Biology / Unit 8: Classification and Diversity of Life
8.3 Viruses and Bacteria
Notes
Bacteria are living prokaryotes; viruses are not considered alive.
- Bacteria reproduce by binary fission and can share genes by conjugation.
- Most bacteria are harmless or helpful: they decompose, fix nitrogen, and aid digestion. Some cause disease (strep throat). Antibiotics kill bacteria.
- A virus is genetic material (DNA or RNA) inside a protein coat (capsid). It has no cells and cannot reproduce on its own.
- Viruses must infect a host cell to make copies. In the lytic cycle the virus copies itself and bursts the cell; in the lysogenic cycle viral DNA hides in the host's DNA.
- Antibiotics do not work on viruses. Vaccines help prevent viral diseases.
Practice
Why are viruses usually not considered living?
Viruses lack cells and metabolism and need a host to reproduce.
A person with the flu (caused by a virus) asks for antibiotics. Why won't antibiotics help?
Antibiotics attack bacterial structures that viruses do not have.
Bacteria reproduce asexually by splitting in two. This is called:
Binary fission copies the DNA and divides the cell into two.
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