• Life on earth depends on resources like soil, water, air and energy from sun.
  • Uneven heating of air over land and water-bodies causes winds.
  • Evaporation of water from water-bodies and subsequent condensation give us rain. 
  • Pollution of air, water and soil affect the quality of life.
  • We need to conserve our natural resources and use them in a sustainable manner.
  • Various nutrients are used again and again in a cycle fashion. This leads to a certain balance between the various components of the biosphere.

NATURAL RESOURCES

  • The resources available on the earth and the energy from the sun are necessary to meet the basic requirements of all life forms on the earth.
  • The stocks of nature which are useful to mankind are known as natural resources. Examples: air, water, soil, minerals etc.

RESOURCES ON EARTH

  • The outermost crust of the earth is called the lithosphere.
  • Water covers 75% of the earth’s surface. It is also found underground. These comprise the hydrosphere.
  • The air that covers the whole of the earth like blanket is called the atmosphere.

BIOSPHERE

  • All living things on earth together with atmosphere, the hydrosphere and the lithosphere interact and make life possible is known as biosphere.
  • It may be:
    (i) Biotic components: Plants and animals.                                                    (ii) Abiotic components: Air, water and soil. 

AIR

  • Air is a mixture of different gases.
  • Air contains oxygen which is essential to living organisms for respiration. So it is called breath of life.

ROLE OF ATMOSPHERE

  • Air is a bad conductor of heat. It keeps the average temperature of the earth constant during the day and even during the course of the whole year.
  • Prevents the sudden increase in temperature during day time and during the night, it slows down the escape of heat into outer space. Example: At moon, there is no atmosphere and so the temperature varies from 190oC to 110oC.

THE MOVEMENT OF AIR: WINDS

  • During the day, the direction of wind is from sea to land. This is because the air above the land gets heated faster and starts rising.
  • During the night, the direction of wind is from land to sea. This is because at night, both land and sea start to cool.
  • The movement of air from one region to the other creates winds.

AIR POLLUTION

An increase in the content of harmful substance (pollutants) in the air like carbon dioxide, carbon monoxide, oxides of sulphur, nitrogen, fluoride, lead, nickel, arsenic and dust particles etc. causes air pollution. Air pollution can cause: In humans: Respiratory and renal problems, high blood pressure, eye irritation, cancer. In plants: Reduced growth, degeneration of chlorophyll, mottling (patches/spots of colour) of leaves. 

RAIN

  • Rain is formed by evaporation and condensation of water through water cycle in which distribution of water takes place.
  • Rain is very important because it carries out all the agriculture processes in the plants.
  • So we should conserve rain by contracting dams, pools etc.

ACID RAIN

  • When fossil fuels are burnt, gases like sulphur dioxide and nitrogen dioxide (NO2) are released.
  • These gases are dissolving in water form nitric acid and sulphuric acid.

GREENHOUSE EFFECT

Carbon dioxide keeps the earth warm much like glass which keeps the green house warm.

EFFECT OF INCREASE IN CARBON DIOXIDE

(i) intensifies green house effect. 
(ii) leads to global warming. 
(iii) increase in average temperature of earth. 
(iv) may lead to melting of polar caps. 
(v) Sub-merging number of coastal cities. Changes in environment affects us and our activities change the environment around us. 

ENVIRONMENTAL PROBLEMS CAUSED BY HUMANS: DEPLETION OF OZONE LAYER

  • Ozone layer is present in the stratosphere which is a part of our atmosphere from 16 km to 60 km above sea level.
  • Ozone is an allotrope of oxygen. Its molecule is made up of three oxygen atoms. Molecular formula is O3.
  • Ozone layer absorbs the ultra-violet rays coming from the sun and protects living being from their harmful effects like skin cancer, cataract in eyes, weaken immune system.
  • The decline of ozone layer thickness in Antartica was first observed in 1985 and was termed as ozone hole.

Reason for Ozone Depletion:

  • Excessive use of CFCs (Chloro Fluoro Carbon) in refrigeratos, jet planes, spray cans, fire extinguishers.
  • Nuclear explosion

SMOG

  • Smog is a type of air pollution.
  • The word ‘smog’ comes from the blend of two words: Smoke and fog.
  • Smog can form in any climate where there is a lot of air pollution especially in cities.

WATER: A WONDER LIQUID

  • The most unusual natural compound found on earth and which fulfills almost various demands of different living things.
  • About three-fourth of the earth surface is 75% are covered with water.
  • It is present underground, a very large area on the surface (sea, ocean etc.) and also in the form of water vapour in the atmosphere.

NECESSITY OF WATER FOR ALL ORGANISMS

  • It maintains a uniform temperature of the body.
  • All cellular processes take place in a water medium.
  • All the reactions that take place within our body and within our cells occur between substances that are dissolved in water.
  • Water forms the habitat of many plants and animals.

WATER POLLUTION

When water becomes unfit for drinking and other uses, then water is said to be polluted.

Causes of Water Pollution

  • Dumping of wastes from the industries into water bodies.
  • Washing of clothes near water bodies.
  • Spraying chemical in water field.
  • Dumping household wastes into the water bodies.

SOIL

Soil is the portion of the earth surface consisting of disintegrated rock and decaying organic material. It provides the support for many plants and animals.

CREATION OF SOIL: VARIOUS FACTORS

Sun:

  • The sun heats up rocks during the day so that they expand. At night these rocks cool down and contract.
  • Since all parts of the rocks do not expand and contract at the same rate, this results in the formation of cracks and ultimately the huge rocks breaks up into smaller pieces.

Water:

Fast flowing water carries big and small particles of rock downstream. These rocks rub against other rocks and the resultant abrasion causes the rocks to wear down into smaller particles.

Wind:

Wind carries sand from one place to another.

Living Organisms:

  • Lichen (A slow growing plant)
  • Lichen, moss also grow on surface of rocks. While growing, they release certain substances that cause the rock surface to powder down and form a thin layer of soil.

SOIL EROSION

Carrying away of upper fertile layer of soil by rain, wind, human activities and wrong agricultural practice is called soil erosion.

Causes of Soil Erosion:

  • Over grazing of land.
  • Removal of top soil by wind and water.
  • Due to lack of trees the upper layer of soil is eroded by air and water.
  • Leaving land uncultivated for long time.

BIOGEOCHEMICAL CYCLES

  • The flow of substances from non-living to living and back to non-living is called the cycling of substances.
  • The cycling of chemical elements like carbon, oxygen, nitrogen, phosphorus, sulphur and water in the biosphere is called biogeochemical cycle.
  • It operates through soil, water, air and biotic factors.
  • The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as water cycle.
  • When sun shines, water evaporates continuously from the water bodies and forms water vapour. This water vapour rises up and goes into the atmosphere.
  • The plants absorb water from the soil and use it during the process of photosynthesis.
  • They also loose water by the process of transpiration.
  • The water vapour produced by transpiration also goes into the atmosphere.
  • The process of respiration and evaporation from the surface of animal body produces water vapour which goes into the atmosphere.
  • The evaporation and condensation of water vapour leads to rain. During winter, the water falls down in the form of dew or snow.
  • All of the water that falls on the land does not immediately flow back into the sea. Some of it seeps into the soil and becomes part of the underground reservoir of fresh water.
  • The underground water is again taken by plants and water cycle continues.

OXYGEN CYCLE

  • The percentage of oxygen in air is 21%.
  • The cyclic process by which oxygen element is circulated continuously through the living and non-living components of the biosphere constitutes oxygen cycle.
  • Human beings and animals take oxygen from the atmosphere during the process of respiration.
  • The decomposition of dead organisms also takes in oxygen from the atmosphere.
  • Respiration and decay of dead organisms release CO2 and water.
  • The carbon dioxide and water are used by the green plants during the process of photosynthesis.
  • They give out oxygen during this process. This oxygen is again used by human beings and animals.
  • Thus, the oxyen cycle keeps repeating in nature.

CARBON CYCLE

  • 0.03-0.04% carbon is present in the atmosphere in the form of CO2.
  • Carbon cycle maintains the balance of the element carbon in the atmosphere. Carbon is found in various forms on the earth.
  • Carbon is present in the atmosphere as carbon dioxide.
  • Carbon can also occur as carbonates and bicarbonate salts in minerals.
  • Carbon is the essential part of nutrients like carbohydrates, fats, proteins, nucleic acids and vitamins.
  • Carbon cycle keeps the level of CO2 constant in the atmosphere.
  • The Carbon Cycle starts in plants as:
    Step I: Plants use CO2 in the atmosphere, convert it into glucose in the presence of sunlight by the process of photosynthesis. Plants and animals break these carbohydrates for energy and release CO2 through respiration.
    Step II: When the plants and animals die, fungi and bacteria decompose the dead remains. This releases the carbon in the remains as carbon dioxide.
    Step III: Some of the dead plants and animals which get buried under the earth under certain temperature and pressure get transformed into fossil fuels like coal and petroleum.
  • On burning these fuels, CO2 is released into the atmosphere.

NITROGEN CYCLE

  • The sequence in which nitrogen passes from the atmosphere to the soil and organisms, and then is eventually released back into the atmosphere, is called nitrogen cycle.
  • Nitrogen makes up 78% of the earth’s atmosphere.
  • Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins and chlorophyll.
  • Plants and animals cannot utilize atmospheric nitrogen readily.
  • It has to be fixed by some organisms called nitrogen fixers.
  • Nitrogen-fixing bacteria like Rhizobium live in symbiotic association in the root nodules of certain leguminous plants.
  • These bacteria convert atmospheric nitrogen into ammonia which is utilized readily by plants.
  • Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90% of nitrogen fixation.
  • Lightning plays an important role in nitrogen fixation. When lightning occurs, the high temperature and pressure convert nitrogen and water into nitrates and nitrites.
  • Nitrates and nitrites dissolve in water and are readily used by aquatic plants and animals.
    •Ammonification: It is the process by which soil bacteria decompose dead organic matter and release ammonia into soil.
    •Nitrification: It is the process by which ammonia is converted into nitrites and nitrates.
    •Denitrification: It is the process by which nitrates are converted into atmospheric nitrogen.
The energy for the ‘life processes’ comes from food. Activities like playing, singing, reading, writing, thinking, jumping, cycling and running requires energy.

WORK

  • For doing work, energy is required.
  • In animals, energy is supplied by food they eat.
  • In machine, energy is supplied by fuel.

Why sometimes not much work is done in spite of working hard?

