric fuse
    (ii) Earth wire
    (iii) MCB (Miniature Circuit Breaker)
  • All living things perform certain life processes like growth, excretion, respiration, circulation etc.
  • All the processes like respiration, digestion, which together keep the living organisms alive and perform the job of body maintenance are called life processes.

MODES OF NUTRITION

NUTRITION IN PLANTS

  • Plants are autotrophs.
  • Make their own food. 
  • Eat animals for their food. 

NUTRITION IN ANIMALS

  • Animals are heterotrophs. 
  • Depends on plants or other. 

AUTOTROPHIC NUTRITION

  • It is a kind of nutrition in which inorganic materials like CO2, water etc. are utilized to prepare organic food by the process of photosynthesis.
    E.g: Green plants.
  • The organisms which carry out autotrophic nutrition are called autotrophs (green plants).
  • Autotrophs use simple inorganic material and convert it into complex high energy molecules (Carbohydrates)
  • Autotrophic nutrition is fulfilled by the process by which autotrophs take in CO2 and H2O and convert these into carbohydrates in the presence of chlorophyll, sunlight is called Photosynthesis.

EQUATION FOR PHOTOSYNTHESIS

RAW MATERIALS FOR PHOTOSYNTHESIS

  • Sunlight: It is inorganic material.
  • Chlorophyll: Sunlight absorbed by chlorophyll.
  • CO2: Enters through stomata and oxygen (O2) is released as a by-product through stomata on the leaf.
  • Water: Water + dissolved minerals like nitrogen, phosphorus etc. are taken up by the roots of the soil.

SITE OF PHOTOSYNTHESIS

Some cells contain green pigments which are cell organelles called chloroplasts which contain chlorophyll.

MAIN EVENTS OF PHOTOSYNTHESIS

  • Absorption of light energy by chlorophyll.
  • Conversion of light energy into chemical energy + splitting (breaking) of water into hydrogen and oxygen.
  • Reduction of CO2 to carbohydrates.

STOMATA

Stomata are the tiny pores present on the surface of the leaves.
Functions of Stomata
  • Exchange of gases O2/CO2.
  • Loses large amounts of water (water vapour) during transpiration.

HETEROTROPHIC NUTRITION

  • Kind of nutrition in which organisms do not possess the ability to synthesize their own food. They depend on autotrophs for their food supply directly or indirectly. Example: Animals, fungi.
  • Holozoic Nutrition: Animals take in solid food and breakdown inside the body. Example: Amoeba, animals.
  • Saprophytic Nutrition: Organisms feed on dead, decaying matter. Example: Fungi.
  • Parasitic Nutrition: Parasites live inside or outside another organism (host) and derive nutrition from it. Example: Cuscuta (plant parasites), Ticks etc.

HOW ORGANISMS OBATIN THEIR FOOD

  • Unicellular/Single celled organisms: Food is taken up through the entire surface. Example: Amoeba, Paramaecium
  • Process of intake of food by Amoeba
  • Paramaecium: Cilia (Present all over the body)
    → Take in food
    → At a specific spot

NUTRITION

Different organisms utilize different nutritional processes as it depends upon the source of carbon from where the food is taken.

NUTRITION IN HUMAN BEINGS

The alimentary canal is basically a long tube extending from the mouth to the anus. Various regions are specialised to perform different functions.

HUMAN DIGESTIVE SYSTEM

(i) Mouth: Intake of whole food. 
(ii) Teeth: Chewing/grinding of food. 
(iii) Tongue: Rolling of food + Tasting of food + Swallowing/Pushing down of the food. 
(iv) Salivary Glands: Secrete saliva + Mucus (It is a sticky, gelatinous material that lines your lungs, throat, mouth, nose, and sinuses.) + Starch is converted into glucose by saliva (Salivary amylase) 
(v) Oesophagus: Taking food from mouth to stomach by Peristaltic  movements (Contraction and expansion of muscles of the oesophagus).
(vi) Stomach: Gastric glands present in stomach secrete gastric juice. 

(vii) Small Intestine: The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. 
(a) Walls of the small intestine secrete intestinal enzymes which convert Carbohydrates into glucose, fats in fatty acid + glycerol and Proteins into amino acids. 
(b) It has Villi (finger like projection) which helps in the absorption of food into the blood. 
(c) It receives the secretions of the liver and pancreas. 
→ The food is acidic which is made alkaline for the pancreatic enzymes to act. The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.
→ Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules which increases the efficiency of enzyme action.
(viii) Large Intestine: 
(a) Absorb excess water. 
(b) The rest of the material is removed from the body via the anus. 

RESPIRATION IN HUMAN BEINGS

Respiration involves: 
(i) Gaseous exchange (Breathing) : Intake of oxygen from the atmosphere and release of CO2.
(ii) Cellular respiration: Breakdown of simple food in order to release energy inside the cell. 

BREAKDOWN OF GLUCOSE BY VARIOUS PATHWYAS

  • The first step is the break-down of glucose (a six-carbon molecule) into a three-carbon molecule called pyruvate which takes place in the cytoplasm.
  • Pyruvate may be converted into ethanol and carbon dioxide which takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration.
  • The pyruvate is broken down into three-carbon pyruvate molecules in the presence of oxygen to give three molecules of carbon dioxide and water. This process takes place in mitochondria. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration.
  • The pyruvate is converted into lactic acid when there is a lack of oxygen in our muscle cells, which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.
  • The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.
  • The rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms because the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air.

The whole process of breakdown of glucose is shown below:

TYPES OF RESPIRATION

HUMAN RESPIRATORY SYSTEM

  • Passage of air through the respiratory system:
  • Nostril: Air is taken into the body.
  • Nasal Passage: It is a channel for airflow through the nose.
  • Nasal Cavity: It is lined with hairs and mucus membrane. It warms, moisturizes, and filters air before it reaches the lungs.
  • Pharynx: It contains rings of cartilage which ensure that the air-passage does not collapse.
  • Larynx: It houses the vocal cords and manipulates pitch and volume, which is essential for phonation. It is also known as a voice box.
  • Trachea: Pharynx splits into trachea and esophagus. It connects the larynx (or voice box) to the bronchi of the lungs. It provides air flow to and from the lungs for respiration.
  • Bronchi: They are the main passageway into the lungs. They are the extensions of the windpipe that shuttle air to and from the lungs. The oxygen goes to the lungs and carbon dioxide leaves the lungs through them.
  • Bronchioles: Bronchi get smaller when they reach closer to lung tissues and are called Bronchioles. They are the passageways by which air passes through the nose or mouth to the alveoli of the lungs
  • Alveoli: They are smaller tubes which finally terminate in balloon-like structures which are called alveoli. They allow oxygen and carbon dioxide to move between the lungs and bloodstream.
  • Blood capillaries: They are the sites of the transfer of oxygen and other nutrients from the bloodstream to other tissues in the body. They also collect carbon dioxide and waste materials and return it to the veins.

