CUET UG Biology Booster Test 3-Microbes in Sewage Treatment -

🚀

CUET UG Biology Booster Test 3-Microbes in Sewage Treatment

⏱️ 30 Minutes

❓ 20 Questions

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

CUET UG Biology Booster Test 3-Microbes in Sewage Treatment

1 / 20

QUESTION 1 OF 20

Which of the following is NOT an accurate deduction regarding the composition and nature of municipal waste?

Answer Review

1 Which of the following is NOT an accurate deduction regarding the composition and nature of municipal waste?

A Its high organic matter content necessitates biological treatment.

B The presence of pathogenic microbes makes direct disposal into rivers hazardous.

C It relies entirely on autotrophic microbes naturally present for treatment.

D Human excreta contributes heavily to its organic load.

💡 Short Explanation

Sewage treatment uses heterotrophic microbes (bacteria and fungi). These form flocs to consume organic matter. It is not reliant on autotrophic microbes.

✅ Correct Answer Explanation

Sewage treatment is a biological process that utilizes heterotrophic microbes (specifically aerobic bacteria and fungi) that form "flocs" to break down complex organic matter. Option C is inaccurate because the process is not reliant on autotrophic microbes. Options A, B, and D are all accurate descriptions of the nature and composition of municipal wastewater.

❓ Why Other Options Are Incorrect

Option A → High organic load is the primary reason biological treatment is required.
Option B → Pathogens make direct discharge unsafe due to water-borne disease risks.
Option D → Human excreta is the major contributor to the organic pollution in sewage.

🎯 Strategy

Used: Elimination

Application: Identify the false statement by distinguishing between heterotrophic (decomposers) and autotrophic (producers) roles in ecology.

Final Logic: Since sewage treatment relies on heterotrophs, the statement claiming reliance on autotrophs is the incorrect deduction.

🧠 Memory Trick

Sewage Treatment = Heterotrophic Helpers.

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

2 Match the type of microbes with their respective role or location in the sewage treatment process:

Column 1	Column 2
1. Pathogenic microbes	P. Digestion of flocs in sludge digesters
2. Heterotrophic microbes	Q. Cause of water-borne diseases in untreated sewage
3. Aerobic useful microbes	R. Naturally present in sewage and carry out treatment
4. Anaerobic bacteria	S. Grow into flocs during mechanical agitation

A 1-Q, 2-S, 3-R, 4-P

B 1-R, 2-Q, 3-P, 4-S

C 1-Q, 2-R, 3-S, 4-P

D 1-P, 2-R, 3-Q, 4-S

💡 Short Explanation

Pathogens = Disease (Q). Heterotrophs = Nature's cleaners (R). Aerobic microbes = Flocs (S). Anaerobic = Digesters (P).

✅ Correct Answer Explanation

Pathogenic microbes in sewage cause water-borne diseases (1-Q). Heterotrophic microbes are naturally found in sewage and facilitate the cleanup (2-R). Aerobic useful microbes (bacteria/fungi) form flocs in the aeration tank (3-S). Finally, anaerobic bacteria digest the sludge in the digesters (4-P). Option C correctly links these roles.

❓ Why Other Options Are Incorrect

Options A, B, and D incorrectly assign the roles to the microbial types.

🎯 Strategy

Used: Option Grouping

Application: Anchor the most certain pairs (Pathogens=Disease; Anaerobic=Digesters) to isolate the correct option.

Final Logic: Option C is the only choice that maintains 100% factual accuracy.

🧠 Memory Trick

1-Q, 2-R, 3-S, 4-P.

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

3 Why must sequential filtration strictly precede grit sedimentation in the physical removal stages of primary treatment?

A Filtration alters the specific gravity of grit, allowing it to settle faster.

B Removing floating debris first prevents large items from interfering with the settling of soil and small pebbles.

C Filtration actively decreases the BOD, preparing the water for sedimentation.

