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Bacteria are microscopic, unicellular organisms.
Bacteria belong to the kingdom Monera.They haven’t a nucleus, their DNA is free inside their cytoplasm. Bacteria are living cells and, in favourable conditions, can multiply fast.
Bacteria
The Mycoplasma genus includes the tiniest bacteria: their size is about 0,2 micrometers
(0,0002 mm)
How big is a bacterium?
Most bacteria measure from 1 to 10 micrometers long (from 0,001 to 0,01 mm)
Animal and vegetal cells are bigger: from 10 to 100 micrometers (0,01 to 0,1 mm)
Bacteria’s diet (I)Many bacteria are saprophytes: they live in the soil and
decompose organic matter (leaves, dead animals' bodies…)
They can also decompose our food!
Bacteria’s diet (II)Some bacteria live with another organism, and they help
each other. This relationship is called symbiosis.
There are bacteria in our bodies: in the large intestine, skin and mouth. Some of them are beneficial
Roots from a legume plant. The nodules are full of bacteria! They make minerals for the plant
Bacteria’s diet (III)
Some bacteria are parasites:they feed on us, making us weak or sick.
Many human diseases are caused by bacteria