NCERT Solutions for Class 8 Science Chapter 2 - Microorganisms: Friend and Foe

NCERT TEXTBOOK QUESTIONS SOLVED
 

Q. 1. Fill in the blanks:
 (a) Microorganisms can be seen with the help of a ______.
 (b) Blue green algae fix ______ directly from air to enhance fertility of soil.
 (c) Alcohol is produced with the help of ______.
 (d) Cholera is caused by ______.
 Ans. (a) microscope
(b) atmospheric nitrogen
(c) yeast
(d) bacteria.

Q. 2. Tick ( ) the correct answer:

(a) Yeast is used in the production of 

(i) sugar
 (ii) alcohol
 (iii) hydrochloric acid
 (iv) oxygen. 

Ans. (ii) alcohol

(b) The following is an antibiotic 

(i) sodium bicarbonate
 (ii) streptomycin
 (iii) alcohol
 (iv) yeast. 

Ans. (ii) Streptomycin
 

(c) Carrier of malaria‑causing protozoan is

(i) female Anopheles mosquito
 (ii) cockroach
 (iii) housefly
 (iv) butterfly. 

Ans. (i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is 

(i) ant
 (ii) housefly
 (iii) dragonfly
 (iv) spider. 

Ans. (ii) housefly

(e) The bread or idli dough rises because of 

(i) heat
 (ii) grinding
 (iii) growth of yeast cells
 (iv) kneading.

Ans. (iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called 

(i) nitrogen fixation
 (ii) moulding
 (iii) fermentation
 (iv) infection 

Ans.  (iii) fermentation.
 

Q. 3. Match the organisms in Column A with their action in Column B.

Ans.

Q. 4. Can microorganisms be seen with the naked eyes? If not, how can they be seen?
 Ans. Microorganisms cannot be seen with the naked eyes. They can be seen with the help of a microscope.

Q. 5. What are the major groups of microorganisms?
 Ans. There are following four major groups of microorganisms: (i) Bacteria (ii) Fungi (iii) Protozoa (iv) Algae.
In addition, viruses are also considered as fifth group of microorganisms.

Q. 6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
 Ans. Bacteria, like Rhizobium and blue green algae can fix atmospheric nitrogen in soil. 

Q. 7. Write 10 lines on the usefulness of microorganisms in our lives.
 Ans. Uses of microorganisms:
(i) Microorganisms help in the preparation of curd, bread, cake, etc.
(ii) Yeasts are used for commercial production of wine and alcohol.
(iii) They are used to control many plant diseases.
(iv) They are used in making vinegar.
(v) They act as cleaning agent and decompose the waste products into manure.
(vi) They destroy the plant and animal dead bodies by decomposing them.
(vii) They increase soil fertility by fixing nitrogen of atmosphere.
(viii) They are used in making medicines like antibiotics and vaccines.
(ix) They are used as preservatives for food items.
(x) They help in various metabolic activities in our body. 

Q. 8. Write a short paragraph on the harms caused by microorganisms.
 Ans. Microorganisms are also very harmful to us. They cause a number of diseases in human as well as in other animals. Common cold, Tuberculosis, Measles, Chicken Pox, Polio, Cholera, Typhoid, Hepatitis B, Malaria, are some common human diseases caused by microorganisms. Anthrax is a serious disease in animals caused by microbes.
They also make food items unfit for use by food poisoning. They also spoil clothes and leather products. They also cause diseases in plants like blights in potatoes, sugarcanes, oranges etc. They also reduce the crop production. 

Q. 9. What are antibiotics? What precautions must be taken while taking antibiotics?
 Ans. The medicines which kill or stop the growth of microorganisms in our body are called antibiotics. These are very useful to us as they prevent us from the effects of microorganisms. Antibiotics are made from bacteria and fungi. The penicillin is the first antibiotics which is discovered by Alexander Fleming in 1929. These days a number of antibiotics are used to cure various human and animal diseases. Streptomycin, Tetracycline, Erythromycin etc. are some common antibiotics. Precautions: We should take antibiotics only by the advice of a qualified doctor. Antibiotics should only be taken when needed. Otherwise, they may be harmful and become less effective in future.