CUET UG Booster Biology Unit 8Test (D4) -

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CUET UG Booster Biology Unit 8Test (D4)

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Booster Biology Unit 8Test (D4)

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QUESTION 1 OF 20

If a bio-engineer intends to optimize the microbial fuel source efficiency in a gobar gas plant, which of the following operational interventions would be biologically counterproductive?

Answer Review

1 If a bio-engineer intends to optimize the microbial fuel source efficiency in a gobar gas plant, which of the following operational interventions would be biologically counterproductive?

A Introducing a strong mechanical aerator to continuously pump dissolved oxygen into the slurry.

B Maintaining a strictly sealed concrete tank to prevent gas leakage.

C Ensuring a consistent feed of cellulosic cattle dung.

D Regulating the temperature to support optimal bacterial metabolism.

💡 Short Explanation

Methanogens are strict anaerobes. Oxygen is toxic to them. Aeration inhibits methane production.

✅ Correct Answer Explanation

Biogas plants must maintain strict anaerobic conditions to facilitate the growth of Methanobacterium. → Introducing oxygen (aeration) would inhibit the methanogenic pathway, effectively halting biogas production, making it \"counterproductive.\"

❓ Why Other Options Are Incorrect

Option B → Sealing is essential to keep the environment anaerobic and prevent gas loss.
Option C → Cellulosic material is the primary substrate for methanogens.
Option D → Regulating temperature ensures metabolic enzymes function at an optimal rate.

🎯 Strategy

Application: Identifying \"aerator/dissolved oxygen as the antithesis of the required anaerobic environment.

Final Logic: Oxygen is the enemy of the methane-producing process.

🧠 Memory Trick

Aerator = Abort (the process).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas Plant Structure

2 Consider the following statements comparing different microbial metabolic pathways:
I. Dough fermentation yields predominantly carbon dioxide, whereas biogas production yields predominantly methane.
II. Methane predominance in a biogas plant is an exclusive result of aerobic microbial respiration.
III. The specific organic substrates utilized dictate whether CO2 or methane is the primary gaseous end-product. Which statements analytically highlight the differences in these pathways?

A I and II only

B II and III only

C I and III only

D I, II, and III

💡 Short Explanation

Dough fermentation (yeast) produces CO2 (leavening). Biogas production (methanogens) produces methane (CH4). Methane is anaerobic, not aerobic.

✅ Correct Answer Explanation

Statement I is correct: Yeast fermentation for dough relies on CO2 release, whereas methanogenesis in biogas plants is methane-dominant. → Statement II is incorrect: Methanogenesis is an anaerobic process, not aerobic. → Statement III is correct: The biochemical pathway chosen by the microbe, which is dictated by the substrate and environmental conditions, determines the major gaseous byproduct.

❓ Why Other Options Are Incorrect

Option A → Includes statement II, which is biologically false (methanogens are anaerobes).
Option B → Includes statement II.
Option D → Includes statement II.

🎯 Strategy

Application: Eliminating any option containing statement II, which contradicts the fundamental nature of methanogens.

Final Logic: Since II is false, only C is possible.

🧠 Memory Trick

Aerobic = Air (Oxygen); Methanogens = Mud (Anaerobic).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Industrial Products/Biogas

3 Match the following metabolic substrates with their primary microbial end-products as described in the NCERT text:

Column 1	Column 2
1. Cellulosic material + Methanogens	a. Coagulated proteins and acids
2. Milk + Lactic acid bacteria	b. Large amount of methane, CO2, and H2
3. Fruit juices + Saccharomyces cerevisiae	c. Ethanol and CO2
4. Dough + Baker\'s yeast	d. Puffed appearance purely due to CO2

A 1-b, 2-a, 3-c, 4-d

B 1-b, 2-c, 3-a, 4-d

C 1-a, 2-b, 3-d, 4-c

D 1-c, 2-a, 3-b, 4-d

💡 Short Explanation

1+Methanogens = Methane/CO2/H2. 2+LAB = Curd/Lactic Acid. 3+Yeast = Fermentation (Ethanol). 4+Yeast = Leavening (CO2).

✅ Correct Answer Explanation

All pairs in A follow the standard biological processes listed in the NCERT chapter on microbes.

