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: 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.

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.

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.

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.

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.