MECHANISM OF BREATHING

EXCHANGE OF GASES BETWEEN ALVELOI, BLOOD AND TISSUES

  • Air (rich in O2) reaches blood which combines with haemoglobin in RBC and O2 is released in alveoli tissues (through blood vessels).
  • CO2 is released in blood and dissolved into it and carried by blood vessels. The carbon dioxide is released in the alveolar sac which is sent out through nostrils.
  • Terrestial organisms: Use atmospheric oxygen for respiration.
  • Aquatic organisms: Use dissolved oxygen for respiration.

RESPIRATION IN PLANTS

Respiration in plants is simpler than the respiration in animals. Gaseous exchange occurs through : 
(a) Stomata in leaves 
(b) Lenticels in stems 
(c) General surface of the root 

TRANSPORTATION IN HUMAN BEINGS

Human beings like other multicellular organisms need a regular supply of food, oxygen etc. This function is performed by the circulatory system.
The circulatory system in human beings consists of:
(i) Heart (pumping organ) 
(ii) Arteries and Veins (Blood vessels) 
(iii) Blood and lymph (Circulatory medium) 

CIRCULATORY SYSTEM IN HUMAN BEINGS

  • The lungs supply oxygen-rich blood to the left atrium of the heart.
  • The left atrium relaxes when it is collecting the blood and contracts when blood is transferred to the left ventricle. The left ventricle expands when it receives blood.
  • The blood is pumped out of the body when the muscles of the left ventricle contracts.
  • De-oxygenated blood comes from the body to the upper chamber on the right i.e. the right atrium when it expands.
  • The corresponding lower chamber i.e. the right ventricle expands when the right atrium contracts. It transfers the blood to the right ventricle which in turn pumps it to the lungs for oxygenation.
  • Right ventricles have thicker muscular walls so that they pump blood into various organs.
  • Valves ensure that blood does not flow backwards when the atria or ventricles contract.

Blood Circulation in Human Body

Double circulation: Blood travels twice through the heart in one complete cycle of the body.

Direction of Blood Flow Through Human Heart

  • Pulmonary Circulation: Blood moves from the heart to the lungs and back to the heart. 
  • Systemic Circulation: Blood moves from the heart to the rest of the body and back to the heart. 

BLOOD

  • Blood is connective tissue which is fluid in nature.
  • Solid components of blood (Blood corpuscles):
    (i) RBC (Red blood cells): It carries O2 and CO2 and also contains Haemoglobin which impart red colour to the blood.
    (ii) WBC (White blood cells): It provides body defence by engulfing the germs and produces antibodies.
    (iii) Blood Platelets: It helps in blood clotting during injury.
  • Liquid components (Plasma): It is a yellow colour fluid which contains 90% water & 10% organic substances.

LYMPH

  • It is a yellowish fluid which escapes from the blood capillaries into the intercellular spaces.
  • It contains less proteins than blood.
  • It flows from the tissues to the heart which helps in transportation and destroying germs.
  • It carries digested and absorbed fat from the intestine and drains excess fluid from extracellular space back into the blood.

TYPES OF BLOOD VESSELS

There are two types of blood vessels
(i) Arteries 
(ii) Veins 

TRANSPORTATION IN PLANTS

There are two main conducting pathways in a plant. 
(i) Xylem 
(ii) Phloem 

TRANSPORTATION AND ITS FUNCTIONS

It is the process of loss of water as vapour from aerial parts of the plant.

FUNCTIONS

(a) Absorption and upward movement of water and minerals by creating PULL. 
(b) Helps in temperature regulation in plants. Transport of food from leaves (food factory) to different parts of the plant is called Translocation. 

EXCRETORY SYSTEM IN HUMAN BEINGS

Excretory/urinary system consists of :
(1) The kidneys : The excretory organ 
(2) The ureters : The ducts which drain out urine from the kidneys                    (3) The urinary bladder : The urinary reservoir 
(4) The urethra : The channel to the exterior 

EXCRETION

  • The metabolic activities in the body generates many kinds of wastes including nitrogenous wastes which are harmful for the body and hence need to be removed.
  • Excretion is a process by which these wastes are removed from our body.
  • Unicellular organisms remove these wastes by simple diffusion.

EXCRETORY WASTES

FUNCTIONS OF ORGANS INVOLVED IN EXCRETORY SYSTEM

  • Each kidney contains many filtration units called nephrons.
  • Nephrons are made up of a cluster of thin walled capillaries called glomerulus which is associated with a cup like structure called as Bowman’s capsule and the long tube which terminates through this
    capsule.
  • The renal artery brings oxygenated blood to the kidneys along with nitrogenous wastes like urea and uric acid and many other substances.
  • The blood gets filtered through the glomerulus and this filtrate enters the tubular part of the nephron.
  • As this filtrate moves down the tubular part, glucose, amino acids, salts and excess of water gets selectively reabsorbed by the blood vessels surrounding these tubules.
  • The amount of water reabsorbed depends upon :
    (i) How much excess of water is there in the body and,
    (ii) How much nitrogenous wastes need to be excreted out.
  • So the fluid now flowing in the tubular part is urine which gets collected in collecting nephrons.
  • These collecting ducts together leave the kidney at a common point by forming the ureter.
  • Each ureter drains the urine in the urinary bladder where it is stored until the pressure of the expanded bladder leads to an urge to pass it out through urethra.
  • This bladder is a muscular structure which is under nervous control.
  • 180 litres of filtrate is formed daily but only 2 litres is excreted out as urine so the rest is reabsorbed in the body.

Structure of Nephron

Functions of Nephron

  • Excretion of nitrogenous wastes.
  • To maintain the water and ionic balance (osmic regulation).

FORMATION OF URINE IN HUMANS

The urine formation involves three steps : 
(i) Glomerular filtration: Nitrogenous wastes, glucose water, amino acid filter from the blood into Bowman’s Capsule of the nephron. 
(ii) Tubular reabsorption: Now, useful substances from the filtrate are reabsorbed back by capillaries surrounding the nephron. 
(iii) Secretion: Urea, extra water and salts are secreted into the tubule which opens up into the collecting duct & then into the ureter. 