❓ Why Other Options Are Incorrect

Options B, C, D → Misidentify the outcomes of the respective fermentations.

🎯 Strategy

Application: Pairing the well-known dough\" (d) and \"milk (a) processes to narrow down the correct option.

Final Logic: Correct identification of two key pairs leads directly to A.

🧠 Memory Trick

Yeast = Ethanol or Carbon dioxide.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Industrial Products

4 Which of the following environmental or physiological parameters is NOT conducive to the optimal biological functioning of Methanobacterium?

A A high concentration of dissolved oxygen in an open-air agitation tank.

B The presence of complex cellulosic materials acting as a substrate.

C An anaerobic environment similar to a cattle rumen.

D Co-existing in an environment with entirely heterotrophic, anaerobic microbial communities.

💡 Short Explanation

Methanogens are obligate anaerobes. Oxygen inhibits/kills them. Open-air tanks are aerobic.

✅ Correct Answer Explanation

Methanogens require a completely oxygen-free environment. → High dissolved oxygen concentrations, such as those found in an aerated or open tank, are incompatible with their metabolism and survival.

❓ Why Other Options Are Incorrect

Option B → Cellulose is their primary food source.
Option C → Rumen is their natural, anaerobic habitat.
Option D → They thrive in consortia with other anaerobes that break down complex matter into acids/hydrogen.

🎯 Strategy

Application: Recognizing that oxygen is the singular environmental factor that prevents methanogen activity.

Final Logic: High oxygen\" and \"methanogen are biologically incompatible.

🧠 Memory Trick

Aerobic = Avoid for Methanogens.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Methanogen Biology

5 Arrange the sequence of events reflecting the complete ecological journey of a cellulose molecule in a typical Indian rural setting:
1. Excretion of partially digested material and rich bacterial flora in gobar.
2. Ingestion of cellulosic plant material by cattle.
3. Further anaerobic digestion and gas release in a concrete biogas tank.
4. Breakdown by Methanobacterium in the specialized rumen.

A 1, 2, 3, 4

B 4, 2, 1, 3

C 2, 1, 4, 3

D 2, 4, 1, 3

💡 Short Explanation

Ingest (2). Rumen breakdown (4). Excrete as dung (1). Biogas tank (3).

✅ Correct Answer Explanation

The cycle begins with the cow eating plant matter (2). → The rumen microbes work on it (4). → The waste, now containing the active microbes, is excreted (1). → This waste then feeds the biogas plant (3).

❓ Why Other Options Are Incorrect

Options A, B, C→ Incorrectly reorder the biological progression of the cellulose/waste.

🎯 Strategy

Application: Logical flow of cattle metabolism leading to waste management.

Final Logic: The sequence must mirror the biological reality: Ingestion → Digestion → Excretion → Fermentation.

🧠 Memory Trick

Ingest → Digest → Excrete → Ferment.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Cattle Rumen Association

6 Consider a hypothetical scenario where all methanogens are completely eliminated from a cows rumen by a highly specific antibiotic. Analytically speaking, what would be the most immediate physiological consequence for the cattle?

A It would immediately start producing high-quality biogas from its mouth.

B It would face a severe nutritional deficit due to the sudden inability to break down and extract energy from cellulosic fodder.

C It would perfectly transition to digesting cellulose using human-like aerobic enzymes.

D It would become highly resistant to butterfly caterpillars.

💡 Short Explanation

Methanogens digest cellulose in the rumen. Cow cannot digest cellulose alone. No methanogens = No energy from grass.

✅ Correct Answer Explanation

Ruminants depend on rumen microbes to degrade cellulose into absorbable nutrients. → Without these bacteria, the cow would lose its primary energy source, resulting in a severe nutritional deficit.

❓ Why Other Options Are Incorrect

Option A → They don\'t produce biogas from their mouth as a fuel; its a by-product of rumen activity.
Option C → Mammals lack cellulase enzymes; they cannot \"transition to this.
Option D → Irrelevant to rumen metabolism.

🎯 Strategy

Application: Identifying that the loss of a symbiont results in a loss of function (cellulose digestion).

Final Logic: Symbiosis is crucial for the hosts nutritional health.

🧠 Memory Trick

Microbes Missing = Malnutrition for Cow.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Cattle Rumen Association

7 An entrepreneur plans to set up a gobar gas plant in a strictly urban area with zero livestock, intending to feed the plant entirely with sterile synthetic polymers. Based on the NCERT text, which of the following statements does NOT represent a direct reason this will fail?

A The starting material lacks the rich natural inoculum of methanogens found in cattle dung.

B Synthetic polymers do not provide the necessary cellulosic substrate for methanogenesis.

C The floating cover will instantly corrode and melt due to the absence of gobar.

D Biogas production fundamentally relies on microbial activity on specific organic substrates.

💡 Short Explanation

A is true (No inoculum). B is true (Substrate mismatch). D is true (Process failure). C is scientifically false (corrosion is not a biological factor of absence of gobar).

✅ Correct Answer Explanation

A, B, and D describe actual biological or operational limitations. → Statement C is a purely imaginative scenario with no basis in the biological or structural design of a biogas plant.

❓ Why Other Options Are Incorrect

Options A, B, D → These are valid reasons for the failure of the plant.

🎯 Strategy

Application: Identifying that C is the only \\\\\\\\\\\\\\\"absurd\\\\\\\\\\\\\\\" statement that lacks a biological or technical basis.

Final Logic: Corrosion is unrelated to the biological process of anaerobic digestion.

🧠 Memory Trick

Corrosion = Completely Irrelevant here.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Gobar Gas Materials

8 Why is the specific preparation of a \\\\\\\\\\\\\\\"slurry\\\\\\\\\\\\\\\" (a semi-liquid mixture of dung and water) a critical biochemical step for the functional efficiency of the biogas plant?

A It ensures maximum surface area contact between the anaerobic bacteria and the complex cellulosic organic matter.

B It creates a highly aerobic environment that inhibits toxic fungi.

C It chemically converts the methane directly into carbon dioxide before entering the tank.

D It solidifies the dung into bricks that slowly release gas over years.

💡 Short Explanation

Slurry = Increased surface area. Facilitates bacterial access to substrate. Proper viscosity for tank environment.

✅ Correct Answer Explanation

Microorganisms work best when substrate is evenly distributed in an aqueous phase. → The slurry method maximizes contact between the cellulolytic/methanogenic bacteria and the dung\'s organic matter, increasing fermentation efficiency.

❓ Why Other Options Are Incorrect

Option B → It must be anaerobic, not aerobic.
Option C → It does not convert gas before entering.
Option D → Bricks would reduce surface area and stop gas release.

🎯 Strategy

Application: Matching \"Biochemical efficiency\" with \"Surface area principles.

Final Logic: Increased contact = Increased metabolic rate.

🧠 Memory Trick

Slurry = Surface Substrate.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Slurry Feed

9 The robust design of the 10-15 feet deep concrete tank in a biogas plant primarily serves an essential ecological function. What is it?

A To maintain a stable, physically contained, oxygen-free environment at the bottom to facilitate strict anaerobes.

B To allow the spent slurry to slowly filter into the groundwater as a direct fertilizer.

C To provide a habitat for dragonflies and ladybirds to breed.

D To concentrate the sunlight via refraction to kill pathogenic microbes.

💡 Short Explanation

Depth = Stability/Isolation. Oxygen-free = Anaerobic requirement. Facilitates methanogen survival.

✅ Correct Answer Explanation

The depth is calculated to minimize oxygen infiltration and ensure a consistent anaerobic environment for the methanogenic bacteria to function optimally at the bottom.

❓ Why Other Options Are Incorrect

Option B → Filtering into groundwater is a pollution risk, not a design feature.
Option C → Biocontrol insects breed in fields, not in sewage/slurry tanks.
Option D → Sunlight concentration is not a function of this depth.

🎯 Strategy

Application: Choosing the only option that addresses the primary requirement: \"Anaerobic.

Final Logic: Strict anaerobes need a depth-isolated, oxygen-free zone.

🧠 Memory Trick

Deep = Deep-down Anaerobic.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biogas Plant Structure

10 Which of the following is NOT an accurate representation of the continuous, closed-loop operational flow of a standard biogas plant?

