Explain the process of eutrophication of water, limited to: - increased availability of nitrate and other ions - increased growth of producers - increased decomposition after death of producers - increased aerobic respiration by decomposers - reduction in dissolved oxygen - death of organisms requiring dissolved oxygen in water

Describe the nitrogen cycle with reference to: • decomposition of plant and animal protein to ammonium ions • nitrification • nitrogen fixation by lightning and bacteria • absorption of nitrate ions by plants • production of amino acids and proteins • feeding and digestion of proteins • deamination • denitrification

Describe how humans have increased food production, limited to: (a) agricultural machinery to use larger areas of land and improve efficiency (b) chemical fertilisers to improve yields (c) insecticides to improve quality and yield (d) herbicides to reduce competition with weeds (e) selective breeding to improve production by crop plants and livestock