When we throw a ball on the floor it starts moving with some velocity.
But once it is rolled ideally no force is acting in the direction of motion and according to Newton’s first law the ball should keep on rolling but this does not happen.
The ball stops after moving a certain distance so a force must be acting on it.
That force is known as friction.

WHAT IS FRICTION?

Friction is defined as:

The resistance offered by the surfaces that are in contact with each other when they move over each other.
Friction works in the opposite direction in which the body is moving, making the body slow down.
Friction is useful in most of these.
Friction is also dependent on external factors.

FACTORS AFFECTING FRICTION

Following are the two factors on which friction depends:

1. On the nature of the two surfaces that are in contact
Friction is dependent on the smoothness or roughness of the two surfaces that are in contact with each other. When the surface is smooth, the friction between the two reduces as there is no much interlocking of irregularities taking place. While the surface is rough, friction increases.

2. On the force that is acting on these surfaces
When force is applied along with the irregularities, friction increases.

WHAT CAUSES FRICTION?

1. When we see any object, we can see the smooth surface but when the same object is viewed under a microscope, it can be seen that even the smooth appearing object has rough edges.
2. Tiny hills and grooves can be seen through the microscope, and they are known as irregularities of the surface.
3. So, when one object is moved over the other, these irregularities on the surface get entangled giving rise to friction.
4. The more the roughness, the more will the irregularities and greater will be the force applied.

FRCITION CAN BE REDUCED BY USING :

1. Grease, oil, powder, ball bearing, and cushion of dry air between the moving surfaces.
2. Using anti-friction alloys.

FRCITION CAN BE INCREASED BY :

1. Making a surface rough.
2. The sole of the shoes and the tyres of the vehicle are treated to increase friction.

LUBRICANTS

The substance which reduces the friction are called lubricants. Examples: PE waxes, paraffin, metal soaps, esters (high esterification), amides, and fatty acids.

TYPES OF FRICTION

There are four types of friction:

1. STATIC FRICTION

1. Static friction is defined as the frictional force that acts between the surfaces when they are at rest.
2. The magnitude of the static force is equal in the opposite direction when a small amount of force is applied. When the force increases, at some point maximum static friction is reached.

EXAMPLES OF STATIC FRICTION :

Following are the examples of static friction:
1. Skiing against the snow
2. Creating heat by rubbing both the hands together
3. Table lamp resting on the table

2. SLIDING FRICTION

Sliding friction is defined as the resistance that is created between any two objects when they are sliding against each other.

EXAMPLES OF SLIDING FRICTION :

Following are the examples of sliding friction:
1. Sliding of the block across the floor
2. Two cards sliding against each other in a deck

3. ROLLING FRICTION

Rolling friction is defined as the force which resists the motion of a ball or wheel and is the weakest types of friction.

EXAMPLES OF ROLLING FRICTION :

Following are the examples of rolling friction:
1. Rolling of the log on the ground

2. Wheels of the moving vehicles

4. FLUID FRICTION

Fluid friction is defined as the friction that exists between the layers of the fluid when they are moving relative to each other.

EXAMPLES OF FLUID FRICTION :

Following are the examples of fluid friction:
1. The flow of ink in pens
2. Swimming

APPLICATIONS OF FRICTION:

1. Friction finds application when matchsticks are ignited.
2. Motion of pistons in a cylinder is an application of friction.
3. It is possible to write on books and board as there is friction between pen and the board.

A push or pull exerted by an object on another is a force. Force arises due to the interaction between at least two objects.

Force has both Magnitude and Direction. Force applied on an object in the same direction add to one another. If the two forces act in the opposite direction on an object, the net force acting on it is the difference between the two forces. In general, more than one force may be acting on an object at any given point. However, a force acting on an object is always the mean net force acting on it.

Two friends pushing a heavy load (a) in the same direction and (b) in the opposite direction. A Force can Change the State of Motion. A change in the speed of an object or the direction of its motion or both implies a change in its state of motion. Force acting on an object may bring a change in its state of motion or a change in its shape. Ex: A rubber band suspended from a hook/nail fixed on a wall. By hanging a weight or by pulling its free end.