ARTIFICIAL KIDNEY

Haemodialysis: The process of purifying blood by an artificial kidney. It is meant for kidney failure patients.

EXCRETION IN PLANTS

  • Plants use different strategies for excretion of different products :
  • Oxygen and carbon dioxide are diffused through stomata. 
  • Excess water is removed by transpiration. 
  • Plants can even lose some of their old parts like old leaves and bark of tree. 
  • Other waste products like raisins and gums especially in old xylem cells which can also be lost by plants. 
  • Plants also secrete some waste substances into the soil around them. 

1. Natural resources are the basic substances present in nature which are being utilized by the living organisms for their survival. 

2. Some natural resources like water, soil, forests, wildlife, coal, petroleum, etc., should be utilized in a sustainable manner in order to conserve our environment. 

3. Overexploitation of natural resources is done by the humans for the following reasons:
(i) To fulfil the demands of an ever-increasing human population.
(ii) Large scale industrialisation and urbanisation.
(iii) Construction of buildings and housing complexes, etc.

4. A number of laws at national and international level are enforced to safeguard our environment. 

5. Ganga Action Plan (GAP) was introduced in 1985, to improve the poor water quality of the Ganga river.

6. We can adopt the 3 R’s – Reduce, Recycle and Reuse, to save our environment. Reduce involves the less use of resources. Recycling involves recycling of used items like plastic, paper, glass, metal, etc., and converting them into new items. Reuse involves using things again and again.                  

 7. The judicious use of resources will prevent wastage and conserve our natural resources.

8. The management should ensure equitable distribution of resources so that all rich and poor benefit from the development of these resources.

9. Forests are ‘biodiversity hotspots’. The loss of its biodiversity leads to a loss of ecological stability.

10. The main aim of conservation is to try to preserve the biodiversity we have inherited.

11. The stakeholders of forests are the local and tribal people of the area, the Forest Department of the Government, the industrialists and the wildlife and nature enthusiasts. Each of these groups of stakeholders make use of forests in the following ways:
(i) The people who live in or around the forests are dependent on forest products for various needs like shelter, food, transport, fuel, medicines and cattle grazing. After the British took control of the forests, these people were forced to depend on much smaller areas and forest resources started becoming overexploited to some extent.
(ii) The Forest Department of India destroyed the huge biodiversity of forests by converting them into monocultures of commercially important plants, such as pine, teak or eucalyptus. Such forests are useful for industrial purposes and not for local needs.
(iii) Industrialists consider the forest as merely a source of raw materials for its factories. They are not interested in the sustainability of the forest in one particular area. They do not have any stake in ensuring that one particulate area should yield an optimal amount of some produce for all generations to come.
(iv) The wildlife and nature enthusiasts play an active role in conserving the forest in its pristine form.

12. The local people should be actively involved in forest management since they ensure its sustainability.

13. Government of India has recently instituted the ‘Amrita Devi Bishnoi National Award’ for Wildlife Conservation in the memory of late Amrita Devi Bishnoi, who laid down her life in 1731 with 363 other people for the protection of ‘Khejri’ trees in Khejrali village near Jodhpur, Rajasthan.

14. Deforestation is mainly caused by industrialism, tourism and development projects. The forests are a vast and complex entity that offers a range of natural resources for our use.

15. There are many movements led by the local people against misuse and overexploitation of forest resources. For example: 

(i) The Chipko Andolan (which originated in the Reni village of Garhwal), the villagers used to hug the forest trees and prevent their mass felling by the contactors.The local people use the forest resources without destroying the trees.The destruction of forests affects the soil quality and water sources, in addition to reduced availability of forest resources.

(ii) In 1972, the West Bengal Forest Department by actively involving the villagers in the management of the Arabari forest range, was able to revive the degraded Sal forests of the region. In return, the villagers were given employment in both siviculture and harvesting operations and allowed fuelwood and fodder collection on payment of a nominal fee. By 1983, a previously worthless forest was valued 12.5 crores.

16. All these movements provide evidence that by involving local people we can ensure the protection and sustainability of forests.

17. Water is a basic necessity as we need it for fulfilling all our needs.

18. Rains in India are largely due to monsoons which are only available for a few months of the year.

19. Irrigation methods like dams, tanks and canals have been used in various parts of India since ancient times. The management of all these water resources was carried out locally and optimally,
according to the agricultural and daily needs of the local people.

20. Large dams serve dual purposes of irrigation and electricity generation. The canal systems leading from these dams can transfer large amounts of water to great distances, e.g., the Indira Gandhi Canal in Rajasthan.

21. The mismanagement of large dams and canal systems leads to unequal distribution of water and its benefits. Therefore, building large dams brings about several social, economic and environmental problems.

22. The construction of several dams like Tehri dam and Tawa dam displaced several poor tribals and peasants without satisfactory rehabilitation or compensation.

23. Watershed management emphasises scientific soil and water conservation in order to increase the biomass production with an aim to conserve the ecosystem. It not only increases the production and income but also mitigates droughts and floods.

24. Restoring the ancient water harvesting systems has recharged groundwater levels and is a viable option to the large scale water storage projects.

  • Charge is a fundamental particle in an atom. It may be positive or negative.
  • Like charges repel each other.
  • Unlike charges attract each other.
  • Coulomb (C) : S. I. unit of charge
  • 1 Coulomb charge = Charge present on approx. 6 × 1018 electrons
  • Charge on 1 electron = Negative charge of 1.6 × 10-19 C i.e. Q = ne
    Where, Q = Charge (total), n = No. of electrons ,e = Charge on 1 electron

CURRENT (I)

  • The rate of flow of charge is called current.
    Current = Charge/Time ⇒ I = Q/T
  • S. I. unit of current = Ampere (A) ⇒ 1 A = 1 Cs-1
    ⇒ 1 mA = 10-3 A
    ⇒ 1 μA = 10-6 A
  • Current is measured by Ammeter.
  • Ammeter has low resistance and always connected in series.
  • Direction of current is taken opposite to flow of electrons as electrons were not known at the time when the phenomenon of electricity was discovered first and current was considered to be flow of positive charge.

