The important natural resources available on Earth are land, water and air. The region of Earth where the atmosphere, hydrosphere and lithosphere interact and support life is called biosphere. Living organisms constitute the biotic component of the biosphere. Air, water and soil constitute the abiotic component of the biosphere. Air is a mixture of gases like nitrogen, oxygen and carbon dioxide.

Plants and animals use oxygen for respiration. The combustion of fossil fuels also requires oxygen.

Combustion Respiration

Marine animals absorb atmospheric carbon dioxide and form carbonic acid. These carbonate ions are used by marine animals to make shells.

Plants use co2 for photosynthesis

The ways by which CO2 is fixed by living organisms

On the planets Venus and Mars carbon dioxide forms the major component constituting up to 95-97% of the atmosphere. On the contrary the major component of the earth’s atmosphere is air which consists of nitrogen, oxygen, carbon dioxide, argon, water vapour and trace components. Moreover, unlike Venus and Mars earth has life on it.     

Its composition is 95% CO2, 3% N2, 2% Ar and less than 1% O2.

How is our atmosphere different from the atmosphere on Venus and Mars

• The mass or body of gases that surrounds the earth or any heavenly body is called atmosphere.

• Earth’s atmosphere extends from the surface to a height of more than 1000 km, beyond which it merges gradually with solar atmosphere. Air is a bad conductor of heat and so, earth’s atmosphere acts as a protective blanket.

• It keeps the average temperature of the earth fairly steady during the day and the whole year.

• The atmosphere prevents the sudden increase in temperature during daytime and also helps in retaining heat of the earth by slowing down the escape of heat during night.    

How does the atmosphere act as a blanket?

What causes winds?• The movement of air from

one region to another creates winds An uneven heating of the Earth’s surface causes winds. On being heated, air becomes lighter and rises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves to a low pressure region, causing wind.

Air is a bad conductor of heat.

• Take an empty long test tube. Hold the test tube tilted with its mouth downwards. Heat the tube at its bottom on the flame of a candle. It is noticed that the fingers do not feel warm. This shows that th air trapped in test tube does not conduct heat from the heated bottom of the test tub to the fingers. This proves that air is a bad conductor of heat.

EXPERIMENT

The movement of air (Winds)• When air gets heated, it rises up and produces

low pressure and cool air moves in to take its place. The movement of air causes winds.

• During the day the land gets heated faster than the sea. So the hot air above the land rises up and cool air from the sea moves towards the land.

• During the night sea cools down slowly than the land. So the hot air above the sea rises up and cool air from the land moves towards the sea

Wind develops as a result of spatial differences in atmospheric pressure. Generally, these differences occur because of uneven absorption of solar radiation at the Earth's surface

Air pollution & its effects• The increase in the content of

harmful substances in the air is called air pollution.

• 1. Fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, it release oxides of sulphur and nitrogen. These oxides dissolve in rain and causes acid rain.

Smog2 Burning of fossil fuels

also release unburnt carbon particles which reduces visibility. During cold weather along with condensed water it forms smog.

City without smog

City with smog

Health disorders

Regular breathing air containing these harmful substances causes allergies, cancer, heart diseases etc.

Water bodies get heated during the day and evaporate into the air. As the vapour rises, it cools. This causes the vapour to condense into tiny water droplets, which fall down as rain.

Organisms need water because it plays a vital role in the reactions taking place within organism’s cells and body. Water acts as a universal solvent, providing a medium for the chemical reactions to occur. Substances are also transported from one part of the body to the other in the dissolved state. Therefore, it is necessary for the organisms to maintain a certain level of water within their bodies in order to stay alive.  

