CUET UG Biology Booster Test 2-Energy Flow and Trophic Levels -

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CUET UG Biology Booster Test 2-Energy Flow and Trophic Levels

⏱️ 30 Minutes

❓ 20 Questions

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

CUET UG Biology Booster Test 2-Energy Flow and Trophic Levels

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QUESTION 1 OF 20

Which statement is NOT associated with the concept of Photosynthetically Active Radiation (PAR) and solar input?

Answer Review

1 Which statement is NOT associated with the concept of Photosynthetically Active Radiation (PAR) and solar input?

A Plants perfectly capture 100% of the available PAR.

B PAR constitutes less than 50% of the incident solar radiation.

C A constant input of solar energy is the basic requirement for any ecosystem to function.

D Except for deep-sea vents, the sun acts as the universal input source.

💡 Short Explanation

Plants are not 100% efficient at capturing light. Only 2–10% of PAR is actually captured by plants. "Perfectly capture" is an ecological impossibility.

✅ Correct Answer Explanation

Ecological efficiency is never 100%. Photosynthesis is constrained by various physiological and environmental factors. → The NCERT clearly states that plants capture only 2–10% of the available PAR. → Therefore, the claim that plants "perfectly capture 100%" is factually incorrect and not associated with ecological principles.

❓ Why Other Options Are Incorrect

Option B → This is a correct fact per NCERT (PAR is less than 50%).
Option C → This is a fundamental principle of ecosystem thermodynamics (need for constant energy).
Option D → This is a standard exception to the rule, making the statement correct.

🎯 Strategy

Used: Extreme Word Filter

Application: The word "perfectly" and "100%" are indicators of an extreme, scientifically incorrect statement in biological contexts.

Final Logic: Energy conversion is never 100% efficient due to thermodynamic losses.

🧠 Memory Trick

"Efficiency ≠100%."

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

2 Why is the deep-sea hydro-thermal ecosystem explicitly mentioned as an exception when discussing incident solar radiation?

A It receives solar radiation through detritus.

B The sun is not its source of energy, unlike all other ecosystems on Earth.

C It has an inverted pyramid of energy.

D It relies heavily on photosynthetically active radiation (PAR).

💡 Short Explanation

Deep-sea vents are chemoautotrophic. They derive energy from inorganic chemical reactions (geothermal). Solar energy does not reach these depths.

✅ Correct Answer Explanation

Almost all life on Earth is solar-powered. The deep-sea hydrothermal vents are unique because they rely on chemoautotrophic bacteria that utilize chemical energy from earth's interior. → This makes them the primary exception to the sun-dependent rule of ecosystems.

❓ Why Other Options Are Incorrect

Option A → Detritus still ultimately traces back to solar energy produced elsewhere.
Option C → Pyramids of energy are never inverted; this is a distractor.
Option D → These vents exist in aphotic zones (no light), so PAR is irrelevant.

🎯 Strategy

Used: Substitution

Application: Replacing the "exception" with the known biological mechanism (chemoautotrophy vs. photoautotrophy).

Final Logic: Chemoautotrophs = No Sun needed.

🧠 Memory Trick

"Deep Vents = Chemical Energy."

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

3 Match the efficiency metrics and pathways related to ecosystem energy capture:

Column 1	Column 2
1. PAR portion of solar radiation	A. 2 to 10 per cent
2. Plant capture rate of PAR	B. Less than 50 per cent
3. Flow of captured energy	C. The entire living world
4. Sustainment target	D. Unidirectional flow

A 1-A, 2-B, 3-C, 4-D

B 1-B, 2-A, 3-D, 4-C

C 1-B, 2-C, 3-A, 4-D

D 1-D, 2-A, 3-C, 4-B

💡 Short Explanation

PAR = <50% (B). Plant capture = 2-10% (A). Flow = Unidirectional (D). Sustainment = Entire living world (C).

