ncert solutions for class 8 science chapter 1

SCIENCE CHAPTER 1 MICROORGANISMS  FRIEND AND FOE : 

MICROORGANISMS : FRIEND AND FOE

 TEXT BOOK EXERCISES

Q.1 ) 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 bacteria.

Q.2 ) Identify the correct answer :

(a) Yeast is used in the production of

• Sugar

• Alcohol

• Hydrochloric acid

• Oxygen

(b) The following is an antibiotic

• Sodium bicarbonate

• Streptomycin

• Alcohol

• Yeast

(c) Carrier of malaria - causing protozoan is :

• Female Anopheles mosquito

• Cockroach

• Housefly

• Butterfly

(d) The most common carrier of communicable disease is

• Ant

• Housefly

• Dragonfly

• Spider

(e) The bread of idli dough rises because of

• Heat

• Grinding

• Growth of yeast cells

• Kneading

(f) The process of conversion of sugar into alcohol is called :

• Nitrogen fixation

• Molding

• Fermentation

• Infection

Q.3 ) Match the organisms in column 'A' with their action in column 'B'.

Q.4 ) Can microorganisms be seen with the naked eye? If no, how can they be seen? 

Ans. No, microorganisms can't be seen with naked eyes because they are too small to be seen.  We can only see them with the help of microscope.

Q.5) What are the major groups of microorganisms?

Ans. The various groups of microorganisms are:

• Bacteria

• Fungi

• Protozoan

• Algae

• Virus

Q.6)Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans. The microorganisms which can fix atmospheric nitrogen are:

• Rhizobium

• Blue green algae

• Azotobacter

• Clostridium

Q.7) Write 10 lines on the usefulness of microorganisms in our lives.

Ans.10 lines on the usefulness of microorganisms in our lives are as follows:

1. Microorganisms are used in making anti-bodies.

2. Microorganisms like lactobacillus helps in the formation of curd.

3. Microorganisms like yeast helps in the formation of alcohol, vinegar and bread.

4. Microorganisms like rhyzobium fix atmospheric nitrogen.

5. Microorganisms are used to prepare medicines.

6. Microorganisms clean our environment.

7. Microorganisms are used to prepare vaccines.

8. Microorganisms increase our soil fertility.

9. Microorganisms are used in various processes like fermentation.

10. Microorganisms like protozoans form an important link in the food chain.

Q.8) Write a short paragraph on the harms caused by microorganisms.

Ans. Microorganisms are harmful to us in many ways.Some microorganisms cause various types of diseases in human beings, animals and also in plants. For example; cholera, tuber tuberculosis, anthrax, foot and mouth disease, black root of cabbage, white rust of mustard etc. The microorganisms which cause diseases are known as pathogens. Some microorganisms spoil food, clothes, leather, etc. Some microorganisms cause poisoning.

Q.9) What are antibiotics? What precautions must be taken while taking antibiotics?

Ans)Antibiotics are the chemicals produced by certain microorganisms and are used to kill or inhibit the growth of other microorganisms. Antibiotics are also called antibacterials.It was discovered by Alexander Flemmings. They are not effective agent viruses.

The precautions while taking antibiotics are:1. Antibiotics should be taken only when prescribed by a qualified doctor.2. Course advised by the doctor should be completed.3. Antibiotics should not be taken in excess because it can damage useful microorganisms in the body.