Ecology

Topic: Population Growth Models; Subtopic: Verhulst-Pearl Logistic Growth Equation

Keyword Definitions:

• Population Growth: The increase in the number of individuals in a population over time, influenced by birth, death, immigration, and emigration.

• Carrying Capacity (K): The maximum number of individuals an environment can support without depletion of resources.

• Intrinsic Rate of Natural Increase (r): The rate at which a population grows under ideal conditions with unlimited resources.

• Exponential Growth: Population increase without environmental resistance, forming a J-shaped curve.

• Logistic Growth: Population growth that slows as it approaches carrying capacity, forming an S-shaped curve.

• Verhulst-Pearl Equation: The mathematical model expressing logistic population growth as dN/dt = rN(K–N)/K.

Lead Question (September 2025)
Which one of the following equations represents the Verhulst-Pearl Logistic Growth of population?
(1) dN/dt = r(K–N)/K
(2) dN/dt = rN(K–N)/K
(3) dN/dt = rN(N–K)/N
(4) dN/dt = N(r–K)/K

Explanation:
The correct answer is (2) dN/dt = rN(K–N)/K. This equation describes logistic population growth where ‘r’ is the intrinsic rate of natural increase, ‘N’ is population size, and ‘K’ is carrying capacity. As the population size approaches K, growth slows and eventually stabilizes, forming an S-shaped growth curve observed in natural populations.

1. In the logistic growth model, population growth is maximum when:
(1) N = K
(2) N = 0
(3) N = K/2
(4) N = 2K
Explanation: The correct answer is N = K/2. In logistic growth, the growth rate is highest when the population reaches half of its carrying capacity. At this stage, environmental resistance begins to increase, but resources are still sufficiently available, leading to the maximum rate of population increase before growth slows down.

2. In the logistic equation dN/dt = rN(K–N)/K, what does (K–N) represent?
(1) Available resources
(2) Environmental resistance
(3) Population density
(4) Birth rate
Explanation: The correct answer is Available resources. In this equation, (K–N) denotes the remaining capacity of the environment to support more individuals. As N approaches K, resources become limited, reducing growth. This term thus represents the unused portion of carrying capacity that influences the rate of population growth.

3. Assertion-Reason Type:
Assertion (A): Logistic growth results in an S-shaped curve.
Reason (R): Population growth slows as it reaches the carrying capacity of the environment.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true
Explanation: The correct answer is (1). Logistic growth produces an S-shaped or sigmoidal curve because initially, population increases exponentially, then slows as resources limit further growth. The carrying capacity (K) acts as the upper limit beyond which population size stabilizes, balancing birth and death rates.

4. Which of the following curves best represents logistic growth?
(1) J-shaped
(2) S-shaped
(3) Linear
(4) Parabolic
Explanation: The correct answer is S-shaped. Logistic growth follows an S-shaped curve due to environmental resistance. It starts with a slow phase, followed by exponential growth, and then a deceleration as the population approaches carrying capacity. This realistic model represents natural population dynamics more accurately than exponential growth.

5. Fill in the Blank:
In the logistic equation, population growth ceases when N = ______.
(1) r
(2) K
(3) 0
(4) K/2
Explanation: The correct answer is K. When population size (N) equals carrying capacity (K), dN/dt becomes zero, meaning no net growth. The environment can no longer support more individuals, as resources become fully utilized and birth and death rates reach equilibrium, stabilizing the population size.

6. Choose the correct statements:
Statement I: Logistic growth takes place under limited resource conditions.
Statement II: Exponential growth occurs when resources are infinite.
(1) Both statements are correct
(2) Both statements are incorrect
(3) Only Statement I is correct
(4) Only Statement II is correct
Explanation: The correct answer is (1) Both statements are correct. Logistic growth is resource-limited, resulting in population stabilization, while exponential growth assumes unlimited resources and space. Natural populations often exhibit logistic growth as they face environmental resistance, limiting further exponential expansion over time.

7. Which of the following represents exponential population growth?
(1) dN/dt = rN
(2) dN/dt = rN(K–N)/K
(3) dN/dt = r(K–N)
(4) dN/dt = N/K
Explanation: The correct answer is dN/dt = rN. Exponential growth occurs when resources are unlimited and environmental resistance is minimal. The population grows proportionally to its size, forming a J-shaped curve. Unlike logistic growth, there is no slowing phase as the carrying capacity limit is not considered.

8. Matching Type Question:
Match the terms with their meanings:
A. r        I. Population size
B. K        II. Carrying capacity
C. N        III. Intrinsic rate of increase
D. dN/dt        IV. Rate of population change
(1) A-III, B-II, C-I, D-IV
(2) A-II, B-I, C-III, D-IV
(3) A-I, B-III, C-IV, D-II
(4) A-IV, B-III, C-II, D-I
Explanation: The correct answer is (1) A-III, B-II, C-I, D-IV. In the logistic growth equation, ‘r’ represents the intrinsic rate of increase, ‘K’ the carrying capacity, ‘N’ the population size, and ‘dN/dt’ the rate of population change over time, defining population dynamics quantitatively.

9. In logistic growth, the early stage of population increase resembles:
(1) Linear growth
(2) Exponential growth
(3) Stationary phase
(4) Decline phase
Explanation: The correct answer is Exponential growth. During the initial phase of logistic growth, population density is low and resources are abundant, leading to rapid, unchecked exponential growth. Later, environmental factors like competition and limited food supply slow the growth rate as the population nears carrying capacity.

10. The shape of logistic growth curve depends primarily on:
(1) Birth rate alone
(2) Carrying capacity and intrinsic rate of increase
(3) Mutation rate
(4) Migration rate
Explanation: The correct answer is Carrying capacity and intrinsic rate of increase. These two parameters determine how quickly a population grows and when it stabilizes. The interplay between ‘r’ (growth potential) and ‘K’ (resource limitation) defines the sigmoidal (S-shaped) curve that characterizes logistic population growth patterns in nature.

Topic: Energy Flow in Ecosystem; Subtopic: Laws of Thermodynamics and Energy Transfer

Keyword Definitions:

• Ecosystem: A biological community of interacting organisms and their physical environment.

• Energy flow: The movement of energy through food chains from producers to consumers and decomposers.

• Producers: Autotrophic organisms that convert solar energy into chemical energy by photosynthesis.

• Second law of thermodynamics: States that energy transformations increase the disorder (entropy) of the universe; no process is 100% efficient.

Lead Question – 2025

Given below are two statements:

Statement I: In ecosystem, there is unidirectional flow of energy of sun from producers to consumers.

Statement II: Ecosystems are exempted from 2nd law of thermodynamics.

In the light of the above statements, choose the most appropriate answer from the options given below:

(1) Both statement I and statement II are correct

(2) Both statement I and statement II are incorrect

(3) Statement I is correct but statement II is incorrect

(4) Statement I is incorrect but statement II is correct

Explanation: The flow of energy in an ecosystem is unidirectional, moving from the sun to producers and then to consumers and decomposers. Energy transfer between trophic levels is never 100% efficient due to heat loss, as explained by the second law of thermodynamics. Hence, ecosystems follow—not exempt—the law. Therefore, option (3) is correct.

1. The major source of energy for all ecosystems is:

(1) Moon

(2) Wind

(3) Sun

(4) Tides

Explanation: The sun is the ultimate source of energy for all ecosystems. Solar energy is captured by producers (plants, algae) through photosynthesis and converted into chemical energy. This energy then flows through the food chain to consumers and decomposers, maintaining the balance of energy in nature.

2. In an ecosystem, the direction of energy flow is always:

(1) Bidirectional

(2) Cyclic

(3) Unidirectional

(4) Random

Explanation: Energy flow in an ecosystem is unidirectional. It begins with solar energy captured by producers, passes to herbivores and carnivores, and ultimately dissipates as heat. Unlike nutrients, energy does not recycle; it moves in one direction, emphasizing the dependence of all trophic levels on producers.

3. According to the 2nd law of thermodynamics, during energy transfer:

(1) Energy remains constant

(2) Some energy is lost as heat

(3) Energy increases after transfer

(4) No energy is lost

Explanation: The second law of thermodynamics states that every energy transfer results in energy loss as heat, increasing entropy. Thus, when energy passes from one trophic level to another, a significant portion is dissipated as heat, limiting the number of trophic levels in an ecosystem.

4. Which of the following correctly represents energy flow in an ecosystem?

(1) Consumers → Producers → Decomposers

(2) Producers → Consumers → Decomposers

(3) Decomposers → Producers → Consumers

(4) Consumers → Decomposers → Producers

Explanation: The correct sequence is Producers → Consumers → Decomposers. Producers capture solar energy, consumers utilize it through feeding, and decomposers break down organic matter to recycle nutrients. This chain ensures energy movement and nutrient cycling for ecosystem sustainability.

5. Energy transfer in an ecosystem follows:

(1) 50% law

(2) 10% law

(3) 90% law

(4) 1% law

Explanation: The 10% law states that only about 10% of the energy at each trophic level is transferred to the next, while the remaining 90% is lost as heat. This principle explains why food chains are short and energy diminishes at higher trophic levels in ecosystems.

6. The process of energy transfer from producers to top consumers is called:

(1) Food chain

(2) Food web

(3) Ecological pyramid

(4) Biomagnification

Explanation: The food chain represents a linear sequence of energy transfer where energy moves from producers to herbivores, then to carnivores and decomposers. Each step involves energy loss as heat, illustrating the efficiency and direction of energy movement within an ecosystem.

