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Textbooks

NCERT Science Std 8

Microorganisms: Friend and Foe

Chapter 2 : Microorganisms: Friend and Foe

Q. 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.

(d) Cholera is caused by _______.

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Q. Where do microorganisms live?

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Q. What are the major groups of microorganisms?

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

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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

(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 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) Moulding (iii) Fermentation (iv) Infection

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Q. Take two pots and fill each pot half with soil. Mark them A and B. Put plant waste in pot A and things like polythene bags, empty glass bottles and broken plastic toys in pot B. Put the pots aside. Observe them after

3 - 4

weeks.

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Q. How do you prevent the spread of communicable diseases?

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Q. Why does the teacher keep telling us not to let water collect anywhere in the neighbourhood?

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Q. Paheli wonders how food can become a 'poison'.

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

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

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Q. Take

1_{/ 2}

kg flour (atta or maida), add some sugar and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough. What do you observe afetr two hours? Did you find the dough rising?

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Q. Write a short paragraph on the harms caused by microorganisms?

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Q. Take a

500

mL beaker filled upto

\frac{3}{4}

with water. Dissolves 2 - 3 teaspoons of sugar in it. Add half a spoon of yeast powder to the sugar solution. Keep it covered in a warm place for 4 - 5 hours. Now smell the solution. Could you get a smell?

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

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

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