Solutions 2. Microorganisms : Friend And Foe - Text Book Exercise | Class 8 Science - Toppers Study

Text Book Exercise 

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Q1. 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

Q2. 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

Q3. 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

Q4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer:

No, we cannot see microorganism with unaided eyes. They can be seen with the help of a microscope.

Q5. What are the major groups of microorganisms?

Answer:

The major groups of microorganisms are bacteria, fungi, protozoa and some algae. 

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

Answer:

They are Rhizobium, Azobacter, blue-green algae, etc.

Q7. Write 10 lines on the usefulness of microorganisms in our lives?

Answer:

i. They are used in winemaking, baking, pickling, and other food making processes.

ii. Alcoholic fermentation by yeast is widely used in the preparation of wine and bread. A bacterium Lactobacillus, promotes the formation of curd. 

iii. Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the doughand increases its volume.

iv. 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. 

v. 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. 

vi. Microbes also play an important role in the preparation of medicines.

vii. Antibiotics are chemicals produced by micro-organisms to kill bacteria. Streptomycin, for example, is an antibiotic. 

viii. Certain microbes are also used in the biological treatment of sewage and industrial effluents.

ix. Antibiotics are used to control many plant diseases.

x. Antibiotics are mixed with the feed of livestock and poultry to check microbial infection in animals.