Assertion–Reason Type Question

7. Assertion (A): Energy flow in an ecosystem is unidirectional.

Reason (R): Energy cannot be recycled in living systems.

(1) Both A and R are true, and R is the correct explanation of A.

(2) Both A and R are true, but R is not the correct explanation of A.

(3) A is true, R is false.

(4) A is false, R is true.

Explanation: Both assertion and reason are true, and the reason correctly explains the assertion. Energy flows in a single direction because once it is used, it cannot be recycled as in nutrient cycles. It eventually dissipates as heat, consistent with thermodynamic principles in ecological systems.

Matching Type Question

8. Match the following components with their roles in energy flow:

A. Producers  1. Convert solar energy into chemical energy

B. Herbivores  2. Consume producers

C. Carnivores  3. Feed on other animals

D. Decomposers 4. Break down organic waste

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

Explanation: The correct match is A-1, B-2, C-3, D-4. Producers convert solar energy into chemical energy; herbivores eat plants; carnivores feed on animals; decomposers break down organic matter. This matching reflects the sequence and efficiency of energy transfer in the food chain.

Fill in the Blanks / Completion Type Question

9. Energy flow in an ecosystem follows the _______ law of thermodynamics.

(1) First (2) Second (3) Third (4) Zeroth

Explanation: Energy flow in ecosystems obeys the second law of thermodynamics, which emphasizes that every energy transfer increases entropy and results in energy loss as heat. This principle ensures that energy flow is unidirectional and non-cyclic within ecological systems.

Choose the Correct Statements Type Question

10. Statement I: Energy in an ecosystem decreases at higher trophic levels.

Statement II: The flow of energy in an ecosystem is cyclic.

(1) Both statements are correct.

(2) Both statements are incorrect.

(3) Only Statement I is correct.

(4) Only Statement II is correct.

Explanation: Only Statement I is correct. Energy decreases at higher trophic levels due to losses at each transfer stage. However, energy flow is not cyclic but unidirectional. Unlike nutrients, energy cannot be reused; it dissipates as heat, conforming to thermodynamic laws governing ecosystem functioning.

Topic: Energy Flow and Productivity; Subtopic: Measurement of Productivity in Ecosystems

Keyword Definitions:

• Ecosystem: A biological community of interacting organisms and their physical environment.

• Productivity: The rate at which energy is produced and stored by producers in an ecosystem per unit area and time.

• Gross Primary Productivity (GPP): The total rate of energy capture by producers through photosynthesis.

• Net Primary Productivity (NPP): The energy left after respiration, available for consumers in the food chain.

• Calorie (KCal): A unit of energy used to measure productivity in ecosystems, often expressed per square meter per year.

Lead Question (2025):
Which of the following is the unit of productivity of an Ecosystem:
(1) gm⁻²
(2) Kcal m⁻²
(3) KCal m⁻³
(4) (KCal m⁻²) yr⁻¹

Explanation: Productivity in an ecosystem is defined as the rate of energy accumulation or biomass production per unit area per unit time. The correct unit is **(KCal m⁻² yr⁻¹)** or sometimes **gm⁻² yr⁻¹** when expressed in biomass. It reflects how efficiently producers convert solar energy into chemical energy. Hence, the correct answer is (4) (KCal m⁻²) yr⁻¹.

1. Primary productivity is mainly carried out by:
(1) Consumers
(2) Producers
(3) Decomposers
(4) Scavengers

Explanation: **Primary productivity** refers to the energy fixed by autotrophs, mainly green plants and phytoplankton, through photosynthesis. They convert solar energy into chemical energy, forming the base of all food chains. Consumers and decomposers depend on this stored energy. Therefore, the correct answer is (2) Producers.

2. The difference between Gross Primary Productivity and Net Primary Productivity is:
(1) Energy lost as heat
(2) Energy used in respiration
(3) Energy stored in consumers
(4) Total solar energy absorbed

Explanation: **Gross Primary Productivity (GPP)** is the total energy captured by producers. **Net Primary Productivity (NPP)** is the energy remaining after respiratory losses. Thus, NPP = GPP – Respiration. This energy becomes available to herbivores and higher trophic levels. Hence, the correct answer is (2) Energy used in respiration.

3. Secondary productivity refers to:
(1) Energy accumulated by producers
(2) Energy stored in consumers
(3) Energy used for photosynthesis
(4) Energy lost through respiration

Explanation: **Secondary productivity** is the rate at which consumers (animals) convert the chemical energy of food into their biomass. It represents energy available for higher consumers in the food chain. Unlike producers, consumers cannot fix solar energy. Hence, the correct answer is (2) Energy stored in consumers.

4. Which of the following ecosystems has the highest primary productivity?
(1) Desert
(2) Tropical rainforest
(3) Open ocean
(4) Tundra

Explanation: **Tropical rainforests** have the highest primary productivity because of abundant sunlight, high temperature, and rainfall supporting dense vegetation. In contrast, deserts and tundras have low productivity due to harsh climates, and oceans, though vast, have limited nutrient availability. Hence, the correct answer is (2) Tropical rainforest.

5. The rate of production of organic matter during photosynthesis is termed as:
(1) Gross Primary Productivity
(2) Net Primary Productivity
(3) Secondary Productivity
(4) Ecosystem Efficiency

Explanation: The **Gross Primary Productivity (GPP)** represents the total energy fixed by producers through photosynthesis in an ecosystem. It includes the energy used in respiration and that stored as biomass. GPP forms the foundation of energy flow in nature. Hence, the correct answer is (1) Gross Primary Productivity.

6. In aquatic ecosystems, primary productivity mainly depends on:
(1) Temperature and light
(2) Water salinity only
(3) Availability of carbon dioxide
(4) Pressure and tides

Explanation: In **aquatic ecosystems**, light and temperature are the major controlling factors for primary productivity. Adequate sunlight supports photosynthesis by phytoplankton, while temperature influences enzyme activity and metabolic rates. Hence, the correct answer is (1) Temperature and light.

Assertion–Reason Type Question

7. Assertion (A): Net Primary Productivity is always less than Gross Primary Productivity.
Reason (R): Some energy is used by plants for respiration.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, R is false.
(4) A is false, R is true.

Explanation: Since plants use part of their captured energy for respiration, **NPP** is always less than **GPP**. The difference represents energy used for maintenance of plant metabolism. Hence, both A and R are true, and R correctly explains A. Correct answer is (1) Both A and R are true, and R is the correct explanation of A.

Matching Type Question

8. Match the following ecosystems with their approximate productivity levels:
A. Tropical rainforest  1. Lowest
B. Desert  2. Moderate
C. Open ocean  3. High
D. Coral reef  4. Very high

(1) A–3, B–1, C–2, D–4
(2) A–4, B–1, C–2, D–3
(3) A–2, B–3, C–4, D–1
(4) A–4, B–2, C–1, D–3

Explanation: **Tropical rainforests** have very high productivity, **deserts** the lowest, **open oceans** moderate, and **coral reefs** high productivity due to nutrient recycling. Thus, the correct match is A–4, B–1, C–2, D–3, corresponding to option (2).

Fill in the Blanks Question

9. The rate at which energy is stored in producers after respiration losses is called __________.
(1) Gross Primary Productivity
(2) Secondary Productivity
(3) Net Primary Productivity
(4) Ecosystem Efficiency

Explanation: **Net Primary Productivity (NPP)** represents the rate at which producers store energy after accounting for respiratory losses. It measures the actual biomass available for consumers and energy transfer across trophic levels. Hence, the correct answer is (3) Net Primary Productivity.

Choose the Correct Statements (Statement I & II)

10. Statement I: Productivity is expressed as energy or biomass per unit area per unit time.
Statement II: Productivity can be measured only in aquatic ecosystems.
(1) Both statements are true.
(2) Both statements are false.
(3) Statement I true, Statement II false.
(4) Statement I false, Statement II true.

Explanation: **Statement I is true** because productivity measures energy flow or biomass accumulation per unit area and time. **Statement II is false** since productivity is measurable in both terrestrial and aquatic ecosystems. Therefore, the correct answer is (3) Statement I true, Statement II false.

Subtopic: History and Pioneers of Ecology

Keyword Definitions:

• Ecology: The branch of biology that studies interactions among organisms and their environment.

• Ecosystem: A functional unit consisting of living organisms and their non-living environment interacting together.

• Biosphere: The global ecological system integrating all living beings and their relationships.

• Population: A group of individuals of the same species living in a specific geographic area.

• Community: All populations of different species living and interacting in a common environment.

Lead Question - 2025
Who is known as the father of Ecology in India?
(1) S.R. Kashyap
(2) Ramdeo Misra
(3) Ram Udar
(4) Birbal Sahni

Explanation:
The correct answer is (2) Ramdeo Misra. He is regarded as the father of Indian Ecology for his pioneering research on ecosystems, productivity, and ecological balance in tropical regions. He emphasized the importance of ecosystem functioning and sustainable development, establishing the foundation of modern ecological studies in India through teaching, research, and policy contributions.

Guessed Questions:

1. Who is known as the father of modern Ecology?
(1) Ernst Haeckel
(2) Charles Darwin
(3) Eugene Odum
(4) E.P. Odum
Explanation: The answer is (1) Ernst Haeckel. He coined the term ‘Ecology’ in 1866, defining it as the study of relationships between organisms and their environment. His foundational work inspired later ecologists like Odum and Lindeman to develop ecosystem theory and ecological models.

