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NCERT Solutions for Class 8th Science


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Chapter 2. Microorganisms : Friend And Foe

Text Book Exercise




Text Book Exercise 

Ques: 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 :     

(i) Microscope

(ii) Nitrogen

(iii) Yeast

(iv) bacterial

Ques: 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)  emale Anopheles mosquito

(ii) cockroach

(iii) housefly

(iv) butterfly

Ans: (i) emale 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

Ques: Match the organisms in Column I with their action in Column II.

    Column I                            Column II

(i) Bacteria                                (a) Fixing Nitrogen

(ii) Rhizobium                              (b) Setting of curd

(iii) Lactobacillus                           (c) Baking of bread

(iv) Yeast                                  (d) Causing Malaria

(v) A protozoan                            (e) Causing Cholera

(vi) A Virus                                (f) Causing AIDS

                     (g) Producing antibodies  


Column I                                           Column II

(i) Bacteria                                    

(ii) Rhizobium                                  (a) Fixing Nitrogen

(iii) Lactobacillus                               (b) Setting of curd

(iv) Yeast                                     (c) Baking of bread

(v) A protozoan                               (d) Causing Malaria

(vi) A Virus                                   (e) Causing Cholera                                             

                                               (f) Causing AIDS


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