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Unit 1 Viruses and Bacteria
Listening Comprehension
Bacteria and viruses are often spoken of in similar terms, especially in regard to their
ability to cause disease. However, beyond this common trait, the two differ in a number of
important ways. For Instance, bacteria are living organisms, and as such can survive
independently of other living things. Viruses, on the other hand, are inactive unless they
find their way into a living host, at which time they are able to grow and reproduce.
One major difference between bacteria and viruses is their composition. Bacteria are the
simplest forms of life on Earth, but are rather complex in their make-up when compared to
viruses. Like any cell, a bacterium is surrounded by a protective wall, or membrane, that
holds its contents together. Inside the membrane is a bundle of DNA that carries the
bacterium's genetic information. Viruses are similar in that they also contain genes in the
form of either DNA or RNA, though in far smaller quantities. In viruses, however, these
materials are contained not in a cell membrane, but in a thinner outer coating of proteins.
Bacteria and viruses also differ greatly in their methods of reproduction. Again, it is the
bacterium's status as a single-celled living organism that sets it apart from the virus.
Bacteria reproduce asexually through cell division. Once they grow to a certain size, the
DNA inside splits into two identical structures, and slowly the cell breaks apart, with one
group of DNA in each new cell. Reproduction of bacteria is limited, however, to the
nutrients available in the environment. Viruses, on the other hand, cannot reproduce until
they have latched onto a host. After a virus attaches itself to a host cell, the virus works
its way into the cell through the membrane. As the virus's protein shell dissolves, the
genetic information in the virus is released into the cell where it can reproduce and spread.
Viruses will continue to reproduce rapidly until the host's resources have been completely
used up, at which time they can simply find a new host.
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Listening Comprehension
Bacteria and viruses are often spoken of in similar terms, especially in regard to their
ability to cause disease. However, beyond this common trait, the two differ in a number of
important ways. For Instance, bacteria are living organisms, and as such can survive
independently of other living things. Viruses, on the other hand, are inactive unless they
find their way into a living host, at which time they are able to grow and reproduce.
One major difference between bacteria and viruses is their composition. Bacteria are the
simplest forms of life on Earth, but are rather complex in their make-up when compared to
viruses. Like any cell, a bacterium is surrounded by a protective wall, or membrane, that
holds its contents together. Inside the membrane is a bundle of DNA that carries the
bacterium's genetic information. Viruses are similar in that they also contain genes in the
form of either DNA or RNA, though in far smaller quantities. In viruses, however, these
materials are contained not in a cell membrane, but in a thinner outer coating of proteins.
Bacteria and viruses also differ greatly in their methods of reproduction. Again, it is the
bacterium's status as a single-celled living organism that sets it apart from the virus.
Bacteria reproduce asexually through cell division. Once they grow to a certain size, the
DNA inside splits into two identical structures, and slowly the cell breaks apart, with one
group of DNA in each new cell. Reproduction of bacteria is limited, however, to the
nutrients available in the environment. Viruses, on the other hand, cannot reproduce until
they have latched onto a host. After a virus attaches itself to a host cell, the virus works
its way into the cell through the membrane. As the virus's protein shell dissolves, the
genetic information in the virus is released into the cell where it can reproduce and spread.
Viruses will continue to reproduce rapidly until the host's resources have been completely
used up, at which time they can simply find a new host.
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