D Grit cannot settle unless the supernatant is completely clear of dissolved organics.

💡 Short Explanation

Sequential filtration removes floating debris. Grit sedimentation removes heavy solids. Removing large surface debris ensures efficient settling of grit.

✅ Correct Answer Explanation

Primary treatment uses physical separation techniques in sequence. Sequential filtration acts as the first step to remove floating debris and large items. If this step were skipped, large floating materials could obstruct or interfere with the controlled sedimentation of grit (soil and small pebbles), reducing efficiency.

❓ Why Other Options Are Incorrect

Option A → Filtration does not change the physical properties (specific gravity) of grit.
Option C → Primary treatment (physical) does not significantly reduce BOD; secondary (biological) treatment does.
Option D → Settling occurs regardless of dissolved organics; grit removal is independent of dissolved matter.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Apply the logic of sequential industrial processes (Step 1 prepares for Step 2).

Final Logic: Removing large debris prevents obstruction of the smaller sedimentation process.

🧠 Memory Trick

Filter debris → Settle grit.

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

4 Evaluate the limitations of primary treatment physics:
I. It only involves physical removal of large and small particles.
II. It significantly reduces the biochemical oxygen demand (BOD) of the sewage.
III. It cannot effectively remove dissolved organic matter and pathogenic microbes.

A I and II are correct

B II and III are correct

C I and III are correct

D All are correct

💡 Short Explanation

Primary treatment is purely physical. It does NOT significantly reduce BOD (that is the goal of Secondary treatment). It does NOT remove dissolved matter.

✅ Correct Answer Explanation

Primary treatment is physical (I). Because it only removes solid particles, it does not significantly reduce the BOD (Statement II is false). The dissolved organic matter and pathogens remain, which necessitates secondary biological treatment (Statement III is true). Thus, I and III are correct.

❓ Why Other Options Are Incorrect

Option A → Incorrect because Statement II claims BOD reduction occurs in primary treatment.
Option B → Incorrect because Statement II is false.
Option D → Incorrect because Statement II is false.

🎯 Strategy

Used: Elimination

Application: Eliminate all options containing Statement II, as it contradicts the primary purpose of secondary treatment.

Final Logic: Since BOD reduction is a biological process, any option with Statement II is logically impossible.

🧠 Memory Trick

Primary = Physical (No BOD reduction).

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

5 Compare the ultimate fates of primary sludge and the major part of activated sludge:

A Both are pumped back as inoculum into the aeration tanks.

B Primary sludge is discarded, while activated sludge is mechanically agitated.

C Both can ultimately be subjected to anaerobic digestion, though the text explicitly states this for activated sludge.

D Primary sludge forms the effluent, while activated sludge forms biogas.

💡 Short Explanation

Primary sludge is solid waste from primary treatment. Activated sludge is biomass from secondary treatment. Both are suitable for anaerobic digestion to produce biogas.

✅ Correct Answer Explanation

While primary sludge and activated sludge arise from different stages (primary vs. secondary), both are organic-rich solids that are routinely sent to anaerobic sludge digesters to produce biogas. The NCERT explicitly mentions this process for activated sludge.

❓ Why Other Options Are Incorrect

Option A → Only a small part of activated sludge is used as inoculum; primary sludge is never used as inoculum.
Option B → Both are treated, not discarded.
Option D → Effluent is the liquid, not sludge; sludge forms biogas.

🎯 Strategy

Used: Elimination

Application: Identify the sludge management process (Digestion) common to both sludge types.

Final Logic: Since both are organic solids, both are candidates for anaerobic digesters.

🧠 Memory Trick

All sludge → Digester → Biogas.

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

6 Which statement is INCORRECT regarding the primary effluent?

A It is formed by the supernatant in the primary settling tank.

B It has a substantially lower BOD than the secondary effluent.

C It is passed into large aeration tanks for biological treatment.

