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 known as anaerobes.
The shape of specific bacteria provides for the next step in the
identification process. Spherical bacteria are called cocci; the bacteria that
have a rodlike shape are known as bacilli; corkscrew shaped bacteria are
spirilla; and filamentous is the term for bacteria with a threadlike appearance.
Hans Christian Joachim Gram, a Danish microbiologist, developed a method
for distinguishing bacteria by their different reaction to a stain. The
process of applying Gram's stain is as follows: the bacteria are stained with a
violet dye and treated with Gram's solution (1 part iodine, 2 parts potassium
iodide, and 300 parts water). Ethyl alcohol is then applied to the medium; the
bacteria will either preserve the blue color of the original dye or they will
obtain a red hue. The blue colored bacteria are gram-positive; the red bacteria
are identified as... [continues]
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(1999, 10). The Effects of Antibiotics on Bacterial Growth. StudyMode.com. Retrieved 10, 1999, from http://www.studymode.com/essays/Effects-Antibiotics-Bacterial-Growth-255.html
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