2. Which branch of ecology deals with the study of individuals and their environment?
(1) Population Ecology
(2) Community Ecology
(3) Autecology
(4) Synecology
Explanation: The correct answer is (3) Autecology. It focuses on the ecological relationships of a single species with its environment, including adaptations, behavior, and environmental tolerances. It helps in understanding how species survive and interact with abiotic factors in their habitat.

3. Which of the following is not an abiotic component of an ecosystem?
(1) Light
(2) Temperature
(3) Decomposers
(4) Water
Explanation: The answer is (3) Decomposers. They are biotic components that break down dead organisms and recycle nutrients into the environment. Abiotic components include non-living elements like light, water, air, and temperature that influence living organisms.

4. The term “ecosystem” was first coined by:
(1) A.G. Tansley
(2) Charles Elton
(3) Raymond Lindeman
(4) Eugene Odum
Explanation: The correct answer is (1) A.G. Tansley. In 1935, he introduced the term “ecosystem” to describe a biological system comprising organisms interacting with their physical environment, emphasizing both living and non-living components as part of a functional whole.

5. The concept of “energy flow in an ecosystem” was first introduced by:
(1) Raymond Lindeman
(2) Eugene Odum
(3) A.G. Tansley
(4) Charles Elton
Explanation: The correct answer is (1) Raymond Lindeman. In 1942, he described energy transfer through trophic levels in ecosystems using the concept of food chains and pyramids, forming the basis for modern ecosystem energy models and ecological efficiency studies.

6. Which of the following levels of ecological organization is the largest?
(1) Population
(2) Community
(3) Ecosystem
(4) Biosphere
Explanation: The answer is (4) Biosphere. It encompasses all ecosystems on Earth and represents the global sum of life and environmental interactions. It includes the atmosphere, hydrosphere, and lithosphere that support all biological processes.

7. Assertion–Reason Type:
Assertion (A): Ecology deals with interactions among organisms and their environment.
Reason (R): Ecology studies only abiotic components of nature.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.
Explanation: The correct answer is (3) A is true, but R is false. Ecology studies interactions of organisms with both biotic and abiotic components. It integrates multiple factors influencing survival, reproduction, and energy flow in ecosystems.

8. Matching Type Question:
Match the following ecologists with their contributions:
A. A.G. Tansley   (i) Energy flow concept
B. E.P. Odum       (ii) Ecosystem concept
C. Raymond Lindeman   (iii) Modern Ecology Textbook
D. Ramdeo Misra      (iv) Indian Ecology pioneer
(1) A–ii, B–iii, C–i, D–iv
(2) A–i, B–ii, C–iv, D–iii
(3) A–iii, B–iv, C–ii, D–i
(4) A–iv, B–i, C–ii, D–iii
Explanation: The correct answer is (1) A–ii, B–iii, C–i, D–iv. Each ecologist made unique contributions: Tansley (ecosystem), Odum (textbook and systems ecology), Lindeman (energy flow), and Misra (Indian ecological research and productivity studies).

9. Fill in the Blanks:
The study of interactions among organisms and their environment is called ________.
(1) Zoology
(2) Ecology
(3) Botany
(4) Taxonomy
Explanation: The correct answer is (2) Ecology. It examines the dynamic relationships between living beings and the physical environment, including energy transfer, resource cycles, and adaptations across different ecosystems.

10. Choose the Correct Statements (Statement I & II):
Statement I: Eugene Odum is called the father of modern ecology.
Statement II: He introduced the concept of ecosystem for the first time.
(1) Both statements are correct.
(2) Both statements are incorrect.
(3) Statement I is correct, Statement II is incorrect.
(4) Statement I is incorrect, Statement II is correct.
Explanation: The correct answer is (3) Statement I is correct, Statement II is incorrect. Eugene Odum is known as the father of modern ecology, while the term “ecosystem” was coined by A.G. Tansley. Odum developed system ecology and ecosystem modeling.

Topic: Energy Flow in Ecosystem; Subtopic: Primary Productivity and Energy Source

Keyword Definitions:
• Solar Energy: The radiant energy emitted by the sun that supports life and drives photosynthesis.
• Photosynthesis: The process by which green plants convert light energy into chemical energy.
• Primary Productivity: The rate at which producers convert solar energy into chemical energy in an ecosystem.
• Gross Primary Productivity (GPP): Total energy captured by producers through photosynthesis.
• Net Primary Productivity (NPP): Energy available to consumers after subtracting respiration losses from GPP.

Lead Question – 2025
Given below are two statements:
Statement - I : The primary source of energy in an ecosystem is solar energy.
Statement - II : The rate of production of organic matter during photosynthesis in an ecosystem is called net primary productivity (NPP).
In the light of the above statements, choose the most appropriate answer from the options given below:
(1) Both statement I and statement II are correct
(2) Both statement I and statement II are incorrect
(3) Statement I correct but statement II is incorrect
(4) Statement I is incorrect but statement II is correct

Explanation:
Solar energy acts as the ultimate source of energy for all ecosystems, driving photosynthesis. The total energy captured by producers is gross primary productivity (GPP), while the energy left after respiration is termed net primary productivity (NPP). Hence, statement I is correct but statement II is incorrect. The correct answer is (3).

Guessed Questions:

1. Single Correct Answer:
Which one of the following is the ultimate source of energy for all ecosystems?
(1) Chemical energy
(2) Solar energy
(3) Wind energy
(4) Geothermal energy
Explanation:
Solar energy is the ultimate energy source supporting life on Earth. Producers convert sunlight into chemical energy via photosynthesis, which flows through food chains. All ecosystem energy originates from the sun. Therefore, the correct answer is (2) Solar energy.

2. Single Correct Answer:
The difference between gross primary productivity (GPP) and net primary productivity (NPP) represents:
(1) Respiration losses
(2) Photosynthetic gain
(3) Decomposition rate
(4) Biomass turnover
Explanation:
Gross primary productivity includes the total energy fixed by producers. Part of this energy is used in respiration, and the remaining energy forms net primary productivity. Thus, GPP – Respiration = NPP. Therefore, the correct answer is (1) Respiration losses.

3. Single Correct Answer:
Which ecosystem shows the highest net primary productivity (NPP)?
(1) Desert
(2) Tundra
(3) Tropical rainforest
(4) Grassland
Explanation:
Tropical rainforests possess abundant sunlight, warmth, and moisture, favoring high photosynthetic rates. Hence, they show the highest net primary productivity among all terrestrial ecosystems. The correct answer is (3) Tropical rainforest.

4. Single Correct Answer:
In an ecosystem, producers convert solar energy into:
(1) Mechanical energy
(2) Chemical energy
(3) Kinetic energy
(4) Electrical energy
Explanation:
Through photosynthesis, green plants convert solar energy into chemical energy stored in glucose molecules. This energy is transferred across trophic levels. Therefore, the correct answer is (2) Chemical energy.

5. Single Correct Answer:
Primary productivity depends on:
(1) Solar radiation and nutrient availability
(2) Rainfall and soil texture only
(3) Herbivore population
(4) Carnivore density
Explanation:
Primary productivity is influenced by solar radiation, nutrient availability, water supply, and temperature. Producers require light and nutrients for effective photosynthesis and biomass production. Hence, the correct answer is (1) Solar radiation and nutrient availability.

6. Single Correct Answer:
Which of the following equations correctly represents the relationship between GPP and NPP?
(1) NPP = GPP + R
(2) NPP = GPP – R
(3) GPP = NPP – R
(4) GPP = NPP + 2R
Explanation:
Producers capture solar energy as GPP, from which some energy is used in respiration (R). The remaining usable energy forms NPP. Thus, NPP = GPP – R. Therefore, the correct answer is (2) NPP = GPP – R.

7. Assertion–Reason Type:
Assertion (A): Primary productivity is the rate of energy storage by producers.
Reason (R): Consumers convert solar energy directly into chemical energy.
(1) Both A and R are true, and R explains A
(2) Both A and R are true, but R does not explain A
(3) A is true, R is false
(4) A is false, R is true
Explanation:
Producers alone convert solar energy into chemical energy through photosynthesis, not consumers. Consumers depend on producers for energy. Hence, A is true but R is false. The correct answer is (3) A is true, R is false.

8. Matching Type:
Match the following:
List I (Term) – List II (Definition)
A. GPP – (i) Total rate of photosynthesis
B. NPP – (ii) Energy available to consumers
C. Respiration (R) – (iii) Energy loss as heat
D. Solar energy – (iv) Ultimate source of energy
(1) A-i, B-ii, C-iii, D-iv
(2) A-ii, B-iii, C-iv, D-i
(3) A-iii, B-i, C-ii, D-iv
(4) A-iv, B-iii, C-i, D-ii
Explanation:
Gross primary productivity (GPP) is the total rate of photosynthesis, net primary productivity (NPP) is the energy left for consumers, respiration (R) represents energy lost as heat, and solar energy is the ultimate energy source. Hence, the correct match is (1) A-i, B-ii, C-iii, D-iv.

9. Fill in the Blanks:
__________ represents the energy remaining after respiration losses in producers.
(1) GPP
(2) NPP
(3) Secondary productivity
(4) Total productivity
Explanation:
Net Primary Productivity (NPP) represents the actual energy available to consumers after subtracting the energy lost during plant respiration from gross productivity. It forms the base energy for food chains. Hence, the correct answer is (2) NPP.

