CBSE Class 9 Answered

how to explain oxygen and carbon cycle if it is for 4-5 marks?

Asked by abhigya chaudhary | 20 Jan, 2012, 07:28: PM

Expert Answer

Carbon cycle:

Carbon is found elemental form as well as combined form on the Earth.

In combined state it is present as carbon dioxide in the atmosphere, as carbonate and hydrogen-carbonate salts in various minerals and as life molecules.

It is through photosynthesis (carried out by life-forms containing chlorophyll) that carbon gets incorporated into life-forms. Photosynthesis converts carbon dioxide (from the atmosphere or dissolved in water) to glucose in the presence of sunlight by all life-forms that contain chlorophyll. These glucose molecules are either converted into other substances or used to provide energy to the organism for carrying out its life processes or building other molecules.

Energy is provided through the process of respiration, which converts glucose back into carbon dioxide. In addition, combustion of fuels to provide energy for various needs like heating, cooking, transportation and industrial processes also releases carbon dioxide to atmosphere. Today the percentage of carbon dioxide in the atmosphere has doubled since the industrial revolution. Thus carbon is cycled repeatedly through different forms by the various physical and biological activities.

Oxygen cycle -

Oxygen exists abundantly on Earth in elemental form as well as in combined form. In combined form it is present as oxides, carbonates, sulphates, nitrates in Earths crust, as carbon dioxide in air and as part of vital life molecules.

Oxygen from the atmosphere is used up in three processes, i.e. combustion, respiration and in the formation of nitrogen oxides. However, oxygen is returned back to the atmosphere in only one major process, that is, photosynthesis.

Oxygen from atmosphere is used by most living organisms during respiration, due to which carbon dioxide is released to atmosphere. Plants use carbon dioxide during photosynthesis and release oxygen to the atmosphere. Oxygen is essential for complete combustion. Oxygen is also utilized for the formation of ozone layer.

Answered by | 23 Jan, 2012, 07:56: AM