CUET UG Biology Booster Test 2-Nutrient Cycling and Ecosystem Services -

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CUET UG Biology Booster Test 2-Nutrient Cycling and Ecosystem Services

⏱️ 30 Minutes

❓ 20 Questions

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

CUET UG Biology Booster Test 2-Nutrient Cycling and Ecosystem Services

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QUESTION 1 OF 20

Trace the logical movement of a nutrient element through an ecosystem's structural components:
1. Breakdown of detritus by soil microbes
2. Uptake of dissolved inorganic substance by autotrophs
3. Transfer of organic matter to primary consumers
4. Accumulation in the physical environmental reservoir

Answer Review

1 Trace the logical movement of a nutrient element through an ecosystem's structural components:
1. Breakdown of detritus by soil microbes
2. Uptake of dissolved inorganic substance by autotrophs
3. Transfer of organic matter to primary consumers
4. Accumulation in the physical environmental reservoir

A 2, 3, 4, 1

B 4, 2, 3, 1

C 4, 1, 2, 3

D 1, 2, 3, 4

💡 Short Explanation

Nutrient starts in the reservoir (4). Autotrophs take it up (2). Primary consumers eat the organic matter (3). Microbes break down the detritus (1), returning it to the pool.

✅ Correct Answer Explanation

Nutrients are released from a reservoir (4) and taken up by autotrophs (2). This organic matter moves to consumers (3), and eventually, detritus is broken down by microbes (1), completing the cycle.

❓ Why Other Options Are Incorrect

A, C, D → Do not follow the logical flow of nutrient transfer from environmental pool to biological organisms and back.

🎯 Strategy

Used: Substitution

Application: Logical sequencing of a biogeochemical cycle.

Final Logic: Reservoir → Producer → Consumer → Decomposer.

🧠 Memory Trick

"Pool → Plant → Animal → Microbe."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Nutrient Cycling

2 Why is the cycling of nutrients essential for the long-term sustainability of an ecosystem, unlike the flow of energy?

A Because nutrients are constantly degraded into heat energy.

B Because there is no external daily input of new nutrients, so they must be repeatedly reused by autotrophs.

C Because autotrophs cannot fix radiant energy without destroying nutrients.

D Because decomposers consume all nutrients permanently.

💡 Short Explanation

Energy has a constant solar input. Nutrients have a finite, fixed supply on Earth. Recycling is the only way to sustain biological life over time.

✅ Correct Answer Explanation

Unlike energy, which has a continuous input from the sun, the Earth has a closed, finite supply of nutrients. Therefore, life depends on the continuous recycling of these elements to ensure they remain available for biological synthesis.

❓ Why Other Options Are Incorrect

Option A → Nutrients are not degraded into heat; energy is.
Option C → Autotrophs do not destroy nutrients during fixation.
Option D → Decomposers release nutrients; they do not consume them permanently.

🎯 Strategy

Used: Elimination

Application: Contrasting energy (open system) and matter (closed system).

Final Logic: Nutrients = Finite/Closed; Energy = Continuous/Open.

🧠 Memory Trick

"Sun = New Energy; Earth = Fixed Matter."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Nutrient Cycling

3 Consider the following statements regarding gaseous nutrient cycles:
I. Their primary reservoir exists in the atmosphere or hydrosphere.
II. They regulate the slow release of minerals from rock weathering.
III. The carbon cycle represents a typical gaseous nutrient cycle. Identify the correct statement(s):

A I only

B I, II, and III

C II and III only

D I and III only

💡 Short Explanation

I is correct: Atmosphere/hydrosphere is the gaseous reservoir. II is incorrect: Rock weathering is a feature of sedimentary cycles. III is correct: Carbon is a gaseous cycle.

✅ Correct Answer Explanation

Statement I and III accurately describe gaseous cycles. Statement II describes sedimentary cycles, which involve the crust and rock weathering, unlike gaseous cycles which involve air and water.

❓ Why Other Options Are Incorrect

Option A → Incomplete; misses statement III.
Option B → Includes the incorrect statement II.
Option C → Includes the incorrect statement II.

🎯 Strategy

Used: Elimination

Application: Separating characteristics of gaseous vs. sedimentary cycles.

Final Logic: Weathering = Sedimentary; Air/Water = Gaseous.