D It contains large amounts of organic matter that need to be consumed by flocs.

💡 Short Explanation

Primary effluent = Untreated (High BOD). Secondary effluent = Treated (Low BOD). Primary effluent BOD > Secondary effluent BOD.

✅ Correct Answer Explanation

Primary effluent has a very high BOD because it still contains all the dissolved organic matter. Secondary effluent has a significantly lower BOD because the aerobic microbes in the aeration tank have already consumed that matter. Therefore, stating primary effluent has a "lower" BOD is incorrect.

❓ Why Other Options Are Incorrect

Option A → Correct; it is the liquid supernatant.
Option C → Correct; it is the input for the aeration tank.
Option D → Correct; organic matter is high and requires biological consumption.

🎯 Strategy

Used: Substitution

Application: Compare the BOD levels of untreated (Primary) vs. treated (Secondary) water.

Final Logic: Untreated water is always more polluted (higher BOD) than treated water.

🧠 Memory Trick

Primary BOD > Secondary BOD.

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

7 Arrange the complex sequence of events occurring in and immediately after the aeration tank process:
1. Consumption of major organic matter
2. Passing of primary effluent into aeration tanks
3. Vigorous growth of aerobic microbes into flocs
4. Significant reduction of BOD
5. Passing of effluent into a settling tank

A 2 → 1 → 3 → 4 → 5

B 2 → 3 → 1 → 4 → 5

C 3 → 2 → 1 → 4 → 5

D 2 → 4 → 3 → 1 → 5

💡 Short Explanation

Entry (2) → Microbe growth (3) → Consumption (1) → BOD reduction (4) → Settling (5).

✅ Correct Answer Explanation

The process begins with the effluent entering the aeration tank (2). This environment promotes the growth of aerobic microbes into flocs (3). These flocs consume the organic matter (1), which directly causes the BOD to drop significantly (4). Finally, the treated water is sent to the settling tank (5) to separate the sludge.

❓ Why Other Options Are Incorrect

Options A, C, and D misrepresent the biological timeline; microbial growth is the prerequisite for consumption.

🎯 Strategy

Used: Substitution

Application: Follow the chronological progression of the secondary treatment process in an STP.

Final Logic: Input → Microbe Growth → Consumption → BOD Drop → Settling.

🧠 Memory Trick

In → Grow → Eat → Drop → Settle.

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

8 If mechanical agitation and air pumping in the aeration tank were abruptly stopped, what would be the most immediate biological consequence?

A Anaerobic bacteria would immediately produce biogas in the aeration tank.

B The aerobic useful microbes would fail to grow vigorously into flocs.

C Sequential filtration would reverse, forming floating debris.

D Primary sludge would spontaneously form in the secondary effluent.

💡 Short Explanation

Aerobic microbes need oxygen. Air pumping provides oxygen. No air = No growth.

✅ Correct Answer Explanation

Aerobic microbes are obligate aerobes. Mechanical agitation and air pumping are essential to maintain high levels of dissolved oxygen. If these are stopped, the aerobic microbes will cease their vigorous growth and metabolic activity, preventing the formation of flocs.

❓ Why Other Options Are Incorrect

Option A → Biogas production is an anaerobic process that requires specialized digesters and a specific environment, not just stopping air in an aeration tank.
Option C → Filtration is unrelated to aeration tank processes.
Option D → Sludge is the result of biological flocs settling; without growth, there is no sludge to form.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Recognize the dependency of aerobic metabolism on oxygen supply.

Final Logic: No oxygen = No aerobic growth.

🧠 Memory Trick

No Air = No Aerobic Growth.

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

9 What analytical significance does the structural composition of biological flocs hold in the efficiency of secondary treatment?

A The fungal filaments prevent the bacteria from consuming organic matter too rapidly.

B The mesh-like structure creates a larger surface area for microbes to associate and efficiently consume organic matter.

C The bacterial-fungal mesh is designed to produce methane anaerobically.