✅ Correct Answer Explanation

1 (PAR) matches B (Less than 50%). → 2 (Capture Rate) matches A (2 to 10 per cent). → 3 (Flow of energy) matches D (Unidirectional). → 4 (Sustainment) matches C (The entire living world).

❓ Why Other Options Are Incorrect

All other options incorrectly pair these definitions.

🎯 Strategy

Used: Option Grouping

Application: Matching known quantitative values (2-10%) and qualitative terms (Unidirectional) to their specific categories.

Final Logic: Proper alignment of definitions yields B.

🧠 Memory Trick

"PAR < 50; Capture 2-10; Flow Uni; Sustain World."

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

4 Consider the following statements about how captured energy sustains the living world:
I. No energy that is trapped in an organism remains in it forever.
II. The energy trapped by a producer is either passed on to a consumer or the organism dies.
III. Death of an organism marks the end of energy flow completely.

A I only

B II and III

C I and II

D I, II, and III

💡 Short Explanation

Energy is transient (I). Energy has two fates: consumption or decomposition (II). Death is not the end of flow; it starts the detritus chain (III is false).

✅ Correct Answer Explanation

Statement I is correct: Energy in organisms is lost via metabolism/heat. → Statement II is correct: Energy is either consumed or enters the detritus pool. → Statement III is incorrect: Death is a transfer point for the Detritus Food Chain, not the end of energy flow.

❓ Why Other Options Are Incorrect

Option A → Incomplete; II is also correct.
Option B → Incorrect; III is false.
Option D → Incorrect; III is false.

🎯 Strategy

Used: Elimination

Application: Eliminating III based on the knowledge of the Detritus Food Chain (DFC).

Final Logic: Death = Transfer to DFC.

🧠 Memory Trick

"Death ≠End, Death = DFC."

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

5 Which scenario is NOT associated with the unidirectional flow compliance in an ecosystem?

A Energy moving from the sun to autotrophs.

B Energy dissipating as heat to the environment.

C Energy moving from primary consumers back to producers.

D Energy moving from herbivores to carnivores.

💡 Short Explanation

Energy flow is strictly unidirectional (Sun →Producer →Consumer). It never flows "back" to producers from consumers. Option C describes bidirectional/reverse flow.

✅ Correct Answer Explanation

Unidirectional flow means energy moves one way through trophic levels. → Option C describes energy returning to the producer level, which violates the Second Law of Thermodynamics and the structure of food chains.

❓ Why Other Options Are Incorrect

Option A → This is the correct start of flow.
Option B → This is the necessary dissipation of energy.
Option D → This is a correct step in forward flow.

🎯 Strategy

Used: Elimination

Application: Eliminating forward-flow steps identifies the backward-flow step as the anomaly.

Final Logic: Flow = Uni, never Backwards.

🧠 Memory Trick

"Uni = One-way."

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

6 Ecosystems are not exempt from the Second Law of Thermodynamics. Conceptually, how do they counteract the universal tendency toward increasing disorderliness?

A By creating an inverted pyramid of biomass.

B By requiring a constant supply of energy to synthesize the molecules they require.

C By perfectly recycling 100% of the heat generated.

D By stopping the unidirectional movement of energy.

💡 Short Explanation

Life is an ordered state (low entropy). Maintaining order requires energy input. Solar energy provides this constant input.

✅ Correct Answer Explanation

Entropy (disorder) is the natural state. To build biological molecules (order), systems need a continuous input of high-quality energy. → This energy prevents the system from running down.

❓ Why Other Options Are Incorrect

Option A → Inverted pyramids are a structural pattern, not a thermodynamic remedy.
Option C → Heat recycling at 100% is physically impossible.
Option D → Unidirectional energy is the requirement, not the solution to entropy.

🎯 Strategy

Used: Substitution

Application: Aligning the Second Law of Thermodynamics with biological growth requirements (energy for synthesis).

Final Logic: Constant Energy Input = Maintenance of Order.

🧠 Memory Trick

"Energy = Order."

