Microorganisms Friend And Foe - Exemplar Solutions 1

CBSE Class 8 Science
NCERT Exemplar Solutions
Microorganisms: Friend and Foe

1. Which of the following reproduces only inside a host cell?
(a) Bacteria
(b) Virus
(c) Amoeba
(d) Fungus.
Ans. (b) Virus reproduction only inside the cells of the host organism which can be a bacterium, plant or even animal.

2. A disease in human beings caused by virus is _______.
(a) typhoid
(b) influenza
(c) dysentry
(d) cholera
Ans. (b) Influenza is a disease caused by viral infection.

3. Pathogenic micro-organisms present in host cells are killed by medicines called
(a) pain killer
(b) antibodies
(c) antibiotics
(d) vaccines
Ans. (c) Pathogenic micro-organisms present in host cells are killed by medicines called antibiotics that kills or stops the growth of the disease-causing microbes.

4. The two micro-organisms which live in symbiotic association in lichens are
(a) fungus and protozoa
(b) alga and bacteria
(c) bacteria and protozoa
(d) alga and fungus
Ans. (d) A relationship where two species live together and their interaction provide benefits to both of them is known as symbiotic relationship. Out of the given options alga and fungus lives in a symbiotic relationship.

5. The gas released during the preparation of bread is
(a) oxygen
(b) carbon dioxide
(c) nitrogen
(d) sulphur dioxide
Ans. (b) In the production of bread yeast is added to the dough to make it soft. It reproduction rapidly leading to the production of carbon-dioxide while it inhales. The buddies of this released gas fills the dough and increases it volume.

6. The disease caused by a protozoan and spread by an insect is_________.
(a) dengue
(b) malaria
(c) polio
(d) measles
Ans. (b) Malaria is a disease caused by protozoans and is spread to the masses by an insect called females Anopheles mosquito.

7. Paheli dug two pits, A and B, in her garden. In pit A, she put a polythene bag packed with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month?
(a) Waste in pit A degraded faster than that in pit B.
(b) Waste in pit B degraded faster than that in pit A.
(c) Waste in both pits degraded almost equally.
(d) Waste in both pits did not degrade at all.
Ans. (b) Pit B consists of organic matter that is capable of getting decomposed within a short period of time by the microorganisms present in soil and turns into manure. Whereas pit A contains agricultural waste in polythene bag that is non-biodegradable and hence cannot get decomposed. Therefore, Pit B will degrade faster than pit A.