Chapter Exam

Chapter 8: Microbes in Human Welfare — Online MCQ Test

Q: Which group of bacteria is mainly responsible for converting milk into curd?

Answer: A. Lactic acid bacteria — Lactic acid bacteria such as Lactobacillus convert lactose in milk into lactic acid, causing milk to coagulate into curd.

Q: The gas responsible for the puffed-up appearance of dough during bread-making is:

Answer: B. Carbon dioxide — Yeast ferments sugars in the dough and releases carbon dioxide, which makes the dough rise.

Q: The yeast commonly used in the production of bread and alcoholic beverages is:

Answer: A. Saccharomyces cerevisiae — Saccharomyces cerevisiae, also called brewer's yeast, is used in bread-making and alcoholic fermentation.

Q: Penicillin was discovered by:

Answer: A. Alexander Fleming — Alexander Fleming discovered penicillin from the fungus Penicillium notatum.

Q: A student observes large holes in a piece of Swiss cheese. Which microbe and product are responsible for these holes?

Answer: B. Propionibacterium sharmanii and carbon dioxide — Swiss cheese has large holes due to carbon dioxide released by Propionibacterium sharmanii during ripening.

Q: Which statement correctly explains why curd is considered nutritionally better than milk in terms of vitamins?

Answer: B. LAB in curd increases vitamin B12 content — Lactic acid bacteria improve the nutritional quality of curd by increasing vitamin B12 content.

BIOLOGY · Grade 12 · CBSE(NCERT)

Practice Chapter 8: Microbes in Human Welfare with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 BIOLOGY. This chapter covers: Microorganisms Fermentation Antibiotics Industrial Enzymes Sewage Treatment Biogas Biofertilisers Biocontrol Food Production Bacteria Fungi. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 8: Microbes in Human Welfare — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 BIOLOGY — Chapter 8: Microbes in Human Welfare, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which group of bacteria is mainly responsible for converting milk into curd?

A. Lactic acid bacteria ✓
B. Methanogens
C. Cyanobacteria
D. Nitrifying bacteria

Answer: A. Lactic acid bacteria
Lactic acid bacteria such as Lactobacillus convert lactose in milk into lactic acid, causing milk to coagulate into curd.

The gas responsible for the puffed-up appearance of dough during bread-making is:

A. Oxygen
B. Carbon dioxide ✓
C. Nitrogen
D. Methane

Answer: B. Carbon dioxide
Yeast ferments sugars in the dough and releases carbon dioxide, which makes the dough rise.

The yeast commonly used in the production of bread and alcoholic beverages is:

A. Saccharomyces cerevisiae ✓
B. Aspergillus niger
C. Rhizobium leguminosarum
D. Trichoderma polysporum

Answer: A. Saccharomyces cerevisiae
Saccharomyces cerevisiae, also called brewer's yeast, is used in bread-making and alcoholic fermentation.

Penicillin was discovered by:

A. Alexander Fleming ✓
B. Louis Pasteur
C. Robert Koch
D. Edward Jenner

Answer: A. Alexander Fleming
Alexander Fleming discovered penicillin from the fungus Penicillium notatum.

A student observes large holes in a piece of Swiss cheese. Which microbe and product are responsible for these holes?

A. Penicillium roqueforti and lactic acid
B. Propionibacterium sharmanii and carbon dioxide ✓
C. Saccharomyces cerevisiae and ethanol
D. Lactobacillus and methane

Answer: B. Propionibacterium sharmanii and carbon dioxide
Swiss cheese has large holes due to carbon dioxide released by Propionibacterium sharmanii during ripening.

Which statement correctly explains why curd is considered nutritionally better than milk in terms of vitamins?

A. Curd contains no proteins and is easier to digest
B. LAB in curd increases vitamin B12 content ✓
C. Curd contains more cellulose than milk
D. LAB convert all milk fat into vitamin C

Answer: B. LAB in curd increases vitamin B12 content
Lactic acid bacteria improve the nutritional quality of curd by increasing vitamin B12 content.

A sewage treatment plant shows a rapid fall in BOD after aeration of the effluent. The most appropriate explanation is:

A. Aerobic microbes consumed most of the organic matter ✓
B. All dissolved oxygen was removed from the sewage
C. Methanogens converted oxygen into methane
D. Heavy metals settled as primary sludge

Answer: A. Aerobic microbes consumed most of the organic matter
During secondary treatment, aerobic microbes oxidise organic matter, reducing the oxygen demand of the effluent.

Which sequence correctly represents the fate of activated sludge in sewage treatment?

A. Entire activated sludge is released into rivers directly
B. A small part is returned to aeration tank and the rest is sent to anaerobic sludge digesters ✓
C. All activated sludge is dried and used immediately as drinking water
D. Activated sludge is first chlorinated and then used to make antibiotics

Answer: B. A small part is returned to aeration tank and the rest is sent to anaerobic sludge digesters
A small portion of activated sludge is used as inoculum in the aeration tank, while the remaining sludge is sent to anaerobic digesters.

Match the microbial product with its correct producer: I. Citric acid, II. Acetic acid, III. Ethanol, IV. Cyclosporin A

A. I-Aspergillus niger, II-Acetobacter aceti, III-Saccharomyces cerevisiae, IV-Trichoderma polysporum ✓
B. I-Acetobacter aceti, II-Aspergillus niger, III-Trichoderma polysporum, IV-Saccharomyces cerevisiae
C. I-Saccharomyces cerevisiae, II-Trichoderma polysporum, III-Acetobacter aceti, IV-Aspergillus niger
D. I-Trichoderma polysporum, II-Saccharomyces cerevisiae, III-Aspergillus niger, IV-Acetobacter aceti

Answer: A. I-Aspergillus niger, II-Acetobacter aceti, III-Saccharomyces cerevisiae, IV-Trichoderma polysporum
NCERT lists Aspergillus niger for citric acid, Acetobacter aceti for acetic acid, Saccharomyces cerevisiae for ethanol and Trichoderma polysporum for cyclosporin A.

In a sewage treatment plant, the effluent from the primary settling tank is passed into large aeration tanks. Which outcome indicates successful secondary treatment before discharge?

A. Formation of flocs and significant reduction in BOD ✓
B. Increase in BOD due to growth of aerobic bacteria
C. Conversion of all aerobic bacteria into methanogens
D. Absence of microbial activity in the aeration tank

Answer: A. Formation of flocs and significant reduction in BOD
Aeration promotes growth of aerobic microbial flocs that consume organic matter, causing a significant reduction in BOD.

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