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

7 Read the following statements regarding ecosystem producers:
I. In terrestrial ecosystems, major producers include herbaceous and woody plants.
II. Phytoplankton, algae, and higher plants serve as producers in aquatic ecosystems.
III. Producers occupy the top vertical strata in all aquatic environments.

A All of the above

B II and III

C I and III

D I and II

💡 Short Explanation

I is true: Terrestrial land is dominated by plants/trees. II is true: Aquatic producers are diverse (phyto/algae/plants). III is false: Producers in aquatic systems (phytoplankton) are often floating/suspended, not necessarily the "top vertical stratum."

✅ Correct Answer Explanation

I and II correctly identify the producers for land and water. → Statement III is incorrect because "top vertical strata" (surface) is where phytoplankton live, but many other producers (macrophytes) exist in lower or marginal strata; it is not a defining characteristic for all aquatic producers.

❓ Why Other Options Are Incorrect

Option A → Incorrect; III is false.
Option B → Incorrect; III is false.
Option C → Incorrect; III is false.

🎯 Strategy

Used: Elimination

Application: Testing the universal claim in III ("all aquatic environments") which is typically false in biology.

Final Logic: I & II are facts, III is a false generalization.

🧠 Memory Trick

"Producers = Diverse."

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

8 Which of the following is NOT an accurate representation of a major aquatic producer grouping?

A Phytoplankton floating at the surface.

B Fungi growing at the bottom of the pond.

C Submerged plants within the water body.

D Marginal plants found at the edges.

💡 Short Explanation

Fungi are saprotrophs (decomposers), not producers. Phytoplankton, submerged plants, and marginal plants are all producers.

✅ Correct Answer Explanation

Producers (autotrophs) perform photosynthesis. → Fungi are heterotrophs (decomposers). They cannot produce food from sunlight.

❓ Why Other Options Are Incorrect

Option A, C, D → These are all recognized autotrophic components of a pond ecosystem.

🎯 Strategy

Used: Odd One Out

Application: Categorizing organisms as either "Autotroph" or "Heterotroph" isolates fungi as the outlier.

Final Logic: Autotroph (Producer) vs Heterotroph (Decomposer).

🧠 Memory Trick

"Fungi = Decomposer, not Producer."

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

9 Arrange the following animals in the correct sequential order starting from the primary consumer (herbivore) to secondary/tertiary heterotrophs in an aquatic/terrestrial mix context:
1. Primary Carnivore (Secondary Consumer)
2. Herbivorous Mollusc (Primary Consumer)
3. Secondary Carnivore (Tertiary Consumer)

A 3, 2, 1

B 1, 2, 3

C 2, 1, 3

D 2, 3, 1

💡 Short Explanation

Primary Consumer = 2. Secondary Consumer = 1. Tertiary Consumer = 3. Sequence: 2 →1 →3.

✅ Correct Answer Explanation

Trophic sequence: Primary Consumer (2) eats Producer. Secondary Consumer/Primary Carnivore (1) eats Primary Consumer. Tertiary Consumer/Secondary Carnivore (3) eats Primary Carnivore.

❓ Why Other Options Are Incorrect

Option A, B, D → Incorrect ordering of trophic levels.

🎯 Strategy

Used: Substitution

Application: Replacing common labels with their numerical trophic rank to establish logical order.

Final Logic: 1st Consumer →2nd Consumer →3rd Consumer.

🧠 Memory Trick

"2-1-3 sequence."

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

10 If an animal feeds directly on a plant, it is a primary consumer. If an animal feeds on the primary consumer, it is conceptually defined as a:

A Saprotroph

B Secondary heterotroph (or secondary consumer)

C Detritivore

D Primary producer

💡 Short Explanation

Consumer of primary consumer = Secondary consumer. Also called secondary heterotroph.

✅ Correct Answer Explanation

Feeding hierarchy: Producer →Primary Consumer (Herbivore) →Secondary Consumer (Primary Carnivore). → An animal that eats a primary consumer is therefore a secondary consumer.

❓ Why Other Options Are Incorrect

Option A → Feeds on dead matter.
Option C → Feeds on detritus.
Option D → Makes own food.

