This computer graphic of a virus attack offers several possibilities, from what viruses are, to using computers for simulation and imagery.
* Viruses What does the picture show? Satellites in space? An attack by aliens? Not a bad guess. So which planet is being attacked? Answer: Planet Me - your cells are invaded by viruses, like those that cause colds and flu. Younger pupils: the spikes attach to body cells and make you ill (say they are young and strong, so they can fight back with antibodies, and win). Older pupils: the chemistry involved (nucleic acids and proteins) and how a virus goes from being dormant (outside a living organism) to colon-ising a cell and reproducing itself.
* Epidemics What is an epidemic (eg, a flu epidemic)? How do diseases spread through viruses (eg, flu) and bacteria (eg, gastric upsets from contami-nated food or water)? How can we prevent diseases spreading (cover up mouth and nose when coughing and sneezing; wash hands before handling food, or after visiting toilet)?
* Computer graphics What can computers show (simulations, eg, virus attack) that cameras cannot always film?; "digitising" (scanning picture and converting dots to numbers). Do you ever see computer graphics (eg, computer games, films, adverts)?
* Writing "Coughs and sneezes spread diseases". Write a health slogan, or poem ("Don't Atishoo! Use a tissue").
* Ted Wragg is professor of education at Exeter University