🧠 Memory Trick

"Rock = Sedimentary."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Types of Nutrient Cycles

4 Which of the following characteristics is NOT associated with the carbon cycle as described in ecosystem functioning?

A It is classified under gaseous nutrient cycling.

B Its major reservoir relies primarily on the Earth's crust.

C It involves the fixation of carbon dioxide by plants.

D It relies on the atmosphere or hydrosphere as a reservoir.

💡 Short Explanation

Carbon is a gaseous cycle. Reservoirs are atmosphere and ocean. Earth's crust is for sedimentary cycles (phosphorus).

✅ Correct Answer Explanation

Option B is false. The Earth's crust is not the major reservoir for the carbon cycle; it is the reservoir for sedimentary cycles. Carbon resides primarily in the atmosphere and hydrosphere.

❓ Why Other Options Are Incorrect

Option A, C, D → These are correct characteristics of the carbon cycle.

🎯 Strategy

Used: Elimination

Application: Identifying the false reservoir association.

Final Logic: Carbon ≠Crust (Sedimentary).

🧠 Memory Trick

"Carbon = Gas, not Stone."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Carbon Cycle

5 Match the cycle characteristics to infer their types:

Column 1	Column 2
1. Reservoir is Earth's Crust	i. Gaseous cycle
2. Cycle of Phosphorus	ii. Atmosphere reservoir
3. Cycle of Carbon	iii. Sedimentary cycle
4. Air and Water mediums	iv. Crustal mineralisation

A 1-iii, 2-iv, 3-i, 4-ii

B 1-iv, 2-iii, 3-i, 4-ii

C 1-iii, 2-iii, 3-i, 4-i

D 1-ii, 2-iv, 3-iii, 4-i

💡 Short Explanation

Reservoir=Crust → Sedimentary (iii). Phosphorus Cycle → Sedimentary (iii). Carbon Cycle → Gaseous (i). Air/Water → Gaseous (i).

✅ Correct Answer Explanation

This grouping matches the reservoir types to their respective cycles. Crust and Phosphorus are associated with Sedimentary cycles, while Carbon and Air/Water mediums are associated with Gaseous cycles.

❓ Why Other Options Are Incorrect

A, B, D → These options fail to group these specific associations accurately.

🎯 Strategy

Used: Option Grouping

Application: Categorizing cycle characteristics by type.

Final Logic: Link Reservoir to Cycle Type.

🧠 Memory Trick

"Crust=Sed; Air=Gas."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Types of Nutrient Cycles

6 If a newly discovered ecosystem process involves the slow leaching of a crucial element from terrestrial rocks into the soil for plant uptake, this element's cycle is functionally identical to the:

A Carbon cycle

B Gaseous cycle

C Phosphorus cycle

D Hydrological cycle

💡 Short Explanation

Process described: Rock weathering/leaching → Soil. This is the definition of a sedimentary cycle. Phosphorus is the primary NCERT example of a sedimentary cycle.

✅ Correct Answer Explanation

The process of elements moving from rocks into the soil via weathering/leaching is the hallmark of a sedimentary cycle. Among the choices, Phosphorus is the classic sedimentary cycle.

❓ Why Other Options Are Incorrect

Option A, B → Gaseous cycles use air/water, not rock weathering.

Option D → Hydrological is the water cycle.

🎯 Strategy

Used: Substitution

Application: Identifying the cycle type from the mechanism (rock weathering).

Final Logic: Rock weathering = Sedimentary = Phosphorus.

🧠 Memory Trick

"Rock = Phosphorus = Sedimentary."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Phosphorus Cycle

7 In a temperate forest, if the process of mineralisation were to suddenly halt, what would be the most immediate ecological consequence?

A A failure in the further degradation of humus, starving autotrophs of released inorganic nutrients.

B An excessive release of inorganic nutrients into the soil.

C An immediate spike in the rate of primary productivity.

D Complete cessation of solar energy capture by trees.

💡 Short Explanation

Mineralisation releases inorganic nutrients from humus. No mineralisation = No nutrient availability for plants (autotrophs). Result = Starvation/Limit to growth.

✅ Correct Answer Explanation

Mineralisation is the process that returns inorganic nutrients (nitrogen, phosphorus) to the soil. If this stops, humus is not degraded, and producers (autotrophs) cannot absorb the necessary nutrients to sustain growth.

