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

NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend and Foe will help you in getting better grades in your exams and have an advantage over your classmates. These NCERT Solutions are in detailed manner and accurate so you can easily extract the useful information from it.

Chapter 2 CBSE Class 8 Science NCERT Solutions will provide a lot of relevant content, making you well versed in variety of topics and able to easily recall your ideas. It will help in building a great foundation of knowledge.

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

Exercises

1. Fill in the blanks:
(a) Microorganisms can be seen with the help of a _______.
(b) Blue green algae fix _______ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of _______.
(d) Cholera is caused by _______.

Solution

(a) microscope
(b) nitrogen
(c) yeast
(d) bacteria

2. Tick the correct answer:

(a) Yeast is used in the production of:
(i) Sugar
(ii) Alcohol
(iii) Hydrochloric Acid
(iv) Oxygen
▶ (ii) Alcohol

(b) The following is an antibiotic:
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
▶ (ii) Streptomycin

(c) Carrier of malaria-causing protozoan is:
(i) Female Anopheles mosquito
(ii) Cockroach
(iii) House fly
(iv) Butterfly
▶ (i) Female Anopheles mosquito

(d) The most common carrier of communicable diseases is :
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
▶ (ii) housefly

(e) The bread or idli dough rises because of :
(i) heat
(ii) grinding
(iii) growth of yeast cell
(iv) kneading
▶ (iii) growth of yeast cell

(f) The process of conversion of sugar into alcohol is called :
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection
▶ (iii) fermentation

3. Match the organisms in Column A with their action in Column B.

A	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

Solution

A	B
(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

4. Can microorganism be seen with naked eye? If not, how can they be seen?

Solution

Microorganisms cannot be seen without magnifying glasses or microscopes.

5. What are the major groups of microorganism?

Solution

The major groups of micro-organisms are bacteria, fungi, protozoa, algae and virus.

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

Solution

Rhizobium bacteria and blue green alga can fix atmospheric nitrogen in the soil.

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

Solution

(i) Microorganisms are the decomposers and they help in the recycling of substances.
(ii) They are used in the preparation of curd and also in the preparation of bread and cake.
(iii) They are used in the preparation of idli, dosa and dhokla.
(iv) They are used in production of alcohol, wine and vinegar.
(v) Algal cell extract such as agar are used for preparing medicines, food and cosmetics.
(vi) They are used in making of vaccines.
(vii) They are used in agriculture to increase the soil fertility.
(viii) They are used in decomposing the tissues of dead organisms.
(ix) They are used to decompose sewage and other wastes in water.
(x) They are used in cleaning the environment.

8. Write a short paragraph on the harmful effects of microorganisms.

Solution

Pathogens can cause diseases in both humans and animals. They can cause diseases such as tuberculosis, cholera, and typhoid in humans. Viruses can cause foot and mouth disease in cattle. The disease anthrax is caused by a bacteria and affects both humans and cattle. In plants, they cause diseases like wheat rust and citrus canker. In animals they cause diseases like foot and mouth disease and anthrax.

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

Solution

Antibiotics are the medicine which kill or stop the disease causing microbes in our body. Precautions to be taken while taking antibiotics are:
(i) Antibiotics should be taken only on the advice of a qualified doctor.
(ii) One must finish the entire course prescribed by the doctor.
(iii) Antibiotics, however, are not effective against cold and flu as these diseases are caused by viruses.