10. Choose the Correct Statements:
Statement I: Solar energy is converted to chemical energy by producers.
Statement II: Net primary productivity is the total energy captured by plants.
(1) Both are true
(2) Both are false
(3) I is true, II is false
(4) I is false, II is true
Explanation:
Producers convert solar energy into chemical energy through photosynthesis, but NPP is not the total captured energy; it is the remaining energy after respiration. Hence, statement I is true and statement II is false. The correct answer is (3) I is true, II is false.

Topic: Ecological Interactions; Subtopic: Symbiotic Relationships

Keyword Definitions:
• Epiphytes: Plants that grow on other plants for physical support but do not obtain nutrients from them.
• Commensalism: An interaction where one species benefits and the other is neither harmed nor benefited.
• Mutualism: Both species involved derive mutual benefits from the relationship.
• Predation: One organism kills and feeds on another organism.
• Amensalism: One organism is inhibited or destroyed while the other remains unaffected.
• Symbiosis: A close and long-term biological interaction between two different biological organisms.

Lead Question – 2025
Epiphytes that are growing on a mango branch is an example of which of the following?
(1) Commensalism
(2) Mutualism
(3) Predation
(4) Amensalism

Explanation:
Epiphytes growing on a mango branch exhibit commensalism. The epiphyte benefits by gaining physical support and access to sunlight without harming the host tree. The mango tree remains unaffected as the epiphyte does not derive nutrients from it. This relationship illustrates how organisms coexist without competition or dependence for nutrition.

1. Lichens represent which type of association?
(1) Mutualism
(2) Commensalism
(3) Parasitism
(4) Amensalism
Explanation: Lichens are mutualistic associations between algae and fungi. The alga performs photosynthesis and provides food, while the fungus offers shelter and absorbs water and minerals. Both organisms benefit, making lichens a perfect example of mutualism essential for ecological balance and nutrient cycling in various environments.

2. The relationship between cattle egrets and grazing cattle represents:
(1) Mutualism
(2) Commensalism
(3) Parasitism
(4) Amensalism
Explanation: The interaction between cattle egrets and grazing cattle is an example of commensalism. As cattle graze, they stir up insects from the grass, which the egrets feed on. The egrets benefit from food availability, while the cattle remain unaffected, demonstrating a classic commensal relationship in nature.

3. Which of the following is an example of amensalism?
(1) Penicillium secreting antibiotics inhibiting bacteria
(2) Orchid growing on a tree
(3) Clownfish and sea anemone
(4) Cuckoo laying eggs in crow’s nest
Explanation: Penicillium secretes antibiotics that inhibit bacterial growth, exemplifying amensalism. In this relationship, one organism (bacterium) is harmed while the other (fungus) is unaffected. It demonstrates how biochemical secretions influence interspecific interactions and contribute to natural selection within microbial communities.

4. Which interaction shows both species harmed?
(1) Competition
(2) Commensalism
(3) Parasitism
(4) Mutualism
Explanation: In competition, both species are negatively affected as they vie for limited resources such as food, space, or mates. This reduces individual growth and reproduction rates. Intraspecific competition occurs within species, while interspecific competition occurs between species sharing similar ecological niches.

5. Which of the following pairs shows mutualism?
(1) Mycorrhizae and roots
(2) Tapeworm and intestine
(3) Mango tree and epiphyte
(4) Tiger and deer
Explanation: Mycorrhizae and roots represent mutualism. The fungus helps the plant absorb water and minerals, while the plant provides carbohydrates to the fungus. This interaction enhances plant nutrition and soil health, forming an essential ecological partnership found in most terrestrial ecosystems worldwide.

6. Which of the following pairs is mismatched?
(1) Predator–Prey : Tiger–Deer
(2) Commensalism : Epiphyte–Tree
(3) Mutualism : Fungi–Algae
(4) Parasitism : Honeybee–Flower
Explanation: Option (4) is mismatched. The relationship between a honeybee and a flower is mutualistic, not parasitic. Both benefit as the bee gains nectar and the flower achieves pollination. Parasitism involves harm to one partner, which is not the case here, making this pair incorrect.

7. Assertion–Reason Type:
Assertion (A): Commensalism is a type of interaction where one organism benefits and the other is unaffected.
Reason (R): In epiphytic orchids, the host tree is harmed by nutrient absorption by orchids.
(1) Both A and R are true and R explains A
(2) Both A and R are true but R does not explain A
(3) A is true but R is false
(4) A is false but R is true
Explanation: The correct answer is (3). A is true but R is false. Epiphytes like orchids do not absorb nutrients from their host trees; they only use them for support. Thus, the host is neither harmed nor benefited, exemplifying true commensalism without resource exploitation.

8. Matching Type:
Match the following interactions:
A. Commensalism    1. Cattle Egret–Cattle
B. Parasitism    2. Tapeworm–Human
C. Mutualism    3. Lichen
D. Amensalism    4. Penicillium–Bacteria
(1) A–1, B–2, C–3, D–4
(2) A–2, B–1, C–4, D–3
(3) A–3, B–4, C–2, D–1
(4) A–4, B–3, C–1, D–2
Explanation: The correct match is A–1, B–2, C–3, D–4. Each pair represents a distinct ecological interaction type: commensalism (benefit–neutral), parasitism (benefit–harm), mutualism (benefit–benefit), and amensalism (harm–neutral), all of which help maintain ecological balance and species coexistence.

9. Fill in the Blank:
When two species live together and both benefit from the association, the relationship is known as ______.
(1) Commensalism
(2) Mutualism
(3) Parasitism
(4) Amensalism
Explanation: The correct answer is mutualism. It is a biological interaction where both species benefit from each other. Examples include nitrogen-fixing bacteria with legume roots and pollinators with flowers. These associations are vital for ecological balance and the survival of many terrestrial and aquatic organisms.

10. Choose the Correct Statements (Statement I & II):
Statement I: Commensalism benefits both partners.
Statement II: Commensalism benefits one partner while the other is unaffected.
(1) Both statements are correct
(2) Statement I is correct, Statement II is incorrect
(3) Statement I is incorrect, Statement II is correct
(4) Both statements are incorrect
Explanation: The correct answer is (3). In commensalism, one organism benefits, and the other remains unaffected. This distinguishes it from mutualism, where both partners benefit, and parasitism, where one benefits at the cost of the other, highlighting ecological diversity in symbiotic relationships.

Topic: Water Pollution; Subtopic: Oxygen Depletion and Sewage Disposal

Keyword Definitions:

• Dissolved Oxygen (DO): The amount of free oxygen present in water, essential for the survival of aquatic organisms.

• Sewage: Wastewater from domestic and industrial sources containing organic matter, chemicals, and pathogens.

• Biodegradation: The microbial breakdown of organic substances into simpler compounds, often consuming oxygen.

• BOD (Biochemical Oxygen Demand): The amount of oxygen required by microorganisms to decompose organic matter in water.

• Water Pollution: Contamination of water bodies through addition of harmful substances that alter water quality and ecosystem balance.

Lead Question - 2024 (Jhajjhar)
Assertion (A): There is always a sharp decline in dissolved oxygen downstream from the point of sewage discharge, which causes mortality of fish and other aquatic creatures.
Reason (R): Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen.

In the light of the above statements, choose the correct answer from the options given below:
1. Both (A) and (R) are True and (R) is the correct explanation of (A).
2. Both (A) and (R) are True but (R) is not the correct explanation of (A).
3. (A) is True but (R) is False.
4. (A) is False but (R) is True.

Explanation: The correct answer is option 1. When sewage enters a water body, microbes decompose the organic matter using dissolved oxygen, leading to reduced DO levels. This depletion of oxygen causes suffocation and death of fish. Hence, both statements are true, and (R) correctly explains (A). The process reflects eutrophication and oxygen sag phenomenon.

Guessed Questions:

1. Which parameter indicates organic pollution in water?
1. Dissolved Oxygen
2. Biochemical Oxygen Demand
3. Chemical Oxygen Demand
4. Total Dissolved Solids
Explanation: The correct answer is option 2. Biochemical Oxygen Demand (BOD) measures the oxygen required by microorganisms to decompose organic matter. Higher BOD means higher organic pollution and lesser oxygen available for aquatic life, thus indicating the level of water pollution.

2. When sewage is discharged into a river, dissolved oxygen:
1. Increases rapidly
2. Decreases sharply
3. Remains unchanged
4. Becomes saturated
Explanation: The correct answer is option 2. The entry of sewage increases microbial activity that consumes dissolved oxygen during organic matter decomposition, causing a sharp decline in oxygen concentration downstream and leading to fish mortality.

3. High value of BOD indicates:
1. Low pollution level
2. High pollution level
3. Good water quality
4. High oxygen availability
Explanation: The correct answer is option 2. A high BOD reflects greater organic load, meaning more oxygen is used by decomposing bacteria, thus indicating high pollution and poor water quality, harmful for aquatic organisms.

4. Which of the following gases is mainly responsible for foul odour in polluted water?
1. Carbon dioxide
2. Methane
3. Hydrogen sulphide
4. Nitrous oxide
Explanation: The correct answer is option 3. Hydrogen sulphide gas is produced by anaerobic bacteria during decomposition of sewage under low oxygen conditions, leading to a foul smell and harmful environment for aquatic organisms.

5. The oxygen sag curve is related to:
1. Photosynthesis
2. Water temperature
3. Sewage pollution
4. Groundwater level
Explanation: The correct answer is option 3. The oxygen sag curve depicts a decrease in dissolved oxygen downstream of sewage discharge, followed by gradual recovery as self-purification of water occurs. It reflects organic pollution and microbial oxygen demand.

6. Eutrophication leads to:
1. Decrease in aquatic plant growth
2. Oxygen enrichment
3. Excess algal growth
4. Reduced microbial activity
Explanation: The correct answer is option 3. Eutrophication results from nutrient enrichment (nitrates and phosphates) causing algal blooms. The subsequent decay of algae depletes oxygen, leading to fish deaths and deterioration of water quality.

7. Assertion-Reason Type:
Assertion (A): Decrease in dissolved oxygen results in fish mortality.
Reason (R): Oxygen is essential for cellular respiration in aquatic organisms.
1. Both (A) and (R) are true and (R) correctly explains (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.
Explanation: The correct answer is option 1. Dissolved oxygen supports respiration in aquatic organisms. A decline in oxygen due to sewage pollution suffocates fish and other species, hence both statements are true and (R) correctly explains (A).

8. Matching Type:
Match the pollutant with its major effect:
A. Phosphates — (i) Eutrophication
B. Oil spills — (ii) Reduced light penetration
C. Sewage — (iii) Oxygen depletion
D. Thermal discharge — (iv) Reduced gas solubility

1. A-(i), B-(ii), C-(iii), D-(iv)
2. A-(iii), B-(i), C-(ii), D-(iv)
3. A-(ii), B-(iv), C-(i), D-(iii)
4. A-(i), B-(iii), C-(ii), D-(iv)
Explanation: The correct answer is option 1. Phosphates cause eutrophication, oil reduces light penetration, sewage depletes oxygen due to microbial action, and hot water lowers gas solubility. Each pollutant alters aquatic balance and harms life.

9. Fill in the Blanks:
The demand for oxygen by microorganisms during decomposition of organic matter is called ________.
1. Chemical Oxygen Demand
2. Biochemical Oxygen Demand
3. Biological Oxygen Requirement
4. Aerobic Demand Value
Explanation: The correct answer is option 2. Biochemical Oxygen Demand (BOD) quantifies oxygen needed for microbial decomposition. Higher BOD signifies greater organic pollution, leading to oxygen depletion and poor water quality in aquatic systems.

10. Choose the Correct Statements:
Statement I: High BOD value indicates clean water.
Statement II: Low BOD value indicates less organic pollution.
1. Both statements are correct.
2. Both statements are incorrect.
3. Only Statement I is correct.
4. Only Statement II is correct.
Explanation: The correct answer is option 4. Clean water has a low BOD as less oxygen is consumed by microorganisms. High BOD signifies organic pollution, oxygen depletion, and adverse impact on aquatic organisms.

Topic: Population Interactions; Subtopic: Competition in Ecological Communities

Keyword Definitions:
• Competition: Interaction among organisms fighting for limited resources like food, space, or light.
• Connell’s Experiment: A classic study on intertidal barnacles demonstrating competitive exclusion.
• Balanus and Chthamalus: Two barnacle species showing competition in the rocky intertidal zone.
• Ecological Niche: The role and position an organism occupies in an ecosystem.
• Competitive Exclusion Principle: States that two species competing for the same resource cannot coexist indefinitely.
• Herbivores: Organisms that feed on plants.
• Carnivores: Organisms that feed on other animals.

Lead Question - 2024 (Jhajjhar)
Given below are two statements: One is labelled as Assertion (A) and the other as Reason (R).

Assertion (A): Connell's elegant field experiment showed that on the rocky sea, the larger and competitively superior barnacles dominate the intertidal area and exclude the smaller barnacle from that area.
Reason (R): Generally, herbivores and plants appear to be more adversely affected by competition than carnivores.

Choose the correct answer from the options given below:
1. Both (A) and (R) are True and (R) is the correct explanation of (A)
2. Both (A) and (R) are True but (R) is not the correct explanation of (A)
3. (A) is True but (R) is False
4. (A) is False but (R) is True

Explanation:
The correct answer is 3. (A) is True but (R) is False. Connell’s experiment with barnacles (Balanus and Chthamalus) demonstrated competitive exclusion in nature. Balanus displaced Chthamalus from the lower intertidal zone due to superior competition. The Reason is unrelated because it discusses herbivore competition, not barnacle interactions, so it is incorrect here.

1. Which principle is demonstrated by Connell’s barnacle experiment?
1. Law of Tolerance
2. Gause’s Competitive Exclusion Principle
3. Principle of Limiting Factors
4. Niche Overlap Theory

Explanation:
The correct answer is 2. Gause’s Competitive Exclusion Principle. Connell’s experiment showed that when two species compete for the same limited resource, the superior competitor will eventually exclude the other. Balanus outcompeted Chthamalus in the lower intertidal zone, illustrating this ecological principle of competition in natural environments.

2. Which two species were studied by Connell in his classic field experiment on competition?
1. Paramecium caudatum and aurelia
2. Balanus and Chthamalus
3. Escherichia coli and Salmonella
4. Lemna and Azolla

Explanation:
The correct answer is 2. Balanus and Chthamalus. Connell’s experiment was conducted on rocky sea shores with these two species of barnacles. Balanus dominated the lower zone due to its superior competitive ability, whereas Chthamalus survived in the upper zone, being more tolerant to desiccation and reduced competition.

3. What does Gause’s principle of competitive exclusion state?
1. Species with similar niches can coexist indefinitely.
2. No two species can occupy exactly the same niche in the same environment.
3. Competition promotes biodiversity.
4. All species avoid competition by niche separation.

Explanation:
The correct answer is 2. No two species can occupy exactly the same niche in the same environment. According to Gause’s principle, one species will outcompete and exclude the other when their ecological requirements completely overlap. This leads to either extinction or niche differentiation among the competing species in an ecosystem.

4. Which ecological factor most directly influences competition among barnacles on the rocky seashore?
1. Temperature
2. Availability of space
3. Salinity
4. Predation pressure

Explanation:
The correct answer is 2. Availability of space. Space on rocky shores is limited and essential for barnacle attachment and growth. Balanus, being competitively superior, occupies more area and prevents Chthamalus from colonizing lower zones. This demonstrates space as a critical limiting factor in intertidal competition.

5. In Connell’s experiment, which barnacle species was competitively superior?
1. Chthamalus
2. Balanus
3. Both equally strong
4. None of the above

Explanation:
The correct answer is 2. Balanus. Balanus balanoides, the larger barnacle, exhibited competitive dominance over Chthamalus stellatus. It excluded Chthamalus from the lower intertidal region by overgrowing or dislodging it, confirming that Balanus had greater competitive ability in favorable conditions compared to the smaller species.

6. Which concept best explains coexistence of Balanus and Chthamalus in different zones?
1. Resource partitioning
2. Predation
3. Parasitism
4. Symbiosis

Explanation:
The correct answer is 1. Resource partitioning. Both barnacle species coexist by occupying distinct zones of the intertidal area. Balanus dominates the lower, wetter region, while Chthamalus survives in the upper, drier zone. This spatial separation minimizes competition and allows both species to survive successfully in the same ecosystem.

7. Matching Type Question:
Match List-I with List-II:
List-I (Ecologist) — List-II (Contribution)
A. G.F. Gause — I. Competitive exclusion principle
B. Joseph Connell — II. Barnacle experiment
C. Charles Darwin — III. Theory of natural selection
D. Robert MacArthur — IV. Resource partitioning in warblers

1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-IV, C-II, D-I
4. A-I, B-III, C-II, D-IV

Explanation:
The correct answer is 1. A-I, B-II, C-III, D-IV. Each scientist contributed uniquely to ecology: Gause described competitive exclusion, Connell demonstrated it experimentally, Darwin developed the natural selection theory, and MacArthur studied niche differentiation in warblers. These foundational works shaped ecological and evolutionary theory on species coexistence.

8. Fill in the Blanks Question:
Connell’s field experiment on barnacles demonstrated the principle of __________.
1. Resource partitioning
2. Competitive exclusion
3. Symbiotic interaction
4. Mutualism

Explanation:
The correct answer is 2. Competitive exclusion. The experiment proved that when two species compete for the same limited space and resources, the superior competitor eliminates the weaker one. This ecological principle explains how competition influences species distribution and helps maintain ecological balance and niche differentiation.

9. Choose the Correct Statements:
Statement I: Balanus dominates the upper intertidal zone due to superior tolerance to desiccation.
Statement II: Chthamalus survives in the upper zone due to tolerance and reduced competition.

1. Both statements are correct.
2. Both statements are incorrect.
3. Only Statement I is correct.
4. Only Statement II is correct.

Explanation:
The correct answer is 4. Only Statement II is correct. Chthamalus can tolerate drier, upper zones, whereas Balanus cannot. Hence, Chthamalus occupies the upper region where Balanus fails to survive. This ecological segregation minimizes competition and demonstrates adaptation to environmental stress and interspecific interaction balance.

