Describe the function of each part of the eye, limited to: (a) cornea – refracts light (b) iris – controls how much light enters the pupil (c) lens – focuses light onto the retina (d) ciliary muscles and suspensory ligaments – control the shape of the lens (e) retina – contains light receptors, some sensitive to light of different colours (f) fovea – contains the greatest density of light receptors (g) optic nerve – carries impulses to the brain

Outline the nitrogen cycle in making nitrogen available for plant and animal protein, limited to: (a) decomposition of plant and animal protein to ammonium ions (b) nitrification (c) nitrogen fixation by lightning and bacteria (d) absorption of nitrate ions by plants (e) production of amino acids and protein (f) feeding and digestion of proteins (g) denitrification (the names of individual bacteria are not required)

Discuss why bacteria are useful in biotechnology and genetic modification, limited to: (a) no ethical concerns over their manipulation and growth (b) presence of plasmids