CBSE Class 12 Biology Microbes in Human Welfare Question bank

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Biology: Chapter 10 – Microbes in Human Welfare (Question Bank)

How does a small amount of curd added to fresh milk convert it into curd? Mention a nutritional quality that gets added to the curd.

Answer: The curd contains a large number of lactic acid bacteria (LAB). They multiply in the milk and convert it into curd by producing lactic acid, which coagulates and partially digests the milk proteins. The nutritional quality improves by the increase in vitamin B₁₂.

Why is the secondary treatment of water in a sewage treatment plant called biological treatment?

Answer: In this treatment, the organic wastes of the sewage water are decomposed by certain microorganisms in the presence of water. So it is called biological treatment.

An antibiotic called 'Wonder Drug' was used to treat the wounded soldiers of America during World War II. Name the drug and the scientist who discovered it.

Answer: The drug is penicillin; it was discovered by Alexander Fleming.

You have observed that fruit juice in bottles bought from the market is clearer as compared to those made at home. Give a reason.

Answer: The bottled juices are clarified by the use of the enzymes pectinase and proteases, which break down the pectin and the proteins.

Alexander Fleming discovered penicillin, but its full potential as an effective antibiotic was established by other scientists. Name the two scientists.

Answer: Ernst Chain and Howard Florey.

Name the plant whose sap is used in making 'toddy'. Mention the process involved in it.

Answer: The palm tree. The sap is fermented (by the yeast) to make toddy.

Name two alcoholic drinks produced in each of the following ways: (i) by distillation and (ii) without distillation.

Answer:

1. By distillation: whisky, brandy and rum (any two).
2. Without distillation: wine and beer.

Lactic acid bacteria (LAB) are commonly used in the conversion of milk into curd. Mention any two other functions of LAB that are useful to humans.

Answer: (i) LAB in the human intestine synthesise vitamin B₁₂. (ii) LAB check the growth of the disease-causing microbes in the stomach (and the intestine).

How do mycorrhizae function as biofertilisers? Explain with an example.

Answer: Mycorrhizae are fungi associated with the roots of plants. Many members of the genus Glomus form mycorrhiza. The fungal symbiont absorbs water and minerals, like phosphorus, from the soil and provides them to the plant. In return, the plant gives the fungus the food. The plants with mycorrhiza show better growth and resistance to the root pathogens, and tolerance to salinity and drought.

Cyanobacteria (Nostoc, Anabaena) are used as biofertilisers in certain crop fields. Name one such crop. Also mention the names of two other microorganisms which perform the same function.

Answer: The crop is paddy (rice). Other microorganisms which fix nitrogen are Rhizobium and Azotobacter (also Azospirillum).

Which ministry of the Government of India initiated the Ganga Action Plan and the Yamuna Action Plan? What are the objectives of these plans?

Answer: The Ministry of Environment and Forests. The objective is to save these rivers from pollution. It was proposed to build a large number of sewage treatment plants, so that only treated sewage is discharged into the rivers.

Fill in the blanks a, b, c, d, e and f given in the following table. (

What is the biochemical oxygen demand (BOD) test? At what stage of sewage treatment is this test performed? The BOD levels of three samples of water labelled A, B and C are 30 mg/L, 10 mg/L and 500 mg/L respectively. Which sample of water is most polluted?

Answer: The BOD test measures the rate of uptake of oxygen by the microorganisms in a sample of water, which shows how much organic matter is present. It is performed at the secondary (biological) treatment stage, to know the quality of the effluent. Sample C is the most polluted, because it has the highest BOD (500 mg/L). The greater the BOD, the greater the polluting potential.

Given below is the flow chart of sewage treatment. Fill in the blank spaces marked a to f. (

Answer:

1. Primary treatment (physical filtration and sedimentation)
2. Aeration tank (the secondary or biological treatment)
3. Flocs (masses of bacteria with fungal filaments)
4. Biochemical oxygen demand (BOD)
5. Activated sludge
6. Water bodies, such as a river or stream

What are biofertilisers? A farmer is advised to add a culture of a bacterium in the soil before sowing the crop. Name the bacterium in the culture. How is this bacterium useful to the crop?