Types of Forces

1. Contact Forces

The forces act on a body when the source of force is in actual contact with the body. (i) Muscular Force: The force exerted by the muscles of the body. (ii) Mechanical Force: The force produced by a machine. (iii) Frictional Force: The force that opposes the motion of an object.

2. Non-Contact Forces

Forces that do not involve physical contact between two bodies on which they act. (i) Magnetic Force: A magnet exerts a non-contact force on objects made of iron, steel, cobalt or nickel. (ii) Electrostatic Force: The force which results due to repulsion of similar charges or attraction of opposite charges. (iii) Gravitational Forces: The force that exists between any two masses because of their mass.

Thrust

The force that acts on a surface in a direction perpendicular to it, is known as thrust.

Pressure

The force acting on per unit area, applied to an object in the direction perpendicular to the surface is called pressure. Liquids exert pressure on the walls of the container in which they are kept. Gases exert pressure in all directions.

Atmospheric Pressure

The pressure exerted by atmospheric air around us is known as atmospheric pressure.

Reproduction

It is one of the important life processes, which ensures the continuation of similar kinds of individuals (species) generation after generation.

Modes of Reproduction

There are two modes by which animals reproduce:

Sexual Reproduction

The process of reproduction, which results from the fusion of male and female gametes is called sexual reproduction.

Male Reproductive Organs

Male reproductive organs are a pair of testes, sperm ducts, and a penis. The testes produce the male gametes called sperms.

Female Reproductive Organs

The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and the uterus. Ovary produces females gametes called ova (Egg).

Fertilisation

In human beings, a single matured egg is released into the oviduct by one of the ovaries every month. Uterus is the part of the female reproductive system where the development of the embryo takes place. Both sperm and ova are single-celled structure. The fusion of the ovum and the sperm is called fertilisation.

1. Internal Fertilisation

Fertilisation that takes place inside the female body is called internal fertilisation. This is observed in human beings and other animals such as cows and dogs.

2. External Fertilisation

Fertilisation that takes place outside the female body is called external fertilisation. This is common in aquatic animals such as frogs, fish, starfish, etc.

During fertilisation, the nuclei of the sperm (n) and the egg in) are fused to form a single nucleus (2n). This fertilised egg is called zygote.

The zygote divides repeatedly to give rise to a ball (mass) of cells. The cells then begin to differentiate into various tissues. This developing structure is called an embryo .

From the above figure:
(a) Zygote formation and development of an embryo from the zygote (b) Ball of cells (enlarged)
(c) Embedding of the embryo in the uterus (enlarged)
The embryo gets implanted within the wall of the uterus, i.e., endometrium for further development. The stage of the embryo in which all the body parts are identifiable is called a foetus.

The animals which give birth to young ones are called viviparous animals. The animals which lay eggs are called oviparous animals. The transformation of larva into an adult through drastic changes is called metamorphosis.

Asexual Reproduction

The type of reproduction in which only a single parent is involved, is called asexual reproduction.

Types of Asexual Reproduction

In small animals like a hydra, new individuals develop from buds. This method of asexual reproduction is called budding.

1. Bud

A lateral outgrowth from the parent body that assumes the shape of the parent. It ultimately gets detached and behaves as a new individual.

2. Binary Fission

In binary fission, a single-celled individual reproduces by dividing itself into two. Example: Amoeba.

3. Tadpoles

In the life process of a frog, we find three distinct stages, that is egg →tadpole → adult. These tadpoles get transformed into adults which are capable of jumping and swimming and are finally transformed into a frog.

4. Cloning

Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two organisms. Dolly was the first mammal to be cloned.

All organisms are made of smaller parts called organs. Organs are made of still smaller parts. The smallest living part of an organism is a ‘cell’.

CELL

The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane. Cells were first observed in cork by Robert Hooke in 1665.