❓ Why Other Options Are Incorrect

Option B → Halting mineralisation prevents release, not excessive release.
Option C → Halting nutrient release would decrease, not increase, productivity.
Option D → Energy capture (photosynthesis) depends on nutrients; it won't cease immediately, but growth will stop.

🎯 Strategy

Used: Elimination

Application: Connecting decomposition function to ecosystem productivity.

Final Logic: No Mineralisation = No Nutrients = Reduced Growth.

🧠 Memory Trick

"Min-stop = Nutrient-drop."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Decomposition

8 Evaluate these statements regarding humus and mineralisation:
I. Humus is highly resistant to microbial action and degrades at an extremely slow rate.
II. Humus serves as a temporary reservoir of nutrients due to its colloidal nature.
III. Mineralisation is the process that forms humus from detritus.

A II and III only

B I and III only

C I and II only

D I, II, and III

💡 Short Explanation

I is correct: Humus is dark, amorphous, and resistant. II is correct: It acts as a nutrient reservoir. III is incorrect: Humification forms humus; Mineralisation releases nutrients from humus.

✅ Correct Answer Explanation

Humus is indeed colloidal and resistant to microbial degradation (I and II). Statement III is false because the formation of humus from detritus is called humification, not mineralisation.

❓ Why Other Options Are Incorrect

A, B, D → All include the false statement III.

🎯 Strategy

Used: Elimination

Application: Correcting definitions of decomposition stages.

Final Logic: Humus-formation = Humification.

🧠 Memory Trick

"Humification makes humus."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Decomposition

📄 Passage

Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.

Based on the passage, a tropical rainforest would exhibit a highly efficient nutrient cycle primarily because:

A Detritus in rainforests lacks lignin and chitin entirely.

B The warm and moist environment optimally favours the activities of soil microbes.

C Anaerobiosis is constantly promoted by heavy rainfall.

D High temperatures inhibit detritivores.

📄 Passage

In waterlogged, poorly aerated soils (anaerobic conditions), which ecological outcome is most directly predicted by the passage?

A Rapid mineralisation of humus

B Increased fragmentation by earthworms

C Quicker decomposition of chitin-rich detritus

D Inhibition of decomposition leading to a build-up of organic materials

📄 Passage

"low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials."

Arrange the flow of energy and matter in a pond ecosystem to demonstrate functional balance:
1. Trapping of radiant energy by phytoplankton
2. Synthesis of organic material from dissolved inorganic substances
3. Free-swimming zooplankton consuming autotrophs
4. Fungi and flagellates breaking down dead matter at the bottom

A 2, 1, 3, 4

B 1, 2, 3, 4

C 1, 3, 2, 4

D 4, 1, 2, 3

💡 Short Explanation

Step 1: Radiant energy capture (1). Step 2: Fixation into organic matter (2). Step 3: Consumer intake (3). Step 4: Decomposer breakdown (4).

✅ Correct Answer Explanation

The logical flow in a functional pond ecosystem is the capture of solar energy (1), its transformation into biomass (2), the transfer of this biomass to consumers (3), and the final recycling of nutrients via decomposers (4).

❓ Why Other Options Are Incorrect

A, C, D → These represent illogical sequences, such as consumption occurring before production or energy capture occurring after breakdown.

🎯 Strategy

Used: Substitution

Application: Correctly ordering the trophic and functional stages in an aquatic ecosystem.

Final Logic: Solar → Fixation → Consumption → Decomposition.

🧠 Memory Trick

"Capture → Synthesize → Consume → Recycle."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Ecosystem Structure and Function

12 Because ecosystems follow the laws of thermodynamics, what functional reality must be balanced by a constant input of solar energy?

A The repeated cycling of carbon and phosphorus

B The unidirectional flow and continuous dissipation of energy as heat

C The complete conversion of all organic matter back into inorganic salts

D The accumulation of humus in terrestrial soils

💡 Short Explanation

Energy flow is unidirectional and lossy (thermodynamics). Solar energy replaces what is lost. Nutrient cycling does not require solar energy for "replacement."

✅ Correct Answer Explanation

According to the Second Law of Thermodynamics, energy in an ecosystem is continuously dissipated as heat. To maintain biological order, this energy loss must be constantly replenished by the sun.

❓ Why Other Options Are Incorrect

Option A → Nutrient cycles do not require external "input" in the same way energy does.
Option C → This is a process of decomposition, not an energy flow requirement.
Option D → Humus accumulation is a result of decomposition, not a thermodynamic deficit.