🎯 Strategy

Used: Substitution

Application: Mapping the "feeder" hierarchy to the standard terminology defined in NCERT.

Final Logic: Consumer of 1st = 2nd.

🧠 Memory Trick

"Eater of Herbivore = Secondary."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Consumer Classifications

11 In the producer to consumer sequence depicted as: Grass -> Goat -> Man. What ecological function does the Man serve in this specific GFC?

A Primary consumer

B Secondary consumer

C Producer

D Detritivore

💡 Short Explanation

Grass = Producer (1st Trophic Level). Goat = Primary Consumer (2nd Trophic Level). Man = Secondary Consumer (3rd Trophic Level).

✅ Correct Answer Explanation

In this food chain, the Goat eats the Producer, making it the primary consumer. → Man feeds on the goat (the primary consumer), making Man a secondary consumer. → This classification follows the standard linear hierarchy of trophic levels in a Grazing Food Chain (GFC).

❓ Why Other Options Are Incorrect

Option A → Incorrect; Man eats the herbivore, not the grass directly.
Option C → Incorrect; Man is a heterotroph, not a producer.
Option D → Incorrect; Man is not consuming dead matter in this specific sequence.

🎯 Strategy

Used: Substitution

Application: Assigning each organism its trophic rank (P -> C1 -> C2) to identify the Man's position.

Final Logic: Consumer of a primary consumer = Secondary consumer.

🧠 Memory Trick

"Producer (1) -> Primary Consumer (2) -> Secondary Consumer (3)."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Grazing Food Chain

12 Which statement is NOT associated with the major conduit for energy flow?

A In a terrestrial ecosystem, the GFC is the major conduit for energy flow.

B In an aquatic ecosystem, the GFC is the major conduit for energy flow.

C In a terrestrial ecosystem, a much larger fraction of energy flows through the DFC than through GFC.

D Unidirectional movement applies to the major conduits.

💡 Short Explanation

Terrestrial ecosystem = DFC is the major conduit. Aquatic ecosystem = GFC is the major conduit. Option A incorrectly identifies GFC as the terrestrial major conduit.

✅ Correct Answer Explanation

The NCERT highlights that in terrestrial ecosystems, a larger fraction of energy flows through the Detritus Food Chain (DFC) compared to the Grazing Food Chain (GFC). → Therefore, calling GFC the major conduit for terrestrial systems is incorrect.

❓ Why Other Options Are Incorrect

Option B → Correct; GFC is the main aquatic conduit.
Option C → Correct; DFC is the main terrestrial conduit.
Option D → Correct; energy flow is unidirectional in all conduits.

🎯 Strategy

Used: Elimination

Application: Identifying that the premise of Option A contradicts the established terrestrial energy flow dominance (DFC > GFC).

Final Logic: Terrestrial dominance = DFC.

🧠 Memory Trick

"Terrestrial = Detritus; Aquatic = Grazing."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Grazing vs Detritus Food Chains

13 Which component is NOT associated with the starting point or raw materials of the Detritus Food Chain (DFC)?

A Dead plant remains like leaves and bark

B Fecal matter

C Herbaceous terrestrial plants actively photosynthesizing

D Dead remains of animals

💡 Short Explanation

DFC starts with dead material. Photosynthesizing plants are living producers. Living producers start the GFC, not the DFC.

✅ Correct Answer Explanation

The DFC begins with detritus, which includes dead leaves, fecal matter, and animal carcasses. → Actively photosynthesizing plants are alive and thus form the base of the Grazing Food Chain (GFC), not the Detritus Food Chain.

❓ Why Other Options Are Incorrect

Option A, B, D → Incorrect; these are all canonical examples of detritus.

🎯 Strategy

Used: Extreme Word Filter

Application: Filtering for "actively photosynthesizing" (living) to disqualify it from a chain defined by "dead" matter.

Final Logic: Living = NOT Detritus.