POTENTIAL DIFFERENCE (V)

  • Work done to move a unit charge from one point to another.
    V = W/Q
  • S. I. unit of Potential difference = Volt (V)
    1 V = 1 JC-1
  • Voltmeter: It is an instrument to measure the potential difference.
  • It has high resistance and is always connected in parallel.
  • Cell is the simplest device to maintain potential
    difference.
  • Current always flow from higher potential to lower potential.

SYMBOLS OF SOME COMMONLY USED COMPONENTS IN CIRCUIT

OHM'S LAW

Potential difference across the two points of a metallic conductor is directly proportional to current passing through the circuit provided that temperature remains constant.

MATHEMATICAL EXPRESSION FOR OHM'S LAW

  • V∝I
  • V = IR
  • R is a constant called resistance for a given metal.

V-I graph for Ohm’s law

RESISTANCE (R)

  • It is the property of a conductor to resist the flow of charges through it.
  • Ohm (Ω): S. I. unit of resistance.
  •  1 ohm = 1 volt/1ampere
  • When potential difference is 1 V and current through the circuit is 1 A, then resistance is 1 ohm.

RHEOSTAT

Variable resistance is a component used to regulate current without changing the source of voltage.

FACTORS ON WHICH THE RESISTANCE OF A CONDUCTOR DEPENDS:

Resistance of a uniform metallic conductor is:
(i) directly proportional to the length of conductor, 
(ii) inversely proportional to the area of cross-section, 
(iii) directly proportional to the temperature and 
(iv) depend on nature of material. 

RESISTIVITY (P)

  • It is defined as the resistance offered by a cube of a material of side 1m when current flows perpendicular to its opposite faces. 
  • Its S.I. unit is ohm-metre (Ωm). 
  • Resistivity does not change with change in length or area of cross-section but it changes with change in temperature.
  • Range of resistivity of metals and alloys is 10-8 to 10-6 Ωm.
  • Range of resistivity of insulators is 1012 to 1017 Ωm.
  • Resistivity of an alloy is generally higher than that of its constituent metals.
  • Alloys do not oxidize (burn) readily at high temperature, so they are commonly used in electrical heating devices.
  • Copper and aluminium are used for electrical transmission lines as they have low resistivity.

RESISTORS IN SERIES

  • When two or more resistors are connected end to end, the arrangement is called series combination.                            Total/resultant/overall/effective resistance in series:
  • Rs = R1 + R2 + R3
  • Current through each resistor is same.
  • Equivalent resistance is larger than
    the largest individual resistance.
  • Total voltage = Sum of voltage drops
  • V = V1 + V2 + V3                                                                                                  Voltage across each resistor: 
  • V1 = IR1
  • V2 = IR2 [V1 + V2 + V3 = V]
  • V3 = IR3V = IR
  •  V = IR1 + IR2 + IR3
  • IR = I(R1 + R2 + R3)
  • R = R1 + R2 + R3

RESISTORS IN PARALLEL

  • Voltage across each resistor is equal to the applied voltage.
  • Total current is equal to sum of currents through the individual
    reistances.
  • I = I1 + I2 + I3
    ⇒ V/R = V/R1 + V/R2 + V/R3
  • Reciprocal of equivalent resistance is equal to sum of reciprocals of individual resistances.
  • 1/Rp = 1/R1 + 1/R2 + 1/R3
  • Equivalent resistance is less than the value of the smallest individual resistance in the combination.

ADVANTAGES OF PARALLEL COMBINATION OVER SERIES COMBINATION

  • In a series circuit, when one component fails, the circuit is broken and none of the components works.
  • Different appliances have different currents. This cannot be satisfied in series as the current remains the same.
  • The total resistance in a parallel circuit is decreased.

HEATING EFFECT OF ELECTRIC CURRENT

  • If an electric circuit is purely resistive, the source of energy will continually get dissipated entirely in form of heat. This is known as the heating effect of electric current.
  • As E = P×T ∝ VIt {E = H}
  • Heat produced, H = VIt {V = IR}
    Or, Heat produced, H = I2Rt

JOULE'S LAW OF HEATING EFFECT OF ELECTRIC CURRENT

  • It states that the heat produced in a resistor is (i) directly proportional to square of current, H ∝ I2
  • It is directly proportional to resistance for a given current, H ∝ R
  • It is directly proportional to time for which current flows through the conductor, H ∝ t. So, H = I2Rt
  • Heating effect is desirable in devices like electric heater, electric iron, electric bulb, electric fuse, etc.
  • Heating effect is undesirable in devices like computers, computer monitors (CRT), TV, refrigerators etc.
  • In electric bulb, most of the power consumed by the filament appears a heat and a small part of it is radiated in form of light.

FILAMENT OF ELECTRIC BULB IS MADE OF TUNGSTEN BECAUSE:

(i) it does not oxidise readily at high temperature. 
(ii) it has high melting point (3380o C). The bulbs are filled with chemically inactive gases like nitrogen and argon to prolong the life of filament.

ELECTRIC FUSE

  • The rate at which electric energy is consumed or dissipated in an electric circuit.
  • P = VI
    ⇒ P = I2R = V2/R
  • S.I. unit of power = Watt (W)
    ⇒ 1 Watt = 1 volt × 1 ampere
  • Commercial unit of electric energy = Kilo Watt hour (KWh)
    ⇒ 1 KWh = 3.6 × 106 J
    ⇒ 1 KWh = 1 unit of electric energy
  • Human eye: The sense organ that helps us to see.
  • Located in eye sockets in skull.
  • Diameter of eye ball – 2.3 cm.

PARTS OF HUMAN EYE

• Cornea: It is the outermost, transparent part. It provides most of the refraction of light. 
• Lens: It is composed of a fibrous, jelly like material. Provides the focused real and inverted image of the object on the retina. This is a convex lens that converges light at retina. 
• Iris: It is a dark muscular diaphragm that controls the size of the pupil. 
• Pupil: It is the window of the eye. It is the central aperture in iris. It regulates and controls the amount of light entering the eye. 
• Retina: It is a delicate membrane having an enormous number of light sensitive cells. 
• Far point: The maximum distance at which an object can be seen clearly is the far point of the eye. For a normal adult eye, its value is infinity. 

NEAR POINT OR LEAST DISTANCE OF DISTINCT VISION

  • The minimum distance at which objects can be seen most distinctively without strain. 
  • For a normal adult eye, its value is 25 cm. 
  • Range of human vision – 25 cm to infinity. 

ACCOMODATION

  • The ability of the eye lens to adjust its focal length is called accommodation. Focal length can be changed with the help of ciliary muscles.
  • Focal length increases when Ciliary muscles relax and lens get thin.
  • Focal length decreases when Ciliary muscles contract and lens get thick.

