CUET UG Categorised PYQ Biology Unit 12 -

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CUET UG Categorised PYQ Biology Unit 12

BIOLOGY

⏱️ 30 Minutes

❓ 17 Questions

📅 2022, 2023, 2024 & 2025

✍️ Long Answers

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

CUET UG Categorised PYQ Biology Unit 12

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QUESTION 1 OF 17

Which of the following statements are correct? (PYQ 2022 Shift 1)
(A) Certain mass of living material at each trophic level is called as standing crop
(B) The crop that can withstand adverse conditions is called standing crop
(C) The amount of nutrients in soil is called Biomass
(D) Only Biotic components make an Ecosystem
(E) Most of Phytoplanktons are member of algae

Answer Review

1 Which of the following statements are correct? (PYQ 2022 Shift 1)
(A) Certain mass of living material at each trophic level is called as standing crop
(B) The crop that can withstand adverse conditions is called standing crop
(C) The amount of nutrients in soil is called Biomass
(D) Only Biotic components make an Ecosystem
(E) Most of Phytoplanktons are member of algae

A (A) and (E) only

B (A), (C), (D) only

C (A), (C) only

D (B), (D) only

💡 Short Explanation

Standing crop is living biomass at a trophic level. Most phytoplanktons are algae. Ecosystems contain both biotic and abiotic components.

✅ Correct Answer Explanation

Statement A is correct because standing crop refers to the quantity of living material present at a trophic level at a given time. Statement E is correct because phytoplanktons mainly consist of microscopic algae. Statements B, C and D are incorrect because standing crop is not a crop variety, biomass is living organic matter (not soil nutrients), and ecosystems consist of both biotic and abiotic components.

❓ Why Other Options Are Incorrect

Option B: Contains incorrect statements C and D.
Option C: Includes incorrect statement C and omits correct statement E.
Option D: Both statements are incorrect.

🎯 Strategy

Used

Elimination
Final Answer → Option A

🧠 Memory Trick

Standing Crop = Living Mass

📚 Topic: Ecosystem Structure

2 Vertical distribution of different species occupying different levels is called: (PYQ 2022 Shift 1, 2023 Shift 3)

A Fragmentation

B Stratification

C Humification

D Primary production

💡 Short Explanation

Species occur in layers. Common in forests. Called stratification.

✅ Correct Answer Explanation

Stratification refers to the vertical arrangement of organisms into different layers within an ecosystem, such as canopy, shrub and herb layers in forests.

❓ Why Other Options Are Incorrect

Option A: Habitat breaking.
Option C: Formation of humus.
Option D: Production of biomass.

🎯 Strategy

Used

NCERT Recall
Final Answer → Option B

🧠 Memory Trick

Strata = Layers

📚 Topic: Ecosystem Structure

3 Match List I with List II (PYQ 2022 Shift 1)

List I	List II
A. Detritus food chain	I. Available biomass for consumption
B. Standing state	II. Dead organic matter
C. Standing crop	III. Amount of nutrients in soil
D. Net Primary Productivity	IV. Mass of living material

A (A)-(I), (B)-(II), (C)-(III), (D)-(IV)

B (A)-(IV), (B)-(II), (C)-(III), (D)-(I)

C (A)-(II), (B)-(III), (C)-(I), (D)-(IV)

D (A)-(II), (B)-(III), (C)-(IV), (D)-(I)

💡 Short Explanation

Detritus = Dead organic matter. Standing state = Nutrient amount. Standing crop = Living biomass. NPP = Available biomass.

✅ Correct Answer Explanation

Detritus food chain → Dead organic matter. Standing state → Amount of nutrients in soil. Standing crop → Mass of living material. Net Primary Productivity → Available biomass for consumption.

❓ Why Other Options Are Incorrect

Option A: Multiple mismatches.
Option B: Standing crop incorrectly matched.
Option C: NPP and standing crop interchanged.

🎯 Strategy

Used

Option Grouping
Final Answer → Option D

🧠 Memory Trick

Standing State = Nutrients

📚 Topic: Productivity

4 In which ecosystem, a larger fraction of energy flows through detritus food chain than grazing food chain? (PYQ 2023 Shift 1)

A Pond ecosystem

B Lake ecosystem

C River ecosystem

D Terrestrial ecosystem

💡 Short Explanation

Most plant biomass becomes litter. Detritivores dominate energy transfer. Characteristic of terrestrial ecosystems.

