(a) Description of the carbon cycle: Carbon occurs in the air/atmosphere/as carbon dioxide/dissolved in the oceans/seas/water bodies; and is circulated continuously; through the activity of microorganisms/ decay bacteria/saprophytic organisms/fungi; which decompose the dead organisms; plants/animals release carbon dioxide and water; the carbon dioxide released increases the concentration of carbon in the atmosphere/ocean/sea/water bodies; this is further increased by respiration in plants and animals; combustion of wood/coal/peat/oil/fuel; some of the excess carbon dioxide is absorbed by the sea/water bodies and also used by plants in photosynthesis; organisms in seas/oceans/wafer bodies release carbon dioxide into the atmosphere/water.
(b) Functions of;
(i) Nitrogen-Fixing Bacteria; Nitrogen fixing bacteria in the nodules of legumes; those living freely in soil; convert atmospheric nitrogen; into ammonia/ammonium compounds.
(ii) Nitrifying Bacteria: They live freely in the soil; oxidize/breakdown the ammonium compounds; to nitrites; which are then oxidized by others/Nitrobacter/named bacteria; to nitrates.
(iii) Denitrifying Bacteria: They live freely in the soil; these break down/oxidise ammonium compounds; into nitrogen; and oxygen; which is released into the atmosphere.