Cells exhibit variety of shapes and sizes. Number of cells also varies from organism to organism. Some cells are big enough to be seen with the unaided eye. Ex : Hen’s egg Some organisms are single-celled, while others contain large number of cells- multi- cellular. The single cell of unicellular organisms performs all the basic functions performed by a variety of cells in multicellular organisms.

The cell has three main parts: (i) the cell membrane, (ii) cytoplasm which contains smaller components called organelles, (iii) the nucleus.

1. CELL MEMBRANE

The basic component of a cell. The cytoplasm and nucleus are enclosed within cell membrane. There is an outer thick layer in cells of plants called cell wall.

2. CYTOPLASM

The jelly-like substance present between the cell membrane and the nucleus. Various organelles present in the cytoplasm are:

(i) Mitochondria

(ii) Plastids (present only in plant cell)

(iii) Endoplasmic reticulum (ER)

(iv) Ribosome

(v) Lysosome

(vi) Vacuole

(vii) Golgi body

(viii) Centrosome (present only in animal cell).

3. NUCLEUS

Nucleus is separated from the cytoplasm by a nuclear membrane. It is generally spherical in the centre of the cell. Nuclear membrane: The nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. Nucleus contains a still smaller round body known as nucleolus. Vacuoles are empty or blank looking structures in the cytoplasm. The nucleus contains thread-like structures called chromosomes. These carry genes. Gene is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring. Cells without a well-organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells.

SIZE OF CELLS

The size may be as small as a millionth of a metre or maybe as large as a few centimetres. The size of the cells has no relation with the size of the body of the animal or plant. It is related to its function.

COMPARISON OF PLANT AND ANIMAL CELL

TABULAR COLUMN

Deforestation and Its Consequences

Deforestation: clearing of forests and using that land for other purposes.

Consequences: Deforestation increases the temperature and pollution level on the earth.
It increases the level of carbon dioxide in the atmosphere.
Groundwater level also gets lowered.

Plants need carbon dioxide for photosynthesis. Fewer trees would mean that less carbon dioxide will be used up resulting in its increased amount in the atmosphere. This will lead to global warming as carbon dioxide traps the heat rays reflected by the earth. The increase in temperature on the earth disturbs the water cycle and may reduce rainfall causing droughts. Deforestation leads to a change in soil properties. The physical properties of the soil get affected by plantation and vegetation.

Deforestation leads to desertification. How?

Fewer trees result in more soil erosion. Removal of the top layer of the soil exposes the lower, hard and rocky layers. This soil has less humus and is less fertile. Gradually the fertile land gets converted into deserts leading to desertification. Deforestation also leads to a decrease in the water holding capacity of the soil. The movement of water from the soil surface into the ground (infiltration rate) is reduced. This results in floods. As a result, the other properties of the soil like nutrient content, texture etc., also change.

Biodiversity

Occurrence of an innumerable number of different types of organisms and the whole range of their varieties (biotypes) adapted to different climates, environments and areas.
OR
Biodiversity refers to the variety of living organisms in a specific area.
Wildlife sanctuary, national park and biosphere reserve are names given to the areas meant for conservation and preservation of forest and wild animals.
Plantation, cultivation, grazing, felling trees, hunting and poaching are prohibited there.

National Parks

Areas reserved for wild life where they can freely use the habitats and natural resources. These are established at the approval of the legislature. Example: Hazaribagh National Park in Jharkhand, Desert National Park in Rajasthan, etc. Project Tiger was launched by the government to protect the tigers in the country. The objective of this project was to ensure the survival and maintenance of the tiger population in the country.

Wildlife Sanctuary

Areas where animals are protected from any disturbance to them and their habitat. Example: Jaldapara in Madarihat (West Bengal), Keoladeo Ghana in Bharatpur (Rajasthan)

Biosphere Reserve

Large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in the area. The biosphere reserves help to maintain the biodiversity and culture of that area. A biosphere reserve may also contain other protected areas. Ex: The Pachmarhi Biosphere Reserve consists of one national park named Satpura and two wildlife sanctuaries named Bori and Pachmarhi

Plants and animals of a particular area are known as the flora and fauna of that area.Flora: Different types of plants belonging to an area. Example: Silver ferns, sal, teak, mango, etc. Fauna: All animals found in an area. Example: dog, frog, insects, bull, jackal, etc.