  • Reading, writing, drawing, thinking, analysing are all energy consuming. But in scientific manner, no work is done in above cases.
  • Example: A man is completely exhausted in trying to push a rock (wall), but work done is zero as wall is stationary.
  • A man standing still with heavy suitcase may be tired soon but he does no work in this situation as he is stationary.
  • When force is applied on the wall, the wall doesn’t move. Therefore, no work is done here.

Work is said to be done when:

(i) a moving object comes to rest. 
(ii) an object at rest starts moving. 
(iii) velocity of an object changes. 
(iv) shape of an object changes. 

Scientific Conception of Work:

  • Work is done when a force produces motion in a body.
  • Work is said to be done when a force is applied on a body and the body moves under the influence of force.

Condition of Work:

  • Force should be applied on the body.
  • Body should be displaced.

Work is done when:

(i) A cyclist is pedalling the cycle.                                                                                    (ii) A man is lifting load in upward or downward direction.

Work is not done when:

(i) A coolie carrying some load on his head stands stationary. 
(ii) A man is applying force on a big rock. 

Work Done by a Fixed Force :

  • Work done in moving a body is equal to the product of force and displacement of body in the direction of force.
    Work = Force × Displacement W =F ×S
  • Work is a scalar quantity.

Unit of Work:

  • Unit of work is Newton metre or Joule.
  • When a force of 1 Newton moves a body through a distance of 1 metre in its own direction, then the work done is 1 Joule.
  • 1 Joule = 1 Newton × 1 metre 1 J = 1 Nm

The amount of work done depends on the following factors:

(i) Magnitude of force: Greater the force, greater is the amount of work & vice-versa. 
(ii) Displacement: Greater the displacement, greater is the amount =of work & vice-versa. 

Negative, Positive and Zero Work

  • Work done by a force can be positive, negative or zero.
    (i) Work done is positive when a force acts in the direction of motion of the body. Example: A child pulls a toy car with a string horizontally on the ground. Here work done is positive. W =F ×S                                                      (ii) Work done is negative when a force acts opposite to the direction of motion of the body. Example: When we kick a football lying on the ground, the force of our kick moves the football. Here direction of force applied & motion of football is same so work done is positive. But when football slows due to force of friction acting in a direction opposite to direction of motion of football, thus work done is negative.                        (iii) Work done is zero when a force acts at right angles to the direction of motion. Example: The moon moves around the earth in circular path. Here force of gravitation acts on the moon at right angles to the direction of motion of the moon. So work done is zero.
  • -ve (negative) sign indicates that work is done against gravity.
  • Note: If work is done against the direction of motion (gravity), then it is taken –ve.

ENERGY

  • The capacity of doing work is known as energy.
    (i) The sun is the biggest source of energy.
    (ii) Most of the energy sources are derived from the sun.
    (iii) Some energy is received from nucleus of atoms, interior of the earth and the tides.
  •  The amount of energy possessed by a body is equal to the amount of work it can do.
  • Working body losses energy, body on which work is done gains energy.
  • Energy is a scalar quantity. Unit: The SI unit of energy is Joule (J) and its bigger unit is kilo joule (kJ). 1 kJ = 1000 J
  • The energy required to do 1 Joule of work is called 1 Joule energy.

FORMS OF ENERGY:

Mechanical Energy:

  • Sum of kinetic energy & potential energy of a body is called mechanical energy.
  • The energy possessed by a body on account of its motion or position is called mechanical energy.

Kinetic Energy:

  • The energy of a body due to its motion is called kinetic energy.
  • Kinetic energy is directly proportional to mass and the square of velocity.
  • Examples of kinetic energy:

→ A moving cricket ball
→ Running water
→ A moving bullet
→ Flowing wind
→ A moving car
→ A running athlete
→ A rolling stone

Formula for Kinetic Energy:
  • If an object of mass ‘m’ moving with uniform velocity ‘u’, it is displaced through a distance ‘s’.
    Constant force ‘f’ acts on it in the direction of displacement.
    Its velocity changes from ‘u’ to ‘v’.
  • Then acceleration is ‘a’. Work done, W = F × s ….(i)   F = ma ….(ii)
  • According to third equation of motion, relationship between u, v, s and a is as follows: v2 – u2 = 2as                  ⇒ s = (v2 – u2)/2a …(iii)
  • Now putting the value of f and s from (ii) and (iii) in equation (i), If u = 0 (when body starts moving from rest) W = 1⁄2mv2 and  KE = 1⁄2mv2

Potential Energy:

The energy of a body due to its position or change in shape is known as potential energy. Examples:

(i) Water kept in the dam : It can rotate the turbine to generate electricity due to its position above the ground.

(ii) Wound up spring of a toy car: It possesses potential energy which is released during unwinding of spring. Therefore, toy car moves.

(iii) Bent string ofbow : Potential energy due to change of its shape (deformation) released in the form of kinetic energy while shooting an arrow.

Factors Affecting Potential Energy:

(i) Potential Energy:
P. E. ∝ m
→ More the mass of body, greater is the potential energy and vice-versa. 

(ii) Height above the ground: 
P. E. ∝ h (Not depend on the path it follows)
→ Greater the height above the ground, greater is the P.E. and vice-versa.  

(iii) Change in shape: Greater the stretching, twisting or bending, more is the potential energy.

Potential Energy of an Object on a Height:
  • If a body of mass ‘m’ is raised to a height ‘h’ above the surface of the earth, the gravitational pull of the earth (m × g) acts in the downward direction.
  • To lift the body, we have to do work against the force of gravity.
    Thus, Work done (W) = Force × Displacement
    ⇒ W = m × g × h = mgh
  • This work is stored in the body as potential energy (gravitational potential energy).
  • Thus, Potential energy, Ep = m × g × h
    where g = acceleration due to gravity.

TRANSFORMATION OF ENERGY

The change of one form of energy to another form of energy is known as the transformation of energy.

Examples:
(i) A stone at a certain height has entire potential energy. But when it starts moving downward, potential energy of stone goes on decreasing as height goes on decreasing but its kinetic energy goes on increasing as the velocity of stone goes on increasing. At the time stone reaches the ground, potential energy becomes zero and kinetic energy is maximum. Thus, its entire potential energy is transformed into kinetic energy.

(ii) At a hydroelectric powerhouse, the potential energy of water is transformed into kinetic energy and then into electrical energy.

(iii) At a thermal powerhouse, the chemical energy of coal is changed into heat energy, which is further converted into kinetic energy and electrical energy.

(iv) Plants use solar energy to make chemical energy in food by the process of photosynthesis.

LAW OF CONSERVATION OF ENERGY

  • Whenever energy changes from one form to another form, the total amount of energy remains constant.
  • “Energy can neither be created nor be destroyed.”
  • Although some energy may be wasted during conversion, the total energy of the system remains the same.

CONSERVATION OF ENERGY DURING FREE FALL OF A BODY

  • A ball of mass ‘m’ at a height ‘h’ has potential energy = mgh.
  •  As the ball falls downwards, height ‘h’ decreases, so the potential energy also decreases.
  • Kinetic energy at ‘h’ is zero but it is increasing during the falling of the ball.
  • The sum of potential energy & kinetic energy of the ball remains the same at every point during its fall.
    1⁄2mv2 + mgh = Constant
  • Kinetic energy + Potential energy = Constant

POWER(Rate of Doing Work)

  •  “Power is defined as the rate of energy consumption.”
  • Power (P) = Work done/Time Taken = W/t
  • where, P = Power, W = Work done, t = Time taken
  • The power of an electrical appliance tells us the rate at which electrical energy is consumed by it.

UNIT OF POWER

  • SI unit of Power is Watt (W) = 1 Joule/second. 1 Watt (W) = 1Joule/1 second = 1J/1s
  • Power is one Watt when one Joule work is done in one second.
  • Average Power = Total work done or total energy used/Total time taken

  • Bigger unit of power is called Kilowatt or KW.
    1 Kilowatt (KW) = 1000 Watt = 1000 W or 1000 J/s

  • Commercial units : Joule is very small unit of energy and it is inconvenient to use it where a large quantity of energy is involved. For commercial purpose, bigger unit of energy is Kilotwatt hour (KWh).

    1 KWh: 1 KWh is the amount of energy consumed when an electric appliance having a power rating of 1 Kilowatt is used for 1 hour.

Relation between Kilowatt hour and Joule

  • 1 Kilowatt hour is the amount of energy consumed at the rate of 1 Kilowatt for 1 hour. 1 Kilowatt hour = 1 Kilowatt for 1 hour
    = 1000 Watt for 1 hour
    = 1000 Watt × 3600 seconds (60 × 60 seconds = 1 hour)
    = 36,00,000 Joules
    ∴ 1 KWh = 3.6 × 106 J = 1 unit 

GRAVITATIONAL FORCE OF EARTH

  • If we release a small stone without pushing it from a height, it accelerates towards earth.
  • The stone is when accelerated towards earth, means some force is acting on it. The force which pulls the objects towards the centre of the earth is known as gravitational force of the earth.
  • Here, stone also attracts earth. It means every object in universe attracts every other object.

NEWTON'S UNIVERSAL LAW OF GRAVITATION

Sir Isaac Newton in 1687 proposed a law about the force of attraction between the two objects in the universe which is known as Newton’s law of gravitation. According to Universal law of Gravitation, every mass in this universe attracts every other mass with a force which is directly proportional to the product of two masses and inversely proportional to the square of the distance between them.

  • Let masses (M) and (m) of two objects are distance (d) apart, then force of attraction (F) between them
    F ∝ M×m
    F ∝ 1/d2
    F ∝ Mm/d2
    F = (GMm)/d2
    where,
    G is a constant and is known as Gravitational constant. Value of G = 6.67×10-11 Nm2/kg2
    G is called universal gravitational constant.
  • If unit of F is in Newton, m is in kg, d is in metre, then unit of G can be calculated as : G = (F×d2)/Mm, therefor unit will be Nm2/kg2

RELATION BETWEEN NEWTON'S THIRD LAW OF MOTION AND NEWTON'S LAW OF GRAVITATION​

  • According to Newton’s third law of motion, “Every object exerts equal and opposite force on other object but in opposite direction.”
  • According to Newton’s law of gravitation, “Every mass in the universe attracts the every other mass.”
    → In case of freely falling stone and earth, stone is attracted towards earth means earth attracts the stone.
  • But according to Newton’s third law of motion, the stone should also attract the earth. It is true that stone also attracts the earth with the same force F = m × a but due to very less mass of the stone, the acceleration (a) in its velocity is 9.8 m/s2 and acceleration (a) of earth towards stone is 1.65×10-24 m/s2 which is negligible and we cannot feel it.

