What are bacteria?
Bacteria are very different from viruses. First of all, bacteria are much larger in size. The largest virus is only as big as the very smallest bacterium (singular for bacteria). But bacteria are still microscopic and cannot be seen with the naked eye. They are so small that the sizes of bacteria are measured in micrometers (10,000 micrometers = 1 centimeter). By comparison, the head of a pin is about 1000 micrometers wide. Though more complex than a virus, the structure of a bacterium is still relatively simple. ￼Structure:Most bacteria have an outer, rigid cell wall. This provides shape and support. Lining the inside of the cell wall is a plasma membrane. This is like the membrane found around all living cells that provides both a boundary for the contents of the cell and a barrier to substances entering and leaving. The content inside the cell is called "cytoplasm." Suspended in the cytoplasm are ribosomes (for protein synthesis), the nucleoid (concentrated genetic material), and plasmids (small, circular pieces of DNA, some of which carry genes that control resistance to various drugs). All living cells have ribosomes, but those of bacteria are smaller than those found in any other cell. Some antibacterial medicines have been made that attack the ribosomes of a bacterium, leaving it unable to produce proteins, and therefore killing it. Because the ribosomes are different, the cells of the host are left unharmed by the antibiotic. Other antibiotics target certain portions of the cell wall. Some bacteria have long, whip-like structures called "flagella" that they use for movement. Bacteria can occur in three basic shapes:
￼(starting to divide)
Reproduction: Bacteria undergo a...
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