Bacteria are unicellular organisms belonging to the kingdom Monera, lacking a nucleus and capable of rapid multiplication under favorable conditions. They vary in size from 0.2 to 10 micrometers and can have different diets including saprophytic, symbiotic, or parasitic relationships. Cyanobacteria, an older life form, perform photosynthesis and contribute to aquatic ecosystems.

1. 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

2. 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)

3. Bacteria have different shapes Bacilli Cocci

4. 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!

5. 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

6. Bacteria’s diet (III) Some bacteria are parasites: they feed on us, making us weak or sick. Many human diseases are caused by bacteria

7. … 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!