IMPORTANCE OF UNIVERSAL LAW OF GRAVITATION

(i) The force that binds us to the earth. 
(ii) The motion of moon around the earth. 
(iii) The motion of earth around the sun. 
(iv) The tides due to moon and the sun. 

FREE FALL OF AN OBJECT AND ACCELERATION (g)

  • When an object is thrown upward, it reaches certain height, then it starts falling down towards earth. It is because the earth’s gravitational force exerts on it.
  • This fall under the influence of earth is called ‘free fall of an object’.
  • During this free fall direction do not change but velocity continuously changes which is called acceleration due to gravity. It is denoted by ‘g’.
  • Its unit is same as acceleration m/s .

GRAVITATIONAL ACCELERATION AND ITS VALUE AT THE SURFACE OF THE EARTH

  • The uniform acceleration produced in a freely falling object due to the gravitational force of earth, is called acceleration due to gravity.
  • It is represented by ‘g’ and it always acts towards the centre of the earth. Value of ‘g’ on the surface of earth
  • The force acting on an object is F = (GMem)/R
  • where,Me = Mass of earth, m = Mass of an object, R = Radius of earth
  • If acceleration due to gravity is ‘g’ due to force F then, F = m×g 

RELATIONSHIP AND DIFFERENCE BETWEEN 'G' AND 'g'

  • G = Gravitational constant
  • g = Acceleration due to gravity g = GM/R2
  • Difference between G (Gravitational constant) and g (Acceleration due to gravity)

  • Gravitation Constant (G) 

    Its value is 6.67×10 Nm /kg . Its value remains constant always and everywhere.  

     

  • Gravitational acceleration (g)  

    Its value is 9.8 m/s . Its value varies at various places. Its unit is Nm /kg . Its unit is m/s . It is a scalar quantity. It is a vector quantity.  

  • Example: If two stones of 150 gm and 500 gm are dropped from a height, which stone will reach the surface of earth first and why ? Explain your answer.  

     

  • Solution 

    → It was Galileo, who first time demonstrated and depicted that the acceleration of an object falling freely towards earth does not depend on the mass of the
    object. 

    → It can be verified by universal law of gravitation. Let an object of mass m, is allowed to fall from a distance of R, from the centre of the earth. Then, the gravitational force, F = (GMem)/R2 (Me= Mass of the earth) The force acting on the stone is F = m×a

    ∴ m × a = (GMem)/R2
    ⇒ a = GMe/R2 

    → So, acceleration in an object falling freely towards earth depends on the mass of earth and height of the object from the centre of the earth. So, stones of mass 150 gm and 500 gm will reach the earth surface together. 

EQUATION OF MOTION WHEN AN OBJECT IS FALLING FREELY TOWARDS EARTH OR THROWN VERTICALLY UPWARDS

  • Case 1: When an object is falling towards earth with initial velocity (u)
    Velocity (v) after t seconds, v = u + ght
    Height covered in t seconds, h = ut + 1⁄2gt2
    Relation between v and u when t is not given: v2 = u2 + 2gh
  • Case 2: When object is falling from rest position means initial velocity u=0
    Velocity (v) after t seconds, v = gt
    Height covered in t seconds, h = 1⁄2gt2
    Relation between v and u when t is not given: v2 = 2gh
  • Case 3: When an object is thrown vertically upwards with initial velocity u, the gravitational acceleration will be negative (-g)
    Velocity (v) after t seconds, v = u − gt
    Height covered in t seconds, h = ut − 1⁄2gt2
    Relation between v and u when t is given: v2 = u2 − 2gh

MASS

  • The mass of a body is the quantity of matter contained in it. Mass is a scalar quantity which has only magnitude but no direction.
  • SI unit of mass is kilogram which is written in short form as kg.
  • Mass of a body is constant and does not change from place to place.
  • Mass of a body is usually denoted by the small ‘m’.
  • Mass of a body cannot be zero.

WEIGHT

  • The force with which an object is attracted towards the centre of the earth, is called the weight of the object.
    Force = m × a
    In case of earth, a = g
    ∴ F = m× g
    But the force of attraction of earth on an object is called its weight (W). ∴W = m × g
  • Weight is the force and its SI unit is Newton (N). It depends on ‘g’ and is a vector quantity.

Relation between 1 kg wt and express it into Newton

  • We know that
  • W = m × g
    If mass (m) = 1 kg, g = 9.8 m/s2, then W = 1 kg × 9.8 m/s2
    ⇒ 1 kg wt = 9.8 N
  • The gravitational force of earth that acts on an object of mass 1 kg is called as 1 kg wt.

DIFFERENCE BETWEEN MASS AND WEIGHT

FACTORS AFFECTING THE VALUE OF 'g'

  • Earth is not a perfect sphere. The radius of the earth increases when we go from pole to equator.
  • The value of gravitational acceleration ‘g’ decreases with increasing height.
  • The weight of an object on the moon is one-sixth of the weight on earth. Let the mass of an object be m, its weight on earth means the force by which earth attracts it towards the centre.

THRUST AND PRESSURE

  • The force acting on an object perpendicular to the surface is called thrust.
  • The effect of thrust per unit area is called pressure.
  • Pressure (P) = Force/Area = F/A
  • SI unit is N/m or Nm .
  • SI unit of pressure is Pascal denoted by ‘Pa’.
  • Pressure depends on two factors :(i) Force applied(ii) Area of surface over which force acts.
  • Examples of Pressure:                                                                                              (i)The base of high buildings is made wider so that weight of walls act over a large surface area and pressure is less.                                    (ii)School bags are having broad strap so that the weight of school bags fall over a larger area of the shoulder and produce less pressure and becomes less painful.                                                                          (iii)The blades of knives are made sharp so very small surface area and on applying force, it produces large pressure and cuts the object easily.(iv)All liquids and gases are fluids and they exert pressure in all directions.

BUOYANCY

  • The upward force experienced by an object when it is immersed into a fluid is called force of buoyancy.
  • It acts in upward direction and it depends on the density of the fluid.
  • When force of gravitational attraction of the earth on the surface of the object < buoyant force exerted by fluid on the surface of the object, object floats in the fluid. 
  • When force of gravitational attraction of the earth on the surface of the object > buoyant force exerted by fluid on the surface of the object, the object sinks in the fluid.
  • This is the reason, why a pin sinks and boat/ship floats on the surface of water. (Archimedes’ principle)

DENSITY

  • The mass per unit volume is called density of an object.
  • If M is the mass and V is the volume, then • Density (d) = Mass(M)/Volume(V)
  • SI unit = kg/m3

ARCHIMEDES' PRINCIPLE

It states, when a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.

APPLICATIONS OF ARCHIMEDES' PRINCIPLE

  • It is used in determining the relative density of substances.
  • It is used in designing ships and submarines.
  • Hydrometers and lactometers are made on this principle.
  • It is because this ship made of iron and steel floats in water whereas a small piece of iron sinks in it.

RELATIVE DENSITY

  • The ratio of the density of a substance to that of the density of water is called relative density.
  • Relative density = Density of a substance/Density of water.
  • It has no unit as it is a ratio.

FORCE

  •  It is the force that enables us to do any work. To do anything, either we pull or push the object. Therefore, pull or push is called force.
  • Example, to open a door, either we push or pull it. A drawer is pulled to open and pushed to close.

EFFECT OF FORCE

  • Force can make a stationary body in object.
    For example: a football can be set to move by kicking it i.e. by applying a force.
  • Force can stop a moving body. For example, by applying brakes, a running cycle or a running vehicle can be stopped.
  • Force can change the direction of a moving object.
    For example: by applying force i.e. by moving handle, the direction of a running bicycle can be changed. Similarly by moving steering, the direction of a running vehicle is changed.
  • Force can change the speed of a moving body.
    By accelerating, the speed of a running vehicle can be increased or by applying brakes the speed of a running vehicle can be decreased.
  • Force can change the shape and size of an object.
    For example: by hammering, a block of metal can be turned into a thin sheet. By hammering, a stone can be broken into pieces.

TYPES OF FORCE

Forces are mainly of two types:
(i)Balanced forces 
(ii)Unbalanced forces 

(i)Balanced Forces

  • If the resultant of applied forces is equal to zero, it is called balanced forces. Example: In the tug of war if both the team apply similar magnitude of forces in opposite directions, rope does not move in either side. This happens because of balanced forces in which resultant of applied forces become zero.
  • Balanced forces do not cause any change of state of an object. Balanced forces are equal in magnitude and opposite in direction.
  • Balanced forces can change the shape and size of an object.
    For example: When forces are applied from both sides over a balloon, the size and shape of balloon is changed.

(ii)Unbalanced Forces

  • If the resultant of applied forces are greater than zero, the forces are called unbalanced forces.
  • An object in rest can be moved because of applying balanced forces.
  • Unbalanced forces can do the following:
    → Move a stationary object
    → Increase the speed of a moving object
    → Decrease the speed of a moving object
    → Stop a moving object
    → Change the shape and size of an object

LAWS OF MOTION

Galileo Galilei:

  • Galileo first of all said that object move with a constant speed when no foRces act on them.
  • This means if an object is moving on a frictionless path and no other force is acting upon it, the object would be moving forever. That is, there is no unbalanced force working on the object.
  • But practically it is not possible for any object. Because to attain the condition of zero, unbalanced force is impossible.
  • Force of friction, force of air and many other forces are always acting upon an object. Newton’s Laws of Motion
  • Newton studied the ideas of Galileo and gave the three laws of motion. These laws are known as Newton’s laws of motion.

