Science class 8 chapter 2- Microorganism: Friend and Foe – NCERT Exercise Solution

Science class 8 chapter 2- Microorganism: Friend and FoeNCERT Exercise Solution ( Question-Answer)

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.


(c) Alcohol is produced with the help of ________.


(d) Cholera is caused by  __________.


Q2. Tick the correct answer. (✓)

(a)  Yeast is used in the production of
(i) sugar           (ii) alcohol             (iii) hydrochloric acid              (iv) oxygen

Answer- (ii) alcohol  

(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 cells  

(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation          (ii) moulding            (iii) fermentation          (iv) infection

Answer- (iii) fermentation

Q.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) Causes malaria
(vi) A virus (f) Causing AIDS

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

Answer – No, microorganisms can’t be seen with the naked eye because they are microscopic in size. They can be seen with the help of high power magnifying glass or a microscope.

Q.5. What are the major groups of microorganisms?

Answer- There are five major groups of microorganisms- bacteria, fungi, protozoa, virus, algae.

Bacteria – Bateria is a single-celled microorganism. They can be spiral or rod-shaped. They cause diseases like cholera.

Fungi – Fungi are mostly multicellular microorganisms. Ex. Bread moulds, etc.

Protozoa – This type of microorganism causes diseases like dysentery and malaria. They can be unicellular or multicellular.

Virus – Virus is different from other microorganisms. They are produced only inside the cells of the host organism, which may be a bacterium, plant or animal.

Algae – Algae are photosynthetic organisms such as spirogyra, Chlamydomonas, etc. They are multicellular organisms.

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

Answer – Some bacteria such as Rhizobium and some blue-green algae which are present in the soil and can fix atmospheric nitrogen in the soil.

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

Answer – There are 10 lines in the usefulness of microorganism in our lives-

  • They are used to increase soil fertility by fixing atmospheric nitrogen in the soil.
  • The microorganism can produce antibiotics that kill bacteria.
  • They are used in the biological treatment of sewage.
  • They are used to reduce pollution.
  • They are used to make the curd.
  • Bacteria like Lactobacillus acidophilus live in the human’s intestine which helps to digest food and destroy disease-causing microbes.
  • They are used in the preparation of vaccines.
  • Yeast is used in the production of alcohol.
  • They are used in pickling and some other food-making process.
  • Antibiotics are used to control many plant diseases.

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

Answer – There are some harmful effects of microorganisms-

Bacteria can cause diseases such as cholera, tuberculosis, typhoid, etc.

They enter our body through contaminated food, air, water and infect our internal body parts which cause some diseases like cold, cough, etc.

Protozoa cause some diseases like dysentery, malaria, etc.

They grow in our food and produce toxic substances. These toxic substances make the food poisonous and cause food poisoning which is a very harmful and serious illness.

In cattle, foot and mouth diseases are caused by viruses.

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

Answer – The medicines which kill or stop the growth of disease-causing microorganism are called antibiotics.

These medicines are commonly obtained from bacteria and fungi.

Ex- Streptomycin, penicillin, etc.

There are some precautions which must be followed while taking antibiotics-

It should be taken at the right time in the right amount.

It should be taken under the supervision of a well-qualified doctor.

Its intake course must follow as per the prescription which is given by the doctor.

Finally Microorganism: Friend and Foe – NCERT Exercise solution & Question ended(✔)🤷‍♂️

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