✅ Correct Answer Explanation

In terrestrial ecosystems, a large amount of plant biomass enters the detritus pathway after death. Consequently, energy flow through the detritus food chain exceeds that through the grazing food chain.

❓ Why Other Options Are Incorrect

Option A: Grazing chain relatively important.
Option B: Aquatic systems have stronger grazing pathways.
Option C: Not predominantly detritus-based.

🎯 Strategy

Used

NCERT Recall
Final Answer → Option D

🧠 Memory Trick

Land = Leaf Litter = Detritus

📚 Topic: Grazing and Detritus Food Chains

5 Identify statements which are not true for natural ecosystem: (PYQ 2023 Shift 1)
(A) Grassland and desert are terrestrial ecosystems
(B) Oceans and rivers are man-made ecosystems
(C) Wetland and estuary are aquatic ecosystems
(D) Crop fields and aquarium are natural ecosystems

A (A) and (C) only

B (B) and (C) only

C (A) and (B) only

D (B) and (D) only

💡 Short Explanation

Oceans and rivers are natural ecosystems. Crop fields and aquariums are artificial ecosystems. Therefore B and D are false.

✅ Correct Answer Explanation

Grasslands and deserts are terrestrial ecosystems, while wetlands and estuaries are aquatic ecosystems. Oceans and rivers are natural ecosystems, not man-made. Crop fields and aquariums are artificial ecosystems maintained by humans.

❓ Why Other Options Are Incorrect

Option A: A and C are true statements.
Option B: C is true.
Option C: A is true.

🎯 Strategy

Used

Elimination
Final Answer → Option D

🧠 Memory Trick

Aquarium = Artificial

📚 Topic: Ecosystem Types

6 Which is the correct statement with respect to ecological pyramid? (PYQ 2023 Shift 1)

A Trophic level represents species

B An organism may occupy more than one trophic level simultaneously

C Pyramid of energy is never upright

D Base of pyramid is always broad

💡 Short Explanation

Omnivores can feed at multiple trophic levels. Humans are common examples.

✅ Correct Answer Explanation

A trophic level represents the functional position of an organism in a food chain, not a species. Many organisms, especially omnivores, feed at different trophic levels. For example, humans act as primary consumers when eating plants and secondary consumers when eating animals.

❓ Why Other Options Are Incorrect

Option A: Trophic levels represent feeding positions, not species.
Option C: Pyramid of energy is always upright.
Option D: Base is not always broad.

🎯 Strategy

Used

Elimination
Final Answer → Option B

🧠 Memory Trick

Omnivore = Multiple Trophic Levels

📚 Topic: Ecological Pyramids

7 The value 3,54,000 represents: (PYQ 2023 Shift 1)

A Number of primary consumers

B Number of secondary consumers

C Dry weight of secondary consumers in kg m⁻²

D Dry weight of primary consumers in kg m⁻²

💡 Short Explanation

Figure represents a biomass pyramid. Value corresponds to primary consumer biomass.

✅ Correct Answer Explanation

In ecological pyramids of biomass, values are expressed as dry weight per unit area. The value 3,54,000 shown at the primary consumer level represents the dry biomass of primary consumers.

❓ Why Other Options Are Incorrect

Option A: Biomass, not number.
Option B: Wrong trophic level.
Option C: Value too high for secondary consumers.

🎯 Strategy

Used

Contextual Matching
Final Answer → Option D

🧠 Memory Trick

Biomass Pyramid = Dry Weight Values

📚 Topic: Pyramid of Biomass

8 Identify the correct statements: (PYQ 2023 Shift 1)
(A) The figure shows the pyramid of biomass.
(B) The value of D will always be lower than A in grassland ecosystem.
(C) The energy at A is higher than the energy at D.
(D) The energy at D is higher than the energy at A.

A (A) and (B) only

B (A) and (C) only

C (B) and (C) only

D (B) and (D) only

💡 Short Explanation

Figure represents biomass pyramid. Energy decreases at higher trophic levels.

✅ Correct Answer Explanation

The figure is a pyramid of biomass. According to the 10% law, energy decreases progressively from producers to top consumers. Therefore, energy at trophic level A is greater than energy at trophic level D.

❓ Why Other Options Are Incorrect

Option A: Statement B is not always true.
Option C: Includes incorrect statement B.
Option D: Statement D is opposite to energy flow.