Newton’s First Law of Motion (Law of Inertia)

  • Any object remains in the state of rest or in uniform motion along a straight line, until it is compelled to change the state by applying external force.
    Explanation: If any object is in the state of rest, then it will remain in rest until a external force is applied to change its state. Similarly, an object will remain in motion until any external force is applied over it to change its state. This means all objects resist to in changing their state. The state of any object can be changed by applying external forces only.
  • Newton’s First Law of Motion in Everyday Life
    (i) A person standing in a bus falls backward when bus starts moving suddenly.
  • This happens because the person and bus both are in rest while bus is not moving, but as the bus starts moving, the legs of the person start moving along with bus but rest portion of his body has the tendency to remain in rest. Because of this, the person falls backward; if he is not alert.
    (ii) A person standing in a moving bus falls forward if driver applies brakes suddenly.
  • This happens because when bus is moving, the person standing in it is also in motion along with bus. But when driver applies brakes the speed of bus decreases suddenly or bus comes in the state of rest suddenly, in this condition the legs of the person which are in contact with the bus come in rest while the rest part of his body have the tendency to remain in motion. Because of this person falls forward if he is not alert.
    (iii) Before hanging the wet clothes over laundry line, usually many jerks are given to the clothes to get them dried quickly. Because of jerks, droplets of water from the pores of the cloth falls on the ground and reduced amount of water in clothes dries them quickly.
  • This happens because when suddenly clothes are made in motion by giving jerks, the water droplets in it have the tendency to remain in rest and they are separated from clothes and fall on the ground.                 (iv) When the pile of coin on the carom-board is hit by a striker, coin only at the bottom moves away leaving rest of the pile of coin at same place.
  • This happens because when the pile is struck with a striker, the coin at the bottom comes in motion while rest of the coin in the pile has the tendency to remain in the rest and they vertically falls the carom-board and remain at same place.
Mass and Inertia:
  • The property of an object because of which it resists to get disturb its state is called inertia.
  • Inertia of an object is measured by its mass. Inertia is directly proportional to the mass. This means inertia increases with increase in mass and decreases with decrease in mass.
  • A heavy object will have more inertia than the lighter one. In other words, the natural tendency of an object that resists the change in state of motion or rest of the object is called inertia.
  • Since a heavy object has more inertia, thus it is difficult to push or pull a heavy box over the ground than the lighter one.
Momentum:
  • Momentum is the power of motion of an object.
  • The product of velocity and mass is called the momentum. Momentum is denoted by ‘p’.
  • Therefore,
    Momentum of the object = Mass × Velocity (p = m × v)
    where, p = momentum, m = mass of the object and v = velocity of the object.
  • Some explanations to understand the momentum:                                  (i)A person get injured in the case of hitting by a moving object, such as stone, pebbles or anything because of momentum of the object.              (ii)Even a small bullet is able to kill a person when it is fired from a gun because of its momentum due to great velocity.                                      (iii)A person get injured severely when hit by a moving vehicle because of momentum of vehicle due to mass and velocity.
Momentum and Mass
  • Since momentum is the product of mass and velocity (p = m × v) of an object. This means momentum is directly proportional to mass and velocity. Momentum increases with increase of either mass or velocity of an object.
  • This means if a lighter and a heavier object is moving with same velocity, then heavier object will have more momentum than the lighter one.
  • If a small object is moving with great velocity, it has tremendous momentum. And because of momentum, it can harm an object more severely. Example: a small bullet having a little mass even kills a person when it is fired from a gun.
  • Usually, road accidents prove more fatal because of high speed than in slower speed. This happens because vehicles running with high speed have greater momentum compared to a vehicle running with slower speed.
Momentum of an object in the state of rest:
  • Let an object with mass ‘m’ is in the rest.
  • Since, object is in rest, therefore, its velocity, v = 0
  • Now we know that, Momentum = mass × velocity
    ⇒p = m × 0 = 0
  • Thus, the momentum of an object in the rest i.e. non-moving, is equal to zero.
Unit of Momentum:
  • SI unit of mass = kg
  • SI unit of velocity = m/s
  • We know that,
    Momentum (p) = m × v
    ∴ p = kg × m/s ⇒ p = kgm/s

Statement of Second Law of Motion

Rate of change of momentum of an object is proportional to applied unbalanced force in the direction of force.
Mathematical Expression:
  • Suppose,
    Mass of an object = m kg
    Initial velocity of an object = u m/s
    Final velocity of an object = v m/s
    ∴ Initial momentum, p1 = mu
    Final momentum, p2 = mv
    ∴ Change in momentum = Final momentum – Initial momentum = mv – mu= m(v – u)
    ∴ Rate of change of momentum = Change in momentum/Time taken = m(v-u)/t
  • According to 2nd law, this rate of change is momentum is directly proportional to force. We know that, a = (v-u)/t (From 1st equation of motion)
    ∴ F = kma
    where, k is a constant. Its value can be assumed as 1.
    ∴ F = 1 × m × a = ma
  • SI unit = kg m/s 2 or Newton
    1 Newton: When an acceleration of 1 m/s2 is seen in a body of mass 1 kg, then the force applied on the body is said to be 1 Newton.

Proof of Newton’s First Law of Motion from Second Law

  • First law states that if external force F = 0, then a moving body keeps moving with the same velocity, or a body at rest continues to be at rest.
  • ∴F = 0
    We know, F = m(v-u)/t
    (i) A body is moving with initial velocity u then,
    m(v-u)/t = 0 ⇒ v – u = 0
    ∴v = u
    Thus, final velocity is also same.
    (ii) A body is at rest i.e., u = 0
    Therefore, from above u = v = 0
    So, the body will continue to be at rest.

Third Law of Motion

For every action there is an equal an opposite reaction.
Applications:

(i) Walking is enabled by 3rd law. 
(ii) A boat moves back when we deboard it. 
(iii) A gun recoils. 
(iv) Rowing of a boat. 

Law of Conservation of Momentum

  • When two (or more) bodies act upon one another, their total momentum remains constant (or conserved) provided no external forces are acting.
  • Initial momentum = Final momentum
  • Suppose, two objects A and B each of mass m1 and mass m2 are moving initially with velocities u1 and u2, strike each other after time t and start moving with velocities v1 and v2 respectively.
  • Now,
    Initial momentum of object A = m1u1
    Initial momentum of object B = m2u2
    Final momentum of object A = m1v1
    Final momentum of object B = m2v2
  • So, Rate of change of momentum in A, F1 = (m1v1 – m1u1)t = m1(v1 – u1)/t ….(i)
    Rate of change of momentum in B, F2 = (m2v2 – m2u2)t = m2(v2 – u2)/t ….(ii)
  • We know from 3rd law of motion, F1 = −F2
    So, m1(v1 – u1)/t = -m2(v2 – u2)/t                                                                        ⇒ m1v1 – m2u2 = −m2v2 + m1u1                                                                            ⇒ m1u1 + m2u2 = m1v1 + m2v2
  • Thus, Initial momentum = Final momentum.

REST

A body is said to be in a state of rest when its position does not change with respect to a reference point.

MOTION

  • A body is said to be in a state of motion when its position change continuously with reference to a point.
  • Motion can be of different types depending upon the type of path by which the object is going through:
    (i) Circulatory motion/Circular motion – In a circular path.
    (ii) Linear motion – In a straight-line path.
    (iii) Oscillatory/Vibratory motion – To and fro path with respect to the origin.

SCALAR QUANTITY

It is the physical quantity having its own magnitude but no direction. Example: distance, speed.

VECTOR QUANTITY

It is the physical quantity that requires both magnitude and direction. Example: displacement, velocity.

DISTANCE AND DISPLACEMENT

  • The actual path or the length travelled by an object during its journey from its initial position to its final position is called the distance.
  • Distance is a scalar quantity that requires only magnitude but no direction to explain it. Example: Ramesh travelled 65 km. (Distance is measured by odometer in vehicles.)
  • Displacement is a vector quantity requiring both magnitude and direction for its explanation. Example: Ramesh travelled 65 km southwest from Clock Tower.
  • Displacement can be zero (when the initial point and final point of motion are the same) Example: circular motion.

DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT

UNIFORM AND NON-UNIFROM MOTIONS

Uniform Motion:

When a body travels an equal distance in an equal interval of time, then the motion is said to be a uniform motion.

Non-uniform Motion:

In this type of motion, the body will travel unequal distances in equal intervals of time.

Types of Non-uniform Motion

(i)Accelerated Motion:
When the motion of a body increases with time.
(i)De-accelerated Motion:
When the motion of a body decreases with time.

SPEED

  • The measurement of distance travelled by a body per unit time is called speed.
  • Speed (v) = Distance Travelled/Time Taken = s/t
  • SI unit = m/s (meter/second)
  • If a body is executing uniform motion, then there will be a constant speed or uniform motion.
  • If a body is travelling with non-uniform motion, then the speed will not remain uniform but have different values throughout the motion of such body.
  • For non-uniform motion, the average speed will describe one single value of speed throughout the motion of the body.
  • Average speed = Total distance travelled/Total time taken

Conversion Factor

Change from km/hr to m/s = 1000m/(60×60)s = 5/18 m/s

VELOCITY

  • It is the speed of a body in given direction.
  • Velocity = Displacement/Time
  • Velocity is a vector quantity. Its value changes when either its magnitude or direction changes.
  • For non-uniform motion in a given line, average velocity will be calculated in the same way as done in average speed.
  • Average velocity = Total displacement/Total time
  • For uniformly changing velocity, the average velocity can be calculated as follows : 
  • Avg. Velocity (vavg) = (Initial velocity + Final velocity)/2 = (u+v)/2
  • Where, u = initial velocity, v = final velocity
  • SI unit of velocity = ms-1
  • Velocity = Displacement/Time
  • It can be positive (+ve), negative (-ve) or zero.

ACCELERATION

  • Acceleration is seen in non-uniform motion and it can be defined as the rate of change of velocity with time.
  • Acceleration (a) = Change in velocity/Time = (v-u)/t
    where, v = final velocity, u = initial velocity
  • If v > u, then ‘a’ will be positive (+ve).

RETARDATION/DECELERATION

  • Deceleration is seen in non-uniform motion during a decrease in velocity with time. It has the same definition as acceleration.
  • Deaceleration (a’) = Change in velocity/Time = (v-u)/t
    Here, v < u, ‘a’ = negative (-ve).

EQUATION OF MOTION(FOR UNIFORMLY ACCELERATED MOTION)

  • First Equation: v = u + at
    Final velocity = Initial velocity + Acceleration × Time
  • Second Equation: s = ut + 1⁄2 at2
  • Third Equation: v2 = u2 + 2as

UNIFORM CIRCULAR MOTION

  • If a body is moving in a circular path with uniform
    speed, then it is said to be executing uniform circular
    motion.
  • In such a motion the speed may be the same throughout
    the motion but its velocity (which is tangential) is different at every point of its motion. Thus, uniform circular motion is an accelerated motion.

ADOLESCENCE

The term is manipulated from a Latin word ‘Adolescence’ meaning “to grow into maturity .” Whenever a kid starts crossing the age of 10 or 11, there is a sudden spurt in growth. This shows that they (boys and girls) are no longer a child but are on the way to becoming an adult. Humans become capable of reproduction after puberty sets in. Between the ages of 11 years and 19 years, children are called adolescents.

PUBERTY

It is the time when sex organs begin to work. It brings about growth in reproductive organs and changes in the body.

CHANGES DURING PUBERTY

(i) Increase in Height: The bones of the legs and arms elongate and the individual becomes tall and lanky. 

