Notes On Composition - CBSE Class 7 Geography
Composition of Atmosphere: The atmosphere is a layer of gases, which protects from the harmful rays of the sun. It regulates the temperature and makes life possible on the earth. All living beings on this earth depend on the atmosphere for their survival. From outer space, the earth's atmosphere, combined with the oceans, make the planet look blue. Thus earth is often referred to as the Blue Planet. The atmosphere is a mixture of many discrete gases. These gases are present in varying quantities, each with its own physical properties. The main constituents of the atmosphere are nitrogen and oxygen. It also includes other gases like carbon dioxide, argon, helium, ozone, hydrogen, water vapour and other components.  Besides, the atmosphere also has suspended dust particles. Nitrogen and oxygen are the two gases that make up the bulk of the atmosphere. Nitrogen (N2): Nitrogen is an essential constituent of all living organisms. Plants and animals need nitrogen to survive, but cannot directly breathe it in. Nitrogen-fixing bacteria take nitrogen from the air and convert it into water-soluble compounds. Plants get the nitrogen they need from the bacteria present in the soil or root nodules. These bacteria convert atmospheric nitrogen into nitrogen compounds, which can be readily absorbed by plants. This process is called nitrogen fixation. Animals acquire nitrogen either from plants or from other animals. Oxygen (O2): Oxygen is the second most plentiful gas in the air. The oxygen content in air remains constant due to the constant exchange of the gas through the processes of photosynthesis and respiration. The balance of oxygen the air gets disturbed mainly due to deforestation. Carbon dioxide (CO2): Carbon dioxide is another important gas. The CO2 content in air remains constant due to photosynthesis and respiration. Plants use carbon dioxide exhaled by humans and animals in the process of photosynthesis.

#### Summary

Composition of Atmosphere: The atmosphere is a layer of gases, which protects from the harmful rays of the sun. It regulates the temperature and makes life possible on the earth. All living beings on this earth depend on the atmosphere for their survival. From outer space, the earth's atmosphere, combined with the oceans, make the planet look blue. Thus earth is often referred to as the Blue Planet. The atmosphere is a mixture of many discrete gases. These gases are present in varying quantities, each with its own physical properties. The main constituents of the atmosphere are nitrogen and oxygen. It also includes other gases like carbon dioxide, argon, helium, ozone, hydrogen, water vapour and other components.  Besides, the atmosphere also has suspended dust particles. Nitrogen and oxygen are the two gases that make up the bulk of the atmosphere. Nitrogen (N2): Nitrogen is an essential constituent of all living organisms. Plants and animals need nitrogen to survive, but cannot directly breathe it in. Nitrogen-fixing bacteria take nitrogen from the air and convert it into water-soluble compounds. Plants get the nitrogen they need from the bacteria present in the soil or root nodules. These bacteria convert atmospheric nitrogen into nitrogen compounds, which can be readily absorbed by plants. This process is called nitrogen fixation. Animals acquire nitrogen either from plants or from other animals. Oxygen (O2): Oxygen is the second most plentiful gas in the air. The oxygen content in air remains constant due to the constant exchange of the gas through the processes of photosynthesis and respiration. The balance of oxygen the air gets disturbed mainly due to deforestation. Carbon dioxide (CO2): Carbon dioxide is another important gas. The CO2 content in air remains constant due to photosynthesis and respiration. Plants use carbon dioxide exhaled by humans and animals in the process of photosynthesis.

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