NCERT Solution for Class 8 Science Chapter 2: Microorganisms: Friends and Foe

NCERT Solutions for class 8 Science Chapter 2 Microorganisms: Friends and Foe: The chapter on Microorganisms: Friends and Foe is important for students approaching the board exams. This article introduces NCERT solutions designed to help students explain the concepts of further learning and how to write to get good grades on exams. The solutions are presented in very simple language for ease of understanding.

Solution of NCERT CBSE Science of Class 8 Chapter 2 Microorganisms: Friends and Foe: This chapter explains how microorganisms can be our friend and foe. It also explains the nature of microbes. It further describes the usefulness and harmful effects of microorganisms in detail. Revise the basic concepts of Microorganisms: Friends and Foe for quick revision and class notes.

Q1: Fill in the Blanks:

• (a) Microorganisms can be seen with the help of a _____.
• (b) Blue-green algae fix ____ directly from the air and enhance the fertility of the 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 the air and enhance the fertility of the soil.
• (c) Alcohol is produced with the help of yeast.
• (d) Cholera is caused by bacteria.

 Q2: Tick the Correct Answer.

• (a) Yeast is used in the production of
  • (i) sugar (ii) alcohol (iii) hydrochloric acid (iv) Oxygen
• (b) The following is an antibiotic
  • (i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
• (c) Carrier of malaria-causing protozoan is
  • (i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly
• (d) The most common carrier of communicable diseases is
  • (i) ant (ii) housefly (iii) dragonfly (iv) spider
• (e) The bread or idli dough rises because of
  • (i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
• (f) The process of conversion of sugar into alcohol is called
  • (i) nitrogen fixation (ii) molding (iii) fermentation (iv) infection

Answer:

• a) Yeast is used in the production of alcohol.
• b) The following is an antibiotic-Streptomycin.
• c) The carrier of malaria-causing protozoan is the female Anopheles mosquito.
• d) The most common carrier of communicable diseases is housefly.
• e) The bread or idli dough rises because of groth of yeast cells.
• f) The process of conversion of sugar into alcohol is called fermentation.

Q3. Match the Organisms in Column A with their Action in Column B.

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	e) 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
	(g) Producing antibodies

Q4: Can Microorganisms be seen with the Naked Eye? If not, how can they be seen?

Answer:

Microorganisms are so tiny in size that they cannot be seen with the naked 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. That is why these are also called microbes.

Q5. What are the Major groups of Microorganisms?

Answer:

Microorganisms are classified into four major groups:

• a) Bacteria
• b) Fungi
• c) Protozoa
• d) Some algae

Viruses, though different from the above-mentioned living organisms, are considered microbes.

Q6: Name the Microorganisms which can fix Atmospheric Nitrogen in the soil.

Answer:

Bacteria such as Rhizobium, Azotobacter, and certain blue-green algae present in the soil fix atmospheric nitrogen in the soil.

Q7: Write 10 lines on the Usefulness of Microorganisms in our lives.

Answer:

Microorganisms play an important role in our lives. They are used for various purposes:

1. They are used in the preparation of curd, bread, and cake.
2. They are also used in cleaning up the environment. For example, organic wastes (vegetable peels, remains of animals, feces, etc.) are broken down into harmless and usable substances by bacteria.
3. Bacteria are used in the preparation of medicines.
4. In agriculture, they are used to increase soil fertility by fixing nitrogen.
5. Bacteria are also involved in the making of cheese, pickles, and many other food items.
6. Bacteria and yeast are also helpful for the fermentation of rice idlis and dosa batter.
7. Microorganisms are used for the large-scale production of alcohol, wine, and acetic acid (vinegar).
8. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline, and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.
9. Some bacteria are able to fix nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility.
10. Microorganisms can be used to degrade harmful and smelly substances and thereby clean up the environment.

Q8: Write a short Paragraph on the Harmful Effects of Microorganisms.

Answer:

Microorganisms are harmful in many ways. Some microorganisms cause diseases in human beings. Microbial diseases spread from an infected person to a healthy person through air, water, food, or physical contact. Examples of such diseases include cholera, the common cold, chicken pox, and tuberculosis. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple, and others. The diseases reduce the yield of crops. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. Some microorganisms spoil clothing and leather.

Q9: What are Antibiotics? What Precautions must be taken while taking Antibiotics?

Answer:

Antibiotics are medicines that fight infections caused by bacteria in humans and animals by either killing the bacteria or making it difficult for the bacteria to grow and multiply.

But some precautions must be taken while taking antibiotics. It should be taken only on the advice of a qualified doctor. Also, the course prescribed by the doctor should be completed. If antibiotics are taken when not needed or in the wrong doses, it may make the drug less effective for future use. Also, antibiotics taken unnecessarily may kill the beneficial bacteria in the body.