🧠 Memory Trick

"DFC = Dead; GFC = Green/Living."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Detritus Food Chain

14 Arrange the chronological steps of Saprotroph degradation based on their nutrient acquisition:
1. Breakdown of waste into simple, inorganic materials
2. Secretion of digestive enzymes
3. Absorption of simple materials

A 1, 2, 3

B 2, 3, 1

C 3, 1, 2

D 2, 1, 3

💡 Short Explanation

Step 1: Enzyme secretion (2). Step 2: Breakdown of waste (1). Step 3: Absorption (3).

✅ Correct Answer Explanation

Saprotrophs perform external digestion: they first secrete enzymes into the environment (2). → These enzymes break down the organic waste into simple inorganic materials (1). → Finally, the organism absorbs these resulting simple nutrients (3).

❓ Why Other Options Are Incorrect

Option A, B, C → Incorrect; they fail to follow the physiological sequence of extracellular digestion.

🎯 Strategy

Used: Substitution

Application: Following the biological process of extracellular digestion: Secrete -> Digest -> Absorb.

Final Logic: 2 (Enzymes) -> 1 (Breakdown) -> 3 (Uptake).

🧠 Memory Trick

"Secrete -> Digest -> Absorb."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Detritus Food Chain

15 In a natural ecosystem, how does the presence of prey links functionally alter the simple food chain model?

A It isolates the GFC from the DFC permanently.

B It creates a natural interconnection of food chains, forming a food web.

C It ensures energy moves bidirectionally.

D It eliminates the need for omnivores.

💡 Short Explanation

Chains are linked because one predator may eat from multiple chains. These links create a web. Energy flow remains unidirectional, just complex.

✅ Correct Answer Explanation

Food chains are rarely linear; they interlink because organisms often occupy multiple roles (e.g., omnivores). → These complex "prey links" connect multiple chains, resulting in a "food web."

❓ Why Other Options Are Incorrect

Option A → Incorrect; prey links connect chains, they don't isolate them.
Option C → Incorrect; energy flow remains unidirectional.
Option D → Incorrect; omnivores are the very reason these webs form.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Defining "food web" as the natural interconnection of multiple food chains.

Final Logic: Interconnected chains = Food Web.

🧠 Memory Trick

"Interconnected chains = Web."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Food Web

16 Match the organism to its functional role highlighting omnivore presence or prey links:

Column 1	Column 2
1. Cockroach	A. Omnivore in a food web
2. Fungi	B. Detritivore breaking down detritus
3. Grass	C. Saprotrophic decomposer
4. Earthworm	D. Producer trapped energy source

A 1-A, 2-D, 3-C, 4-B

B 1-B, 2-D, 3-A, 4-C

C 1-C, 2-A, 3-B, 4-D

D 1-A, 2-C, 3-D, 4-B

💡 Short Explanation

Cockroach = Omnivore (A). Fungi = Saprotrophic decomposer (C). Grass = Producer (D). Earthworm = Detritivore (B).

✅ Correct Answer Explanation

Cockroach acts as an omnivore (1-A). → Fungi act as decomposers (2-C). → Grass is the producer providing energy (3-D). → Earthworm acts as a detritivore (4-B).

❓ Why Other Options Are Incorrect

Option A, B, C → Incorrect; they fail to map the functional roles correctly to the specific organisms.

🎯 Strategy

Used: Option Grouping

Application: Matching each organism to its established ecological functional group.

Final Logic: Proper alignment of definitions.

🧠 Memory Trick

"Cockroach-Omni; Fungi-Decompose; Grass-Producer; Earthworm-Detritivore."

📚 Class XII – Biology – Chapter: Ecosystem – Topic: Food Web

📄 Passage

"Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third."

Conceptually, what is the defining factor that determines an organism's specific trophic level placement?

A The physical habitat it occupies

B Its standing crop mass

C Its feeding relationship and source of nutrition

D The number of offspring it produces

💡 Short Explanation

Trophic level is determined by nutritional source. Producers (1) →Herbivores (2) →Carnivores (3). Nutrition is the functional definition of the trophic level.

