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

Class :-8

Subject:- विज्ञान (Science)

Chapter:- 2 

Chapter name: Microorganisms Friend and Foe 

Question-1 

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------------------

Answer-

1. Microscope
2. nitrogen
3. microorganisms
4. bacteria

Question-2

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 

Question-3

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

S.No.	Column I	S.No.	Column II
1	Bacteria	A	Fixing Nitrogen
2	Rhizobium	B	Setting of curd
3	Lactobacillus	C	Baking of bread
4	Yeast	D	Causing Malaria
5	A Protozoa	E	Causing Cholera
6	A Virus	f	Producing antibodies

Answer-

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

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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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Chapter-2 Microorganisms friend and foe 

Chapter-3 Synthetics Fibres and Plastics