Most candidates avoided this question. The few that attempted it did poorly as most were drawing the carbon cycle without explaining it while drawing carries no mark. Candidates performed better in 7(b).
Expected answers are:
7(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/water 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/oxidize ammonium compounds; into nitrogen; and oxygen; which is released into the atmosphere.
