Page 22 - Science Class 08
P. 22
nucleus organelles. This single cell carries out Virus
all life-processes. A virus is a microbe that lives in the cell of
We can study the four groups of protozoa are another organism. Though very small, viruses
as follows: cause diseases like influenza, bad cold and
v Flagellates : These protozoa have one or measles in human beings. They also infect
more hair-like projec ons on their bodies. plants and animals and a ack bacteria as well.
They are oval in shape and move by They damage the cells of their hosts.
whipping their flagella. They posses chloro- Strangely, a virus is a non-living par cle. But
phyll and can make their food. inside a cell, it acts like an organism and
v Sarcodines : These protozoa push their mul plies very fast. Viruses are of different
membranes to form false feet (pseudopods) shapes— spherical or rod-like. They have no
and move forward. cells and that is why enter the cells of other
living beings to live and reproduce there.
v Ciliates : These protozoa have hair-like cilia
to move and to capture their prey. A virus has a ny speck of DNA and RNA
material enclosed in a protec ve coat of
v Apicomplexans : They move by gliding and
protein. The material wakes up to ac vity only
live as parasites. Plasmodium is a protozoan
inside the cell of another organism.
of this group that lives inside the body of a
mosquito called anopheles. So, a bite by Viruses are found everywhere in the air, water,
the mosquito sends this protozoan in the soil and in the bodies of living things. It is
body of the prey and causes it to be laid up believed that viruses stand for the earliest
with malaria. Protozoa cause other disease stage of the evolu on of life from non-living
like dysentery, abdominal pain, repeated material. Viruses possess some physical and
mo ons and sleeping sickness. chemical proper es. They are classified as
animal viruses, plant viruses and bacteria
Most protozoa reproduce by fission or by
viruses according to their hosts.
budding asexually. But some protozoa
reproduce sexually as well. Important features of viruses are as follows:
Protozoa are important as under: v Viruses are not affected by an bio cs as
they have no metabolic system.
v Oceans-protozoa are eaten by sea animals.
v Viruses cause disease like rabies, polio,
v Some protozoa (plankton) feed on algae
chicken pox, common cold, influenza and
forming a food-chain.
mosaic of tobacco, maize, sugarcane, etc.
v Protozoa are used for research of body-
features like reproduc on and cell-division. v Viruses cause the organic ma er to rot by
killing its bacteria.
v The protozoa living in the bodies of other
organisms help them process the eaten v Viruses are used for research— to know
things into useful food. how they are caused and also how they can
be destroyed.
v Some protozoa are covered with tough
shells. When they die, these shells se le at v They are also used for insect control and to
the sea-bo om to form limestone. produce vaccines.
22 Science-8