Endemic Species

Species of plants and animals found exclusively in a particular area. These are not naturally found anywhere else. Ex: sal and wild mango examples of the endemic flora of the Pachmarhi Biosphere Reserve. Bison, Indian giant squirrel and flying squirrel are endemic fauna of this area.

Extinct Species

Species of plants and animals which have already been lost. Example: Dodo, Indian cheetah, Pink-headed duck, etc.

Threatened Species

Species that is liable to become extinct if it is not allowed to realise its full biotic potential by removed the caused of threat.

Types of threatened Species

1. Endangered Species

A species of animal or plant that is seriously at risk of extinction. Example: Indian rhinoceros, Asiatic lion, Asiatic wild ass, etc. Red Data Book contains a record of endangered species. Red Data Book is maintained internationally by an organisation. India also maintains Red Data Book for plants and animals found in India.

2. Vulnerable Species

A vulnerable species is a species of animals or plants which are likely to become endangered unless something changes. Example: Chinkara deer and blackbuck, golden langur, etc.

3. Rare Species

Species whose population are originally small and scattered in the world.

Migration

Migration is the phenomenon of movement of a species from its habitat to some other habitat for a particular period every year for a specific purpose like breeding.
OR

It is the regular, periodic, two-way movements of birds and some animals from their place of residence to some other place along well-definedroutes. It is linked to seasonal factors, breeding, shortage of foods, etc. The Bharatpur bird sanctuary is known for migratory birds.

Reforestation

It is the restocking destroyed forests by planting new trees. The planted trees should generally be of the same species which were found in that forest. Reforestation can take place naturally also. When the deforested area is left undisturbed, it re-establishes itself. In natural reforestation, there is no role of human beings.

Metals and non-metals are used widely in everyday life. Metals can be distinguished from non-metals on the basis of their physical and chemical properties.

Uses of Metals and Non-metals

Metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils, water boilers, etc. Non-metals used in fertilisers to enhance the growth of plants, in the water purification process, in crackers, in the purple coloured solution which is applied on wounds as an antiseptic (iodine).

Combustion is a chemical process in which a substance reacts with oxygen to give off heat. The substance that undergoes combustion is said to be combustible. It is also called fuel. The fuel may be solid, liquid or gas. Oxygen (in the air) is essential for combustion. During the process of combustion, heat and light are given out. The lowest temperature at which a substance catches fire is called its ignition temperature. The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. Ex: petrol, alcohol, Liquified Petroleum Gas (LPG) etc

Types of Combustion

Spontaneous combustion of coal dust has resulted in many disastrous fires in coal mines. Spontaneous forest fires are sometimes due to the heat of the sun or due to lightning strike.

Flame

It is a zone or burning vapour. The substances which vapourise during burning give flames. Example: Kerosene oil and molten wax.

There are three different zones of a flame – dark zone, luminous zone and non-luminous zone.

Fuel

An ideal fuel is cheap, readily available, readily combustible and easy to transport. It has a high calorific value. It does not produce gases or residues that pollute the environment. Fuels differ in their efficiency and cost.

Fuel Efficiency

The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg).

Effects of Burning of Fuels

(i) Carbon fuels like wood, coal petroleum release unburnt carbon particles. These are dangerous pollutants causing respiratory diseases, such as asthma. (ii) Incomplete combustion of carbon fuels gives carbon monoxide which is a poisonous gas. (iii) Increased concentration of carbon dioxide in the air is believed to cause global warming. (iv) Oxides of Sulphur and nitrogen dissolve in rainwater and form acids. Such rain is called acid rain. It is very harmful to crops, buildings and soil. (v)Unburnt carbon particles in the air are dangerous pollutants causing respiratory problems. (vi)Incomplete combustion of fuel gives poisonous carbon monoxide gas. (vii) an Increased percentage of carbon dioxide in the air has been linked to global warming.