(ii) Changes in Body Shape: In boys, the body becomes more muscular, the shoulder becomes wider. In girls, the body shows curves in certain parts and the region below the waist become wider and broader. 

(iii) Change in Voice: In boys, the voice becomes hoarse and heavy due to the extra growth of larynx (voice box). In girls, the voice becomes high pitched and shriller. 

(iv) Sweat and sebaceous glands: It become more active and secrete more sweat and oil. 

(v) Emotional aspects develop. 

(vi) Mental and intellectual development is at its peak.

SECONDARY SEXUAL CHARACTERS

Developed breasts in girls and facial hair in boys etc. are called the Secondary Sexual Characters. The onset of puberty and maturity from reproductive parts are controlled by hormones. Hormones are the secretions from endocrine glands, which pour them directly into the bloodstream.

HORMONES OF PITUITARY GLAND

The pituitary gland also called master gland, secretes hormones like growth hormone and the hormones that stimulate other glands such as the testes, ovaries, thyroids and adrenals to secrete harmonies. Ex: the thyroid secretes thyroxine and adrenals secrete adrenalin. Insulin is a hormone secreted from the pancreas to hydrolyse the sugar content in the body.

MALE AND FEMALE HORMONES

Testosterone is the male hormone and estrogen the female hormone. The uterine wall in females, i.e., the endometrium prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down along with degenerated corpus luteum and egg and goes out of the body along with blood. This is called menstruation. The sex of the unborn child depends on whether the zygote has XX or XY chromosomes. It is important to eat balanced food and maintain personal hygiene during adolescence.

BALANCED DIET

A diet which contains all the necessary nutrients such as proteins, carbohydrates, fats and vitamins in proper proportions is called a balanced diet.
All living organism are grouped on the basis of their similarities and increasing complexities into different complexities.
  • Biodiversity means the variety of living organisms present in a particular region.
  • There are about 20 lac organisms known on the earth that differ from one another in external form, internal structure, mode of nutrition, habitat, etc.

TAXONOMY

It is a branch of biology which deals with the identification, nomenclature and classification of organisms. Carolus Linnaeus is called the father of taxonomy.

CLASSIFICATION

The method of arranging organisms into groups or sets based on similarities and differences is called classification.

IMPORTANCE OF CLASSIFICATION

  • It makes the study of a wide variety of organisms easy and in a systematic manner.
  • It helps to understand how the different organisms have evolved with time.
  • It helps to understand the inter-relationships among different groups of organisms.
  • It forms a base for the study of other biological sciences, like biogeography.

BASIS OF CLASSIFICATION

  • There are certain features or properties used for the classification of living organisms which are known as characteristics.
  • Organisms with the same characteristics are placed in the same groups.

CLASSIFICATION SYSTEM

TWO KINGDOM CLASSIFICATION

Carolus Linnaeus in 1758 classified the living organisms into two groups as plants and animals.

FIVE KINGDOM CLASSIFICATION

  • H. Whittaker in 1959 further classified the organisms into five kingdoms as Kingdom Monera, Kingdom Protista, Kingdom Fungi, Kingdom Plantae and Kingdom Animalia.
  • Carl Woese in 1977 further divided Kingdom Monera into archaebacteria (or Archae) and Eubacteria (or Bacteria).

HIERARCHY OF CLASSIFICATION

Linnaeus proposed a classification system by arranging organisms into taxonomic groups at different levels according to the characteristics they have.

GROUPS OR LEVELS FROM TOP TO BOTTOM

The major characteristics considered for classifying all organisms into five major kingdoms.

TYPES OF CELLULAR ORGANIZATION

(i) Prokaryotic cells: These are primitive and incomplete cells without a well-defined nucleus. 
(ii) Eukaryotic cells: These are advanced and complete cells with a well-defined nucleus. 

BODY ORGANIZATION

(i) Unicellular organisms: These are organisms made up of a single cell with all activities performed by the single cell. 
(ii) Multicellular organisms: These are organisms made up of a large number of cells with different functions performed by different cells. 

MODE OF OBTAINING FOOD

(i) Autotrophs: These are the organisms that make their own food by photosynthesis. 
(ii) Heterotrophs: These are the organisms which depend on other organisms for food. 

FIVE KINGDOM CLASSIFICATION

R. H. Whittaker taxonomist was the first one to propose five kingdom classification.

MONERA

(i) Type: Unicellular Prokaryotic 
(ii) Mode of nutrition: Autotrophic or heterotrophic 
(iii) Body: Lack well-defined nucleus and cell organelles 
(iv) Examples: Bacteria, Blue-green algae 

PROTISTA

(i) Type: Unicellular Eukaryotic 
(ii) Mode of nutrition: Autotrophic or Heterotrophic 
(iii) Body: Some organisms use pseudopodia or cilia or flagella for movement 
(iv) Examples: Amoeba, Paramecium, Euglena 

FUNGI

(i) Type: Multicellular Non-green Eukaryotic 
(ii) Mode of nutrition: Saprophytic or Parasitic Sometimes symbiotic 
(iii) Body: Fungus is made up of long filaments called hyphae. The network of hyphae is mycelium. 
(iv) Examples: Yeast, Rhizopus, Mushrooms moulds 

PLANTAE

(i) Type: Multicellular Eukaryotic 
(ii) Mode of nutrition: Autotrophic 
(iii) Body: Exhibits high level of tissue differentiation and have specialized body organs. 
(iv) Examples: Trees, Plants, Shrubs 

ANIMALIA

(i) Type: Multicellular Eukaryotic 
(ii) Mode of nutrition: Heterotrophic 
(iii) Body: Exhibits high level of tissue differentiation and have specialized body organs. They have well developed nervous system. 
(iv) Examples: Fish, Insects, Animals, Humans, Birds 

KINGDOM I: MONERA

(i)Prokaryotic, unicellular. 
(ii)Can be autotrophs or heterotrophs. 
(iii)May or may not have a cell wall. 
(iv)Examples: Anabaena and Bacteria (heterotrophic), Cyano-bacteria or Blue-green algae (autotrophic). 

KINGDOM II: PROTISTA

(i) Eukaryotic, unicellular. 
(ii) Can be autotrophic or heterotrophic. 
(iii) May have cilia, flagella or pseudophodia for locomotion. 
(iv) Examples: Plants like unicellular algae, diatoms; animals like protozoans (Amoeba,  Paramecium, Euglena); fungi like slime molds and water molds. 

KINGDOM III: FUNGI

(i)Eukaryotic.
(ii)Mostly multicellular but sometimes unicellular (yeast).
(iii)Source of food:

  • Mostly saprophytes: These organisms use decaying material for
    food.
  • Some parasitic: These organisms live inside the body of another living organism to have food and can be disease-causing.
  • Symbiotic relation: These are relations between two organisms in which they live together for benefit of one or both. Lichens are a symbiotic relationship between fungi and cyanobacteria. Here fungi get food from cyanobacteria and in return, cyanobacteria get water and protection from sunlight through fungi.

(iv) Cell wall is made of chitin.
(v) Examples: Mushrooms (Agaricus), green mould (Penicillium), smut(Aspergillus).

KINGDOM IV: PLANTAE

(i) Eukaryotic, multicellular. 
(ii) Autotrophs. 
(iii) Cell wall present. 

BASIS OF DIVISION IN KINGDOM PLANTAE

(i)DIFFERENTIATED BY BODY PARTS

Body is differentiated into leaves, stems, roots, flowers, etc.

(ii)PRESENCE OF VASCULAR TISSUE

There are two types of vascular tissues present in the plants.
• Xylem: Helps in the transport of water. 
• Phloem: Helps in the transport of food. 

(iii)REPRODUCTION THROUGH SEEDS OR SPORES

• Phanerogamae: Plants with seeds are called phanerogamae. They contain embryo with stored food and are multicellular. 
• Cryotogamae: Plants with spores are called cryptogamae. They contain only naked embryo and are generally unicellular. 

(iv)SEEDS ARE INSIDE THE FRUIT OR NAKED?

• Angiospermae: These are plants with seeds inside the fruit and bears flowers. 
• Gymnospermae: These are plants with naked seeds and do not bear flowers. 

DIVISION 1: THALLOPHYTA

(i) Basic and elementary plants with undifferentiated body parts. 
(ii) Generally called algae. 
(iii) No vascular tissue present. 
(iv) Reproduce through spores. 
(v) Mainly found in water. 
(vi) Example: Ulva, Spirogyra, Ulothrix, Cladophora, Chara. 

DIVISION 2: BRYOPHYTE

(i) Body structure differentiated but not fully developed. 
(ii) No vascular tissues present. 
(iii) Reproduce through spores. 
(iv) Found on both land and water therefore known as ‘Amphibians of Plantae Kingdom’. 
(v) Example : Liverwort (Marchantia, Riccia), Mosses (Funaria), Hornwort (Dendrocerous). 

DIVISION 3: PTERIDOPHYTA

(i) Differentiated body structure – leaves, stems, roots, etc. 
(ii) Vascular tissues present. 
(iii) Reproduce through spores. 
(iv) Examples : Marsilea, fern, horsetails. 

DIVISION 4: GYMNOSPERMS

(i) Differentiated body parts. 
(ii) Vascular tissues. 
(iii) Naked seeds without fruits or flowers. 
(iv) Perennial, evergreen and woody. 
(v) Examples : Pines (deodar), Cycus, Ginkgo. 

DIVISION 5: ANGIOSPERMS

(i) Also known as flower-bearing plants. 
(ii) Later on flower becomes fruit. 
(iii) Seeds are inside the fruit. 
(iv) Embryos in seeds have structure called cotyledons. 
They are also called seed leaves because in many plants they emerge and become green when they germinate. 
Angiosperms are further divided on the basis of number of cotyledons into two parts i.e. Monocots and Dicots. 

KINGDOM V: ANIMALIA

Basis of classification of Animalia kingdom:

(i)Symmetry

  • Bilateral symmetry: It is when an organism can be divided into right and left halves, identical but mirror images, by a single vertical plane.
  • Radial symmetry: It is when an organism is equally spaced around a central point, like spokes on a bicycle wheel.

(ii)Germ Layers

In embryonic stages there are different layers of cells called germ cells.
The three different types of germ cells are:

(i) Ectoderm: It is the outermost layer which forms nail, hair, epidermis, etc.
(ii) Endoderm: It is the innermost layer which forms stomach, colon, urinary, bladder, etc.
(iii) Mesoderm: It is the middle layer between ectoderm and endoderm which forms bones, cartilage, etc.

