Biology II 1996 Bacteria are the most common and ancient
microorganisms on earth. Most bacteria are microscopic,
measuring 1 micron in length. However, colonies of bacteria
grown in a laboratory petri dish can be seen with the unaided
eye. There are many divisions and classifications of bacteria
that assist in identifying them. The first two types of bacteria
are archaebacteria and eubacteria. Both groups have common
ancestors dating to more than 3 billion years ago.
Archaebacteria live in environments where, because of the high
temperature, no other life can grow. These environments include
hot springs and areas of volcanic activity. They contain lipids
but lack certain chemicals in their cell wall. Eubacteria are
all other bacteria. Most of them are phototrophic, i.e. they use
the sun's energy as food through the process of Another
classification of bacteria is according to their need of oxygen
to live. Those who do require oxygen to live are considered
aerobes. The bacteria who don't use oxygen to live are