MYOPIA (Near Sightedness)

  • A myopic person can see nearby objects clearly but cannot see distant objects clearly.
  • Image is formed in front of retina.

CAUSES OF MYOPIA

  • Excessive curvature of eye lens.
  • Elongation of eye ball

CORRECTION OF MYOPIA

  • It is done by using a concave lens of appropriate power.
(i) In a myopic eye, an image of a distant object is formed in front of the retina. (and not on the retina)
(ii) The far point (F) of a myopic eye is less than infinity.
(iii) Correction of myopia. The concave lens placed in front of the eye forms a virtual image of a distant object at far point (F) of the myopic eye.

HYPERMETROPIA (Far Sightedness)

  • Affected person can see far objects clearly but cannot see nearby objects clearly.
  • The near point of the eye moves away.
  • Image is formed behind the retina.

CAUSES OF HYPERMETROPIA

  • Focal length of the eye lens becomes too long.
  • Eye ball becomes too small.

CORRECTION OF HYPERMETROPIA

Using a convex lens of suitable power can correct the defect.

PRESBYOPIA (Old Age Hypermetropia)

  • It is the defect of vision due to which an old person cannot see the nearby objects clearly due to loss of power of accomodation of the eye.
  • The near-point of the old person having presbyopia gradually recedes and becomes much more than 25 cm away.

CAUSES OF PRESBYOPIA

  • Gradual weakening of ciliary muscles.
  • Diminishing flexibility of eye lens.

CORRECTION OF PRESBYOPIA

  • Use of convex lens of suitable power.
  • Sometimes a person may suffer from both myopia and hypermetropia.
  • Such people require bifocal lens for correction.

ADVANTAGE OF THE EYES IN FRONT OF THE FACE

  • It gives a wider field of view.
  • It enhances the ability to detect faint objects.
  • It provides three dimensional view.

REFRACTION THROUGH A GLASS PRISM

  • Prism: It is a pyramidal piece of glass with two triangular bases and three rectangular lateral surfaces.
  • Angle of Prism: The angle between two adjoining lateral surfaces. Refraction through a glass prism.
  • Angle of deviation (d): It is the angle between incident ray and emergent ray.When white light is passed through a glass prism, it splits into its seven constituent colours to form a band of seven colours. This phenomenon is called dispersion.
  • Spectrum: The band of seven colours formed due to dispersion of white light is called spectrum.
  • Acronym: It is a group of alphabets that represent sequential colours in spectrum.

VIBGYOR

  • Angle of deviation ∝ 1/wavelength
  • Red is the least deviated colour as it has the largest/longest wavelength.
  • Violet is the most deviated colour as it has the smallest wavelength in the visible spectrum.

Issac Newton was the first person who proved that sunlight is made up of seven colours :
(i) He passed sunlight through a glass prism to form a band of seven colours.

(ii) He tried to split the colours further by putting another prism ahead of the prism forming spectrum but he failed to obtain more colours. 

(iii) He formed a spectrum from sunlight and placed an identical but inverted prism in front of prism forming the spectrum. All the seven colours combined by the inverted prism and emerged as white light.  

TOTAL INTERNAL REFLECTION

When light enters obliquely from a denser medium to a rarer medium and the angle of incidence exceeds critical angle, the light reflects in the denser medium. This is called internal reflection.

CONDITIONS NECESSARY FOR INTERNAL REFLECTION

  • Light should enter obliquely from a denser to a rarer medium.
  • The angle of incidence should exceed critical angle, the light reflects in the denser medium.
  • Critical angle: The angle of incidence for which the angle of refraction is 90o.
  • Rainbow: It is a natural spectrum appearing in the sky after rain showers. Rainbow is observed in the direction opposite to the sun.
  • Three phenomenon which are involved in rainbow formation are :
    (i) Dispersion
    (ii) Refraction
    (iii) Internal reflection
  • Some water droplets remain suspended in air after rain. These
    droplets behave as glass prism.
  • When light enters the rain drop, it first refracts and disperses.
  • Then it reflects internally and again refracts as it come out of the drop and the seven colours reach the eye of observer in form of rainbow.

ATMOSPHERIC REFRACTION

The refraction by different layers of atmosphere is called atmospheric refraction. 
(i) Apparent flickering of objects placed behind a hot object or fire.
(ii) Stars near the horizon appear slightly higher than their actual position.
(iii) Advanced sunrise and delayed sunset.
(iv) Apparent flattening of the sun’s disc.
(v) Twinkling of stars.

(i) An object placed behind the fire or a hot surface appears to flicker when seen through the air.

  • The air above the hot surface becomes hot and rises. The space is occupied by cool air. The refractive index of hot air is less than that of cool air.
  • So, the physical condition of the medium is not constant.
  • Due to the changing Refractive Index (RI) of the medium, the light appears to come from different directions.
  • It results in fluctuation in the apparent position of the object.

(ii) Stars when seen near the horizon appear slightly higher than their actual position due to atmospheric refraction.

  • The refractive index of earth’s atmosphere in general increases from top to bottom.
  • So, the light coming from a star near the horizon has to travel from rarer to denser medium and it bends towards the
    normal.
  • As a result the star appears higher.

(iii) Advanced sunrise

  • The sun appears about two minutes earlier than the actual sunrise and the sun remains visible for about two minutes after the actual sunset.
  • When the sun is below the horizon, the rays have to pass from rarer to denser medium.
  • So rays bend towards the normal. As a result the sun appears higher than its actual position.

(iv) Twinkling of stars

  • Stars are very far from us, so they behave as point sources of light.
  • Since the physical conditions of the earth’s atmosphere are not constant the light from stars appears to come from different
    directions.
  • This results in fluctuation of the apparent position of the star.
  • The amount of light coming from stars also varies due to changing Refractive Index of the atmosphere.
  • The star appears bright when more light from star reaches our eyes and the same star appears dull when less amount of light reaches our eyes.
  • Both these effects are responsible for the twinkling of stars.

SCATTERING EFFECT

Spreading of light in various directions by colloid particles. Scattering ∝ 1/wavelength

TYNDALL EFFECT

When light passes through a colloid its path becomes visible. This is called the Tyndall effect. Example:
(i) Path of light becomes visible when light enters a dark and dusty room through a slit or ventilator. 
(ii) Path of light becomes visible when light passes through a dense canopy of trees in a forest. 