Importance of water in living organisms

•The dissolved fertilizers, chemicals, pesticides percolated with rain water from the fields• wastes from industries•Breeding of decomposers (micro- organisms) in water are the major sources or causes

Soil formation• Soil is formed by breaking down of rocks at

or near the surface of the Earth through various physical, chemical, and biological processes by various factors such as the sun, water, wind, and living organisms.(i) Sun:During day time, the rocks are heated. This causes the rocks to expand. During night time, these rocks cool down and contract. Since all parts of the rock do not undergo expansion and contraction at the same rate, this causes the formation of cracks in these rocks. These cracks lead to the breaking up of huge rocks into smaller pieces.(ii) Water:Water catalyses the process of formation of soil in two ways.(a) Water goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks..

• 3 Running water wears away hard rocks over long periods of time. Water moving in fast speed carries big and small particles of rock downstream. These rocks rub against each other, resulting in breaking down of rocks. These smaller particles are carried away by running water and deposited down its path.4, Wind:Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles. Living organisms:Some living organisms like lichens help in the formation of soil. Lichens also grow on rocks. During their growth, lichens release certain substances, which cause the rock surface to powder down forming a thin layer of soil. On this thin layer of soil, some small plants like moss also grow. They further cause the breaking down of the rock particles

• (iv) Living organisms:Some living organisms like lichens help in the formation of soil. Lichens also grow on rocks. During their growth, lichens release certain substances, which cause the rock surface to powder down forming a thin layer of soil. On this thin layer of soil, some small plants like moss also grow. They further cause the breaking down of the rock particles

Living organisms depend on soil• The top surface layer of earth capable of supporting plant life is called

soil. Soil is a complex mixture, comprising of minerals (45%), organic matter (5%), water (25%), air (25%) and living organisms. It is an important resource that determines the diversity of life in an area. Plants are dependent on the soil from where they obtain various types of minerals, water and air. All these three components are essential for the growth of plants. Animals (herbivores) depend on plants for food. Other animals (carnivores) depend on these herbivores. Hence, all living organisms directly or indirectly depend on the soil.

• Aquatic organisms are not entirely independent of soil as a resource. Microscopic decomposers (e.g. fungi, archaebacteria and bacteria) present in the bottom sediments of water bodies decompose dead, decaying organic matter into simple, inorganic substances (minerals). The latter get dissolved in water and are available as nutrients for aquatic plants and they indirectly through plants to animals. Also, water bodies get supply of minerals from soil through rivers, spring etc. without which minerals present in the water bodies will exhaust. Aquatic green plants and animals get these minerals from water

Composition of soil

Soil is a mixture of rock particles, decayed organisms called humus, living organisms, minerals, air and water. The amount of minerals, humus, air and water are the factors which decides the biodiversity in that area.

Soil pollution• The addition of harmful substances which

affects the fertility of the soil and kills the diversity of organisms living in it is called soil pollution.

• Soil pollution is caused by the excessive use of fertilisers and pesticides. It kills the organisms like earthworms and bacteria which makes the soil rich in humus. The removal of useful components and addition of other harmful substances reduces the fertility of soil and causes soil pollution.

Soil erosion The carrying away of soil from one place to the other by flowing water and wind is called soil pollution. Large scale deforestation also causes soil erosion. Soil erosion can reduced or prevented by vegetative cover on the ground, afforestation, construction of bunds, terraces, dams etc.Activity :- Effect of flowing water on top soil. Take two trays of the same size and fill them with soil. Plant mustard or green gram in one of the trays. Water both the trays for a few days till the first tray is covered by plant growth. The tilt both the trays at the sane angle. Pour equal amount of water gently on both the trays. More soil is carried out of the tray which did not have plant growth. This shows that vegetative cover reduces soil erosion.

Biogeochemical cycles :- Biogeochemical cycles are the transfer of matter and energy between the biotic and abiotic components of the biosphere. The common biogeochemical cycles are :- i) Water cycle, ii) Nitrogen cycle, iii) Carbon cycle iv) Oxygen cycle..

Water cycle• When water bodies are heated

during the day, a large amount of water evaporates and rises up. Some water vapour also get into the atmosphere due to biological activities like transpiration and respiration.

