class 8 ch 2

CBSE Class VIII (8th) - Science Chapter 2. MICROORGANISMS : FRIEND AND FOE | Lesson Exercises

1.Question:  Fill in the blanks:

(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  yeast.

(d) Cholera is caused by  pathogens.

2.Question: 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 

3. Question: Match the organisms in Column I with their action in Column II.

Column A	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

Answer : 

Column A	Column B
(i) Bacteria	(g) Producing antibodies
(ii) Rhizobium	(a) Fixing Nitrogen
(iii) Lactobacillus	(b) Setting of curd
(iv) Yeast	(c) Baking of bread
(v) A protozoan	& (d) Causing Malaria & (e) Causing Cholera
(vi) A Virus	(f) Causing AIDS

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

Answer : The microorganism can not be sean with naked eyes. Microorganisms are too small and are not visible to the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass.Others cannot be seen without the help of a microscope.

5.  Question: What are the major groups of microorganisms?

Answer: Microorganisms are classified into four major groups.

1. Bacteria
2. Fungi
3. Protozoa
4. Algae

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

Answer : Bacteria like Rhizobium and blue green algae are  microorganisms which can fix atmospheric nitrogen in the soil thus increase soil fertility.These microbes are commonly called biological nitrogen fixers.

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

Answer :

1. Microorganisms are quite usefull in our lives in many way :
2. Yeast - a microorganism is used for the large scale production of alcohol, wine and acetic acid (vinegar).
3. Lactobacillus- a bacterial microorganism helps us  in truning milk into curd.
4. Yeast a microorganism is used in  baking industry for making breads, pastries and cakes
5. Bacteria are also used for commercial production of antibiotics medicines like Streptomycin, tetracycline and erythromycin.
6. They help in Increasing Soil Fertility. Microorganisms like Rhizobium and blue green algae are of great importance in agriculture.
7. They increase soil fertility by fixing atmospheric nitrogen and converting it into nitrogenous compounds..
8. Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is released to the atmosphere.
9. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.
10. Some microorganisms inside our bodies help in food digestion.

8. Question: 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. Pathogens spread a number of Microbial diseases or communicable diseases like cholera, common cold, chicken pox and tuberculosis from an infected person to a healthy person through air, water, food or physical contact.

Some microorganisms spoil food, clothing and leather.

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

Answer : Antibiotics is a medicine which kills or stop the growth of the disease-causing microorganisms in human and animals. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics medicines like Streptomycin, tetracycline and erythromycin are commercially produced from bacteria and fungi.

Precaution in taking Antibiotics

It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. We must finish the course prescribed by the doctor. If we take antibiotics when not needed or in wrong doses, it may make the drug less effective when you might need it in future. Also antibiotics taken unnecessarily may kill the beneficial bacteria in our body. Antibiotics,  should not be taken for common cold and flu as these are caused by viruses and antibiotics are not effective against virus causing them.

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Chapter 2. MIICROORGANISMS : FRIIEND AND FOE | Science | Lesson Exercises |CBSE  NCERT |Class VIII (8th)