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

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

Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain