Microbes in Human Welfare: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. Name the microbe in Swiss cheese.
2. Which enzyme clarifies fruit juice?
3. Name the immunosuppressant from a fungus.
4. Expand BOD.
5. Which beetle controls aphids?
6. Name a free-living nitrogen-fixing bacterium.
7. Who developed biogas technology in India?
8. Name the vessel used for industrial fermentation.
9. Name a drink made by distillation.
10. What is SCP?

D. Short answer I (2 marks each)

1. How is curd formed from milk?
2. Why does dough rise?
3. Give two uses of microbial enzymes.
4. Why is cow dung used in biogas plants?
5. What is activated sludge? What happens to it?
6. How does Bt kill caterpillars?
7. Why are baculoviruses ideal for IPM?
8. Why do organic farmers not eradicate pests completely?

Rough work

E. Short answer II (3 marks each)

1. Describe the discovery of penicillin.
2. Name three bioactive molecules, their microbial sources and uses.
3. Describe the secondary treatment of sewage.
4. Describe the working of a biogas plant.
5. Name three biofertilisers from different groups and their roles.
6. What is BOD? How is it related to pollution?

F. Long answer (5 marks each)

1. Describe sewage treatment from raw sewage to the release of effluent, with a flow chart.
2. What are biocontrol agents? Describe the role of a bacterium, a fungus and a virus.

G. HOTS (higher-order thinking)

1. Why is the floc stage aerobic but the sludge digester anaerobic?
2. Why should antibiotics not be used carelessly?
3. Why is biogas popular in villages, not cities?
4. Why does Bt toxin not kill the Bacillus itself?

20 MCQs

1. Curd is formed by
   (a) yeast (b) Aspergillus (c) Lactobacillus (d) Acetobacter
2. Large holes in Swiss cheese are due to
   (a) CO₂ (b) O₂ (c) N₂ (d) methane
3. Baker's yeast is
   (a) Lactobacillus (b) Monascus (c) Penicillium (d) Saccharomyces cerevisiae
4. Distilled beverage
   (a) beer (b) whisky (c) wine (d) toddy
5. Penicillin is from
   (a) Streptomyces (b) Penicillium notatum (c) Aspergillus (d) Trichoderma
6. Acetic acid is made by
   (a) Clostridium (b) Lactobacillus (c) Aspergillus niger (d) Acetobacter aceti
7. Clot buster
   (a) streptokinase (b) statin (c) cyclosporin (d) lipase
8. Cyclosporin A source
   (a) Monascus (b) Streptococcus (c) Trichoderma polysporum (d) Penicillium
9. Lipases are used in
   (a) juices (b) cheese (c) bread (d) detergents
10. Primary treatment removes
    (a) organic matter by microbes (b) floating debris and grit (c) BOD fully (d) methane
11. Flocs are formed in
    (a) primary tank (b) digester (c) aeration tank (d) river
12. Biogas does not contain much
    (a) oxygen (b) methane (c) CO₂ (d) H₂S
13. Methanogens live in
    (a) human skin (b) rumen of cattle (c) leaves (d) air
14. Ladybird beetles control
    (a) mosquitoes (b) caterpillars (c) aphids (d) nematodes
15. Bt is a
    (a) fungus (b) protozoan (c) virus (d) bacterium
16. Nucleopolyhedrovirus is a
    (a) baculovirus (b) bacterium (c) fungus (d) plasmid
17. Symbiotic N₂ fixer in legume nodules
    (a) Rhizobium (b) Azotobacter (c) Glomus (d) Anabaena
18. Glomus provides plants with
    (a) nitrogen (b) potassium (c) water only (d) phosphorus
19. Biofertiliser in paddy fields
    (a) Glomus (b) cyanobacteria (c) Trichoderma (d) Bt
20. Ganga Action Plan aims to
    (a) make dams (b) grow fish (c) build sewage treatment plants (d) make biogas

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: Curd is more nutritious than milk. R: LAB increase vitamin B₁₂.
2. A: Secondary treatment reduces BOD. R: Aerobic microbes in flocs consume organic matter.
3. A: Biogas plants are common in rural areas. R: Cow dung is rich in methanogens.
4. A: Baculoviruses harm non-target insects. R: They are species-specific.
5. A: Wine is made without distillation. R: Whisky and brandy are distilled.
6. A: Mycorrhizal plants tolerate drought better. R: Glomus absorbs phosphorus for the plant.

Key: 1 (a) · 2 (a) · 3 (a) · 4 (d) · 5 (b) · 6 (b)

Answers to the practice set