Natural Resources

Resources include everything provided by the nature. They form the wealth of a country.

Types of Natural Resources:

(i) Inexhaustible: There are some resources that are present unlimited in nature and will not be exhausted even if used continuously. Ex: Sunlight, Air. (ii) Exhaustible: These resources are limited and can soon get exhausted because of their excessive use. Ex: Forests, wildlife, minerals, coal, petroleum, etc.

Fossil Fuels

Fossil fuels were formed from the dead remains of living organisms millions of years ago. Fossil fuels are exhaustible resources. Coal, petroleum and natural gas are fossil fuels.

1. Coal

Coal, one of the most important primary fossil fuels, a solid carbon-rich material that is usually brown or black and most often occurs in stratified sedimentary deposits. Coke, coal tar and coal gas are the products of coal.

i. Coke

It is a tough, porous and black substance. It is an almost pure form of carbon. Coke is used in the manufacture of steel and in the extraction of many metals.

ii. Coal Tar

It is a black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances.

Uses of Coal Tar:

Used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Naphthalene balls used to repel moths and other insects are also obtained from coal tar.

iii. Coal Gas

Coal gas is obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near coal processing plants.

2. Petroleum

Petrol and diesel are obtained from a natural resource called petroleum. The word petroleum is derived from petra (rock) and oleum (oil) as it is mined from between the rocks under Earth. Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, the absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas. Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by refining petroleum. Refining: Petroleum is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc. Refining is the process of refracting the various constituents/fractions of petroleum. It carried out in a petroleum refinery.

3. Natural Gas

A very important fuel as it easy to transport through pipes and can be compressed and stored under high pressure as Compressed Natural Gas. It causes no pollution and has a high calorific value. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes. Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers.

Introduction

The clothes which we wear are made of fabrics. Fabrics are made from fibres obtained from natural or artificial sources. EX- natural fibres- Obtained from plants: Wool, silk, cotton synthetic fibres-made by human beings: polyesters, terylene.

What are Synthetic Fibres?

A synthetic fibre is a chain of small units joined together. Each small unit is actually a chemical substance.

Many such small units combine to form a large single unit called a polymer.

Types of Synthetic Fibres

Rayon(also called artificial silk )

It is cheaper than silk and can be woven like silk fibres.
It is made from cellulose obtained from wood pulp.
It can also be dyed in a wide variety of colours.
It is used to make carpets , bed sheets etc.

Nylon

It is prepared from coal, water and air.
It was the first fully synthetic fibre.
Nylon fibre is strong, elastic and light.
It is lustrous and easy to wash.
It is used to make socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains, parachutes and ropes for rock climbing

Polyester

A versatile man-made fabric.
It has an outstanding characteristic of resisting wrinkle.
It is strong and soft.
Ex: Terylene
It is used in dresses, suits, rainwear etc.
PET (polyethylene terephthalate) is a very familiar form of polyester.
It is used for making bottles, utensils, films, wires and many other useful products.

Acrylic

A fibre similar to that of wool and is used to make sweater, blankets, shawls, etc.
It is lightweight, soft and warm.
It is cheaper than natural wool.
It is resistant to chemicals, moths and sunlight.

Characteristics of Synthetic Fibres

They are durable
They dry up quickly
They are less expensive
They are readily available
They are easy to maintain.

Plastics

1. Like synthetic fibres, plastic is also a polymer.
2. Some plastics have a linear arrangement of the units and some have a cross-linked arrangement of the units.
3. Example: Polythene.
4. Plastic is easily mouldable i.e. can be shaped in any form.
5. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires.

Thermoplastics : plastic which deform and bend easily on heating. Ex: Polythene and PVC

Uses: manufacturing toys, combs and various types of containers

Thermosetting plastics: plastics which when moulded once, can not be softened by heating.

Ex: bakelite and melamine.

Bakelite is a poor conductor of heat and electricity.

It is used for making electrical switches, handles of various utensils, etc.
Melamine is a versatile material.
It resists fire and can tolerate heat better than other plastics.
It is used for making floor tiles, kitchenware and fabrics which resist fire.