D The flocs primarily act as a physical net to catch remaining grit.

💡 Short Explanation

Flocs are mesh-like. Mesh = High surface area. High surface area = Efficient organic consumption.

✅ Correct Answer Explanation

The "mesh-like" association of bacteria and fungal filaments is highly efficient because it increases the surface-area-to-volume ratio. This large surface area allows the microbial community to come into maximum contact with the organic matter in the effluent, significantly accelerating the rate of consumption.

❓ Why Other Options Are Incorrect

Option A → Fungi assist in the structure; they do not inhibit consumption.
Option C → Methane production occurs in anaerobic digesters, not in the aerobic flocs.
Option D → Grit removal is a physical process completed in primary treatment.

🎯 Strategy

Used: Substitution

Application: Define the structural advantage of a "mesh" in biological systems.

Final Logic: Mesh structure = Max contact/surface area = Max Efficiency.

🧠 Memory Trick

Floc Mesh = Big Surface Area = High Consumption.

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

10 Select the correct statements regarding organic matter consumption by flocs:
I. Consumption of organic matter by flocs increases the polluting potential of the water.
II. As flocs consume organic matter, the oxygen demand of the effluent decreases.
III. The process indirectly measures the organic matter present in the water.

A II and III

B I and II

C I and III

D All of the above

💡 Short Explanation

Consumption DECREASES pollution (I is false). Consumption DECREASES BOD (II is true). BOD indirectly measures organic matter (III is true).

✅ Correct Answer Explanation

Statement I is false because consuming organic matter decreases (not increases) the polluting potential. Statement II is true because oxygen demand (BOD) is a measure of the organic content; as it is consumed, the demand drops. Statement III is true; BOD is the accepted indirect measurement of the organic load.

❓ Why Other Options Are Incorrect

Option B → Includes Statement I, which is false.
Option C → Includes Statement I, which is false.
Option D → Includes Statement I, which is false.

🎯 Strategy

Used: Elimination

Application: Evaluate the impact of organic consumption on pollution.

Final Logic: Since consumption cleans the water, Statement I is clearly incorrect, leaving Option A.

🧠 Memory Trick

Eat Organic → Low BOD → Cleaner Water.

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

11 Match the conceptual relationships regarding BOD dynamics:

Column 1	Column 2
1. High organic matter	P. Measures oxygen uptake rate
2. BOD reduction	Q. Correspondingly high BOD
3. BOD test principle	R. Correlates with significantly reduced BOD
4. Low polluting potential	S. Signal to move effluent to settling tank

A 1-R, 2-P, 3-S, 4-Q

B 1-P, 2-R, 3-Q, 4-S

C 1-S, 2-Q, 3-R, 4-P

D 1-Q, 2-S, 3-P, 4-R

💡 Short Explanation

High organic matter = High BOD. BOD reduction = Signal for settling. BOD test = Oxygen uptake measurement. Low polluting = Low BOD.

✅ Correct Answer Explanation

High organic matter (1) results in a high amount of substrate for microbes, hence a high BOD (Q). Once significant BOD reduction (2) has occurred, it is a signal to transfer the mixture to a settling tank (S). The BOD test principle (3) is based on measuring the rate of oxygen uptake (P) by microbes. A low polluting potential (4) in the final effluent correlates with a significantly reduced BOD (R).

❓ Why Other Options Are Incorrect

Options A, B, and C → Misalign the definitions and causal relationships (e.g., misassociating oxygen uptake with BOD levels).

🎯 Strategy

Used: Option Grouping

Application: Establishing the primary definition of BOD (Oxygen uptake rate = P) and identifying the result of treatment (Low BOD = Low pollution = R).

Final Logic: The only option that correctly links the fundamental definition of BOD to the outcomes of the treatment process is A.

🧠 Memory Trick

BOD = Oxygen Uptake (P).