10. Which type of interaction is represented in Connell’s barnacle study?
1. Mutualism
2. Commensalism
3. Competition
4. Predation

Explanation:
The correct answer is 3. Competition. The experiment demonstrated interspecific competition, where two barnacle species compete for the same habitat space. Balanus, the dominant competitor, excludes Chthamalus from the lower intertidal region, leading to resource segregation and niche partitioning as a survival strategy in nature.

Topic: Population Interactions; Subtopic: Commensalism

Keyword Definitions:
• Commensalism: An interaction where one species benefits while the other is neither harmed nor benefited.
• Mutualism: Both species benefit from the interaction.
• Parasitism: One organism benefits while the other is harmed.
• Amensalism: One organism is harmed while the other is unaffected.
• Competition: Interaction where both species are negatively affected by limited resources.
• Egrets: Birds that follow cattle to catch insects disturbed by grazing activity.

Lead Question - 2024 (Jhajjhar)
Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): The interaction, in which one species benefits and the other is neither harmed nor benefitted, is known as commensalism.
Reason (R): Egrets always forage close to where the cattles are grazing, otherwise it is difficult for the egrets to find the insect and catch.

In the light of the above statements, choose the correct answer from the options given below:
1. Both (A) and (R) are True and (R) is the correct explanation of (A).
2. Both (A) and (R) are True but (R) is not the correct explanation of (A).
3. (A) is True but (R) is False.
4. (A) is False but (R) is True.

Explanation:
The correct answer is 1. Both (A) and (R) are True and (R) is the correct explanation of (A). Commensalism describes interactions where one species benefits while the other remains unaffected. Egrets benefit by feeding on insects stirred up by grazing cattle, while the cattle experience neither harm nor benefit. This perfectly illustrates a commensal relationship in nature.

1. Which of the following is an example of mutualism?
1. Orchid growing on a mango tree
2. Lichen
3. Barnacle on whale
4. Cattle and egret
Explanation: The correct answer is 2. Lichen. Lichen represents mutualism, where algae and fungi live together. The algal partner performs photosynthesis providing food, while the fungal partner offers protection and moisture. Both benefit equally, demonstrating a perfect example of mutualistic association in nature’s symbiotic relationships.

2. Which of the following correctly represents amensalism?
1. Cattle and egret
2. Algal bloom and fish
3. Penicillium and bacteria
4. Deer and grass
Explanation: The correct answer is 3. Penicillium and bacteria. Penicillium secretes penicillin, inhibiting bacterial growth. Here, bacteria are harmed, but Penicillium remains unaffected, making it an example of amensalism. Such natural interactions regulate microbial populations and help maintain ecological balance.

3. Which of the following pairs is an example of commensalism?
1. Cattle and egret
2. Clownfish and sea anemone
3. Both 1 and 2
4. Tick and dog
Explanation: The correct answer is 3. Both 1 and 2. In both examples, one species benefits without harming or benefiting the other. Clownfish gain protection among sea anemone tentacles, while egrets feed on insects disturbed by grazing cattle. Such associations illustrate classic commensal interactions.

4. Which of the following interactions benefits both species involved?
1. Mutualism
2. Commensalism
3. Amensalism
4. Parasitism
Explanation: The correct answer is 1. Mutualism. In mutualistic interactions, both organisms gain advantages from each other’s presence, often enhancing survival and reproduction. Examples include lichens (fungus + algae) and mycorrhiza (fungus + plant roots). These relationships exemplify cooperation and ecological interdependence.

5. Which statement is true regarding parasitism?
1. Both species benefit equally
2. Only host benefits
3. Parasite benefits, host is harmed
4. Neither benefits
Explanation: The correct answer is 3. Parasite benefits, host is harmed. In parasitism, one species (parasite) derives nourishment or shelter from another organism (host), causing harm. Classic examples include tapeworms in human intestines and Plasmodium in human blood, both causing diseases to their hosts.

6. Which of the following represents competition?
1. Cattle and egret
2. Lion and tiger in same habitat
3. Fungi and bacteria in bread
4. Lichen association
Explanation: The correct answer is 2. Lion and tiger in same habitat. Competition occurs when two species use similar resources, such as food or territory. Both lions and tigers compete for prey in overlapping habitats, reducing resource availability, making this interaction detrimental to both species.

7. Assertion-Reason Type Question:
Assertion (A): Commensalism benefits one organism without harming the other.
Reason (R): Lichen shows commensalism.
1. Both A and R are true and R is correct explanation
2. Both A and R are true but R is not correct explanation
3. A is true but R is false
4. A is false but R is true
Explanation: The correct answer is 3. A is true but R is false. Commensalism benefits one species without affecting the other. However, lichen shows mutualism, not commensalism. Thus, while A is true, R is incorrect in explaining it.

8. Matching Type Question:
Match List-I with List-II:
List-I (Interaction Type) – List-II (Example)
A. Commensalism – I. Cattle and Egret
B. Mutualism – II. Lichen
C. Parasitism – III. Plasmodium and Human
D. Competition – IV. Lion and Tiger
1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-IV, C-II, D-I
4. A-I, B-III, C-II, D-IV
Explanation: The correct answer is 1. A-I, B-II, C-III, D-IV. These examples clearly represent ecological interactions. Commensalism involves one-sided benefit, mutualism benefits both, parasitism harms the host, and competition affects both organisms negatively.

9. Fill in the Blanks Question:
In ________, one species benefits while the other remains unaffected, as seen between cattle and egret.
1. Parasitism
2. Commensalism
3. Mutualism
4. Amensalism
Explanation: The correct answer is 2. Commensalism. In this relationship, egrets gain food by catching insects disturbed by cattle movement. Cattle neither gain nor lose, making it a commensal interaction. This ecological relationship ensures resource sharing without direct harm or benefit to the host species.

10. Choose the Correct Statements:
Statement I: Commensalism is an association where both species benefit.
Statement II: Mutualism involves reciprocal benefit to both species.
1. Both statements are correct
2. Both statements are incorrect
3. Only Statement I is correct
4. Only Statement II is correct
Explanation: The correct answer is 4. Only Statement II is correct. In commensalism, only one species benefits, while the other is unaffected. In mutualism, both species benefit equally, as in lichens and mycorrhizae. Thus, only the second statement correctly describes mutualistic interactions.

Topic: Food Chain and Trophic Levels; Subtopic: Trophic Interactions and Energy Flow

Keyword Definitions:

• Food Chain: A sequence of organisms where each is eaten by the next in line for energy transfer.

• Trophic Level: The position an organism occupies in a food chain, such as producer, consumer, or decomposer.

• Primary Producer: Organisms that synthesize food using sunlight or chemical energy (e.g., plants).

• Primary Consumer: Herbivores that feed directly on producers.

• Secondary Consumer: Carnivores that eat herbivores.

• Tertiary Consumer: Top-level carnivores feeding on other carnivores.

Lead Question - 2024 (Jhajjhar)

Match List-I with List-II:
List-I        List-II
A. Tertiary consumer    I. Grass
B. Secondary consumer    II. Lion
C. Primary consumer    III. Wolf
D. Primary producer    IV. Goat

Choose the correct answer from the options given below:

1. A-I, B-II, C-III, D-IV
2. A-III, B-IV, C-II, D-I
3. A-III, B-II, C-IV, D-I
4. A-II, B-III, C-IV, D-I

Explanation: The correct answer is option 4 (A-II, B-III, C-IV, D-I). In a food chain, producers like grass form the base, herbivores such as goats are primary consumers, wolves act as secondary consumers, and lions occupy the tertiary level. Energy flows from producers to top carnivores. This trophic hierarchy maintains ecological balance through energy transfer and population control across levels.

Guessed Questions:

1. Which among the following organisms represents a secondary consumer in a forest ecosystem?
1. Deer
2. Rabbit
3. Snake
4. Grass
Explanation: The correct answer is 3. Snake acts as a secondary consumer by feeding on herbivores like rats and frogs. It occupies the third trophic level, helping to regulate prey populations. This trophic role is vital for maintaining ecosystem equilibrium and supporting the energy pyramid structure within the food web.

2. Which of the following forms the base of all food chains?
1. Primary consumers
2. Primary producers
3. Secondary consumers
4. Decomposers
Explanation: The correct answer is 2. Primary producers, mainly green plants, convert solar energy into chemical energy via photosynthesis. They form the foundation of all food chains, supplying energy to herbivores and higher trophic levels. This process ensures continuous energy flow and sustains life in all ecosystems.

3. In an aquatic food chain, which organism acts as a primary consumer?
1. Phytoplankton
2. Zooplankton
3. Small fish
4. Shark
Explanation: The correct answer is 2. Zooplankton feed on phytoplankton, thus acting as primary consumers. They form a crucial link between producers and higher consumers in aquatic ecosystems, transferring energy to fishes and larger organisms. This trophic relationship helps sustain marine biodiversity and nutrient cycling.

4. The transfer of energy from producers to top consumers is governed by:
1. Ten percent law
2. Pyramid of biomass
3. Pyramid of numbers
4. Law of tolerance
Explanation: The correct answer is 1. The Ten Percent Law states that only about 10% of energy is transferred from one trophic level to the next. The remaining energy is lost as heat or used for metabolism. This principle explains why food chains rarely exceed four or five levels.

5. Which of the following is a detritivore?
1. Earthworm
2. Deer
3. Tiger
4. Crow
Explanation: The correct answer is 1. Earthworms feed on decomposing organic matter, acting as detritivores. They help in the breakdown of dead material, enriching the soil and facilitating nutrient recycling. Their activity is essential for maintaining soil fertility and sustaining plant growth in terrestrial ecosystems.

