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class 8 science chapter 2 microorganisms friend and foe notes pdf


Class 8 Science, Chapter 2 Microorganisms friend and foe notes pdf  

Class :-8

Subject:- विज्ञान (Science)

Chapter:- 2 

Chapter name: Microorganisms Friend and Foe 


Fill in the blanks:

  1. Microorganisms can be seen with the help of a---------
  2. Blue green algae fix---------------directly from air to enhance fertility of soil.
  3. Alcohol is produce with the help of----------
  4. Cholera is caused by------------------
  1. Microscope
  2. nitrogen
  3. microorganisms
  4. bacteria

Tick the correct answer

(a) Yeast is used in the production of-

  1. Sugar 
  2. alcohol ✔️
  3. hydrochloric acid
  4. oxygen

(b) The following is an antibiotic-

  1. Sodium bicarbonate
  2. Streptomycin ✔️
  3. Alcohol
  4. Yeast

(c) Carrier of malaria-causing protozoan is-

  1.  female Anopheles mosquito ✔️
  2. cockroach
  3. housefly
  4. butterfly

(d) The most common carrier of communicable disease is-

  1. ant
  2. housefly ✔️
  3. dragonfly
  4. spider

(e) The bread or idly dough rises because of 

  1. heat 
  2. grinding
  3. growth of yeast cell ✔️
  4. kneading  

(f) The process of conservation of sugar inti alcohol is called-

  1. nitrogen fixation 
  2. moulding
  3. fermentation ✔️
  4. infection 


Match the organisms in column I with their action in column II


Column I


Column II




Fixing Nitrogen




Setting of curd




Baking of bread




Causing Malaria


A Protozoa


Causing Cholera


A Virus


Producing antibodies


  1. -e
  2. -a
  3. -b
  4. -c
  5. -d
  6. -f

Question-4 Can microorganisms been seen with the necked eyes. ? If not, how can they be seen?

Answer- No, Microorganisms can not seen by necked eyes 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 in to four major groups are-
  1. Bacteria
  2. Fungi
  3. Protozoa
  4. Algae
Download PDF Chapter 2 Microorganisms friend and foe👇👇👇

Question-6 Name the microorganisms that can fix atmospheric nitrogen in the soil.

Answer  Bacteria such as Rhizobium and certain blue-green present in the soil. They can fix atmospheric nitrogen in soil 

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

Answer -

  • Microorganisms are used in baking, pickling and other food makings process
  • They used in making of wine and bread.
  • They used in dairy for formation of cured.
  • Microbes are used to reduce pollution.
  • Microorganisms are used to increase the soil fertility.
  • They are used for fixing atmospheric nitrogen into the soil.
  • Microbes are used in preparing many medicine and antibiotic.
  • They are 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 disease in human being, plant and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.
Some of the common disease affecting humans by microorganisms are cholera, common cold, chicken pox and tuberculosis . Several microorganisms not only cause disease in human but also in animals also in crops.

Question-9 What are antibiotics? What precaution must be taken while taking antibiotics?
Answer- Following precaution must be taken while taking antibiotics:-
  • Antibiotics must be taken only on the advice of a qualified doctor.
  • One must finish the course prescribed by the doctor.
  • Antibiotic must be avoid when not need or in wrong does. 

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