• As the water vapour rises, it cools and condenses to form tiny droplets of water. This appears as clouds. When the tiny droplets of water join together to form bigger drops of water, they fall down as rain, snow

• Some of this water enters the ground and forms ground water. When water flows from the land to the seas it carries many nutrients and minerals which are used by marine organisms

Nitrogen cycle• The nitrogen in the atmosphere is fixed into nitrogen

compounds in the soil by nitrogen fixing bacteria in the root nodules of leguminous plants and also during lightning. These nitrogen compounds are taken by plants and used to make proteins. When animals eat plants they also get proteins.

• When plants and animals die, bacteria convert the proteins into nitrogen compounds like nitrites and nitrates. Other bacteria convert these nitrogen compounds back into nitrogen in the atmosphere.

• Nitrogen is an essential component of biological molecules like proteins, nucleic acids and some vitamins

NITROGEN CYCLE

Nitrogen in atmosphere

Nitrogenfixation

ProtoplasmIn plants

Protoplasmin animals

Ammonia

NitrificationAmmonification

Atmospheric fixation

Nitrification

Nitrates

Nitrites

Dentrification

Carbon in the form of carbon dioxide is used by plants to prepare glucose by the process of photosynthesis. The glucose is used to provide energy and to convert into other organic compounds When animals eat plants it enters the body of animals. During respiration energy and carbon dioxide are produced. The carbon dioxide goes back into the atmosphere. Another process which adds carbon dioxide back into the atmosphere is the combustion of fuels like coal and petroleum. The organic compound in plants and animals are also converted into carbonates, limestone, coal, petroleum, exoskeletons (shells) of some animals. Carbon is an essential component of biological molecules like carbohydrates, fats, proteins, vitamins, nucleic acids etc.

CARBON CYCLE

0011

Organic compoundsIn animals

CoalPetroleum

Carbonates in water

LimestoneInorganic carbonates

shells

CO2 in atmosphere

Organic compoundsIn plants

Respiration anddecomposition

Combustion

Oxygen cycle :- Oxygen in the atmosphere is used for respiration, combustion and formation of oxide of elements. Oxygen is sent back into the atmosphere during photosynthesis. Oxygen is an essential component of biological molecules like carbohydrates, fats, and proteins.

Atmospheric oxygenO2

Organic moleculesGlucose C6H1206

Photosynthesis Respiration

Carbon dioxideCO2

WaterH2O

Green house effect• A part of the sunlight incident on the

earth is reflected back in the form of infrared light. Some gases such as carbon dioxide, methane, chlorofluorocarbons (CFCs), also known as greenhouse gases, present in the earth’s atmosphere prevent the escape of heat from the earth by absorbing this infrared light which is reflected back by the earth. An increase in the percentage of this greenhouse gases in the atmosphere would cause an increase in the average temperature world-wide and this phenomena is known ‘Greenhouse Effect’.

• Thus, the heating of the atmosphere due to the absorption of infrared radiations by carbon dioxide molecules and other greenhouse gases is called the ‘Greenhouse Effect’

Oxygen & Ozone

• Oxygen is found in the atmosphere in the form of

• (i) A diatomic molecule having two atoms of oxygen, with chemical formula O2.

• (ii) A tri-atomic molecule having three atoms of oxygen, with chemical formula O3 called Ozone

Location of Ozone elayer• Ozone is present in

the tratosphere.  The stratosphere reaches 30 miles above the Earth, and at the very top

• it contains ozone. 

Functions of Ozone layer

• The ozone layer shields the entire Earth from much of the harmful ultraviolet radiation that comes from the sun.

Depletion of Ozone layer

• The main cause of this is the release of CFCs, chlorofluorocarbons.

Depletion of Ozone layer

Sources of CFCsAerosol can propellants

Refrigerant gasses

Ill effects of depletion of Ozone layer

• UV rays reach to the earth surface & cause skin cancer in human beings