6. Which type of ecological pyramid is always upright?
1. Pyramid of numbers
2. Pyramid of energy
3. Pyramid of biomass
4. Inverted pyramid
Explanation: The correct answer is 2. The pyramid of energy is always upright because energy diminishes at each successive trophic level due to loss as heat. This demonstrates the unidirectional flow of energy and the inefficiency of transfer between trophic levels, highlighting why higher-level consumers are fewer.

7. Assertion-Reason Type:
Assertion (A): The number of trophic levels in a food chain is limited.
Reason (R): Energy transfer efficiency decreases at each trophic level.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.
Explanation: The correct answer is 1. Energy loss occurs at each trophic level, making long chains energetically unsustainable. As only 10% of energy passes upward, organisms at higher levels receive less energy, restricting the number of trophic levels and ensuring energy balance in ecosystems.

8. Matching Type: Match the following:
List-I     List-II
A. Herbivore    I. Tiger
B. Carnivore    II. Rabbit
C. Omnivore    III. Human
D. Decomposer    IV. Bacteria
1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-III, D-IV
3. A-II, B-III, C-I, D-IV
4. A-IV, B-II, C-III, D-I
Explanation: The correct answer is 2. Rabbits are herbivores feeding on plants, tigers are carnivores eating other animals, humans are omnivores consuming both plants and meat, and bacteria act as decomposers, breaking down organic matter. These categories highlight energy transfer roles in ecosystems.

9. Fill in the Blanks:
__________ are organisms that feed on dead and decaying organic matter, releasing nutrients back into the soil.
1. Producers
2. Decomposers
3. Herbivores
4. Carnivores
Explanation: The correct answer is 2. Decomposers such as fungi and bacteria break down organic waste into simpler compounds, releasing essential nutrients into the environment. This recycling process sustains soil fertility, supports primary producers, and completes the ecosystem’s nutrient cycle.

10. Choose the Correct Statements (Statement I & Statement II):
Statement I: Energy flow in an ecosystem is unidirectional.
Statement II: Energy can be recycled in ecosystems like nutrients.
1. Both statements are correct.
2. Both statements are incorrect.
3. Statement I is correct, but Statement II is incorrect.
4. Statement I is incorrect, but Statement II is correct.
Explanation: The correct answer is 3. Energy flows in one direction—from the sun to producers, then to consumers, and finally lost as heat. Unlike nutrients, energy cannot be recycled. This one-way flow underpins all ecological systems and defines ecosystem sustainability.

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Topic: Population Interactions; Subtopic: Types of Ecological Interactions

Keyword Definitions:

• Amensalism: Interaction where one species is harmed and the other remains unaffected.

• Anemophily: Pollination by wind.

• Floral reward: Benefit provided by flowers (like nectar, shelter, or egg-laying sites) to pollinators in exchange for pollination.

• Commensalism: Interaction where one species benefits while the other is neither harmed nor benefited.

Lead Question - 2024 (Jhajjar)
The flowers of Amorphophallus provide a safe place for the pollinator to lay eggs. This is an example of:
1. Amensalism
2. Anemophily
3. Floral reward
4. Commensalism

Explanation: The correct answer is Floral reward. Flowers of Amorphophallus attract insects such as flies for pollination by providing a protected site for egg-laying, ensuring successful pollination. This mutual benefit helps both species. Such adaptive floral traits ensure reproductive success and maintain ecosystem balance through intricate plant-pollinator relationships.

1. The interaction in which both species benefit is known as:
1. Mutualism
2. Parasitism
3. Commensalism
4. Amensalism

Explanation: The correct answer is Mutualism. In mutualism, both organisms benefit from each other’s presence. For example, lichens represent mutualism between fungi and algae, where fungi provide protection and algae offer food through photosynthesis, ensuring survival in harsh environments and ecological stability for both partners involved.

2. In which type of interaction does one species derive benefit while the other is harmed?
1. Parasitism
2. Mutualism
3. Commensalism
4. Competition

Explanation: The correct answer is Parasitism. In parasitism, one species (parasite) benefits by deriving nutrients or shelter from the host, causing harm to it. Examples include Plasmodium in humans and Cuscuta on plants. This relationship affects population dynamics and evolutionary adaptations in both species over time.

3. The association between barnacles and whales represents:
1. Amensalism
2. Commensalism
3. Mutualism
4. Competition

Explanation: The correct answer is Commensalism. Barnacles attach themselves to whales to gain mobility and access to food without harming the host. This interaction helps barnacles disperse widely while the whale remains unaffected, showing an example of ecological coexistence without negative impact on the host species.

4. When both species are harmed due to competition for the same resources, it is called:
1. Mutualism
2. Competition
3. Parasitism
4. Predation

Explanation: The correct answer is Competition. When two species compete for the same limited resources like food or habitat, both suffer reduced growth, reproduction, or survival. This negative interaction regulates population size, promotes niche differentiation, and maintains ecological equilibrium through natural selection.

5. Which of the following is an example of mutualism?
1. Cuscuta growing on host plant
2. Lichens (fungi and algae)
3. Barnacles on whale
4. Tiger preying on deer

Explanation: The correct answer is Lichens (fungi and algae). Lichens demonstrate mutualism, where fungi provide structural support and protection, while algae synthesize food through photosynthesis. This relationship enables both partners to survive in nutrient-poor environments and contributes to ecological succession on rocks and barren surfaces.

6. Which one is not a positive interaction?
1. Mutualism
2. Commensalism
3. Parasitism
4. Protocooperation

Explanation: The correct answer is Parasitism. It is a negative interaction since one organism (parasite) benefits at the expense of the other (host). Positive interactions include mutualism, commensalism, and protocooperation, where at least one species benefits without harming the other, maintaining ecological balance and coexistence.

7. Assertion-Reason Type:
Assertion (A): Pollination in Amorphophallus involves mutual benefit between insect and plant.
Reason (R): The plant offers nectar to insects for pollination.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. Both A and R are false.

Explanation: The correct answer is 3. A is true but R is false. In Amorphophallus, pollinators receive protection or an egg-laying site, not nectar. Thus, mutual benefit exists but not through nectar reward, showing ecological adaptation through specialized non-nectar rewards in plant-pollinator interactions.

8. Matching Type Question:
Match the following:
A. Mutualism – (i) Cuscuta on Hibiscus
B. Commensalism – (ii) Lichen
C. Parasitism – (iii) Barnacle on whale
D. Competition – (iv) Lions and hyenas
1. A-(ii), B-(iii), C-(i), D-(iv)
2. A-(iii), B-(iv), C-(ii), D-(i)
3. A-(iv), B-(i), C-(ii), D-(iii)
4. A-(i), B-(ii), C-(iii), D-(iv)

Explanation: The correct answer is 1. A-(ii), B-(iii), C-(i), D-(iv). Mutualism occurs in lichens; commensalism in barnacles on whales; parasitism in Cuscuta; and competition between lions and hyenas. These examples illustrate key ecological relationships maintaining species balance in ecosystems.

9. Fill in the Blanks:
__________ is an association where one species benefits while the other remains unaffected.
1. Parasitism
2. Commensalism
3. Mutualism
4. Predation

Explanation: The correct answer is Commensalism. In this relationship, one organism gains advantages like shelter, food, or mobility, while the other experiences no significant effect. Such associations demonstrate coexistence and resource optimization without negative impact on the unaffected partner.

10. Choose the Correct Statements:
Statement I: Mutualism always involves both species benefiting.
Statement II: Commensalism harms one of the species.
1. Only Statement I is correct.
2. Only Statement II is correct.
3. Both statements are correct.
4. Both statements are incorrect.

Explanation: The correct answer is 1. Only Statement I is correct. Mutualism benefits both organisms. However, commensalism does not harm either species. Misunderstanding arises when neutral effects are confused with negative impacts, emphasizing the importance of precise ecological terminology and understanding in species interaction studies.

Topic: Structure and Function of Ecosystem; Subtopic: Energy Flow and Nutrient Cycling

Keyword Definitions:

• Ecosystem: A functional unit of nature consisting of living organisms interacting with each other and their non-living environment.

• Energy Flow: The movement of energy through the trophic levels of an ecosystem from producers to consumers and decomposers.

• Nutrient Cycling: The circulation of nutrients like carbon, nitrogen, and phosphorus between biotic and abiotic components.

• Anthropogenic Ecosystem: Ecosystems created or heavily modified by human activities, such as cities, croplands, or aquaculture systems.

Lead Question – 2024 (Jhajjhar)

What is incorrect about ecosystem?
1. It can vary from small sized pond to large sized sea
2. It may be anthropogenic in origin
3. It may be temporary or permanent
4. It involves the function of flow of energy but not recycling of nutrients

Explanation: The correct answer is option 4. Every ecosystem involves both energy flow and nutrient cycling. Energy flows unidirectionally from producers to decomposers, while nutrients are recycled through biogeochemical cycles. Without recycling, ecosystems would collapse due to nutrient depletion. Hence, both energy flow and nutrient cycling are vital functional components maintaining ecological balance.

1. Which of the following components is not a biotic part of an ecosystem?
1. Producers
2. Decomposers
3. Consumers
4. Minerals

Explanation: The correct answer is option 4 (Minerals). Biotic components include all living organisms such as producers, consumers, and decomposers. Minerals belong to the abiotic component and form the non-living environment. Abiotic factors like temperature, sunlight, water, and minerals regulate life processes and energy exchange within every ecosystem on Earth.