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

12 Why is the BOD test considered an "indirect" measure of the organic matter present in the water?

A Because it measures the volume of flocs, not the organic matter itself.

B Because it calculates the amount of methane produced rather than organic molecules.

C Because it measures the rate of oxygen uptake by micro-organisms, which is proportional to the organic matter they metabolise.

D Because organic matter cannot be physically separated from water.

💡 Short Explanation

Direct measurement of organic matter is complex. Microbes consume organic matter using oxygen. Oxygen consumption is a proxy for organic load.

✅ Correct Answer Explanation

BOD (Biochemical Oxygen Demand) measures the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. Since we are measuring the demand (the oxygen consumed) rather than weighing the organic matter directly, it is an indirect measure. This consumption is proportional to the available food (organic matter) for the microorganisms.

❓ Why Other Options Are Incorrect

Option A → The volume of flocs is not the focus of a BOD test.
Option B → Methane is produced in anaerobic conditions, not during the aerobic BOD test.
Option D → Organic matter can be separated, but it is not the primary purpose of a BOD test.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identifying the core definition of BOD as "Oxygen Demand."

Final Logic: If the test measured the substance itself, it would be direct; since it measures the metabolic response to the substance, it is indirect.

🧠 Memory Trick

BOD = Proxy (Indirect).

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

13 Which statement does NOT correctly differentiate activated sludge from primary sludge?

A Primary sludge consists of settled physical particles, while activated sludge consists of sedimented bacterial flocs.

B Activated sludge requires a settling tank after aeration, while primary sludge forms before aeration.

C Activated sludge is partially pumped back as inoculum, whereas primary sludge is not.

D Primary sludge is produced anaerobically, whereas activated sludge is completely devoid of aerobic bacteria.

💡 Short Explanation

Primary sludge is a physical settling product. Activated sludge is composed of aerobic bacteria (flocs). Statement D falsely claims activated sludge lacks aerobic bacteria.

✅ Correct Answer Explanation

Activated sludge is primarily composed of aerobic bacterial flocs. Claiming it is "devoid of aerobic bacteria" is the exact opposite of reality. Therefore, this statement is incorrect.

❓ Why Other Options Are Incorrect

Option A → Correct; primary is physical, activated is biological.
Option B → Correct; primary settling happens before aeration, secondary settling after.
Option C → Correct; a portion of activated sludge is reused as "activated" inoculum (seed).

🎯 Strategy

Used: Extreme Word Filter

Application: Looking for an absolute/extreme term. "Completely devoid" is a red flag in biology.

Final Logic: Since activated sludge is made of aerobic bacteria, any statement claiming it has none is logically false.

🧠 Memory Trick

Activated = Aerobic bacteria.

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

14 Analytically, why is the term "activated" used to describe the sedimented sludge in secondary treatment?

A Because it is highly radioactive due to municipal waste.

B Because it is actively producing biogas in the settling tank.

C Because it contains a high concentration of active, living aerobic microbes (flocs) capable of initiating biological treatment.

D Because it has a higher biochemical oxygen demand than the raw sewage.

💡 Short Explanation

Sludge contains living flocs. Used as "inoculum" to seed new tanks. Active = living/functional microbes.

✅ Correct Answer Explanation

A portion of the sedimented sludge from the secondary settling tank is pumped back into the aeration tank. Because this sludge contains a dense, living population of aerobic microbes (flocs) that are ready to immediately start consuming organic matter, it acts as an "inoculum" or "seed" to activate the process in fresh sewage.

❓ Why Other Options Are Incorrect

Option A → Irrelevant and scientifically inaccurate.
Option B → Biogas production happens in a digester, not the settling tank.
Option D → Activated sludge has a low BOD compared to raw sewage.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Defining "Active" in a biological context as living/functioning.

Final Logic: The term "activated" refers to the biological capability of the sludge to restart or speed up the treatment process in a new batch of sewage.