🎯 Strategy

Used: Elimination

Application: Applying thermodynamic principles to ecosystem energy requirements.

Final Logic: Energy Loss = New Energy Needed.

🧠 Memory Trick

"Dissipation requires Replenishment."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Energy Flow

13 Which of the following principles is NOT correct regarding trophic levels in an ecosystem?

A A trophic level strictly represents a single specific species in nature.

B Trophic levels are based on the source of nutrition.

C Organisms at each trophic level depend on the lower level for energy.

D Energy decreases at successive trophic levels.

💡 Short Explanation

Trophic levels are functional, not taxonomic. A single species can occupy multiple levels if it is an omnivore. Therefore, A is false.

✅ Correct Answer Explanation

Trophic levels are functional units, not species-specific. Many species can occupy multiple levels depending on their diet, and a single level can contain many species from different taxonomic groups.

❓ Why Other Options Are Incorrect

Option B, C, D → These are all fundamentally correct principles of ecosystem trophic structure.

🎯 Strategy

Used: Elimination

Application: Disproving the species-level association of trophic tiers.

Final Logic: Species ≠Trophic Level.

🧠 Memory Trick

"Functional, not Taxonomic."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Trophic Levels

14 A sparrow eats seeds and fruits from a tree, and later catches an insect to feed its young. This observation proves that:

A The sparrow belongs exclusively to the first trophic level.

B A given species may occupy more than one trophic level simultaneously based on its nutrition source.

C Food webs do not exist in natural terrestrial ecosystems.

D Seed-eating birds are considered secondary consumers.

💡 Short Explanation

Seeds = Primary consumer (herbivore). Insects = Secondary consumer (carnivore). Occupying two levels = Omni-vore behavior.

✅ Correct Answer Explanation

Since the sparrow acts as both a primary consumer (when eating seeds) and a secondary consumer (when eating insects), it demonstrates that species are not locked into a single trophic tier.

❓ Why Other Options Are Incorrect

Option A → Contradicts its insect diet.
Option C → It proves food webs do exist.
Option D → Incorrect categorization; seed-eating is primary consumption.

🎯 Strategy

Used: Substitution

Application: Identifying omnivory as proof of trophic level flexibility.

Final Logic: Multi-diet = Multi-level.

🧠 Memory Trick

"More than one diet = More than one level."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Trophic Levels

15 Match the ecosystem processes with their functional products (services):

Column 1	Column 2
1. Plant Photosynthesis	i. Mineralisation of organic matter
2. Forest Ecosystems	ii. Purification of air and water
3. Humification	iii. Capture of solar energy and biomass production
4. Microbial action	iv. Accumulation of dark amorphous substance

A 1-iv, 2-i, 3-iii, 4-ii

B 1-ii, 2-iii, 3-i, 4-iv

C 1-iii, 2-iv, 3-ii, 4-i

D 1-iii, 2-ii, 3-iv, 4-i

💡 Short Explanation

Photosynthesis = Biomass (iii). Forests = Purification (ii). Humification = Humus (iv). Microbial action = Mineralisation (i).

✅ Correct Answer Explanation

Matches: Photosynthesis captures energy/produces biomass (iii). Forests purify water/air (ii). Humification creates dark humus (iv). Microbial mineralisation releases inorganic nutrients (i).

❓ Why Other Options Are Incorrect

A, B, C → Incorrect process-to-product mapping.

🎯 Strategy

Used: Option Grouping

Application: Categorizing ecosystem functions and their respective services.

Final Logic: Match definitions.

🧠 Memory Trick

"1-iii, 2-ii, 3-iv, 4-i."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Ecosystem Services

16 The capacity of a large forest to naturally filter rainwater and absorb carbon dioxide from the atmosphere is best classified ecologically as:

A A sedimentary nutrient cycle

B Net primary productivity

C Ecosystem services

D Secondary productivity

💡 Short Explanation

Filtering and gas absorption are benefits to the environment and humanity. These are called "Ecosystem Services."

✅ Correct Answer Explanation

Ecosystem services are the direct and indirect benefits provided by natural ecosystems. Air purification and water filtration are classic examples of these services.

❓ Why Other Options Are Incorrect

Option A → Cycling involves elements moving, not the filtering capacity itself.
Option B → NPP is biomass production.
Option D → Secondary productivity involves consumer biomass.

