Important Questions Class 12 Biology Chapter 8 Microbes in Human Welfare

Microbes in Human Welfare is an important chapter of  Class 12 Biology that plays a key role in board exams and competitive exams like NEET. This topic explains how microorganisms are useful in food production, medicine, sewage treatment, agriculture, and biogas generation. 

Preparing Microbes in Human Welfare class 12 important questions helps students focus on high-weightage areas, while practicing Microbes in Human Welfare MCQ strengthens conceptual clarity and exam accuracy. 

Well-structured Microbes in Human Welfare Class 12 question answers are essential for writing precise and scoring responses in the upcoming class 12 board exams. Regular practice of these questions ensures better understanding, quick revision, and improved confidence during exams.

Important Questions Class 12 Biology Chapter 8 Microbes in Human Welfare

Important Questions Class 12 Biology Chapter 8 Microbes in Human Welfare are provided below to help students focus on exam-oriented, high-weightage questions. Refer to the questions and answers given below for quick revision and better understanding of key concepts:

1. The vitamin whose content increases following the conversion of milk into curd by lactic acid bacteria is

(1) Vitamin C
(2) Vitamin D
(3) Vitamin B12
(4) Vitamin E.

Ans. (3)
Vitamin B12

2. Big holes in Swiss cheese are made by a:

(1) a machine
(2) a bacterium that produces methane gas
(3) a bacterium producing a large amount of carbon dioxide
(4) a fungus that releases a lot of gases during its metabolic activities.

Ans. (3)
a bacterium producing a large amount of carbon dioxide

3. Methanogens do not produce:

(1) oxygen
(2) methane
(3) hydrogen sulfide
(4) carbon dioxide.

Ans. (1)
oxygen

4. Name some traditional Indian foods made of wheat, rice, and Bengal gram (or their products) which involve use of microbes.

Ans. Some Indian food made of wheat, rice and Bengal gram are:
(i) Wheat: Bread, Bhatura and Cake are made of Wheat
(ii) Rice: Idli, Dosa and Uttapam are made of Rice
(iii) Bengal gram: Dhokla and Khandvi are made of Bengal gram

5. Give examples to prove that microbes release gases during metabolism.

Ans. Microbes release gases during metabolism; some examples are as follows:
(i) Methano bacterium observed in anaerobic sludge releases large amounts of methane along with hydrogen gas and carbon dioxide
(ii) The process of fermentation of cheese, dough and the production of beverages releases carbon dioxide. The microbes involved in the process are Propionibacterium sharmanii, lactic acid bacteria and Saccharomyces cerevisiae.

6. In which food would you find lactic acid bacteria? Mention some of their useful applications.

Ans. We can find lactic acid bacteria in curd. Some of the useful applications of these bacteria are:
(i) It causes an increase in the Vitamin B12 level of curd, thus increasing the nutritional value of curd
(ii) It can be used to ferment or culture food
(iii) They improve the health of the gut

7. Name any two species of fungus, which are used in the production of the antibiotics.

Ans. Several microbes produce antibiotics, that kill other microbes which cause diseases. These antibiotics are typically acquired from fungi and bacteria. Two species of fungus that are used in the production of antibiotics are:
(i) Penicillin - the fungal source is Penicillium notatum
(ii) Cephalosporin - the fungal source is Cephalosporium acremonium

8. What is the key difference between primary and secondary sewage treatment?

Ans. The key differences are as follows:

Primary sewage treatment
It is the mechanical or physical removal of small and large substances from sewage
The process deployed is through sedimentation and filtration
Less complicated and relatively low-priced method of treatment

Secondary sewage treatment
It includes the removal of organic matter by microbes
The process used is the biological digestion of wastes
It is a complicated process and is expensive.

9. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

Ans. Organic farming is carried out without the use of any pesticides and chemical fertilizers. Microbes play a major role in organic farming. Bio-fertilizers involve picking advantageous microbes to help improve plant growth by supplying nutrients. Bio-fertilizers are living entities that are known to increase soil fertility. These are introduced into roots, seeds and soil in order to make nutrients available, thus enriching the soil with organic nutrients. Many species of cyanobacteria and bacteria have the potential to fix free atmospheric nitrogen.

A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants. Some free-living nitrogen-fixing bacteria are Azotobacter and Azospirillium, while Nostoc, Oscillitoria, and Anabaena are examples of nitrogen-fixing cyanobacteria. These biofertilizers are eco-friendly and cost-effective.

On the other hand, microbes can also serve as bio-pesticides to check insect pests in plants. The Bacillus thuringiensis, a bio-pesticide, produces a toxin which kills insect pests.

Withered bacterial spores are mixed with water and sprinkled in fields. These spores enter the gut of the larvae to release toxins when larvae of various insects feed on the crops. Likewise, the free-living fungi, Trichoderma, are found in the roots of higher plants, safeguarding them from pathogens. Another bio-pesticide, Baculovirus, is used as a biological control agent against other arthropods and insects.

10. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/L and 400 mg/L, respectively. 

Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Ans. BOD or biochemical oxygen demand refers to the amount of oxygen which would be consumed if all the organic matter in one litre of water were to be oxidized by bacteria. This BOD test measures the rate of uptake of oxygen by microbes in a sample of water; hence BOD is said to be a measure of the organic matter found in water. Therefore, the greater the BOD of wastewater, the greater the polluting potential.

Sample A with BOD 20 mg/L can be assigned as the secondary effluent discharged from a sewage treatment plant.
Sample B with BOD 8 mg/L can be assigned as river water
Sample C with BOD 400 mg/L can be assigned as untreated sewage water.

This assignment is on the basis that the highest BOD value is the sample carrying the most polluted water.

How Important Questions Class 12 Biology Chapter 8 Helps in Board Exams?

Check below the Important Questions for Class 12 Biology Chapter 8 Microbes in Human Welfare, carefully selected to help students revise key concepts, understand exam-oriented topics, and prepare effectively for board examinations with better clarity and confidence.

1. Covers High-Weightage Topics
   Important questions focus on frequently asked areas from Microbes in Human Welfare, helping students prepare topics that have higher chance of appearing in board exams.

2. Improves Answer-Writing Skills
   Practising these questions helps students learn how to frame accurate, well-structured answers as per the CBSE marking scheme.

3. Aids in Quick Revision
   Important questions act as a ready-made revision tool, allowing students to revise the entire chapter efficiently before the exam.

4. Boosts Confidence and Accuracy
   Regular practice improves conceptual clarity and reduces exam stress, enabling students to answer questions with confidence and precision.