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Many living things are so small that they can only be seen through a microscope. These living things are called microorganisms or microbes. There are three main types of microbe:

  • fungi

  • bacteria

  • viruses


Diagram of a yeast cell showing the cell membrane, which surrounds the cytoplasm. The cytoplasm contains the vacuole, the food storage granules, and the nucleus

Mushrooms and toadstools are fungi, but these are made of lots of cells, so they are not microbes. Yeasts are single-celled fungi, so they are microbes. Fungi are usually the biggest type of microbe. If there is just one of them, we call it a fungus.


A bacteria cell has a cell wall, which surrounds the cell membrane. Inside this is the cytoplasm. Bacteria cells have a chromosome instead of a nucleus

Bacteria are usually smaller than fungi. If there is just one of them, we call it a bacterium. Bacteria have many different shapes. Some have 'tails' (called flagella) that let them swim.


Diagram of a virus cell showing the protein coat around the edge of the cell and the strand of genesi instead of a nucleus.

Viruses are the smallest type of microbe. As a virus can only reproduce inside a cell, some people are not convinced that viruses are really living things.

Differences between fungi, bacteria and viruses

The table shows some of the similarities and differences between the three types of microbe.

Feature Fungi Bacteria Viruses
Cell membrane A green tick A green tick a red cross
Cell wall
A green tick
A green tick
a red cross
(protein coat)
Cell nucleus A green tick
a red cross
a red cross


Disease activity

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