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

Students will learn in detail about the types and classification of microbes, and how they can be identified as harmful or helpful. Many microorganisms are used in food preparation and fermentation.

Curd is one such food item prepared through the fermentation process. This chapter of NCERT solutions for class 8 science will also explains the medical definitions of antibiotics and vaccinations and how these are prepared with the help of microorganisms.

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1. Fill in the blanks.

(a) Microorganisms can be seen with the help of a microscope.

An instrument that is used for visualizing very small organisms is called microscope.

(b) Blue green algae fix nitrogen directly from air and enhance the fertility of soil.

Organisms like blue-green algae fix the atmospheric nitrogen directly and are also useful in increasing soil’s fertility. These are called biological fixers of nitrogen.

(c) Alcohol is produced with the help of yeast.

A form of bacteria that is involved in fermentation process is called yeast. It produces alcohol as an end product.

(d) Cholera is caused by Vibrio cholerae

Microorganisms cause diseases. Bacteria cause cholera and the organisms is Vibrio cholera.

2. Tick the correct answer.

(a) Yeast is used in the production of

(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen

Ans. Alcohol

(b) The following is an antibiotic

(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast

Ans. Streptomycin

(c) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly

Ans. female Anopheles mosquito

(d) The most common carrier of communicable diseases is

(i) ant (ii) housefly (iii) dragonfly (iv) spider

Ans. housefly

(e) The bread or idli dough rises because of

(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading

Ans. growth of yeast cells

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

(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection

Ans. fermentation

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

A bacterial disease called cholera is caused by the pathogen Vibrio cholera. Rhizobium is called the nitrogen fixer organism. Curd that we settle in our houses comprise of Lactobacillus bacteria. A process of fermenting bread involves yeast as an organism.

Plasmodium causes malaria which is a protozoan. Virus damage the immune system of the body. Human immunodeficiency virus (HIV) virus causes Acquired immunodeficiency syndrome (AIDS).

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

Ans. We cannot see microorganisms as they are very small in size. An instrument that increases the size of smaller organisms, so that they can be viewed is called microscope.

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NCERT Solutions for Class 8 Maths

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5. What are the major groups of microorganisms?

Ans. 4 major groups are:

• Algae
• Fungi
• Bacteria
• Protozoa.

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

Ans. Fixers of atmospheric nitrogen are:

• Rhizobium
• Acetobactor
• Blue-green algae

Also download the PDF for: Class 8 Science Syllabus and Class 8 Maths Syllabus

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

Ans. Usefulness of microorganisms:

• Preparation of bread, curd and cake by fermentation process.
• Alcohol production
• Keeping the environment clean by reducing pollution
• Medicinal preparations
• Increase fertility of soil
• Treatment of effluents
• Used as preservatives like pickles
• Production of cheese
• Production of wine and beer
• Enzyme production

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

Ans. Diseases are caused by microorganisms in animals, plants and also in humans. They are termed as pathogens. In humans, diseases are caused by intake of dirty water or food or by direct/indirect contact.

Examples include common cold, tuberculosis, cholera and chicken pox. In animals, anthrax is caused in cattles, the virus causes the disease of foot & mouth. In plants, diseases occur in rice, orange, potato, sugarcane and many others which reduce the yield.

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

Ans. The medications provided by doctors for killing or stopping the microorganisms that cause disease are called antibiotics. These can be prepared with the help of fungi or bacteria like tetracycline and streptomycin.

Thus certain precautions should be considered like consulting from a doctor (qualified), course completion, correct dosage and non-utilization of unnecessary medications.

Links to Other Resources for Class 8 Science

Other Class 8 Science Related Links
Understanding Structure and Functions of a Cell
Deforestation, Afforestation and Reforestation
Frictional Force Definition, and Types with Example
Compare LPG and Wood as Fuel
Water Pollution Causes and Effects with Example