The tiniest living things can be seen only by using powerful microscopes. This "micro-life" is more correctly known as micro-organisms or microbes. They include bacteria, protists and some types of fungi. They are each made of just one living “unit”, called a cell. Some micro-organisms cause diseases in animals. We call them germs.

Viruses

Viruses are even smaller than bacteria. They are shaped like rods, balls, golfballs or even rockets. They are tiny things that can only reproduce by invading the cells of a living thing. All viruses cause disease, such as colds, flu and measles.

Protists are much bigger than viruses or bacteria, but still microscopic in size. They also consist of a single cell. Some protists, called algae, are like tiny plants. Others, called protozoa, take in food.

An amoeba, a kind of protozoa, hunts bacteria and eats them. It can change shape and move along like a flowing blob of jelly. A few protists cause diseases. They include plasmodia, which produce malaria.