DEPENDENCE OF COLOR ON SCATTERED LIGHT

(i) If particles are very fine, they scatter mainly the blue colour of light (shorter wavelength). 
(ii) Medium sized particles scatter mainly the red colour (longer wavelength). 
(iii) Even larger particles scatter all the colours of light that is why it appears white. Wavelength of red light is about 1.8 times to that of blue light.

Anger signs are made in red colour

Red is the least scattered colour. It is least scattered by fog and smoke and can be seen in the same colour over a long distance. So, danger signs are made in red colour.

Colour of sky appears blue on a clear day

The upper layer of the atmosphere contains very fine particles of water vapours and gases. These particles are more effective in scattering light of shorter wavelength, mainly blue, than larger wavelength. So, the sky appears blue.

Appearance of sky to an astronaut in the space

The sky would appear dark to an astronaut in the space as scattering is not very prominent at such high altitude due to absence of particles.

Clouds appear white

Clouds are formed by water vapours. Water vapours condense to form water droplets due to larger size of droplets, all colours of light are scattered and clouds appear white.

Colour of sun appear red during sunrise and sunset

  • While sunset and sunrise, the colour of the sun and its surrounding appear red. During sunset and sunrise, the sun is near horizon and therefore the sunlight has to travel larger distance in atmosphere.
  • Due to this most of the blue light (shorter wavelength) are scattered away by the particles. The light of longer wavelength (red colour) will reach our eye. This is why sun appear red in colour.
  • Light is the form of energy that provides the sensation of vision.
  • Some common phenomena associated with lights are image formation by mirrors, the twinkling of stars, the beautiful colours of a rainbow, bending of light by a medium and so on.

PROPERTIES OF LIGHT

  • Electromagnetic waves do not require any medium to travel.
  • Light tends to travel in a straight line.
  • Light has dual nature i.e. waves as well as particles.
  • Light casts shadow.
  • Speed of light is maximum in vaccum. Its value is 3 × 108 ms-1.
  • When light falls on a surface, the following may happen:
    (i) Reflection
    (ii) Refraction
    (iii) Absorption

REFLECTION

Bouncing back of light when it strikes on a polished surface like a mirror.

LAWS OF REFLECTION

(i) Angle of incidence is equal to the angle of reflection. 
(ii) The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane. 

VIRTUAL AND REAL IMAGE

Image is a point where atleast two light rays actually meet or appear to meet.

IMAGE FORMED BY PLANE MIRROR

Characteristics of Image formed by Plane Mirror

(i) Virtual and erect. 
(ii) Size of the image is equal to the size of the object. 
(iii) Image is formed as far behind the mirror as the object is in front of it. 
(iv) Laterally inverted. 

LATERAL INVERSION

The right side of the object appears left side of the image and vice-versa.

APPLICATION OF LATERAL INVERSION

The word AMBULANCE is written in reverse so that it can be read correctly in the rear view mirror of vehicles going in front of it.

SPHERICAL MIRRORS

→ Mirrors whose reflecting surface is curved.

TYPES OF SPHERICAL MIRRORS

(i) Properties of Concave mirror
• Reflecting surface is curved inwards.
• Converging mirror

(ii) Properties of Convex mirror
• Reflecting surface is curved outwards.
• Diverging mirror

COMMON TERMS FOR SPHERICAL MIRRORS

  • Principal axis: The line joining the pole and center of curvature.
  • Pole (P): The centre of the spherical mirror.
  • Aperture (MN): It is the effective diameter of the spherical mirror.
  • Center of Curvature (C): The centre of the hollow glass sphere of which the mirror was a part.
  • Radius of Curvature (R): The distance between the pole and the centre of curvature.
  • Focus (F): The point on principal axis where all the parallel light rays actually meet or appear to meet after reflection.
  • Focal length (f): The distance between the pole and the focus. 
  • Relationship between focal length and radius of curvature: f = R/2

RULES FOR MAKING RAY DIAGRAMS BY SPHERICAL MIRRORS

(i) A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of a concave mirror or appear to diverge from the principal focus in case of a convex mirror.
(ii) A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, after reflection, will emerge parallel to the principal axis                                                  (iii) A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror, after reflection, is reflected back along the same path.                                                  (iv) A ray incident obliquely to the principal axis, towards a point P (pole of the mirror), on the concave mirror or a convex mirror, is reflected obliquely.          (v) The incident and reflected rays follow the laws of reflection at the point of incidence (point P), making equal angles with the principal axis.

RAY DIAGRMAS FOR IMAGES FORMED BY CONCAVE MIRROR

(i) When object is at infinity

  • Image Position − At ‘F’
  • Nature of image –
  • Real, inverted
  • Size – Point sized or highly diminished

(ii) When object is beyond ‘C’

  • Image Position – Between ‘F’ and ‘C’
  • Nature of image – Real, inverted
  • Size – Diminished

(iii) When object is at ‘C’

  • Image Position – At ‘C’
  • Nature of image – Real, inverted
  • Size – Same size as that of object

(iv) When object is placed between ‘F’ and ‘C’

  • Image Position – Beyond ‘C’
  • Nature of image– Real, inverted
  • Size – Enlarged

(v) When object is placed at ‘F’

  • Image Position – At Infinity
  • Nature of image – Real, inverted
  • Size – Highly enlarged

(vi) When object is between ‘P’ and ‘F’

  • Image Position – Behind the mirror
  • Nature of image – Virtual, erect
  • Size – Enlarged

Uses of Concave Mirror

(i) Used in torches, searchlights and vehicle headlights to get a powerful parallel beam of light. 
(ii) Concave mirrors are used by dentists to see large images of patients’ teeth .(Teeth have to be placed between pole and focus). 
(iii) Concave mirror is used as a shaving mirror to see a larger image of the face. 
(iv) Large concave mirrors are used to concentrate sunlight to produce heat in a solar furnace. 

RAY DIAGRMAS FOR IMAGES FORMED BY CONVEX MIRROR

(i) When object is placed at infinity

  • Image Position − At ‘F’
  • Nature of image – Virtual, erect
  • Size – Point sized

(ii) When object is placed between pole and infinity

  • Image Position – Between ‘P’ and ‘F’
  • Nature of image– Virtual, erect
  • Size – Diminished
  • A full length image of a tall building/tree can be seen in a small convex mirror.

