8 Chapter: Microorganisms – Friend and Foe NOTES

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 8 Class - Chapter: Microorganisms – Friend and Foe  NOTES

1. Fill in the blanks.

(a) Microorganisms can be seen with the help of a ____________.
Answer: Microscope

(b) Blue-green algae fix __________ directly from the air and enhance the fertility of the soil.
Answer: Nitrogen

(c) Alcohol is produced with the help of __________.
Answer: Yeast

(d) Cholera is caused by __________.
Answer: Bacteria (Vibrio cholera)

2. Tick the correct answer.

(a) Yeast is used in the production of
Answer: (ii) alcohol

(b) The following is an antibiotic
Answer: (ii) Streptomycin

(c) Carrier of malaria-causing protozoan is
Answer: (i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is
Answer: (ii) housefly

(e) The bread or idli dough rises because of
Answer: (iii) growth of yeast cells

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

3. Match the organisms in Column A with their action in Column 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 microorganisms be seen with the naked eye? If not, how can they be seen?

Microorganisms cannot be seen with the naked eye because they are very small.
They can be seen using a microscope.

5. What are the major groups of microorganisms?

  1. Bacteria

  2. Fungi

  3. Protozoa

  4. Algae

  5. Viruses

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

Answer: Rhizobium

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

  1. They help in cleaning the environment.

  2. Lactobacillus helps in making curd.

  3. Used in making cheese and pickles.

  4. Help in fermentation of idli and dosa batter.

  5. Yeast helps in making bread and cakes.

  6. Used to produce alcohol and vinegar.

  7. Used to produce antibiotics.

  8. Help in producing vaccines.

  9. Some bacteria fix nitrogen in soil.

  10. They decompose dead plants and animals.

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

Microorganisms cause diseases in plants, animals, and humans.
For example, cholera in humans is caused by bacteria.
They spoil food and cause food poisoning.
They can also damage clothes and leather.

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

Antibiotics: Medicines that kill or stop the growth of disease-causing microorganisms.

Precautions:

  • Take antibiotics only on a doctor’s advice.

  • Complete the full course prescribed by the doctor.