Answer: Biofertilisers are organisms that enrich the nutrient quality of the soil. The bacterium is Azotobacter/Azospirillum (free living). (Rhizobium is used for leguminous crops.) The bacterium fixes the atmospheric nitrogen into organic forms which are used by the plant as a nutrient.

What are statins? Name the microorganism that produces this substance. How is it medically important?

Answer: Statins are cholesterol-lowering agents. They are produced by the yeast Monascus purpureus. They act by competitively inhibiting the enzyme responsible for the synthesis of cholesterol, and are used as blood cholesterol-lowering agents.

How does primary sludge differ from activated sludge? What type of changes in the sludge is carried out in the anaerobic sludge digester? Give the composition of biogas produced in the sewage treatment plant.

Answer: Primary sludge is all the solids, like soil and small pebbles, that settle down in the settling tank during the primary treatment of sewage. Activated sludge is the sediment of the bacterial flocs in the settling tank during the biological treatment. Flocs are masses of bacteria held together by slime and fungal filaments. A part of the activated sludge is used as an inoculum in the aeration tank, and the rest is passed into a large tank called the anaerobic sludge digester. In this tank, bacteria which grow anaerobically digest the bacteria and the fungi in the sludge. The biogas produced is a mixture of methane, hydrogen and carbon dioxide.

Tina went to a supermarket with her mother to buy rice. They saw that two types of products were available: one organically grown and the other conventionally grown. The organically grown crops are costlier, so Tina's mother does not want to purchase them. (i) Which rice should be purchased? Why? (ii) What values are exhibited by Tina?

Answer:

1. The organically grown rice should be purchased, since biofertilisers and biopesticides are used for it, which are not harmful to health or to the environment.
2. Sensitivity and awareness about the use of harmful chemicals, decision making and critical thinking.

After a rainy day Shruti found many dragonflies flying over stagnant water. She thinks these flies come to drink water. (i) Is Shruti's explanation correct? Give your views. (ii) What values are shown by Shruti?

Answer:

1. No. The dragonflies come to eat the mosquito larvae. They act as biological control agents of mosquitoes.
2. Awareness about the environment, observation and critical thinking.

Manoj was going home from school. On his way he saw a 'panipuri' vendor cleaning the dishes with bare hands and then serving the customers with the same hands without washing his hands with soap or wearing plastic gloves. Manoj went to the vendor and told him the need for washing hands before touching any eatables. The vendor hushed him away and told him there was no harm as he had rinsed his hands with water. (a) In the given situation, whose perspective do you think is correct? Justify your answer with reasons. (b) Suggest a few ways by which cleanliness can be promoted.

Answer:

1. Manoj's concern for everyone's health is correct. Tiny microbes do not get cleaned by just water, and most of the microbes are disease-causing. So the unwashed hands can spread diseases like diarrhoea and typhoid.
2. By pasting posters in public places about the importance of cleanliness, by educating people about the harms of uncleanliness, and by advertisements in the media such as television and newspapers.

(ANSWER KEY)

BIOLOGY

Q.No Value points Marks

5 Ernest chain and Howard Florey 

6 Palm tree, by fermentation 

7 (i) Whisky, brandy, rum . by distillation 

(ii) Wine, beer . without distillation

8 (i) LAB in human intestine synthesizes Vitamin B12. 

(ii) LAB in human stomach checks the growth of harmful microbes

14 a) Primary treatment (b) Aeration (c) Flocs (d) Biochemical Oxygen Demand (BOD) (e) Activated sludge (f) Water bodies like river stream.

18 Organically grown rice, since bio fertilisers & bio pesticide are used, which are not harmful to health. sensitivity & awareness about use of

19 No, dragonflies come to eat mosquito larvae & act as bio control agents Awareness about environment, critical thinking