Uses of Convex Mirror

(i) Convex mirrors are used as rear view mirrors in vehicles because
→ they always give an erect though diminished image.
→ they have a wider field of view as they are curved outwards.
(ii) Convex mirrors are used at blind turns and on points of merging traffic to facilitate vision of both side traffic. 
(iii) Used in shops as security mirror. 

SIGN CONVENTION FOR REFLECTION BY SPHERICAL MIRROR

(i) The object is placed to the left of the mirror. 
(ii) All distances parallel to the principal axis are measured from the pole of the mirror. 
(iii) All distances measured in the direction of incident ray (along + X-axis) are taken as positive and those measured against the direction of incident ray (along – X-axis) are taken as negative. 
(iv) Distance measured perpendicular to and above the principal axis are taken as positive. 
(v) Distances measured perpendicular to and below the principal axis are taken as negative. 
• Object distance = ‘u’ is always negative.
• Focal length of concave mirror = Negative
• Focal length of convex mirror = Positive

MIRROR FORMULA

  • 1/v + 1/u = 1/f
  • where, v = Image distance,, u = Object distance, f = Focal length

MAGNIFICATION OF SPHERICAL MIRRORS

  • It is the ratio of the height of image to the height of object.
  • m = Height of image/Height of object ⇒ m = hi/ho
  • Also, m = -v/u
    → If ‘m’ is negative, image is real.
    → If ‘m’ is positive, image is virtual.
  • If hi = ho then m = 1, i.e., image is equal to object.
  • If hi > ho then m > 1 i.e., image is enlarged.
  • If hi < ho then m < 1 i.e., image is diminished.
  • Magnification of plane mirror is always + 1.
    ‘+’ sign indicates virtual image.
    ‘1’ indicates that image is equal to object’s size.
  • If ‘m’ is ‘+ve’ and less than 1, it is a convex mirror.
  • If ‘m’ is ‘+ve’ and more than 1, it is a concave mirror.
  • If ‘m’ is ‘-ve’, it is a concave mirror.
  • Genetics deals with the study of Heredity and Variation.
  • The transmission of characters/traits from one generation to the next generation is called Heredity.
  • The differences in the characters/traits between the parent and offspring is called Variation.

TYPES OF VARIATIONS

Variation are of two types:
(i) Somatic Variation 
(ii) Gametic Variation 

(i) Somatic Variation

  • It takes place in the body cell.
  • It is neither inherited nor transmitted.
  • It is also known as acquired traits.
  • Examples: cutting of tails in dogs, boring of pinna etc.

(ii) Gametic Variation

  • Takes place in the gametes/Reproductive cells.
  • Inherited as well as transmitted.
  • Also known as inherited traits.
  • Example: human height, skin colour.

ACCUMULATION OF VARIATION DURING REPRODUCTION

Variation occurs during reproduction whether organisms multiply sexually or asexually.

VARIATIONS IN ASEXUAL REPRODUCTION

  • Variations are fewer.
  • Occurs due to small inaccuracies in DNA copying. (Mutation)

VARIATIONS IN SEXUAL REPRODUCTION

  •  Variations are large.
  • Occurs due to crossing over, separation of chromosomes, mutation.

IMPORTANCE OF VARIATION

  • Depending upon the nature of variations different individuals would have different kinds of advantage. Example, Bacteria that can withstand heat will survive better in a heat wave.
  • Main advantage of variation to species is that it increases the chances of its survival in a changing environment.
  • Free earlobes and attached earlobes are two variants found in human populations.

MENDEL AND HIS WORK ON IHERITANCE

  • Gregor Johann Mendel (1822 & 1884) started his experiments on plant breeding and hybridisation. He proposed the laws of inheritance in living organisms.
  • Mendel was known as Father of Genetics.
  • Plant selected by Mendel: Pisum sativum (garden pea). He used a number of contrasting characters for garden pea.

MENDEL'S EXPERIMENTAL MATERIAL

  • He chose Garden Pea (Pisum sativum) as his experiment material because of:
  • Availability of detectable contrasting traits of several characters.
  • Short life span of the plant.
  • Normally allows self-fertilization but cross-fertilisation can also be carried out.
  • Large no. of seeds produced.
  • Mendel’s Experiments: Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time).

MONOHYBRID CROSS

  • Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross.
    Example: Cross between a tall and a dwarf plant (short).
  • First-generation or F1 progeny are no ‘medium-height’ plants. All the plants were tall.
  • Second-generation or F2 are progeny (descendants) of the F1 tall plants are not all tall.
  • Both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. Thus, two copies of the trait are inherited in each sexually reproducing organism.
  • These two may be identical or may be different depending on the parentage.

(a) Pure or homozygous condition:

(TT, tt) : Both are dominant traits, Both are recessive alleles

(b) Heterozygous condition (Hybrid):

  • Tt : One is dominant, one recessive trait
  • Phenotypic ratio → 3 : 1 (Three tall and one short)
  • Genotypic ratio → 1 : 2 : 1 (TT-one, Tt-two, tt-one)
  • Phenotype means Physical appearance either they are Tall or Short.
  • Genotype means Genetic makeup that is TT, Tt or tt.

Observations of Monohybrid Cross

(i) All F1 progeny were tall, no medium height plant. (Half way characteristic)
(ii) F2 progeny 1⁄4 were short, 3⁄4 were tall. 
(iii) Phenotypic ratio F2 – 3 : 1 (3 tall : 1 short) 

Conclusions

  • TT and Tt both are tall plants while tt is a short plant.
  • A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
  • Characters/traits like ‘T’ are called dominant traits (because they express themselves) and ‘t’ are recessive traits (because they remain suppressed).

DIHYBRID CROSS

  • A cross between two plants having two pairs of contrasting characters is called a dihybrid cross.
  • Parent → Round green × Wrinkled yellow:
    (i) When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds. 
    (ii) Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow and wrinkled green) seeds plants in the ratio of 9 : 3 : 3 : 1. 

Conclusions

  • Round and yellow seeds are Dominant characters.
  • Occurrence of new phenotype combinations show that genes for round and yellow seeds are inherited independently of each other.

HOW DO THESE TRAITS GET EXPRESSED?

  • Cellular DNA is the information source for making proteins in the cell.
  • A section of DNA that provides information for one protein is called the gene for that protein.
  • Plant height can thus depend on the amount of a particular plant hormone.
  • The amount of the plant hormone made will depend on the efficiency of the process for making it.
  • Cellular DNA (Information source) → For synthesis of Proteins (Enzyme) → Works efficiently → More Hormone → produced Tallness of plant
  • Therefore, genes control characteristics/traits.

