Drawing the eye helps develop observation. Eye colour inheritance is interesting, but constructing family trees could reveal unexpected parenting. It is best to use ready-made trees from textbooks. Genetics can kept simple at key stages 3 and 4 by assuming the inheritance of eye colour is controlled by a single gene. Drugs affect the iris, too. Opticians put Atropine drops on the lower lid and as the patient blinks, the drug spreads across the eyeball acting on the dilator muscles and enlarging the pupil.
Discuss why an optician needs to enlarge the pupil and why there are risks in going out into very bright light immediately after an eye test.
Eyes in the Body Focus series, which is due to be published in early December by Heinemann Library (pound;7.50), is a useful reader for all levels of secondary school.