Bacteria

Bacteria are probably the most common form of life on earth. They are also the simplest and smallest living things. They are micro-organism, which mean they can be seen only under microscope.

Some bacteria cause disease, but most do not. There are at least 2000 species of bacteria. Most of them are harmless or helpful to other forms of life including people. Others live on fallend leaves or animal wastes, in water, milk and most food, and no dust and soil. Some bacteria can cause hydrogen gas, ammonia and iron compounds as their food. A few bacteria feed on gases and acids that are poisonous to us.

Most bacteria are killed by heat, yet they are a few kinds that live in hot springs. Freezing does not usually kill resist drying strong chemicals or extreme temperatures by changing into though-walled spores. The bacteria may last very long time in the sesting form. Under favorable conditions, that spore will burst and the bacteria become octive again.