SEX DETERMINATION

Determination of sex of an offspring is known as Sex Determination.

FACTORS RESPONSIBLE FOR SEX DETERINATION

  •  Environmental: In some animals, the temperature at which the fertilized eggs are kept decides the gender. Example: Turtle
  • Genetic: In some animals like humans gender or individual is determined by a pair of chromosomes called sex chromosome.
    XX – Female XY – Male

SEX CHROMOSOMES

  • In human beings, there are 23 pairs of chromosomes.
  •  Out of these 22 chromosomes pairs are called autosomes and the last pair of chromosome that help in deciding gender of that individual is called sex chromosome. XX – Female XY – Male
  • This shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls.
  • Thus, sex of children will be determined by what they inherit from their father, and not from their mother.

EVOLUTION

Evolution is the sequence of gradual changes which takes place in the primitive organisms, over millions of years, in which new species are produced.

Situation I (Group of Red and Green Beetles)

  • Colour variation arises during reproduction
  • All beetles red except one that is green
  • Crows feed on red beetle → No. of beetles reduces
  • One beetle green → Progeny beetles green → Crows could not feed on green beetles as they got camouflaged (hide) in green bushes 
  • Number of green bettles increases

Conclusion

  • Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes.
  • This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment.

Situation II (Group of Red and Blue Beetles)

  • Reproduction in group of red beetles
  • All beetles are red except one that is blue
  • Number of red beetles increases as they reproduces
  • One blue beetle reproduces and no. of blue beetles also increases
  • Crows can see both blue and red beetles and can eat the
  • Number reduces but still red beetles are more and blue ones are few
  • Suddenly elephant comes and stamps on the bushes
  • Now beetles left are mostly blue

Conclusion

  • Blue beetles did not have a survival advantage. Elephants suddenly caused major havoc in the beetle population, otherwise their number would have been considerably large.
  • From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage. This is called genetic drift and it leads to variation.

Situation III (Group of Red Beetles and Bushes)

  • Group of red beetles
  • Habitat of beetles (bushes) suffer from plant disease
  • Average weight of beetles decreases due to poor nourishment
  • Number of beetles kept on reducing
  • Later plant disease gets eliminated
  • Number and average weight of beetles increases again

Conclusion

  • No genetic change has occurred in the population of beetle.
  • The population gets affected for a short duration only due to environmental changes.

ACQUIRED AND INHERITED TRAITS

WAYS BY WHICH SPECIATION TAKES PLACE

Speciation takes place when variation is combined with geographical isolation. 
(i) Gene flow: Occurs between populations that are partly but not completely separated. 
(ii) Genetic drift: It is the random change in the frequency of alleles (gene pair) in a population over successive generations. Genetic drift takes place due to:
(a) Severe changes in the DNA
(b) Change in number of chromosomes
(iii) Natural selection: The process by which nature selects and consolidates those organisms which are more suitable, adapted and possess favourable variations. 
(iv) Geographical isolation: It is caused by mountain ranges, rivers etc. Geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population. 

EVOLUTION AND CLASSIFICATION

  • Both evolution and classification are interlinked.
  • Classification of species is a reflection of their evolutionary relationship.
  • The more characteristic two species have in common the more closely they are related.
  • The more closely they are related, the more recently they have a common ancestor.
  • Similarities among organisms allow us to group them together and to study their characteristics.

EVIDENCES OF EVOLUTION

(i) Homologous Organs (Morphological and anatomical evidence)

  • These are the organs that have same basic structural plan and
    origin but different functions.
  • Homologous organs provides evidence for evolution by telling
    us that they are derived from the same ancestor. Example:
    Forelimb of horse (Running), Winds of bat (Flying), Paw of a cat (Walk/scratch/attack)
  • Same basic structural plan, but different functions perform.

(ii) Analogous Organs:

  •  These are the organs that have different origin and structural plan but same function.
  • Analogous organs provide mechanism for evolution. Example:
    Wings of bat → Elongated fingers with skin folds
    Wings of bird → Feathery covering along the arm
  • Different basic structure, but perform similar function i.e., flight.

(iii) Fossils: (Paleontological evidences)

  • The remains and relics of dead organisms of the past.
  • They are preserved traces of living-organisms.
  • Fossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds have evolved from reptiles. Example:
    Ammonite: Fossil-invertebrate, Trilobite: Fossil-invertebrate, Knightia: Fossil-fish, Rajasaurus: Fossil-dinosaur skull
  • Age of the fossils:
    (a) Deeper the fossil, older it is.
    (b) Detecting the ratios of difference of the same element in the fossil material Radio- carbon dating [C-(14) dating]

EVOLUTION BY STAGES

Evolution takes place in stages i.e. bit by bit generations.

(i) Fitness Advantage

  • Evolution of Eyes: Evolution of complex organs is not sudden. It occurs due to minor changes in DNA, however takes place bit by bit over generations.
  • Flat worm has rudimentary eyes. (Enough to give fitness advantage)
  • Insects have compound eyes.
  • Humans have binocular eyes.

(ii) Functional Advantage

  • Evolution of Feathers: Feathers provide insulation in cold weather but later they might become useful for flight. Example:
    (i) Dinosaurs had feathers, but could not fly using feathers.
    (ii) Birds seem to have later adapted the feathers to flight.
  • Evolution by Artificial Selection: Humans have been a powerful agent in modifying wild species to suit their own requirements throughout ages by using artificial selection. Example: From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and kohlrabi were obtained by artificial selection. Wheat (many varieties obtained due to artificial selection)

(iii) Molecular Phylogeny

  • It is based on the idea that changes in DNA during reproduction are the basic events in evolution.
  • Organisms which are most distantly related will accumulate greater differences in their DNA.

HUMAN EVOLUTION

  • Excavating, Time dating, Fossils and Determination of DNA sequences are the tools to study Human evolutionary relationship.
  • Although there is great diversity of human forms all over the world, yet all humans are a single species.
  • All humans come from Africa. The earliest members of the human species, Homo sapiens, can be traced there. Our genetic footprints can be traced back to our African roots.
  • The residents spread across Africa, the migrants slowly spread across the planet from Africa to West Asia, then to Central Asia, Eurasia, South Asia, East Asia. They travelled down the islands of Indonesia and the Philippines to Australia, and they crossed the Bering land bridge to the Americas.
  • They did not go in a single line.
  • Sometimes came back to mix with each other.
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