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

Download the exclusive NCERT Solutions for Class 8 Science Chapter 2 - Microorganisms Friend and Foe. These solutions are prepared and reviewed by the subject matter experts.

Created On: Jun 8, 2021 00:17 IST
NCERT Solutions for Class 8 Science Chapter 2
NCERT Solutions for Class 8 Science Chapter 2

NCERT Solutions for Class 8 Science Chapter 2 - Microorganisms Friend and Foe will help you find the best answers to all questions given at the end of this chapter. All these answers have been put together by the subject experts after analysing the concepts presented in the latest NCERT Book for Class 8 Science. You will get here the appropriate answers that are written in the simplest manner so that all the class 8th students can easily understand these answers and prepare well for their Science Exam 2021-2022. NCERT Solutions can be downloaded in PDF and used as and when required.

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

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 _________.

Answer:

(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.

2. 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. Match the organisms in Column I with their action in Column II.

Column I

Column II

(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 I

Column II

(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 microorganisms be seen with the naked eye? If not, how can they be seen?

Answer:

No, microorganisms are very small so they cannot be seen with the naked eye. They can be seen with the help of a magnifying glass or a microscope.

5. What are the major groups of microorganisms?

Answer:

Microorganisms are classified into four major groups.  These  groups  are:

(i) Bacteria

(ii) Fungi

(iii) Protozoa

(iv) Algae

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

Answer:

Certain bacteria such as Rhizobium and blue green algae can fix atmospheric nitrogen in the soil.

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

Answer:

(i) Micro organisms are useful for us in the following ten ways:

(ii) Bacterium  Lactobacillus promotes the formation of curd from milk.

(iii) Certain bacteria such as Rhizobium and blue green algae fix the atmospheric nitrogen and increase soil fertility.

(iv) Microbes such as bacteria and fungi help to reduce pollution by breaking down dead bodies and waste into manure.

(v) Microbes are used to prepare antibiotics that help to control some diseases. Streptomycin, tetracycline, anderythromycin are some commonly used antibiotics.

(vi) Microbes are also used in preparation of vaccines

(vii) Yeast is used in the commercial production of alcohol and wine.

(viii) Yeast is also used in the preparation of bakery products like cake and bread.

(ix) Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.

(x) Certain microbes are also used in the biological treatment of sewage.

8. 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. For example, diseases in humans like common cold, tuberculosis, chicken pox, polio, typhoid, malaria, etc. are caused by microorganisms. In animals, anthrax is a dangerous disease which is also caused by the microorganisms. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others that reduce the yield of crops.  Some microorganisms spoil food, clothing and leather products.

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

Answer:

Antibiotics are medicines produced by growing certain microorganisms to kill or stop the growth of the disease-causing microorganisms.

→ Precautions to be taken while using antibiotics are:

→ Antibiotics should be taken only on the advice of a qualified doctor.

→ One must complete the course prescribed by the doctor.

→ If taken unnecessarily antibiotics may kill the beneficial bacteria in the body.

→ Antibiotics should be taken in the right amount because a wrong dose of antibiotics makes the drug ineffective.

Download NCERT Solutions for Class 8 Science Chapter 2 in PDF

Also, check below the NCERT Books and NCERT Solutions for all major subjects of Class 8:

NCERT Books for All Subjects of Class 8 (Latest Editions for 2021-2022)

NCERT Solutions for All Subjects of Class 8 (Updated for 2021-2022)

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