Protists

Protists are a mixed kingdom of living things, most of them single cells, whose cells have a nucleus. Some, the algae, have chlorophyll and make food by photosynthesis; seaweeds are many-celled algae. Others, like the paramecium and the amoeba, catch and swallow their food. Algae make a large share of the world's oxygen and are the start of food chains in water. We make agar, food supplements and health products from them, and scientists are working on fuels made from algae. Diatoms build tiny glass-like shells of silica.