According to the number of germ layers present in embryonic stage, animal could be:
(i) Diploblastic: Organisms which are derived from two embryonic germ layers (ecto and endo).
(ii) Triploblastic: Organisms which are derived from all the three embryonic germ layers.

(iii)Coelom

Body cavity or coelom is important for proper functioning of various organs.
For example, heart which has to contract and expand needs some cavity or empty space, which is provided by the coelom. On the basis of presence or absence of coelom, organisms are divided into:
(i) Acoelomates: These are the simple organisms having no body cavity.
(ii) Coelomates: These are complex organisms having true cavity lined by mesoderm from all sides. These are further sub-divided into schizocoelomates or protostomes (coelom formed due to splitting or mesoderm) and enterocoelomates or dueterostomes (coelom formed from pouches pinched off from endoderm).
(iii) Pseudo coelamate: These are organisms having false coelom. They have pouches of mesoderm scattered between endoderm and ectoderm.

(iv)Notochord

  • It is a long rod like structure, which runs along the body between nervous tissues and gut and provides place muscle to attach for ease of movement.
  • Organisms could be:
    • without notochord
    • with notochord
    • with notochord in initial embryonic stages and vertebral column in adult phase.

PHYLUM 1: PORIFERA OR SPONGES

(i) Cellular level of organization 
(ii) Non-motile animals 
(iii) Holes on body which led to a canal system for circulation of water and food 
(iv) Hard outside layer called as skeletons 
(v) Examples: Sycon, spongilla, euplectelia 

PHYLUM 2: COELENTERATA

(i) Tissue level of organization 
(ii) No coelom 
(iii) Radial symmetry, diploblastic 
(iv) Hollow gut 
(v) Can move from one place to another 
(vi) Examples: Hydra, sea anemone, jelly fish (solitary), corals (colonies) 

PHYLUM 3: PLATYHELMINTHES

(i) Also called flat worms 
(ii) No coelom present 
(iii) Bilateral symmetry, triploblastic 
(iv) Free living or parasite  
(v) Digestive cavity has one opening for both ingestion and egestion 
(vi) Examples: Planaria (free living), liver fluke (parasitic) 

PHYLUM 4: MOLLUSCA

(i) Coelom present 
(ii) Triploblastic, bilateral symmetry 
(iii) Soft bodies sometimes covered with shell 
(iv) Generally not segmented 
(v) No appendages present 
(vi) Muscular foot for movement 
(vii) Shell is present 
(viii) Kidney like organ for excretion 
(ix) Examples: Chiton, octopus, pila, unio 

PHYLUM 5: ANNELIDA

(i) Second largest phylum 
(ii) Coelom present 
(iii) Bilateral, triploblastic 
(iv) Segmented (segments specialized for different functions) 
(v) Water or land 
(vi) Extensive organ differentiation 
(vii) Examples: Earthworm, leech, nereis 

PHYLUM 6: ARTHROPODA

(i) Largest phylum (consist of 80% of species) 
(ii) Generally known as insects 
(iii) Coelom present 
(iv) Bilateral, triploblastic 
(v) Segmented, sometimes fused 
(vi) Tough exo-skeleton of chitin 
(vii) Joing appendages like feet, antenna 
(viii) Examples : Prawn, scorpio, cockroach, housefly, butterfly, spider 

PHYLUM 7: ECHINODERMATA

(i) Spiny skin, marine 
(ii) No notochord 
(iii) Coelom present, bilateral symmetry, triploblastic 
(iv) Endoskeleton of calcium carbonate 
(v) Water vascular system for locomotion 
(vi) Bilateral symmetry before birth and radial symmetry after birth 
(vii) Examples : Antedon, sea cucumber, star fish, echinus 

PHYLUM 8: PROTOCHORDATA

(i) Marine animals. 
(i) Bilaterally symmetrical, triploblastic and have a coelom. 
(ii) Gills present at some phase of life 
(iii) Notochord is present which is a long rod- like support structure  (chord=string) that runs along the back of the animal separating the nervous tissue from the gut. 
(iv) Notochord provides a place for muscles to attach for ease of movement. 
(v) Examples : Balanoglossus, Herdmania and Amphioxus 

PHYLUM 9: NEMATODA

(i) Bilaterally symmetrical and triploblastic. 
(ii) Body is cylindrical rather than flattened. 
(iii) Tissues, but no real organs. 
(iv) Sort of body cavity or a pseudocoelom, is present. 
(v) Familiar as parasitic worms causing diseases. 
(vi) Worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm or pinworms). 
(vii) Examples: Ascaris, Wuchereria 

PHYLUM 10: VERTEBRATA

(i) Notochord converted to vertebral column 
(ii) 2, 3, 4 chambered heart 
(iii) Organs like kidney for excretion 
(iv) Pair appendages 
(v) Examples: Humans (4-chambered), frog (3-chambered), fishes (2-chambered) 
(vi) Vertebrates are divided into five classes namely:

(a)Pisces

(b)Amphibia

(c)Reptilia

(d)Aves

(e)Mammalia. 

Warm Blooded Organisms

These are organisms which maintain same body temperature irrespective of outside temperature.
Example: Humans. Human’s body temperature is approximately 37.

Cold Blooded Organisms

These are organisms which change their body temperature as per surrounding temperature. Example : Frog.

(a)Pisces(Fishes)

  • They are fishes living in water.
  • Their skin is covered with scales or plates.
  • They respire using gills.
  • They have streamlined body and fins which help them to move in water.
  • They are cold blooded and their heart has only two chambers.
  • They lay eggs from which the young ones hatch out.
  • Fishes are divided into two categories on the basis of skeleton:
    (i) Fishes with cartilage skeleton called cartilaginous fishes. Example : Shark, Rays etc.
    (ii) Fishes with bony skeleton called bony fishes. Example : Tuna, Rohu etc.

(b)Amphibia(Amphibians)

→ They are found in land and water. 
→ They do not have scales but have mucous glands on their skin. 
→ They are cold blooded and the heart is three chambered. 
→ Respiration is through gills or lungs. They lay eggs in water.  Example: Frogs, Toads, Salamanders etc.  

(c)Reptilia(Reptiles)

  • They have scales and breathe through lungs.
  • They are cold blooded.
  • Most of them have three chambered heart but crocodiles have four chambered heart.
  • They lay eggs with hard covering in water. Example: Snakes, Turtles, Lizards, Crocodiles etc.

(d)Aves(Birds)

  • They are warm blooded animals.
  • They have four chambered heart.
  • They breathe through lungs.
  • They have an outer covering of feathers.
  • Their two fore limbs are modified into wings for flying. They lay eggs. Example: Crow, Sparrow, Pigeon, Duck, Stork, Ostrich et

(e)Mammalia(Mammals)

  • They are warm blooded animals.
  • They have four chambered heart.
  • They have mammary glands for production of milk to nourish their young ones.
  • The skin has hairs and sweat glands. Most of them give birth to their young ones.
  • Some of them lay eggs (like Platypus and Echidna). Example: Cat, Dog, Lion, Tiger, Whale, Bat, Humans etc.

NOMENCLATURE

  • An organism can have different names in different languages. This creates confusion in naming organism.
  • A scientific name is needed which is the same in all languages.
  • The binomial nomenclature system given by Carolus Linnaeus is used to name different organisms.

SOME CONVENTIONS IN WRITING THE SCIENTIFIC NAMES

(i) Genus should be written followed by the species. 
(ii) First letter of the genus should be capitalized and that of the species should be in small letter. 
(iii) When printed the name should be written in italics and when written with hands genus and species should be underlined separately. Example: Homo sapiens for humans, Panthera tigris for tiger. 

  • The contraction and relaxation of these cells result in movement.
  • Blood flows and carries various substances from one part of the body to the other.
  • Blood and muscles are both examples of tissues found in our body.
  • Different types of animal tissues, such as epithelial tissue, connective tissue, muscular tissue and nervous tissue.
  • Blood is a type of connective tissue, and muscle forms muscular tissue.

EPITHELIAL TISSUE

  • Always grows on some other types of tissue.
  • Cells of epithelium are set very close to each other and the tissue rests on a non-cellular basement membrane.
  • Consists of single layer of cells.
  • Blood vessels are absent and non-nervous in nature.
  • It covers all the organs and lines the cavities of hollow organs like stomach.
  • It is primarily protective in function.
EPITHELIAL TISSUE

TYPES OF EPITHELIUM

Epithelium tissues are classified as :

  • Squamous epithelium,
  • Cubical epithelium,
  • Columnar epithelium and
  • Ciliated epithelium.

(i)SQUAMOUS EPITHELIUM

  • It is also called pavement epithelium.
  • Cells arranged end to end like tiles on a floor.
  • Cells are polygonal in surface view.
  • It forms the delicate lining of cavities (mouth, oesophagus, nose, pericardium, alveoli etc.) blood vessels and covering of the tongue and skin.
  • Epithelial cells are arranged in many layers (stratum) to prevent wear and tear in skin.
    This pattern is stratified squamous epithelium.
SQUAMOUS EPITHELIUM

(ii)CUBICAL EPITHELIUM

  • They are cube like cells that fit closely, cells look like squares in section, but free surface appears hexagonal.
  • It is found in kidney tubules, thyroid vesicles & in glands (salivary glands, sweat glands).
  • It forms germinal epithelium of gonads (testes & ovaries).
  • It involves in absorption, excretion & secretion. It also provides mechanical support.
CUBICAL EPITHELIUM

(iii)COLUMNAR EPITHELIUM

  • Columnar means ‘pillar-like’ epithelium. It forms lining of stomach.
  • Small intestine & colon, forming mucous membranes.
  • Border of micro villi is present at the free surface end of each cell which increases absorption efficiency in small intestine.
COLUMNAR(CILIATED) EPITHELIUM

(iv)CILIATED EPITHELIUM

  • Cells may be cubical or columnar.
  • On its free surface are present protoplasmic outgrowths called cilia.
  • It helps in the movement of ova in the fallopian tube.

CONNECTIVE TISSUE

  • The cells of the connective tissue are widely spaced and embedded in an intercellular matrix.
  • The mature of matrix decides the function of tissue.
  • White and yellow fibres are present in the matrix.
  • Their basic function is to provide support to different organs & keeping them in place.

(i)FLUID OR VASCULAR TISSUE

BLOOD AND LYMPH

Blood is a connective tissue, fluid matrix of blood is plasma having wandering or floating cells, called corpuscles, blood helps in the transportation of various materials such as nutritive substances, gases, excretory products, hormones etc.