✅ Correct Answer Explanation

Trophic level is a functional categorization. → It represents the "distance" an organism is from the primary energy source (the producer). → The source of nutrition dictates this rank.

❓ Why Other Options Are Incorrect

Option A, B, D → Incorrect; these are structural or demographic factors, not energetic/trophic ones.

🎯 Strategy

Used: Substitution

Application: Replacing "trophic level" with its definition as an "energy/nutrition level."

Final Logic: Feeding source = Trophic Level.

🧠 Memory Trick

"Trophic = Feeding Level."

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

📄 Passage

Based on the passage, why must plants consistently act as the first trophic level?

A They are the source of nutrition for primary consumers.

B They possess the most diverse feeding relationships.

C They are the apex organisms in the community.

D They consume carnivores upon their death.

💡 Short Explanation

Producers (Level 1) convert solar energy. Primary consumers (Level 2) depend on producers for nutrition. Apex status belongs to carnivores, not plants.

✅ Correct Answer Explanation

Plants are the entry point for energy into the ecosystem (producing food). → Because they serve as the food base for primary consumers (herbivores), they must occupy the first trophic level.

❓ Why Other Options Are Incorrect

Option B → Incorrect; they are autotrophic, not diverse feeders.
Option C → Incorrect; carnivores are apex.
Option D → Incorrect; they are not carnivorous.

🎯 Strategy

Used: Elimination

Application: Identifying that the definition of a primary consumer's food source determines the producer's position.

Final Logic: Plant = Food source for Level 2 = Level 1.

🧠 Memory Trick

"Base = Plant (1st)."

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

19 Conceptually, the amount of energy decreases at successive trophic levels. What happens to the energy that is NOT passed to the next trophic level or lost as heat when the organism dies?

A It reverses flow back to the sun.

B It converts to detritus biomass serving as an energy source for decomposers.

C It remains as a permanent standing crop forever.

D It gets locked in living tissues permanently.

💡 Short Explanation

Death leads to detritus. Detritus is the fuel for decomposers. This is the bridge between GFC and DFC.

✅ Correct Answer Explanation

Energy not passed up the food chain remains in the body of the organism. → Upon death, this energy becomes "detritus." → This detritus is then utilized by decomposers (saprotrophs) in the Detritus Food Chain.

❓ Why Other Options Are Incorrect

Option A → Incorrect; energy flow is unidirectional.
Option C → Incorrect; energy is not permanent.
Option D → Incorrect; energy is transient.

🎯 Strategy

Used: Substitution

Application: Mapping the fate of organic biomass after death to the DFC.

Final Logic: Death →Detritus →Decomposers.

🧠 Memory Trick

"Death = Detritus fuel."

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

20 Applying the ten per cent transfer law, if producers in a grass field hold 10,000 units of energy, how much energy is roughly available to the secondary consumers (primary carnivores) occupying the third trophic level?

A 1,000 units

B 100 units

C 10 units

D 1 unit

💡 Short Explanation

Producers (Level 1) = 10,000. Primary Consumer (Level 2) = 10% of 10,000 = 1,000. Secondary Consumer (Level 3) = 10% of 1,000 = 100.

✅ Correct Answer Explanation

10% transfer law: Level 1 (Producer) = 10,000. Level 2 (Primary Consumer) = 10,000 × 0.1 = 1,000. Level 3 (Secondary Consumer) = 1,000 × 0.1 = 100.

❓ Why Other Options Are Incorrect

Option A → Incorrect; this is Level 2.
Option C → Incorrect; this is Level 4.
Option D → Incorrect; this is Level 5.

🎯 Strategy

Used: Dimensional/Unit Analysis

Application: Iterative multiplication by 0.1 for each step in the trophic ladder.

Final Logic: Two steps from Level 1 to Level 3 = 10% × 10% = 1% total. 1% of 10,000 = 100.

🧠 Memory Trick

"Step 1 to 3 = 1% remaining."

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

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