what is carbon cycle?
Carbon occurs in elemental form as well as in organic and inorganic compounds. The basic structure of all life molecules like carbohydrates, proteins, fats, nucleic acids and vitamins is composed of carbon. Carbon dioxide is fixed by green plants during photosynthesis as well as by marine animals during shell formation. Photosynthesis converts carbon dioxide to glucose, which is converted back to carbon dioxide through respiration. Combustion of fuels also releases carbon dioxide to atmosphere. Carbon dioxide is an important green house gas that prevents the escape of heat from Earth and causes global warming.
Thus carbon is cycled repeatedly through different forms by the various physical and biological activities. The figure is given in NCERT (fig 14.7)