Class 12/Question Bank/Competency Based
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Competency Based Questions on Microbes in Human Welfare
1. Analyze the Process: In a sewage treatment plant, the "Primary Treatment" step removes floating debris and grit. If this step is skipped, what will be the most immediate consequence for the "Secondary Treatment"? a) The anaerobic sludge digesters will fail. b) The aeration tanks will get clogged with solid inorganic matter, reducing efficiency. c) Biogas production will increase. d) Flocs will not form. Answer: b) The aeration tanks will get clogged... Explanation: Primary treatment is a physical process to remove solids (pebbles, sand, plastic). If these enter the aeration tank, they can damage the mechanical agitators and occupy space meant for biological activity, reducing the overall efficiency of the secondary (biological) treatment.
2. Evaluate the Application: A farmer wants to grow a crop without using chemical nitrogen fertilizers. Which of the following microbes should he use as a biofertilizer for a paddy (rice) field? a) Rhizobium b) Glomus (Mycorrhiza) c) Anabaena (Cyanobacteria) d) Lactobacillus Answer: c) Anabaena (Cyanobacteria) Explanation: Anabaena and Nostoc are autotrophic nitrogen-fixers. In waterlogged paddy fields, they are often associated with the Azolla fern, serving as an excellent natural source of nitrogen. Rhizobium is used for legumes, not rice.
3. Assertion (A): Bottled fruit juices bought from the market are clearer than those made at home. Reason (R): The bottled juices are treated with pectinases and proteases. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: Pectinases and proteases break down the pectin and protein fibers present in fruit pulp that cause cloudiness, resulting in a clear, commercially attractive juice.
4. Identify the Bioactive Molecule: A patient undergoing a kidney transplant is prescribed a drug derived from Trichoderma polysporum. What is the function of this drug? a) To bust blood clots. b) To lower blood cholesterol. c) To suppress the immune system and prevent organ rejection. d) To treat bacterial infection. Answer: c) To suppress the immune system and prevent organ rejection. Explanation: Trichoderma polysporum produces Cyclosporin A, a powerful immunosuppressant that prevents T-cells from attacking the transplanted foreign organ.
5. Predict the Outcome: If oxygen supply to the activated sludge tank (aeration tank) in an STP is cut off, what will happen to the BOD of the effluent? a) BOD will decrease rapidly. b) BOD will increase or remain high because aerobic bacteria will die. c) BOD will become zero. d) Methane production will start immediately in the aeration tank. Answer: b) BOD will increase or remain high... Explanation: Aerobic microbes (flocs) require oxygen to decompose organic matter. Without oxygen, they die or become inactive, so the organic pollutants remain in the water, keeping the Biochemical Oxygen Demand (BOD) high.
6. Biocontrol Logic: Why is Nucleopolyhedrovirus (NPV) considered an excellent candidate for Integrated Pest Management (IPM)? a) It kills all insects in the field. b) It is a broad-spectrum insecticide. c) It is species-specific and does not harm non-target organisms like bees and birds. d) It acts faster than chemical pesticides. Answer: c) It is species-specific... Explanation: NPVs are narrow-spectrum biocontrol agents. They only target specific pests, allowing beneficial insects (like pollinators) to survive, which is the core principle of IPM.
7. Microbial Product: Which of the following matches is incorrect regarding the microbe and its industrial product? a) Acetobacter aceti - Acetic Acid b) Clostridium butylicum - Lactic Acid c) Aspergillus niger - Citric Acid d) Saccharomyces cerevisiae - Ethanol Answer: b) Clostridium butylicum - Lactic Acid Explanation: Clostridium butylicum produces Butyric Acid. Lactic acid is produced by Lactobacillus and other Lactic Acid Bacteria (LAB).
8. Analyze the Graph: During sewage treatment, as the microbial "flocs" grow in the aeration tank, the BOD of the water drops. What does this drop in BOD indicate? a) Increase in polluting potential. b) Decrease in dissolved oxygen. c) Consumption of organic matter by microbes. d) Increase in pathogenic bacteria. Answer: c) Consumption of organic matter by microbes. Explanation: BOD measures the amount of oxygen required to oxidize the organic matter in water. As microbes eat the waste, less organic matter remains, so the BOD (polluting potential) decreases.
9. Differentiate: What is the key difference in the production of Whisky versus Wine? a) Whisky is fermented; Wine is distilled. b) Whisky is distilled; Wine is produced without distillation. c) Whisky uses fruit juices; Wine uses cereals. d) Whisky uses bacteria; Wine uses yeast. Answer: b) Whisky is distilled; Wine is produced without distillation. Explanation: Wine and Beer are made by fermentation only. Whisky, Brandy, and Rum require the additional step of distillation to increase alcohol concentration.
10. Reasoning: Why does "Swiss Cheese" have large holes? a) Due to the burrowing of mites. b) Due to the production of large amounts of CO2 by Propionibacterium shermanii. c) Due to the escape of water vapor during baking. d) Due to the addition of baking soda. Answer: b) Due to the production of large amounts of CO2... Explanation: During the ripening of Swiss cheese, the bacterium ferments lactic acid and produces large bubbles of Carbon Dioxide, which create the characteristic holes.
