Class 8 science Chapter 2 Microorganisms friends and Foe Textbook solutions - YB Study -->

Class 8 science Chapter 2 Microorganisms friends and Foe Textbook solutions

NCERT Solutions For Class 8 Science Chapter 2: Microorganism Friends and Foe

As the days are nearing the Board examination, we are starting the Online All India NCERT Textbook Solution series program for class 8 sciences Students. It is the ultimate preparation kit to prepare yourself for the upcoming board examination exam. It is unique & different as it not only tests your knowledge but also helps you evaluate your performance in real-time against other Students rank who take the test from all across the country.

Chapter 2 Microorganisms friend and Foe Textbook solutions

Below in this Page, you can get the complete NCERT Solution for Class 8 Science Chapter 2 Microorganism Friends and Foe which is presented in a very well-structured format. Then You can easily Solve the Questions of the NCERT Syllabus

Q.1 Fill in the blanks.

(a) Microorganisms can be seen with the help of a ____________.

Answer: Microscope

(b) Blue-green algae fix __________ directly from the air and enhance the fertility of the soil.

Answer: Nitrogen

(c) Alcohol is produced with the help of __________

Answer: Yeast

(d) Cholera is caused by __________

Answer: Bacteria

2. Tick the correct answer.

(a) Yeast is used in the production of_______

(i) sugar 

(ii) alcohol 

(iii) hydrochloric acid 

(iv) oxygen

Answer: (i) sugar

(b) The following is an antibiotic_________

(i) Sodium bicarbonate 

(ii) Streptomycin 

(iii) Alcohol 

(iv) Yeast

 Answer: (ii) Streptomycin

(c) Carrier of malaria-causing protozoan is_________

(i) female Anopheles mosquito

(ii) cockroach

(iii) housefly

(iv) butterfly

Answer: (i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is__________

(i) ant 

(ii) housefly 

(iii) dragonfly 

(iv) spider

Answer:  (ii) housefly

(e) The bread or idli dough rises because of____________

(i) heat 

(ii) grinding

(iii) growth of yeast cells 

(iv) kneading

Answer: (iii) growth of yeast

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

(i) nitrogen fixation 

(ii) moulding 

(iii) fermentation 

(iv) infection

Answer:  (iii) fermentation

3. 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 protozoan (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 (f) causing AIDS

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

Answers: microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes.

5. What are the major groups of microorganisms?

Answers: Microorganisms are classified into four major groups. 

These groups are bacteria, fungi, protozoa, and some algae. 

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

Answer: Rhizobium can fix atmospheric nitrogen in the soil.

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


  •  Microorganisms play an important role in our lives. Some of them are beneficial for us. 
  • Microorganisms are used in the preparation of curd, bread, and cake.
  • 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 the fermentation of rice idlis and dosa batter.
  • They are also used in cleaning up the environment. For example, the organic wastes (vegetable peels, remains of animals, feces, etc.) are broken down into harmless and usable substances by bacteria.
  •  In agriculture, they are used to increase soil fertility by fixing nitrogen.
  • Microorganisms are used for the large-scale production of alcohol, wine, and acetic acid(vinegar). 
  • Yeast is used for the commercial production of alcohol and wine. 
  •  The source of these medicines is microorganisms. These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.
  •  These days several antibiotics are being produced from bacteria and fungi.

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

Answer: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants, and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing, and leather. Microbial diseases that can spread from an infected person to a healthy person through the air, water, food, or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chickenpox, and tuberculosis. anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple, and others. The diseases reduce the yield of crops. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

9. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics. These days several antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline, and erythromycin are some of the common antibiotics. It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. Also, you must complete the course prescribed by the doctor. If you take antibiotics when not needed or in the wrong doses, it may make the drug less effective when you might need it in the future. Also, antibiotics taken unnecessarily may kill the beneficial bacteria in the body. Antibiotics, however, are not effective against cold and flu as these are caused by viruses.

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