NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe

NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe help students to clear all their doubts. These solutions provide you with the answers to all the questions given in the NCERT textbook. CBSE Class 8 Science Chapter 2 Solutions is prepared by expert teachers as per the latest CBSE syllabus and guidelines.

Solving NCERT Solutions will help you to understand the concepts related to Microorganisms Friend and Foe. NCERT Solutions for Class 8 Science Chapter 2 contains an in-depth explanation of each question of NCERT Science textbook. These solutions cover important concepts in different patterns like MCQs and short answer questions, worksheets and more and help you top score good marks in the exam.

NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe PDF

Question 1: Fill in the blanks:

(a) Microorganisms can be seen with the help of a ____________.
(b) Blue green algae fix __________ directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.

Answer: (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 a 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.

Usefulness of microorganisms are listed below:

  • 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: 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. Some of the common diseases affecting humans are cholera, common cold, chickenpox and tuberculosis. Several microorganisms not only cause diseases in humans but also in animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Disease-causing microorganisms in plants like wheat, rice, potato, sugarcane, orange, apple and others reduce the yield of crops.

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.

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