11. Mechanism of Action: How do Statins lower blood cholesterol? a) By breaking down cholesterol in the blood. b) By inhibiting the absorption of cholesterol in the intestine. c) By competitively inhibiting the enzyme responsible for cholesterol synthesis. d) By increasing the excretion of cholesterol. Answer: c) By competitively inhibiting the enzyme... Explanation: Statins (from Monascus purpureus) mimic the substrate of the enzyme HMG-CoA reductase, which is essential for making cholesterol in the liver.
12. Identify the Component: In a biogas plant, the "slurry" consists of: a) Only Methane. b) Dung and water. c) Only dry leaves. d) Activated sludge. Answer: b) Dung and water. Explanation: Slurry is the semi-liquid mixture of organic waste (cattle dung) and water that is fed into the digester for microbial breakdown.
13. Biofertilizer Application: Which of the following is a free-living nitrogen-fixing bacterium? a) Rhizobium b) Glomus c) Azospirillum d) Frankia Answer: c) Azospirillum Explanation: Azospirillum and Azotobacter are free-living in the soil. Rhizobium and Frankia are symbiotic fixers.
14. Process Analysis: In the secondary treatment of sewage, what happens to the "Activated Sludge"? a) It is all pumped back into the aeration tank. b) A small part is pumped back as inoculum, and the rest goes to anaerobic sludge digesters. c) It is released into the river. d) It is dried and sold as chemical fertilizer. Answer: b) A small part is pumped back as inoculum... Explanation: The small part keeps the aeration tank populated with active microbes. The rest is digested anaerobically to produce biogas.
15. Critical Thinking: Why are antibiotics not effective against the common cold? a) The virus has a cell wall that is resistant. b) The common cold is caused by a virus, and antibiotics only target bacteria. c) The dose is usually too low. d) The virus mutates too fast. Answer: b) The common cold is caused by a virus... Explanation: Antibiotics work by disrupting bacterial structures (like cell walls or 70S ribosomes). Viruses lack these structures and use the host's machinery, so antibiotics have no target to hit.
Rohan adds a small amount of curd (inoculum) to fresh milk and keeps it at room temperature. After a few hours, the milk turns into curd. However, his friend tries the same experiment but keeps the milk in the refrigerator. The milk does not set.
16. Explain: Why did the milk not turn into curd in the refrigerator? Answer: The low temperature in the refrigerator inhibits the growth and metabolic activity of Lactic Acid Bacteria (LAB). Curd formation requires an optimal temperature (warm) for the bacteria to multiply and produce enough lactic acid to coagulate the milk.
17. Identify: Curd is more nutritious than milk because it contains increased: Answer: Vitamin B12. LAB improve the nutritional quality of milk by synthesizing this essential vitamin during fermentation.
18. Application: Role of LAB in the human stomach? Answer: LAB play a beneficial role by checking the growth of disease-causing (pathogenic) microbes in the digestive tract, acting as a natural probiotic.
A city discharges untreated sewage into a river. Fish start dying.
19. Predict: Relationship between BOD and DO at the point of discharge? Answer: (c) High BOD, Low DO. The influx of organic matter increases the "demand" for oxygen by microbes, which quickly "deplete" the dissolved oxygen in the water.
20. Reasoning: Why do the fish die? Answer: Fish die due to hypoxia (suffocation). The aerobic bacteria decomposing the sewage consume the dissolved oxygen, leaving none for the fish to breathe.
21. Solution: Which stage reduces this high BOD? Answer: (b) Secondary (Biological) Treatment. This stage uses microbes to specifically consume the organic matter, thereby lowering the BOD.
A farmer uses Bt Cotton to avoid pesticide costs.
22. Mechanism: How does it protect against Bollworms? Answer: The plant contains the cry gene from Bacillus thuringiensis. This gene produces a pro-toxin. When the insect eats the plant, the alkaline pH of its gut activates the toxin, which creates pores in the gut lining and kills the insect.
23. Safety: Is it harmful to humans? Answer: No. The Bt toxin is inactive in the acidic pH of the human stomach. Humans also lack the specific gut receptors that the toxin binds to in insects.
24. Designing a Biogas Plant: You are designing a biogas plant for a village.
25. Creating a Process Flow: Industrial Penicillin. Answer: Strain Selection (P. chrysogenum) -> Sterile Media Preparation -> Inoculation in Bioreactor -> Aeration/Agitation (Continuous supply of O2) -> Fermentation -> Downstream Processing (Filtration, Extraction, Crystallization) -> Final Antibiotic.
26. Formulating a Hypothesis: Legume vs. Cereal. Answer:
27. Scenario Analysis (Biofertilizers): "Instant" vs "Slow". Answer:
28. Critical Analysis: "Antibiotic Resistance." Answer:
29. Developing a Product: Super Detergent. Answer:
30. Debating Energy: Biofuels vs Biogas. Answer:
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