PLASMA

It forms 55% part of blood. It constitute of 90-91% of water, 7% of protein (Albumin, fibrinogen, globulin), 0.9% of inorganic salt etc.

CORPUSCLES

Forms 45% part of blood.

RBCs

They are also called as erthyrocytes, containing red coloured respiratory pigment called haemoglobin that helps in transportation of oxygen.

WBCs(LEUCOCYTES)

  • They are also called ‘Soldiers of the body’.
  • They are irregular, amoeboid, phagocyte cells that protect our body by engulfing bacterial & other foreign particles.
  • They are of five types: Monocytes,Lymphocytes,Basophils,Neutrophiles,Eosinophils.

BLOOD PLATELETS OR THROMBOCYTES

They are spindle-shaped cells that are involved in clotting of blood.

(ii)SKELETAL TISSUE

  • It is hard connective tissue that forms a supportive framework of the body.
  • It is of two types: Bone and Cartilage.

BONE

  • Matrix of bone is very hard because of salts such as calcium phosphate, CaCO3 (60- 70%) etc. and a protein ossein.
  • Bone cells (osteoblasts) are embedded in this hard matrix.
  • Matrix is deposited in the form of concentric layers of lamellae formed around a central canal, the done cells occupy small spaces between the concentric layers of matrix.
  • The long bones are usually hollow containing cavity called as marrow cavity. It is full of bone marrow.

CARTILAGE

  • This tissue is elastic, less harder as compared to bones.
  • Elasticity is due to the presence of chondrin (protein).
  • Cells are called chondroblast, which is widely spaced and the matrix is reinforced by fibres.
  • It occurs at the joint of bones, in the nose, ear, trachea & larynx.
  • It provides flexibility and great tensile strength.

(iii)CONNECTIVE TISSUE

  • It is the most abundant type of connective tissue.
  • It is further divided into two types i.e Yellow fibrous connective tissue and White fibrous connective tissue.

YELLOW FIBROUS CONNECTIVE TISSUE

They are very elastic due to the presence of a network of yellow fibres in its matrix called as ligament which attaches bone to bone.

WHITE FIBROUS CONNECTIVE TISSUE

  • They are very little matrix containing abundant white fibres forming layers.
  • Bundles of this tissue are called as tendons, which attaches muscles to the bones.

(iv)AREOLAR TISSUE

AREOLAR TISSUE
  • It is the most distributed connective tissue in the body.
  • This tissue fills spaces inside organs and is found between the skin & muscles, around blood vessels, nerves and in the bone marrow.

(v)ADIPOSE TISSUE

ADIPOSE TISSUE
  • These are oval and round cells, filled with fat globules.
  • The cells are called as adipocytes.
  • It is found in the subcutaneous layer below the skin, around the heart, brain and below the eyeballs.
  • It acts as an insulator and prevents loss of heat from the body.

MUSCULAR TISSUE

  • Movements are brought about in our body with the help of muscular tissues.
  • They are long fibre-like cells called muscle fibres.
  • They are capable of contraction or relaxation.
  • Types of Muscular Tissue are Striated muscles, cardiac muscle fibres and Non-striated muscles.

(i)STRIATED MUSCLES

  • They are also called voluntary muscles because these are under the control of one’s will.
  • Muscle fibres or cells are multinucleated and unbranched.
  • Each fibre is enclosed by a thin membrane which is called sarcolemma.
  • The cytoplasm is called sarcoplasm.
  • These muscles get tired and need rest.

(ii)CARDIAC MUSCLE FIBRES

  • They are only involuntary muscles. 
  • Only found in the walls of the heart.
  • Their structure is in between the striated and non-striated muscles.
  • They are uninucleated and branched. Branches are united by intercalated disc.
  • In these muscles, rhythmic contraction and relaxation occur throughout life.

(iii)NON-STRIATED MUSCLES

  • They are involuntary muscles also called smooth muscles.
  • These muscle fibres are uninucleated and spindle-shaped.
  • They are not enclosed by a membrane but many fibres are joined together in bundles.
  • Such muscles are found in the walls of the stomach, intestine, urinary bladder, bronchi, iris of the eye etc.
  • Peristaltic movements in alimentary canal are brought about by smooth muscles.

NERVOUS TISSUE

  • Their functional unit is called as nerve cell or neuron.
  • They are highly specialized tissue due to which the animals are able to perceive and respond to the stimuli.
  • Cell body is called cyton which is covered by plasma membrane.

DENDRON

Short hair like extensions rising from cyton are Dendron which are further subdivided into dendrites.

AXON

  • Axon is a long, tail like cylindrical process with fine branches at the end.
  • Axon is covered by a sheath.
  • The Axon of one neuron is very closely placed to the dendrons of another neuron to carry impulses from one to another neuron in the form of electrochemical waves.
  • This proximity is called a synapse.
  • Cell is the structural and functional unit of life. It is the basic unit of life.
  • It is discovered by Robert Hook in 1831 in cork slice with the help of primitive microscope.
  • Leeuwenhoek (1674), discovered the free living cells in pond water with the improved microscope.
  • Robert Brown discovered the nucleus in the cell in 1831.
  • Purkinje coined the term ‘protoplasm’ for the fluid substance of the cell in 1839.

THE CELL THEORY

  •  The theory that all the plants and animals are composed of cells and the cell is the basic unit of life, was presented by two biologists, Schleiden and Schwann.
  • The cell theory was further expanded by Virchow by suggesting that all cells arise from pre-existing cells.

TYPES OF ORGANISMS

On the basis of no. of cells, organisms are of two types:
(i) Unicellular Organism 
(ii) Multicellular Organism 

(i)UNICELLULAR ORGANISMS

These organisms are single celled which perform all the functions. Example: Amoeba, paramecium, bacteria.

(ii)MULTICELLULAR ORGANISMS

Many cells grouped together to perform different function in the body and also form various body parts. Example: fungi, plants, animals.

CELLS

  • The shape and size of the cell are different according to the kind of function they perform. There is a division of labour in cells.
  • Each cell has a certain kind of cell organelles to perform a different type of function like mitochondria for respiration.

TYPES OF CELLS

There are two types of cells: 
(i) Prokaryotes 
(ii) Eukaryotes 

DIFFERENCE BETWEEN PROKARYOTES AND EUKARYOTES

DIFFERENCE BETWEEN ANIMAL CELLS AND PLANT CELLS

ANIMAL CELL
PLANT CELL

DIFFUSION

  • The spontaneous movement of a substance from a region of high concentration to the region of low concentration is called diffusion.
  • Some substances like carbon dioxide or oxygen can move across the cell membrane by a process called diffusion. Cell also obtains nutrition from the environment.

OSMOSIS

  • The movement of water molecules through selectively permeable membrane along the concentration gradient is called osmosis.
  •  Plant cell tend to obtain water through osmosis.

HYPERTONIC OR HYPOTONIC OR ISOTONIC

What happened to the cells in the sugar or salt solution?

PLASMA MEMBRANE OR CELL MEMBRANE

  • This is the outermost covering of the cell that separates the contents of the cell from its external environment.
  • The plasma membrane allows or permits the entry and exit of some materials in and out of the cell.
  •  It also prevents movement of some other materials. The cell membrane is called selectively permeable membrane.
  •  It is made up of lipid and protein.

PROPERTIES OF PLASMA MEMBRANE

  • It is flexible (made up of organic molecules called lipids and proteins).
  • Its flexibility enables cell to engulf in food and other from the external environment.
  • This process is called endocytosis.
  • Amoeba acquire food through this process.

FUNCTIONS OF PLASMA MEMBRANE

  • It permits the entry and exit of some materials in and out of the cell.
  • It prevents movement of some other materials not required for the cell as it acts like selectively permeable membrane.

CELL WALL

  • Cell wall is another rigid outer covering in addition to the plasma membrane found in plant cell. The cell wall lies outside the plasma membrane.
  •  The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance which provides structural strength to plants.

FUNCTIONS OF CELL WALL

  • Cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external media without bursting.
  • In such media the cells tend to take up water by osmosis. The cell swells, building up pressure against the cell wall. The wall exerts an equal pressure against the swollen cell.
  • Because of cell wall, cells can withstand much greater changes in the surrounding medium than animal cells.

PLASMOLYSIS

When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.

NUCLEUS

It is called the brain of the cell as it controls all the activities of cell.

COMPOSITION OF NUCLEUS

  • The nucleus has a double layered covering called nuclear membrane.
  • The nuclear membrane has pores which allow the transfer of material from inside the nucleus to the cytoplasm.
  • The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.

FUNCTIONS OF NUCLEUS

  • The nucleus plays a central role in cellular reproduction. It is the process by which a single cell divides and forms two new cells.
  •  It also plays a crucial part, along with the environment, in determining the way the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of the cell.

FUNCTIONS OF CHROMOSOMES

  • Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein.
  •  DNA molecules contain the information necessary for constructing and organising cells. 
  • Functional segments of DNA are called genes.
  •  In non-dividing cell, this DNA is present as part of chromatin material.
  •  Chromatin material is visible as entangled mass of thread like structures. Whenever the cell is about to divide, the chromatin material gets organised into chromosomes and perform cell division.

NUCLEOID

  • In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane.
  • Such an undefined nuclear region containing only nucleic acids is called a nucleoid.

CYTOPLASM

  • The cytoplasm is the fluid content inside the plasma membrane.
  • It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

FUNCTIONS OF CYTOPLASM

  • It helps in exchange of material between cell organelles.
  • It act as store of vital chemicals such as amino acid, glucose, vitamins and iron etc.
  • It is the site of certain metabolic pathways such as glycolysis.

ENDOPLASMIC RETICULUM(ER)

  • The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
  • It looks like long tubules or round or oblong bags (vesicles).
  • The ER membrane is similar in structure to the plasma membrane. It is also made up of lipid and proteins.
  • There are two types of Endoplasmic Reticulum:
  • (i) Rough endoplasmic reticulum (RER)
  • (ii) Smooth endoplasmic reticulum (SER)

FUNCTIONS OF ENDOPLASMIC RETICULUM(ER)

  • RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on need, using the ER.
  • The SER helps in the manufacture of fat molecules, or lipids, important for cell function.
  • Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis.
  • Some other proteins and lipids function as enzymes and hormones.
  • Although the ER varies greatly in appearance in different cells, it always forms a network system.
  • One function of the ER is to serve as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus.
  • The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.
  • In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying many poisons and drugs.

GOLGI APPARATUS

  • The Golgi apparatus consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cisterns.
  • These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.