🧠 Memory Trick

Activated = Alive (Inoculum).

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

15 Which of the following is NOT a characteristic condition or output of the anaerobic sludge digesters?

A Presence of bacteria that grow anaerobically

B Digestion of bacteria and fungi present in the activated sludge

C Generation of a mixture of gases that is inflammable

D Production of a gas mixture primarily containing oxygen and nitrogen

💡 Short Explanation

Anaerobic digesters produce biogas. Biogas = Methane, H₂S, CO₂. Oxygen/Nitrogen are not the output gases.

✅ Correct Answer Explanation

Anaerobic digesters break down organic matter in the absence of oxygen. The gases produced are methane, hydrogen sulfide, and carbon dioxide (collectively known as biogas). Oxygen and nitrogen are not typical products of this anaerobic fermentation process.

❓ Why Other Options Are Incorrect

Option A → Correct; the environment is anaerobic by definition.
Option B → Correct; digesters consume the biomass (flocs) produced in the aeration tank.
Option C → Correct; methane is highly inflammable.

🎯 Strategy

Used: Elimination

Application: Knowing the components of biogas from NCERT (Methane, H₂S, CO₂).

Final Logic: Since O₂ and N₂ are not in the list of biogas components, C is the outlier.

🧠 Memory Trick

Biogas = Methane (M), Hydrogen sulfide (H), Carbon dioxide (C).

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

16 Arrange the precise biological pathway occurring within the anaerobic digester:
1. Production of a mixture of methane, hydrogen sulphide, and carbon dioxide
2. Anaerobic bacteria consume the cellular structures of aerobic bacteria and fungi
3. Formation of an inflammable source of energy (biogas)

A 2 → 1 → 3

B 1 → 2 → 3

C 3 → 2 → 1

D 2 → 3 → 1

💡 Short Explanation

Step 1: Breakdown of biomass. Step 2: Gas formation. Step 3: Resulting energy source.

✅ Correct Answer Explanation

First, the anaerobic bacteria consume the biological flocs (bacteria and fungi) (2). As a result of this digestion, they release gases (methane, H₂S, CO₂) (1). This mixture of gases is collectively known as biogas, which serves as an inflammable source of energy (3).

❓ Why Other Options Are Incorrect

Options B, C, D → These misalign the order of digestion (the cause) and gas production (the effect).

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Cause-and-effect sequence (Action → Product → Use).

Final Logic: The biological breakdown is the primary action, which leads to gas emission, which is then identified as the energy source.

🧠 Memory Trick

Digest → Gas → Energy.

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

17 What critical biological threshold must be crossed before secondary effluent is considered safe for disposal into natural water bodies?

A The flocs must completely dissolve back into the water.

B The effluent must undergo a second round of sequential filtration.

C The BOD must be reduced significantly, indicating low organic matter and polluting potential.

D Biogas must be dissolved into the effluent to sanitize it.

💡 Short Explanation

Goal of STPs is reducing BOD. Low BOD = Safe for rivers. High BOD = Dangerous pollution.

✅ Correct Answer Explanation

The entire point of sewage treatment is to convert sewage into a form that does not deplete the oxygen of natural water bodies. If the BOD is significantly reduced, it indicates that most organic pollutants have been removed. Discharging water with high BOD would deplete oxygen in rivers, harming aquatic life.

❓ Why Other Options Are Incorrect

Option A → Flocs are removed in a settling tank; they should not remain in effluent.
Option B → Secondary treatment is biological, not a second round of filtration.
Option D → Biogas is a fuel, not a disinfectant.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identifying the core mission of STPs (Water Quality Improvement).

Final Logic: BOD is the measure of potential harm; therefore, reducing it is the threshold for safety.

🧠 Memory Trick

BOD Down = River Up.

