Bacteria
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Bacteria (or "one bacterium") are very small organisms (living things). They are so tiny they can be only seen with a microscope. Bacteria are formed with very few cells. Many of them have only one cell. This kind of organism is called a unicellular organism. Bacteria are among the oldest living organisms on Earth.
There are more bacteria than any other living organism on the planet. Most bacteria live in the ground or in water, and many live inside of other living organisms. Some bacteria can cause diseases in other organisms, but others are helpful in everyday activities like eating, producing food and producing oxygen (blue-green algae).
A bacterium reproduces (creates more bacteria) by dividing itself into two new "child" bacteria, each the same as the first one, but smaller.
A typical bacterium is about 1um (one micrometre) in diameter.
Bacteria lives everywhere and lives within everyone.
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