NCERT Solutions For Class 8 Science Chapter – 2 Microorganisms: Friend and Foe

NCERT Solutions For Class 8 Science Chapter – 2 Microorganisms: Friend and Foe

Q1. Fill in the blanks.

  • Microorganisms can be seen with the help of a ________.
  • Blue green algae fix _________ directly from air and enhance fertility of soil.
  • Alcohol is  produced with the help of ______.
  • Cholera is caused by ________.  



  1. Microscope
  2. Nitrogen
  3. Yeast
  4. Bacteria – Vibrio cholera


Q2. Tick the correct answer.

  1. Yeast is used in the production of
  • Sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen
  1. The following is an antibiotics
  • Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
  1. Carrier of malaria – causing protozoan is
  • Female Anopheles (ii) Cockroach (iii) Housefly (iv) Butterfly
  1. The
    most common carrier of communicable diseases  is
  • Ant (ii) housefly (iii) dragonfly (iv) spider
  1. The bread or idli dough rises in because of
  • Heat (ii) grinding (iii) growth of yeast cells  (iv) Kneading
  1. The process of conversation  of sugar into alcohol is called
  • Nitrogen fixation (ii) moulding (iii) fermentation (iv) infection




  • (ii) Alcohol
  • (ii) Streptomycin
  • (i) female anopheles mosquito
  • (ii) housefly
  • (iii) Growth of yeast cells.
  • (iii) fermentation
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Q3. Match the organisms in Column A with their action in Column B.

(i) Bacteria (a) Fixing nitrogen
(ii) Rhizobium (b) Setting of curd
(iii) Lactobacillus ( c ) Baking of bread
(iv) Yeast ( d ) Causing malaria
(v) A protozan ( e ) Causing cholera
(vi) A virus ( f ) Causing AIDS
  ( g ) Producing antibodies




(i) Bacteria ( e ) Causing cholera
(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 AIDS



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



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


Q5.  What are the major groups of microorganisms ?



Major group of miroorganisms are as follows

  1. Bacteria
  2. Fungi
  3. Protozoans
  4. Algae
  5. Viruses


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





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



Uses of microorganisms are listed below


  • They  are helpful in cleaning up of the environment  . For example, the organic wastes are broken down into harmless and usable substances by bacteria.
  • Curd contains several microorganisms . Of these the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
  • Bacteria are also involved in the making of cheese,  pickles and many other food items.
  • Bacteria and yeast are also helpful for fermentation of rice idlis and dosa better.
  • Yeast reproduce rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increases its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
  • Microorganisms are used for the large scale production of alcohol wine and acetic acid.
  • Some bacteria are able to fix nitrogen  from the atmosphere to enrich the soil with nitrogen and increases its fertility.
  • Antibiotics are being produced from bacteria and fungi.
  • Microorganisms are helpful in producing vaccines against diseases – causing agents.
  • Microorganisms decomposes dead organic waste of plants and animals to convert them  into simple substances. These substances are again used by other plants and animals. Thus microorganisms  can be used to  degrade the harmful and smelly substances and thereby clean up the environment.


Q8. Write a short  paragraph on the harmful effects of microorganisms



Microorganisms cause diseases in plants and animals Ex; Cholera  in humans is caused by bacteria called VIBIRO 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.


Q9. What are the antibiotics ? What precautions must be taken while taking antibiotics?



Chemicals agents that kill or stop the growth of diseases – 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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NCERT Solutions For Class 8 Science Chapter – 2 Microorganisms: Friend and Foe Q1. Fill in the blanks. Microorganisms can be…