A The entire gas supply outlet must be completely sealed off and dismantled every time slurry is added.

B The outlet pipe channels the accumulated gas directly to nearby households.

C Gas generated by microbial action exerts upward pressure on the holder.

D The spent slurry is continuously pushed out through a secondary outlet as new slurry is fed.

💡 Short Explanation

Biogas plants are designed for continuous, automated operation. Dismantling or sealing the system during feeding would destroy the pressure gradient. The system operates on continuous input and output.

✅ Correct Answer Explanation

The correct answer is (A). Biogas plants are designed to be continuous\\\\\\\\\\\\\\\" or \"semi-continuous systems. Feeding new slurry and removing spent slurry occurs without dismantling the gas supply system. Dismantling the system would release the gas and disrupt the anaerobic pressure balance.

❓ Why Other Options Are Incorrect

Option B → This is accurate; the outlet pipe is the primary delivery mechanism for the fuel.
Option C → This is accurate; gas production creates the pressure needed for supply.
Option D → This is accurate; the displacement of old slurry by new feed is standard operation.

🎯 Strategy

Application: The phrase \"dismantled every time contradicts the concept of a \"continuous\" plant. It is logically inconsistent with the goal of daily energy production.

Final Logic: C describes a procedure that would stop gas production, which is the exact opposite of the system\\\\\\\\\\\\\\\'s purpose.

🧠 Memory Trick

\"Continuous feed = No dismantling needed.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Production of Biogas

11 Consider the mechanics of the floating gas holder:
I. It operates on the principle of buoyancy, rising due to microbial gas production.
II. The physical weight of the cover aids in providing pressure to push the gas through the supply pipe.
III. It requires continuous daily lifting by heavy machinery to allow aerobic respiration. Which statements analytically describe its functional utility?

A I and III only

B I and II only

C II and III only

D I, II, and III

💡 Short Explanation

I: Buoyancy/Rising (Correct).

II: Weight/Pressure (Correct).

III: Aerobic respiration (False; it is anaerobic).

✅ Correct Answer Explanation

I is correct: Buoyancy causes the holder to rise as gas accumulates.
II is correct: The downward weight of the holder acts as a press to maintain consistent gas pressure in the delivery lines.
III is incorrect: The process is anaerobic, and no machinery is needed to \\\\\\\\\\\\\\\"lift\\\\\\\\\\\\\\\" it for respiration.

❓ Why Other Options Are Incorrect

Options A, C, D → Include statement III, which is false.

🎯 Strategy

4.Strategy Used: Elimination

Application: Rejecting the premise of \\\\\\\\\\\\\\\"Aerobic\\\\\\\\\\\\\\\" (III) and \\\\\\\\\\\\\\\"heavy machinery\\\\\\\\\\\\\\\" (III).

Final Logic: Since III is false, only B remains.

🧠 Memory Trick

Weight = Working Pressure.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Floating Gas Holde

12 Match the specific outputs of a biogas plant with their subsequent ecological or human utility:

Column 1	Column 2
1. Methane gas mixture	a. High-nutrient organic fertilizer for crop fields
2. Spent slurry	b. Fuel source for domestic cooking and lighting
3. CO2 and H2	c. Initiates the continuous anaerobic digestion process
4. Inoculum in dung	d. Co-produced gases alongside the main fuel component

A 1-b, 2-d, 3-a, 4-c

B 1-a, 2-b, 3-c, 4-d

C 1-b, 2-a, 3-d, 4-c

D 1-c, 2-a, 3-b, 4-d

💡 Short Explanation

Methane is the fuel (b). Spent slurry is used as fertilizer (a). CO2/H2 are co-products (d). Dung provides the microbial inoculum (c).

✅ Correct Answer Explanation

The correct answer is (A). Methane is the primary fuel (1-b). Spent slurry is nutrient-rich and used as fertilizer (2-a). CO2 and H2 are gaseous components produced alongside the main fuel (3-d). The dung contains the methanogens that kickstart the process (4-c).

❓ Why Other Options Are Incorrect

Option A → Mismatches CO2 with fertilizer.
Option B → Mismatches the fuel component with fertilizer.
Option D → Incorrectly assigns inoculum as a fuel.