🎯 Strategy

Used

Elimination
Final Answer → Option B

🧠 Memory Trick

Energy Always Decreases Upward

📚 Topic: Ecological Pyramids and Energy Flow

9 Match the following (Ecological Pyramid): (PYQ 2023 Shift 1)

List I	List II
A. Number/Trophic level	I. B
B. Number of individuals	II. A
C. Primary consumer	III. D
D. Top Carnivore	IV. E

A (A)-(IV), (B)-(I), (C)-(II), (D)-(III)

B (A)-(I), (B)-(IV), (C)-(II), (D)-(III)

C (A)-(II), (B)-(III), (C)-(I), (D)-(IV)

D (A)-(III), (B)-(II), (C)-(IV), (D)-(I)

💡 Short Explanation

Producers form the base. Primary consumers occupy the second trophic level. Top carnivores occupy the highest level.

✅ Correct Answer Explanation

The ecological pyramid organizes organisms according to trophic levels. Producers occupy the base, primary consumers occupy the second level and top carnivores occupy the highest trophic level.

❓ Why Other Options Are Incorrect

Option A: Incorrect assignments.
Option C: Multiple mismatches.
Option D: Incorrect ecological hierarchy.

🎯 Strategy

Used

Option Grouping
Final Answer → Option B

🧠 Memory Trick

Producer → Herbivore → Carnivore → Top Carnivore

📚 Topic: Ecological Pyramids

10 Complete statement: "The organisms at each trophic level depend on those at ______." (PYQ 2023 Shift 1)

A Higher trophic level for their energy demands

B Lower trophic level for their shelter demands

C Higher trophic level for their food demands

D Lower trophic level for their energy demands

💡 Short Explanation

Energy flows upward. Consumers obtain energy from lower trophic levels. Producers form the energy base.

✅ Correct Answer Explanation

Energy enters ecosystems through producers and moves upward through trophic levels. Each trophic level depends on organisms at lower trophic levels as its source of food and energy.

❓ Why Other Options Are Incorrect

Option A: Energy does not flow downward from higher levels.
Option B: Shelter is not the ecological principle involved.
Option C: Organisms do not obtain food from higher trophic levels.

🎯 Strategy

Used

Contextual Matching
Final Answer → Option D

🧠 Memory Trick

Energy Climbs Upward

📚 Topic: Energy Flow

11 The rate of decomposition is slower if: (PYQ 2023 Shift 2)

A Availability of large amount of oxygen

B Warm and moist environment

C The detritus is rich in nitrogen and sugars

D The detritus is rich in lignin and chitin

💡 Short Explanation

Lignin and chitin are difficult to degrade. Decomposers act slowly. Decomposition rate decreases.

✅ Correct Answer Explanation

Detritus rich in lignin and chitin resists microbial degradation. Therefore decomposition proceeds much more slowly compared with detritus rich in nitrogen and soluble sugars.

❓ Why Other Options Are Incorrect

Option A: Oxygen increases decomposition.
Option B: Warm and moist conditions accelerate decomposition.
Option C: Nitrogen-rich material decomposes rapidly.

🎯 Strategy

Used

Elimination
Final Answer → Option D

🧠 Memory Trick

Lignin Lasts Long

📚 Topic: Decomposition

12 An example of inverted ecological pyramid is: (PYQ 2023 Shift 2)

A Pyramid of energy of forest

B Pyramid of energy of grassland

C Pyramid of biomass of sea

D Pyramid of number in a grassland

💡 Short Explanation

Aquatic biomass pyramid is inverted. Producers have low standing biomass. Phytoplankton reproduce rapidly.

✅ Correct Answer Explanation

In marine ecosystems, phytoplankton have lower standing biomass than consumers at a given moment. Therefore the biomass pyramid appears inverted even though productivity remains high.

❓ Why Other Options Are Incorrect

Option A: Energy pyramid is always upright.
Option B: Energy pyramid is always upright.
Option D: Grassland pyramid of numbers is upright.

🎯 Strategy

Used

NCERT Recall
Final Answer → Option C

🧠 Memory Trick

Sea Biomass = Inverted

📚 Topic: Ecological Pyramids

13 When a snake eats a rat that feeds on leaves of green plants, the snake is a ______ in the food chain. (PYQ 2023 Shift 3)

A Primary consumer

B Secondary consumer

C Tertiary consumer

D Secondary carnivore

💡 Short Explanation

Plants = Producers. Rat = Primary consumer. Snake = Secondary consumer.

