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 have different shapesBacilli

Cocci

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

… and Cyanobacteria’s diet

• Cyanobacteria are green or blue. They live in the sea (as plankton) and in fresh water (see photos)

• They need sunlight because they do photosynthesis• They are older than plants. In fact, plants “learned” photosynthesis

from cyanobacteria!