🎯 Strategy

Application: Start with the most certain match: Methane (1) is fuel (b). Eliminate options not starting with 1-b.

Final Logic: C is the only choice that aligns all components correctly.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Gas to Burn, Slurry to Farm, Dung for the Bugs.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Production of Biogas

13 The successful deployment of biogas technology in rural India by the IARI highlights the intersection of which two major socio-economic needs?

A The need for synthetic urban fertilizers and chemical weedicides.

B The demand for clean, self-sustaining rural energy and the efficient management of abundant cattle waste.

C The eradication of pest insects and the breeding of high-yield cattle.

D The development of activated sludge plants and broad-spectrum antibiotics.

💡 Short Explanation

IARI and KVIC developed biogas for rural development. The primary rural resources are cattle and the need for fuel. This creates a perfect circular economy.

✅ Correct Answer Explanation

The correct answer is (B). The Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC) promoted biogas specifically to solve the energy crisis in villages using the freely available animal waste, thereby fulfilling two needs simultaneously.

❓ Why Other Options Are Incorrect

Option A → Biogas does not provide synthetic fertilizers or weedicides.
Option C → While beneficial, pest control is not the primary objective of a biogas plant.
Option D → Activated sludge is for municipal sewage, not rural gobar gas.

🎯 Strategy

Application: The question asks about the intersection of socio-economic needs in rural India. Option B is the only one that focuses on rural energy and the specific agricultural byproduct (cattle waste) mentioned in the chapter.

Final Logic: B directly addresses the source and utility explained in the text.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Waste to Wealth: Cattle waste → Energy.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Production of Biogas

14 Which of the following does NOT represent a strategic rationale for KVIC promoting biogas plants primarily in rural Indian villages?

A Rural villages have an abundance of cattle used for various agricultural purposes.

B Large quantities of cattle dung are readily available as raw material.

C Rural areas require the massive amounts of pure oxygen generated by the biogas plants.

D The produced biogas serves essential local needs like cooking and lighting.

💡 Short Explanation

Biogas plants do not produce oxygen. They produce methane, an anaerobic byproduct. This option is scientifically false.

✅ Correct Answer Explanation

The correct answer is (C). Biogas plants rely on anaerobic digestion, which consumes no oxygen and produces no oxygen. In fact, oxygen is the enemy of the process. Therefore, this is not a strategic rationale.

❓ Why Other Options Are Incorrect

Option A → Accurate; cattle are common in rural settings.
Option B → Accurate; dung is the primary raw material.
Option D → Accurate; fuel for cooking and lighting is the primary benefit.

🎯 Strategy

Application: The prompt asks for what is NOT a rationale. Since biogas plants are anaerobic and produce CH4 (not O2), (C) is the only illogical statement.

Final Logic: C is fundamentally incorrect regarding the biochemistry of the biogas process.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Biogas plants = Methane, never Oxygen.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Production of Biogas

15 In the context of a \\\\\\\\\\\\\\\"living and vibrant ecosystem,\\\\\\\\\\\\\\\" what is the ultimate ecological objective of relying on natural predation for pest control?

A To chemically sterilize the soil to prevent any insect reproduction.

B To establish a self-sustaining system of checks and balances where pest populations are restricted but not eradicated.

C To entirely eliminate all native flora and replace it with genetically modified crops.

D To promote the uncontrolled exponential growth of one single predator species.

💡 Short Explanation

Biological control aims for balance. Eradication is rarely achieved or even desired in an ecosystem. Predation maintains population equilibrium.

✅ Correct Answer Explanation

The correct answer is (B). Biological control (biocontrol) uses natural predators to keep pest populations at a manageable, sub-economic level. It does not aim to \\\\\\\\\\\\\\\"eradicate\\\\\\\\\\\\\\\" the pest (which would disrupt the food web), but to manage it within a functional ecosystem.

❓ Why Other Options Are Incorrect

Option A → Chemical sterilization is the hallmark of conventional farming, not biocontrol.
Option C → This contradicts the goal of maintaining a vibrant ecosystem.
Option D → Promoting only one species is an ecological disaster, not a control strategy.

