NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend And Foe

NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend And Foe are given below. Here we have provided the best and error-free answers to all the exercise questions that will strengthen your foundation in science. Solving NCERT questions will assist you in grasping the content in the Crop Production and Management chapter in a better way.

In these solutions, we have answered all the intext and exercise questions provided in NCERT class 8 science textbook. NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend And Foe provided in this article are strictly based on the CBSE syllabus and curriculum. Students can easily download these solutions in PDF format for free or can read them online.

Microorganisms: Friend And Foe Class 8 Science NCERT Solutions

Exercise Questions

Question 1: 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 ________.


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

(b) Blue green algae fix nitrogen directly from air to enhance fertility of soil.

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

(d) Cholera is caused by bacteria.

Question 2: 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

Question 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

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

Answer: No, microorganisms cannot be seen by naked eye as they are very small and are called microbes. They can be seen with the help of microscope.

Question 5: What are the major groups of microorganisms?

Answer: Microorganisms are classified into four major groups are bacteria, fungi, protozoa and some algae.

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

Answer: Bacteria such as rhizobium and certain blue-green algae present in the soil can fix atmospheric nitrogen and convert into usable nitrogenous compounds, which are used by plants for the synthesis of plant proteins and other compounds.

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

Answer: Microorganisms are too small to be seen through naked eyes. However, they are vital to plants and the environment.

Importance of microorganisms:

  • They are used in winemaking, baking, pickling and other food-making processes.
  • Alcoholic fermentation by yeast is widely used in the preparation of wine and bread.
  • A bacterium Lactobacillus promotes the formation of curd.
  • Microbes are used to reduce pollution.
  • They are used to increase soil fertility by fixing atmospheric nitrogen.
  • Microbes are also useful in preparing many medicines and antibiotics.
  • Certain microbes are also used in the biological treatment of sewage and industrial effluents.

Question 8: Write a short paragraph on the harms caused by microorganisms.

Answer: Harmful effects of micro-organisms:

Micro-organisms cause diseases in animals. For example, in humans, bacteria cause diseases such as tuberculosis, cholera, typhoid, etc. In cattle, the foot and mouth disease is caused by a virus. Also, several microbes cause diseases in plants. For example, the productivity of wheat, orange, apple, etc. is reduced due to microbial diseases in plants. Certain microbes, on entering into our body, produce toxic substances. This leads to food poisoning. Some micro-organisms such as fungus spoil our food. For example, bread when left unused under moist conditions gets spoilt by fungus, producing a white cotton-like growth on the bread.

Question 9: What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: The medicines that kill or stop the growth of the disease-causing microorganisms are called antibiotics.
For example: Streptomycin, tetracycline, etc.

Following precautions must be taken while taking antibiotics:

  • Antibiotics should be taken only on the advice of a qualified doctor.
  • One must finish the course prescribed by the doctor.
  • Antibiotics must be avoided when not needed or in wrong doses.

CBSE Class 8 NCERT solutions Science Chapter 2 PDF

Below we have listed the topics discussed in NCERT Solutions for Class 8 Science Chapter 2. The list gives you a quick look at the different topics and subtopics of this chapter.

Section in NCERT BookTopics Discussed
2.2Where do Microorganisms Live?
2.3Microorganisms and Us
2.4Harmful Microorganisms
2.5Food Preservation
2.6Nitrogen Fixation
2.7Nitrogen cycle

NCERT Solutions for Class 8 Science Chapter 2 – A Brief Discussion

CBSE Class 8 Science NCERT Solutions Chapter 2 helps students to clear their doubts and to score good marks in the board exam. All the questions are solved by experts with a detailed explanation that will help students complete their assignments & homework. Having a good grasp over CBSE NCERT Solutions for Class 8 Science will further help the students in their preparation for board exams and other competitive exams such as NTSE, Olympiad, etc.

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