Meet the microorganisms

Microorganisms (microbes) are living things too small to see with the naked eye. Bacteria are single cells without a nucleus, shaped like rods, spheres or spirals. Fungi include single-celled yeasts and moulds made of fine threads. Protozoa are single cells with a nucleus that move and feed like tiny animals. Algae are simple plant-like organisms with chlorophyll that make their own food. Viruses are far smaller than bacteria, can only be seen with an electron microscope, and can only reproduce inside other cells. Many microbes are useful, making curd, bread and soil nutrients, while others cause diseases such as typhoid, malaria and flu.