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

18 Analyze the cascading effects of ignoring the biological treatment of sewage on natural water body health:
I. Direct discharge of untreated sewage increases the BOD of rivers drastically.
II. It leads to the proliferation of pathogenic organisms in natural water bodies.
III. It results in a robust, balanced ecosystem due to the added organic nutrients.

A Only I and II are correct

B Only II and III are correct

C Only I and III are correct

D All are correct

💡 Short Explanation

Untreated sewage = High BOD. Pathogens = Disease. Ecosystems suffer, they don't become "robust."

✅ Correct Answer Explanation

Untreated sewage is rich in organic load (high BOD) and pathogens. Discharging it into rivers will cause BOD levels to skyrocket, potentially leading to fish kills and ecosystem collapse, not "robustness." Pathogens will also multiply, increasing the risk of water-borne diseases. Thus, I and II are correct, and III is false.

❓ Why Other Options Are Incorrect

Options B, C, D → All contain the false claim in Statement III.

🎯 Strategy

Used: Elimination

Application: Recognizing that sewage causes pollution and disease (negative), not a "robust ecosystem" (positive).

Final Logic: Since statement III is objectively incorrect in an environmental context, the only valid answer is A.

🧠 Memory Trick

Sewage = Sickness (Pathogens) + Suffocation (High BOD).

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

📄 Passage

"Till date, no man-made technology has been able to rival the microbial treatment of sewage. You are aware that due to increasing urbanisation, sewage is being produced in much larger quantities than ever before. ... The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan to save these major rivers of our country from pollution. Under these plans, it is proposed to build a large number of sewage treatment plants so that only treated sewage may be discharged in the rivers."

Analytically speaking, why do the Ganga and Yamuna Action Plans focus strictly on building more sewage treatment plants rather than relying on new chemical purification methods?

A Because chemical methods are too slow for fast-flowing rivers.

B Because no man-made technology has yet rivaled the efficiency of microbial treatment of sewage.

C Because building STPs does not require Ministry approval.

D Because STPs exclusively use primary physical treatment which is cheaper.

💡 Short Explanation

Passage explicitly states microbial treatment is unrivaled. Microbes are natural and highly efficient. Chemical methods are not mentioned as better.

✅ Correct Answer Explanation

The provided passage explicitly states: "Till date, no man-made technology has been able to rival the microbial treatment of sewage." This sentence is the justification for why the Ministry of Environment and Forests focuses on building STPs (which use microbial treatment).

❓ Why Other Options Are Incorrect

Option A, C, D → These are not supported by the passage or general biological facts in the NCERT.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Direct retrieval from the provided passage.

Final Logic: The text identifies the superiority of microbial treatment as the primary reason for policy.

🧠 Memory Trick

Microbes are Master cleaners (unrivaled).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: National Action Plans

📄 Passage

Based on the passage's premise, what is the ultimate environmental and epidemiological goal of ensuring "only treated sewage may be discharged"?

A To capture floating debris to sell to recycling plants.

B To extract heavy metals from river beds.

C To increase the overall biological oxygen demand of the major rivers.

D To prevent river pollution and curb the consequent increase in water-borne diseases.

💡 Short Explanation

"Save these major rivers... from pollution." Pathogens in sewage cause water-borne diseases. Goal: Protect river health + public health.

✅ Correct Answer Explanation

The passage indicates the plans were initiated to "save these major rivers... from pollution." By treating sewage, we remove the organic matter (pollution) and the pathogenic microbes. This directly prevents river pollution and reduces the transmission of water-borne diseases.

❓ Why Other Options Are Incorrect

Option A, B → Not the purpose stated in the passage.

Option C → Increasing BOD is exactly what pollution does; treatment decreases BOD.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Aligning the goal with public health and environmental protection.

Final Logic: Sewage treatment protects the river (Environment) and human health (Epidemiology).

🧠 Memory Trick

Treated = Transmission avoided.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: National Action Plans

CUET UG Biology Booster Test 3-Microbes in Sewage Treatment

Test Complete!

Answer Review