Page 22 - Genius Kidz Prudence Learning Sc-8

(ii) Cholera : Caused by Vibriocholerae is surrounded by a protein coat. Protein

(iii) Typhoid : Caused by Salmonella coat and the genetic material together
typhi form the head of virion and the tail
comprises of a hollow core surrounded
(b) Spoilage of food : Bacteria act on food
and produce toxic substances that, in by a protective sheath.

turn, spoil the food.
2. Viruses (singular virus) : The term “virus”
implies poison. They are the smallest

organisms and can be seen only with the help
of electron microscope. They form an
important link between living and non-living
entities. Study of viruses is called virology.
(a) Habitat : Viruses are also omnipresent.

They are the most abundant type of
biological organisms.
(b) Size : Viruses are the smallest organisms
present on earth. An average virus is of

1/100th of size of bacterium.

Virus
(e) Nutrition : Virus depends on its host for
nutrition. Its mode of nutrition is thus
parasitic.

(f) Reproduction : Virus like bacteriophage
reproduces either by a lytic or a
lysogenic life cycle.

Virus as a friend : Viruses usually are not useful
Different shapes of virus
for human as such but they can be used in
research for new medications by exploring the
(c) Shape : Viruses can be spherical, rod-
upcoming science of biology called
shaped, cuboidal or polygonal shape.
biotechnology.
(d) Structure : Virus is a small infectious
agent, it can replicate only inside the Virus as a foe : Viruses cause a large number of
diseases in human beings. Some of the
body of a living organism. Virus or a
diseases are enlisted here :
virion consists of single stranded DNA or
RNA as a genetic material that is, in turn, (a) Poliomyelitis

The thermometer was invented in 1607 by Galileo.

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