Page 72 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

(f) Most viruses are infectious: This forms the core. The core is enclosed
means they can cause diseases to by a protein coat called capsid as in
their hosts. bacteriophage. DNA or RNA are of
various shapes and sizes according
The structure of viruses to the type of the virus. Examples of
FOR ONLINE READING ONLY
Viruses are composed of strands of the structures of viruses are shown in
genetic material (DNA or RNA) which
Figure 5.3.

Envelope

Protein coat
(capsid)
Nucleic acid
(core)

(a)

Capsid
Nucleic acid
Collar
Tail sheath
Tail fibers (for
attachment to the
bacterium)
(b)

Figure 5.3: Structure of (a) Human Immunodeficiency Virus (b) Bacteriophage

Advantages of viruses On recovering from cowpox, the
(a) Viruses are important in the study body developed antibodies that
of cell and molecular Biology. could resist both cowpox and
They are used by scientists to smallpox.
manipulate and investigate the (c) Bacteriophages are viruses that
functions of cells. attack bacteria. They help in
(b) Some viruses are used to make controlling bacterial infections
vaccines. For example, the first and diseases.
vaccine against smallpox was a (d) Some viruses are used in
small dose of the virus that causes biological control to eradicate
cowpox, which is a mild infection. pests, such as insects. This is due

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