Page 73 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

to their characteristics of being Kingdom Monera consists of bacteria
host specific and infectious. and blue-green algae. The scientific
study of bacteria is called Bacteriology.
Disadvantages of viruses
(a) Most viruses are pathogenic. They Characteristics of bacteria
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cause infections and diseases, (a) They are prokaryotic as their cells
such as tobacco mosaic disease, lack a well-defined nucleus. Their
tomato spotted wilt disease, nucleus has no nuclear membrane.
cassava mosaic disease, rabies, They also lack other membrane
chickenpox, COVID-19, polio, bound organelles.
and AIDS. Pathogenic viruses can (b) They are small unicellular
reproduce very fast, leading to organisms. Some bacteria stick
large-scale epidemics. together to form chains or clusters
(b) Viruses can alter themselves called colonies.
often, and thus become difficult to (c) Some are free-living while others
cure viral infections. For example, are parasites or saprophytes.
there are many different types of Free-living bacteria means
viruses that can cause common that they exist on their own.
cold and influenza. Parasitic bacteria depend on other
organisms known as hosts for
Exercise 5.1 their needs. Examples of hosts are
human beings and other animals.
1. Why are viruses regarded as non- Saprophytic bacteria get their
living things? food from dead organic matter by
2. Explain why some viruses are used external digestion.
in agriculture to fight against pests (d) Free-living bacteria and some
and disease vectors. parasitic bacteria have flagella for
3. Viruses can be regarded as a threat movement.
to human health. Explain. (e) Bacteria have a slimy outer layer.

This layer helps to protect them
Kingdom Monera from parasites like viruses and
predators, such as protozoa.
Task 5.2 (f) They reproduce asexually by

From different reliable internet sources binary fission or through spores.
and biology books, read about the (g) They occur in various shapes.
characteristics of bacteria, their advantages There are five known shapes of
and disadvantages. bacteria. These are spherical-

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