Characteristics of Plastics

(i) Non-reactive: Not affected by air, water, soil, etc.

(ii) Light, strong and durable: Light, strong and durable and can be moulded into different shapes and sizes.

(iii) Poor Conductors: Do not allow heat and electricity to flow through them.

Effect of Plastics on Environment

Natural materials like wood and paper are biodegradable (bio = living; degeradable = able to broken down).
In contrast, most plastics do not decay, therefore, they are non-biodegradable.
The lightweight nature of plastics can also be a problem.
Burning of plastics also release poisonous fumes into the atmosphere thus polluting the environment.

We need to use synthetic fibres and plastics in such a manner that we can enjoy their good qualities and at the same time minimise the environmental hazards for the living communities.

During the rainy season one may have observed that moist bread gets spoilt and its surface gets covered with greyish white patches. When these patches are observed through a magnifying glass we see tiny, black rounded structures. These structures are called Microbes or Microorganisms. Microorganisms are tiny microscopic organisms that are not visible to the naked eye. They may be unicellular or multicellular. They can live in all kinds of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. Microorganisms are found in air, water and in the bodies of plants and animals. Microorganisms are classified into four major groups:

Viruses are also microscopic but are different from other microorganisms. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses.

MICROORGANISMS USES

BENEFICIAL MICROORGANISMS

They are used in:
1. The preparation of curd (Lactobacillus), bread and cake.
2. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.
3. The preparation of medicines- penicillin, antibiotics (Streptomycin, tetracycline and erythromycin ).
4. The manufacture of vaccines (substance which is used to stimulate the production of antibodies, thereby providing immunity against certain diseases.).
5. In agriculture they are used to increase soil fertility by fixing nitrogen (Cyanobacteria-blue green algae).

HARMFUL MICROORGANISMS

Some insects and animals which act as carriers of disease- causing microbes.
Ex: Housefly – carrier of harmful pathogens:
Anopheles mosquito -carries the parasite of malaria (Plasmodium).
Female Aedes mosquito – carrier of dengue virus.

1. DISEASE CAUSING MICROORGANISMS IN HUMANS

2. DISEASE CAUSING MICROORGANISMS IN PLANTS

3. DISEASE CAUSING MICROORGANISMS IN ANIMALS

1. Anthrax – caused by a bacterium.
2. Foot and mouth disease- caused by a virus.

FOOD POISONING

When food contaminated with pathogens or toxins are consumed, it causes food poisoning. The most common symptom is a pain in the stomach. In severe cases, food poisoning can also cause death.

FOOD PRESERVATION

Chemical methods:
1. Chemical preservatives are used in food preservations by major food industries as they are harmless to humans.
2. Salts and edible oils -common chemicals generally used to check the growth of microorganisms.
3. Sodium meta-bisulphate and sodium benzoate are commonly used chemical preservatives.

Preservation by common salt:
1. Common salt (sodium chloride) is used as a preserve meat and fish, amla, raw mangoes, tamarind, etc.

Preservation by Sugar:
1. Sugar is used for the preservation of jams, jellies and squashes.
2. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.

Preservation by oil and Vinegar:
1. Many food preparations like pickles are preserved by adding either oil or vinegar to them.
Bacteria cannot grow in such medium.
2. Vegetables, fruits, fish and meat can also be preserved.

Pasteurization:
1. Pasteurization is a process of superheating and cooling the beverages.
2. This prevents the growth of microbes.

Storage and Packing:
1. Dry fruits and many vegetables are preserved in airtight/air sealed containers.
2. The absence of air prevents the growth of bacteria or fungi.

NITROGEN CYCLE

Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins.

PROCESS

The atmospheric nitrogen cannot be taken directly by plants and animals.

Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.

Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system.

Nitrogen is then used for the synthesis of plant proteins and other compounds.

Animals feeding on plants get these proteins and other nitrogen compounds.

When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.

Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere.

This ensures that the percentage of nitrogen in the atmosphere remains more or less constant.