FUNCTIONS OF GOLGI APPARATUS

  • The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus.
  • Its functions include the storage, modification and packaging of products in vesicles. In some cases, complex sugars may be made from simple sugars in the Golgi apparatus.
  • The Golgi apparatus is also involved in the formation of lysosomes.

LYSOSOMES

  • Lysosomes are a kind of waste disposal system of the cell.
  • It helps to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.
  • Lysosomes have membrane-bounded structure whose sacs are filled with digestive enzymes.

FUNCTIONS OF LYSOSOMES

  • Lysosomes break foreign materials entering the cell, such as bacteria or food as well as old organelles into small pieces.
  • They contain powerful digestive enzymes which are made in RER which is capable of breaking down all organic material made in RER.
  • During the disturbance in cellular metabolism such as when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the ‘suicide bags’ of a cell.

MITOCHONDRIA

Mitochondria are known as the powerhouses of the cell.

STRUCTURE OF MITOCHONDRIA

  • Mitochondria have two membrane coverings.
  • The outer membrane is very porous while the inner membrane is deeply folded.
  • These folds create a large surface area for ATP-generating chemical reactions.

FUNCTIONS OF MITOCHONDRIA

  • The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphopshate) molecules.
  • ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work.
  • Mitochondria have their DNA and ribosomes. Therefore, mitochondria can make some of their own proteins.

PLASTIDS

  • Plastids are present only in plant cells.
  • There are three types of plastids:
    (i) Chromoplasts (coloured plastids).
    (ii) Leucoplasts (white or colourless plastids).
    (iii) Chloroplasts (contains the pigment chlorophyll).

STRUCTURE OF PLASTIDS

  • The internal organisation of the plastids consists of numerous membrane layers. Embedded in a material called the stroma.
  • Plastids also have their DNA and ribosomes like mitochondria and similar to their structure.

FUNCTIONS OF PLASTIDS

  • Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll.
  • Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.

VACUOLES

Vacuoles are storage sacs for solid or liquid contents. They are small-sized in animal cells while plant cells have very large vacuoles.

FUNCTIONS OF VACUOLES

  • The central vacuole of some plant cells may occupy 50-90% of the cell volume.
  • In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.
  • Many important substances in the life of the plant cell is stored in vacuoles which include amino acids, sugars, various organic acids and some proteins.
  • In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has consumed.
  • In some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.
  • John Dalton considered the atom to be an indivisible entity, but his concept had to be discarded at the end of nineteenth century, when scientists through experiments were able to find existence of charged (electrons and protons) and neutral particles (neutrons) in the atom.
  • These particles were called the ‘Sub-atomic Particles’.

DISCOVERY OF ELECTRONS-CATHODE RAYS(BY J.J. THOMSON)

Thomson explained presence of electrons by cathode rays experiment.

FACTS ABOUT ELECTRONS

  • Charge on electron = −1.6 × 10-19 C (C = Coloumb) (As calculated by Robert E. Millikan)
  • Mass of electron = 9.1 × 10-31 kg

DISCOVERY OF PROTONS-ANODE RAYS/CANAL RAYS(BY E. GOLDSTEIN)

E. Goldstein by his famous anode rays/canal rays experiment was able to detect presence of positively charged particles called protons in the atom.

FACTS ABOUT PROTONS

  • Charge on proton = + 1.6 × 10-19 C
  • Mass of proton = 1.673 × 10-24 gm
    i.e., Mass of proton ≅ 1840 × Mass of electron

DISCOVERY OF NEUTRONS(BY J. CHADWIK)

  •  J. Chadwick bombarded lighter elements (like lithium, boron etc.) with α-particles and observed emission of new particles having zero charge but having mass equal to that of proton.
  • These particles were called ‘Neutron’ i.e., neutral particle of the atom. 
  • Neutron are absent in Protium isotope of hydrogen atom.(1H1)
  • Since, mass of electrons are negligible as compared to that of proton and neutrons hence, sum of masses of protons and neutrons in an atom will compose its atomic mass.

ATOMIC MODELS

From the knowledge of existence of subatomic particles like electron, proton and neutron in an atom, various atomic models were proposed by different scientists.

SOME ATOMIC MODELS

  • Thomson’s Model of Atom
  • Rutherford’s Model of Atom
  • Bohr’s Model of Atom
  • The most trusted and scientifically established model of atom which is adopted these days is ‘Quantum Mechanical Model of Atom’. It will be dealt in higher classes.

THOMSON'S ATOMIC MODELS

  • This model is often called the ‘Water Melon Model’.
  • In this model, Thomson predicted the presence of electrons inside positive sphere (made up of protons), just same as seeds of watermelon are embedded in red edible part of watermelon.
  • Although this model explained neutrality of atom but couldn’t able to explain other scientific experiments conducted on atom. Hence it was discarded.
THOMSON'S MODEL OF AN ATOM

RUTHERFORD'S ATOMIC MODELS

In his famous ‘α-ray Scattering Experiment’, Rutherford bombarded α-ray (Helium nucleus 2He4) upon thin gold foil.

SCATTERING OF ALPHA PARTICLES BY A GOLD FOIL

OBSERVATIONS MADE BY RUTHERFORD IN HIS EXPERIMENT

(i) Most of α-particles passed through gold foil undeflected.
(ii) Some of the α-particles deflected by foil by small angles.
(iii) One out of every 12000 particles appeared to rebound.

CONCLUSIONS MADE BY RUTHERFORD

(i) Atom consists of predominantly empty space as most of α-particles passed through gold foil undeflected.  
(ii) Atom contains centrally placed positively charged nucleus (carrying positively charged particles), because few α-particles suffered deflected and very few i.e., one in 12000 bounced back. 
(iii) Since a minute fraction of α-particles suffered deflections and very few bounced back, this lead to conclusion that most of the space an atom is empty and the space occupied by nucleus is negligible compared to this empty space. Size of nucleus was about 10-5 times that of size of atom. 
(iv) Whole of the atomic mass concentrated in the nucleus. 

FEATURES OF RUTHERFORD PROPOSED MODEL OF ATOM

(i) There is positively placed nucleus in an atom. Nearly all the mass resides in nucleus (Proton + Neutron). 
(ii) Electrons revolves round the nucleus in well defined orbits.  
(iii) Size of nucleus is very small compared to the size of atom. 

DRAWBACKS OF RUTHERFORD'S MODEL(UNSTABILITY OF ATOM)

  • According to Rutherford, electrons revolve round the nucleus in well-defined orbits, but electrons being charged particles will lose their energy and finally will fall into the nucleus.
  • This will make atom highly unstable.
  • This was the major drawback of Rutherford which was unexplained by him.
  • To overcome drawbacks of Rutherford’s Model, Neil Bohr in 1912 proposed modified model of structure of atom.

ASSUMPTIONS MADE BY NEIL BOHR

  • Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.
  • While revolving in discrete orbits, the electrons do not radiate energy.
  • Energy is emitted or absorbed by an atom only when an electron moves from one orbit to another.

ATOMIC NUMBER

  • The total number of proton lying in the nucleus of any atom is called the atomic number.
  • An atomic number is the identity of an atom, changing atomic number means changing the atom.
  • Atomic number is denoted by ‘Z’.
  • Atomic number = no. of protons or a neutral atom, no. of protons and electrons are equal.

MASS NUMBER

  • It is the sum of total number of protons and no. of neutrons lying in the nucleus of an atom.
  • It is denoted by ‘A’.
  • Mass number = no. of protons + no. neutrons
  • Representation of an atom: ZEA or AZE (E= symbol of an element)
    Example: Calculate number of protons, electrons and neutrons for 17Cl35 or 3517Cl
    Since Cl is neutral,
    No. of electrons = no. of protons = 17
    Mass no. of Cl = 35
    No. of neutrons = 35 – 17 =18

DISTRIBUTION OF ELECTRONS IN VARIOUS SHELLS

The distribution of electrons in various shells is done in accordance to ‘Bohr-Bury Scheme’.

BOHR-BURY SCHEME

(i) The filling of electrons in an atom is done in accordance to ‘2n2’, where ‘n’ is the number of shell and ‘2n2’ represents the total number of electrons that can be accommodated in that particular shell. Maximum number of electrons that can be filled in particular shell.
If n = 1, i.e., K = shell, 2n2 = 2×12 = 2 electrons
If n = 2, i.e., L = shell, 2n2 = 2×22 = 8 electrons
If n = 3, i.e., M = shell, 2n22 = 2×32 = 18 electrons
If n = 4, i.e., N = shell, 2n2 = 2×42 = 32 electrons
(ii) The outermost shell can’t hold more than 8 electrons, while second last shell can’t have more than 18 electrons, even though they may have capacity to hold more electrons. Example: ‘Ca20’, the electron distribution will be :
Ca20 = 2(K), 8(L), 8(M), 2(N)
But Ca20 = 2, 8, 10 is wrong although ‘M’ shell can contain upto 18 electrons.

A FEW ENERGY LEVELS IN A CELL
(iii) The outermost shell can’t hold more than 2 electrons and the penultimate shell can’t hold more than 8 electrons unless the preceding inner shell (antepenultimate shell) is filled completely obeying ‘2n2’ rule. Some examples: Ka19 = 2, 8, 8, 1 Al13 = 2, 8, 3 F9 = 2, 7 Ne10 = 2, 8 Na11 = 2, 8, 1

VALENCE SHELL AND VALENCE ELECTRONS

  • From the Bohr-Bury sequence, we know that the maximum number of electrons that can be accommodated in the outermost shell is 8.
  • Every element has an urge to have 8 electrons in its outermost shell, in achieving 8 electrons an atom can either gain electrons or lose electrons.
  • The number of electrons lost or gained by an element in achieving 8 electrons in its outermost shell will be called its Valence.
  • For elements like H, He, Li, Be and B, these elements lose their outermost electron to achieve 2 electrons in their outermost shell. These elements will have valence as per this act.

ISOTOPES

Isotopes are atoms of the same elements having the same atomic number and different mass numbers. Example: Chlorine has two isotopes of mass numbers 35 and 37 respectively 17Cl35, 17Cl37

USES OF ISOTOPES

(i) Uranium isotope is used as fuel in nuclear reactor. 
(ii) Isotope of cobalt is useful in the treatment of cancer. 
(iii) An isotope of iodine is used in the treatment of goitre. 

ISOBARS

  • Isobars are the atoms of those elements which have the same mass number but different atomic numbers are called isobars.
  • 20Ca40 and 18Ar40 have the same mass number and different atomic number. 11Na24 and 12Mg24 are other examples.
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