🎯 Strategy

Application: The phrase \\\\\\\\\\\\\\\"living and vibrant ecosystem\\\\\\\\\\\\\\\" implies sustainability and balance. Option B is the only choice that reflects ecological balance rather than destruction.

Final Logic: B defines the core philosophy of Integrated Pest Management (IPM).

🧠 Memory Trick

\\\\\\\\\\\\\\\"Biocontrol = Balance, not total banishment.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

16 How does the holistic, analytical approach of an organic farmer fundamentally contradict the philosophy of conventional pest management systems?

A Organic farmers believe biodiversity furthers health, while conventional farming uses chemicals that indiscriminately kill both useful and harmful life forms.

B Organic farmers aim for 100% eradication of pests using natural means, while conventional farmers preserve pests.

C Organic farming relies exclusively on deep concrete tanks to trap pests, unlike conventional spraying.

D Conventional systems utilize complex webs of interaction, whereas organic farming uses single-chemical treatments.

💡 Short Explanation

Organic farming promotes ecological biodiversity. Conventional farming relies on harsh, broad-spectrum chemicals. These chemicals kill predators and pests alike.

✅ Correct Answer Explanation

The correct answer is (A). NCERT highlights that conventional pesticides kill both pests and their natural predators. Organic farming, in contrast, recognizes that biodiversity (the presence of diverse insects) is essential to keep the system in check, as predators (like dragonflies) manage the pests.

❓ Why Other Options Are Incorrect

Option B → Incorrect; organic farmers do not aim for 100% eradication.
Option C → Incorrect; organic farming does not use concrete tanks to trap pests.
Option D → Incorrect; the roles are reversed—conventional farming uses simple chemical solutions, not complex biological webs.

🎯 Strategy

Application: Identify the core difference: Biodiversity (Organic) vs. Chemical Eradication (Conventional).

Final Logic: A accurately reflects the ecological philosophy taught in the chapter.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Organic = Biodiversity (Life), Conventional = Chemical (Death).\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

17 Arrange the logical ecological sequence of an integrated pest management Strategy utilizing Ladybirds:
1. Aphid population drops to a manageable level without chemical toxicity.
2. Identification of a severe aphid infestation on agricultural crops.
3. Ladybirds engage in the natural predation of the target pests.
4. Ladybirds are introduced or naturally encouraged within the field ecosystem.

A 2, 3, 4, 1

B 2, 4, 3, 1

C 4, 2, 3, 1

D 1, 2, 3, 4

💡 Short Explanation

Identify the pest (2). Introduce the predator (4). Predation occurs (3). Pest population drops (1).

✅ Correct Answer Explanation

The correct answer is (B). First, the farmer detects the problem (aphid infestation). Then, they introduce or encourage the predator (Ladybirds). The ladybirds eat the aphids, and finally, the aphid population is reduced to a harmless level.

❓ Why Other Options Are Incorrect

Option A, C, D → These sequences violate the logical cause-effect chain of pest control.

🎯 Strategy

Application: Logical order requires identifying the problem first (2). This eliminates C and D. Between A and B, one must introduce the ladybird (4) before they can eat (3).

Final Logic: B represents the only correct chronological and causal flow.

🧠 Memory Trick

\\\\\\\\\\\\\\\"See pest → Add predator → Predator eats → Pest dies.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

18 An organic farmer managing a marshy agricultural plot observes a spike in mosquito populations. To employ a highly targeted biocontrol Strategy without harming beneficial field insects, why is the dragonfly the optimal choice according to NCERT guidelines?

A Because dragonflies act as a broad-spectrum viral pathogen that infects all arthropods.

B Because dragonflies are natural specific predators of mosquitoes, suppressing their population without contaminating the aquatic ecosystem.

C Because dragonflies produce a chemical toxin in their gut that poisons the marsh water.

D Because dragonflies compete with mosquitoes for the exact same plant nectar.

💡 Short Explanation

Dragonflies are predators of mosquitoes. They provide natural, chemical-free control. This preserves the health of the aquatic ecosystem.

