NCERT solutions for class 8 Science Chapter 2 Microorganisms Friend And Foe

Solution for Exercise

Q6.Name the microorganisms which can fix atmospheric nitrogen in the soil.


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Answer :

Rhizobium

Q.1 Fill in the blanks.
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue green algae fix __________ directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________


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Answer :

(a) Microorganisms can be seen with the help of a __microscope__.
(b) Blue green algae fix __nitrogen__directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of __yeast__.
(d) Cholera is caused by ___Bacteria- Vibrio cholera__.

Q.2 Tick the correct answer. (a) Yeast is used in the production of
(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen
(b) The following is an antibiotic
(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly
(d) The most common carrier of communicable diseases is
(i) ant (ii) housefly (iii) dragonfly (iv) spider
(e) The bread or idli dough rises because of
(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection


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Answer :

a) (ii) alcohol
b) (ii) Streptomycin
c) (i) female Anopheles mosquito
d) (ii) housefly
e) (iii) growth of yeast cells
f) (iii) fermentation

Q.3 Match the organisms in Column A with their action in Column B.
A
I) Bacteria
II) Rhizobium
III) lactobacillus
IV) yeast
V) A protozoan
VI) A virus
B
a) fixing nitrogen
b) setting of curd
c) baking of bread
d) causing malaria
e) causing cholera
f) causing AIDS
g) producing antibodies


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Answer :

A
i) Bacteria
ii) Rhizobium
iii) lactobacillus
iv) yeast
v) A protozoan
vi) A virus
B
e) causing cholera
a) fixing nitrogen
b) setting of curd
c) baking of bread
d) causing malaria
f) causing aids

Q.4 Can microorganisms be seen with the naked eye? If not, how can they be seen?


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Answer :

Microorganisms cannot be seen by the naked eye because they are very small. They can be seen by using a microscope.

Q.5 What are the major groups of microorganisms?


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Answer :

Major group of microorganisms are as follows
Bacteria, Fungi, Protozoans, Algae and Viruses

Q.7 Write 10 lines on the usefulness of microorganisms in our lives.


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Answer :

Micro-organisms are too small to be seen through naked eyes. However, they are vital to plants and the environment.
They are used in winemaking, baking, pickling, and other food making processes.
Alcoholic fermentation by yeast is widely used in the preparation of wine and bread. A bacterium Lactobacillus, promotes the formation of curd.
Microbes are used to reduce pollution. For example, decomposers such as bacteria and fungi break down dead bodies and excreta to form inorganic compounds, which can be absorbed by plants.
They are used to increase the soil fertility by fixing the atmospheric nitrogen with the help of bacterium Rhizobium and some other blue-green algae.
Microbes also play an important role in the preparation of medicines. Antibiotics are chemicals produced by micro-organisms to kill bacteria. Streptomycin, for example, is an antibiotic.
Certain microbes are also used in the biological treatment of sewage and industrial effluents.

Q.8 Write a short paragraph on the harmful effects of microorganisms.


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Answer :

Microorganisms cause diseases in plants and animals Ex; Cholera in humans is caused by bacteria called Vibrio cholera. In animals, the virus causes foot and mouth diseases. Microorganisms spoil the foods by decomposing the food material. Some microorganisms spoil leather and clothes. Microorganisms are responsible for food poisoning.

Q.9 What are antibiotics? What precautions must be taken while taking antibiotics?


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Answer :

Chemical agents that kill or stop the growth of disease-causing microorganisms are called antibiotics. Antibiotics should be taken only on the advice of a qualified doctor. Also, one must complete the course prescribed by the doctor.



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