🎯 Strategy

Used: Substitution

Application: Identifying the term for environmental utility.

Final Logic: Natural filtration/absorption = Ecosystem Service.

🧠 Memory Trick

"Nature works for us = Service."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Ecosystem Services

17 When considering man-made ecosystems, which of the following is NOT an example of one?

A An aquarium

B An aquarium

C A mature, undisturbed tropical forest

D An intensively managed agricultural land

💡 Short Explanation

Undisturbed = Natural. Aquarium/Agricultural land = Man-made.

✅ Correct Answer Explanation

A mature, undisturbed tropical forest is a natural ecosystem. It develops over time without human direction or modification, unlike agricultural fields or aquaria.

❓ Why Other Options Are Incorrect

Option A, B, D → These are human-managed artificial systems.

🎯 Strategy

Used: Elimination

Application: Differentiating between human-managed and natural ecosystems.

Final Logic: Undisturbed = Natural.

🧠 Memory Trick

"Wild = Natural."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Ecosystem Types

18 Despite being artificial, an aquarium is studied as an ecosystem because:

A It strictly represents a global ecosystem.

B Living organisms within it interact among themselves and with the surrounding physical environment as a functional unit.

C It has no requirement for an energy source.

D It completely lacks abiotic components.

💡 Short Explanation

Definition of ecosystem = biotic + abiotic interactions. Aquariums have these interactions (fish-plants-water-light).

✅ Correct Answer Explanation

An ecosystem is defined by the interaction between organisms and their physical environment. An aquarium functions as an ecosystem because it maintains these biotic-abiotic exchanges, regardless of its artificial design.

❓ Why Other Options Are Incorrect

Option A → It is a model, not a global ecosystem.
Option C → It requires electricity/light.
Option D → Water, light, and rocks are abiotic components.

🎯 Strategy

Used: Substitution

Application: Defining an ecosystem based on structural interaction.

Final Logic: Interaction = Ecosystem.

🧠 Memory Trick

"Interaction = Ecosystem."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Introduction to Ecosystems

19 Which of the following statements about energy flow in an ecosystem is NOT true?

A Energy is repeatedly recycled and returned to the autotrophs by decomposers.

B It is unidirectional from producers to consumers.

C A significant portion is dissipated and lost as heat.

D Only 10 per cent of energy is typically transferred to each successive trophic level.

💡 Short Explanation

Energy is not recycled. Nutrients are recycled. Energy flow is unidirectional.

✅ Correct Answer Explanation

This statement is false because energy is not recycled. Energy flow is unidirectional (one-way). Nutrients, not energy, are what decomposers recycle back to autotrophs.

❓ Why Other Options Are Incorrect

Option B, C, D → These are all true descriptions of energy flow dynamics.

🎯 Strategy

Used: Elimination

Application: Correcting the confusion between energy flow and nutrient cycling.

Final Logic: Energy ≠Recycled.

🧠 Memory Trick

"Energy = One-way; Nutrient = Cycle."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Energy Flow

20 How do decomposition and nutrient cycling functionally link together in an ecosystem?

A Decomposition produces radiant energy, driving nutrient cycling.

B Decomposers convert complex organic compounds into inorganic nutrients, making them available for repeated use by autotrophs.

C Nutrient cycling prevents decomposers from breaking down detritus.

D Decomposition only occurs in gaseous cycles, while nutrient cycling occurs in sedimentary cycles.

💡 Short Explanation

Decomposition is the engine that drives nutrient cycling. Decomposers = Organic to Inorganic. Autotrophs = Inorganic to Organic.

✅ Correct Answer Explanation

Decomposition is the functional bridge in nutrient cycling; it mineralizes organic matter into inorganic nutrients that autotrophs can then re-assimilate, thus completing the cycle.

❓ Why Other Options Are Incorrect

Option A → Decomposition does not produce radiant energy.
Option C → Cycling is the result of decomposition.
Option D → Both occur in all cycle types.

🎯 Strategy

Used: Substitution

Application: Defining the operational link between decomposition and nutrient reuse.

Final Logic: Organic → Inorganic → Reuse.

🧠 Memory Trick

"Decomposition feeds Cycling."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Ecosystem Function

CUET UG Biology Booster Test 2-Nutrient Cycling and Ecosystem Services

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