✅ Correct Answer Explanation

Food chain: Green plants → Rat → Snake Rat feeds directly on plants and is therefore a primary consumer. Snake feeds on the rat and occupies the next trophic level, making it a secondary consumer.

❓ Why Other Options Are Incorrect

Option A: Rat is the primary consumer.
Option C: Requires one more consumer level before snake.
Option D: Snake is the first carnivore in the chain, not a secondary carnivore.

🎯 Strategy

Used

Trophic Level Analysis
Final Answer → Option B

🧠 Memory Trick

Producer → Herbivore → Snake

📚 Topic: Food Chain

14 Choose the correct equation showing the relationship between Gross Primary Productivity (GPP), Respiration Losses (R) and Net Primary Productivity (NPP). (PYQ 2025 Shift 1)

A GPP = R/(NPP)²

B GPP = 2NPP + R

C GPP = NPP − R

D GPP − R = NPP

💡 Short Explanation

GPP is total productivity. Respiration consumes part of GPP. Remaining productivity is NPP.

✅ Correct Answer Explanation

Net Primary Productivity (NPP) is the biomass available after plants use some energy for respiration. Formula: Thus: GPP − R = NPP

❓ Why Other Options Are Incorrect

Option A: No ecological basis.
Option B: Incorrect relationship.
Option C: Rearranged incorrectly.

🎯 Strategy

Used

Formula Recall
Final Answer → Option D

🧠 Memory Trick

GPP − Respiration = NPP

📚 Topic: Productivity

15 If a man is eating fish as his food, which trophic level is he in? (PYQ 2025 Shift 1)

A First

B Second

C Third

D Fourth

💡 Short Explanation

Phytoplankton = Producers. Zooplankton = Primary consumers. Fish = Secondary consumers. Human = Tertiary consumer.

✅ Correct Answer Explanation

Food chain: Phytoplankton → Zooplankton → Fish → Human Trophic levels: 1st = Producer 2nd = Primary consumer 3rd = Secondary consumer 4th = Tertiary consumer (Human) Hence, humans occupy the fourth trophic level.

❓ Why Other Options Are Incorrect

Option A: Producer level.
Option B: Primary consumer level.
Option C: Secondary consumer level.

🎯 Strategy

Used

Food Chain Analysis
Final Answer → Option D

🧠 Memory Trick

Plant → Zooplankton → Fish → Human = 4 Levels

📚 Topic: Trophic Levels

16 A small standing crop of phytoplankton supports large zooplankton. This represents: (PYQ 2025 Shift 1)

A Inverted pyramid of energy

B Inverted pyramid of biomass

C Upright pyramid of biomass

D Sometimes upright and inverted pyramid of energy

💡 Short Explanation

Common in aquatic ecosystems. Producer biomass is low. Consumer biomass can be higher.

✅ Correct Answer Explanation

In aquatic ecosystems, phytoplankton reproduce rapidly and are consumed quickly, resulting in a small standing biomass at any given time. Despite this, they support a larger biomass of zooplankton. This creates an inverted biomass pyramid.

❓ Why Other Options Are Incorrect

Option A: Energy pyramids are always upright.
Option C: Not true for this aquatic situation.
Option D: Energy pyramids never become inverted.

🎯 Strategy

Used

NCERT Recall
Final Answer → Option B

🧠 Memory Trick

Aquatic = Inverted Biomass, Upright Energy

📚 Topic: Ecological Pyramids

17 Humification leads to: (PYQ 2025 Shift 1)

A Soil erosion

B Soil conservation

C Accumulation of humus

D Accumulation of salts

💡 Short Explanation

Organic matter decomposes. Stable dark substance forms. Humus accumulates.

✅ Correct Answer Explanation

Humification is the process through which decomposed organic matter is converted into humus. Humus is a dark-coloured, nutrient-rich colloidal substance that improves soil fertility and water-holding capacity. Therefore, humification directly results in accumulation of humus.

❓ Why Other Options Are Incorrect

Option A: Refers to loss of topsoil.
Option B: May occur indirectly but is not the direct outcome.
Option D: Related to salinization, not humification.

🎯 Strategy

Used

NCERT Recall
Final Answer → Option C

🧠 Memory Trick

Humification → Humus Formation

📚 Topic: Decomposition

CUET UG Categorised PYQ Biology Unit 12

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