✅ Correct Answer Explanation

The correct answer is (B). NCERT explicitly mentions that dragonflies are used to control mosquitoes. This is a \\\\\\\\\\\\\\\"targeted\\\\\\\\\\\\\\\" biological control method because it does not involve adding toxic chemicals to the water, ensuring the surrounding ecosystem remains unharmed.

❓ Why Other Options Are Incorrect

Option A → Incorrect; dragonflies are predators, not pathogens.
Option C → Incorrect; they do not poison the water.
Option D → Incorrect; mosquitoes and dragonflies are not plant-nectar competitors.

🎯 Strategy

Application: The term \\\\\\\\\\\\\\\"biocontrol\\\\\\\\\\\\\\\" implies using a natural predator. Dragonflies are the natural predator of mosquitoes.

Final Logic: B aligns with the ecological principle of biological predation.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Dragonfly = Mosquito Police.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

📄 Passage

An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed.

Analytically speaking, based on the provided text, why are Bacillus thuringiensis spores supplied commercially in a \\\\\\\\\\\\\\\"dried\\\\\\\\\\\\\\\" state in sachets before agricultural application?

A To ensure they immediately release their toxin into the air.

B To maintain the bacteria in a dormant, stable state until they are mixed with water for spraying.

C To chemically burn the leaves of the brassica plants upon contact.

D To prevent ladybirds from accidentally eating the wet spores.

💡 Short Explanation

Spores are the dormant, hardy form of bacteria. Drying ensures they remain viable but inactive. Water reactivation is needed for application.

✅ Correct Answer Explanation

The correct answer is (B). The text explains that Bacillus thuringiensis (Bt) is provided as dried spores. In biological terms, spores are dormant, resistant structures that allow bacteria to survive adverse conditions. Keeping them dry ensures they remain stable until the farmer activates them by mixing with water.

❓ Why Other Options Are Incorrect

Option A → The toxin is not air-released; it must be ingested.
Option C → The bacteria are safe for plants; they only target specific insect larvae.
Option D → There is no biological concern about ladybirds eating the spores.

🎯 Strategy

Application: Spores are scientifically known as survival/dormant structures. Only (B) relates to this biological function.

Final Logic: B uses biological principles to explain the commercial form of the product.

🧠 Memory Trick

\\\\\\\\\\\\\\\"Spores = Sleeping (Dormant) until splashed.\\\\\\\\\\\\\\\"

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

📄 Passage

The high specificity of the Bt toxin is a hallmark of biological control. Based on the passage, what specific mechanism ensures that the toxin does not indiscriminately kill beneficial insects landing on the sprayed brassicas?

A The toxin requires direct ingestion by the insect larvae and strictly releases its lethal payload within the specific environment of the larval gut.

B The toxin is only effective during the night when beneficial insects are asleep.

C Beneficial insects possess a thick outer shell that repels the dried spores.

D The spores actively crawl away from beneficial insects and hunt only caterpillars.

💡 Short Explanation

Bt toxin requires specific pH conditions (alkaline gut). It is only activated after ingestion. Non-target insects do not have the gut conditions to activate the toxin.

✅ Correct Answer Explanation

The correct answer is (A). The Bt toxin is a \\\\\\\\\\\\\\\"pro-toxin\\\\\\\\\\\\\\\" that requires a specific, highly alkaline gut environment to be converted into its active, toxic form. Since this specific condition is unique to the caterpillar\\\\\\\\\\\\\\\'s gut, other insects (like ladybirds or bees) are not affected, making it highly specific and safe for beneficial insects.

❓ Why Other Options Are Incorrect

Option B → Nighttime has nothing to do with biological toxicity.
Option C → The toxin is not repelled by shells; it is activated by chemical conditions.
Option D → Spores do not hunt; they are passive particles.

🎯 Strategy

Application: The prompt asks for the \\\\\\\\\\\\\\\"mechanism\\\\\\\\\\\\\\\" of specificity. Option A explains the chemical/biological mechanism (ingestion + gut pH) required for activation.

Final Logic: A is the scientifically accurate explanation of why Bt is selective.

🧠 Memory Trick

\\\\\\\"Bt needs a Larval Gut to work; nothing else will do.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Biocontrol Agents

CUET UG Booster Biology Unit 8Test (D4)

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