Bacteria

 

The bacteria are surely the most numerous beings on earth: we consider their mass total 15 times higher than the mass of all the animals. Its structure is very simple surrounded by a protective outer membrane. It can be observed under different shapes, some are spherical (cocci), some rod-shaped (bacilli), and others spiral (bacilli). Usually, its size is at most 2 µm.

Bacteria multiply by binary fission, which is called asexual reproduction. If the conditions are favorable, they can divide themselves every 40 minutes, thus a single cell can produce as many as 2³⁶ cells in only 12 hours.

However, they can also reproduce in a sexual way: in this case, they exchange genetic information, located on chains bicatenary of circular DNA .

Some bacteria may live under very tough temperature and pressure conditions (the black smokers under the sea contain bacterial colonies) and they may reach phenomenal sizes.

Anyway, a few bacteria are pathogenic which means that they can lead to diseases for human beings. Mainly, bacteria are part of many biological phenomena such as fermentation, nitrogen fixation...