2. Which ecosystem shows the highest productivity?
1. Desert
2. Tundra
3. Estuary
4. Open ocean

Explanation: The correct answer is option 3 (Estuary). Estuaries are highly productive due to nutrient enrichment from land runoff and sunlight availability. They support diverse food webs linking marine and freshwater organisms. Their high primary productivity sustains fish nurseries, mangroves, and aquatic birds, making estuaries ecologically and economically important transitional ecosystems.

3. In an ecosystem, the flow of energy is always:
1. Unidirectional
2. Bidirectional
3. Cyclic
4. Reversible

Explanation: The correct answer is option 1 (Unidirectional). Energy flows in one direction—from the Sun to producers, then to consumers and decomposers. It is lost as heat at each trophic level and cannot be recycled. This unidirectional flow supports life functions but emphasizes the need for continuous solar input to sustain the biosphere.

4. Assertion-Reason Question:
Assertion (A): Energy flow in an ecosystem is unidirectional.
Reason (R): Energy, once lost as heat, cannot be reused by autotrophs.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, R is false
4. A is false, R is true

Explanation: The correct answer is option 1. Energy enters the ecosystem as sunlight, is transformed into chemical energy by autotrophs, and passes through trophic levels. It dissipates as heat during respiration, making its flow unidirectional and non-reusable. Thus, continuous solar energy input is essential for sustaining ecological processes.

5. Match List-I with List-II:
List-I (Ecosystem Types)    List-II (Examples)
A. Natural Ecosystem      I. Cropland
B. Artificial Ecosystem      II. Pond
C. Aquatic Ecosystem      III. Estuary
D. Terrestrial Ecosystem      IV. Forest

1. A-II, B-I, C-III, D-IV
2. A-I, B-II, C-IV, D-III
3. A-IV, B-III, C-I, D-II
4. A-II, B-IV, C-III, D-I

Explanation: The correct answer is option 1 (A-II, B-I, C-III, D-IV). Natural ecosystems like ponds function without human interference, while artificial ones like croplands are man-made. Aquatic ecosystems include estuaries, and terrestrial ecosystems include forests. This classification helps in understanding the structure, energy flow, and ecological balance among different environmental systems.

6. Which of the following cycles is sedimentary in nature?
1. Nitrogen cycle
2. Carbon cycle
3. Phosphorus cycle
4. Oxygen cycle

Explanation: The correct answer is option 3 (Phosphorus cycle). The phosphorus cycle is sedimentary because it does not include an atmospheric component. Phosphorus moves slowly from rocks into soils and water bodies through erosion and returns via geological uplift. It is essential for nucleic acids, ATP, and bones, regulating productivity in aquatic and terrestrial ecosystems.

7. Fill in the blank:
The pyramid of energy in any ecosystem is always ________.
1. Upright
2. Inverted
3. Irregular
4. Rectangular

Explanation: The correct answer is option 1 (Upright). The pyramid of energy represents energy content at successive trophic levels. Since energy decreases due to metabolic losses as heat at each level, it is always upright. This universal pattern highlights the inefficiency of energy transfer and the dependence of all trophic levels on primary producers.

8. Choose the correct statements:
Statement I: Decomposers convert organic matter into inorganic substances.
Statement II: Energy is recycled in an ecosystem like nutrients.
1. Both statements are correct
2. Only Statement I is correct
3. Only Statement II is correct
4. Both statements are incorrect

Explanation: The correct answer is option 2. Decomposers play a key role in nutrient recycling by converting dead matter into inorganic nutrients like nitrates and phosphates. However, energy cannot be recycled; it flows in one direction and is lost as heat. Nutrient cycling and energy flow together maintain ecological stability and productivity.

9. Which of the following ecosystems has the highest annual net primary productivity?
1. Desert
2. Tundra
3. Tropical rainforest
4. Grassland

Explanation: The correct answer is option 3 (Tropical rainforest). Tropical rainforests have the highest productivity due to abundant sunlight, rainfall, and biodiversity. High leaf area and rapid nutrient cycling promote photosynthesis year-round. These forests act as global carbon sinks, contributing significantly to oxygen production and climate regulation through efficient energy capture.

10. Which of the following is not an example of an artificial ecosystem?
1. Aquarium
2. Cropland
3. Forest
4. Urban park

Explanation: The correct answer is option 3 (Forest). Forests develop naturally through ecological succession without human control, hence are natural ecosystems. Artificial ecosystems like aquariums, croplands, and urban parks require human management and external energy inputs to maintain stability. This distinction is essential for understanding human influence on natural ecological balance.

Topic: Population Interactions; Subtopic: Mutualism and other ecological relationships

Keyword Definitions:

• Mutualism: A biological interaction where both species involved benefit from each other, such as lichens and mycorrhizae.

• Commensalism: One species benefits while the other remains unaffected, like orchids growing on mango branches.

• Symbiosis: A close and long-term biological interaction between two different biological organisms.

• Mycorrhiza: A symbiotic association between a fungus and the roots of a plant, improving nutrient absorption.

Lead Question – 2024 (Jhajjhar)
Which of the following is not an example of Mutualism?
1. Lichens
2. Mycorrhizae
3. An orchid on a branch of mango plant
4. The wasp pollinating fig inflorescence

Explanation: Mutualism is a relationship where both organisms benefit. Lichens, mycorrhizae, and wasps pollinating figs are mutualistic associations. However, an orchid growing on a mango tree gains support without harming or benefiting the host. This is a commensal relationship. Therefore, the correct answer is Option (3).

1. The association between nitrogen-fixing bacteria and leguminous plants is an example of:
1. Parasitism
2. Commensalism
3. Mutualism
4. Competition

Explanation: Rhizobium bacteria live in the root nodules of leguminous plants. The bacteria fix atmospheric nitrogen, supplying it to the plant, while receiving carbohydrates and shelter in return. Both benefit from this association, making it a mutualistic interaction. Correct answer: Option (3).

2. Which of the following is an example of commensalism?
1. Cattle egrets and grazing cattle
2. Cuscuta growing on other plants
3. Malarial parasite and human
4. Algae and fungi in lichens

Explanation: Cattle egrets feed on insects flushed out by grazing cattle. The cattle remain unaffected while egrets benefit. This represents commensalism. In contrast, Cuscuta and parasites cause harm to hosts, while lichens are mutualistic. Correct answer: Option (1).

3. Which of the following interactions harms both species?
1. Competition
2. Parasitism
3. Mutualism
4. Commensalism

Explanation: In competition, both species suffer as they compete for limited resources like food or space. It reduces growth, reproduction, and survival rates of both species. Parasitism harms only one species, and mutualism benefits both. Correct answer: Option (1).

4. The relationship between a cow and the microorganisms present in its rumen is an example of:
1. Commensalism
2. Parasitism
3. Mutualism
4. Amensalism

Explanation: Microorganisms in the rumen of cattle digest cellulose, enabling the animal to absorb nutrients. The microbes receive shelter and food from the cow. Both organisms benefit mutually, hence it is mutualism. Correct answer: Option (3).

5. Which one of the following pairs shows a parasitic relationship?
1. Orchid and mango
2. Lichen
3. Mycorrhiza
4. Cuscuta and hibiscus

Explanation: Cuscuta (dodder plant) is an obligate parasite that absorbs nutrients directly from the host plant such as hibiscus using haustoria. This harms the host, while Cuscuta benefits. Thus, this is parasitism. Correct answer: Option (4).

6. In mutualism, the interaction is:
1. + / +
2. + / 0
3. + / –
4. – / –

Explanation: In ecological interactions, the symbols represent effects on each species. “+” indicates benefit, “–” indicates harm, and “0” indicates no effect. Mutualism benefits both interacting species, so it is a + / + relationship. Correct answer: Option (1).

7. Assertion-Reason Question:
Assertion (A): Mycorrhiza is an example of symbiotic association.
Reason (R): Fungi help plants in absorbing water and nutrients, while plants provide carbohydrates to fungi.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Explanation: Mycorrhiza is a mutualistic symbiosis where fungi enhance nutrient uptake, especially phosphorus, while receiving organic food from the host plant. Both A and R are true, and R correctly explains A. Correct answer: Option (1).

8. Matching Type Question:
Match List I with List II:
A. Lichen – I. Fungus and Alga
B. Mycorrhiza – II. Fungus and Root
C. Orchid on mango – III. Commensalism
D. Cuscuta on host – IV. Parasitism

1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-III, D-IV
3. A-I, B-III, C-II, D-IV
4. A-IV, B-I, C-II, D-III

Explanation: Lichen involves a fungus and an alga (I), mycorrhiza is between fungus and plant root (II), orchid on mango represents commensalism (III), and Cuscuta on host is parasitism (IV). Thus, A-I, B-II, C-III, D-IV. Correct answer: Option (1).

9. Fill in the Blanks:
The interaction where one organism is harmed and the other remains unaffected is called __________.
1. Amensalism
2. Parasitism
3. Commensalism
4. Mutualism

Explanation: Amensalism is a type of interaction where one species is inhibited or destroyed while the other remains unaffected. For example, Penicillium releases penicillin that kills bacteria without affecting itself. Correct answer: Option (1).

10. Choose the Correct Statements:
Statement I: Mutualism is obligatory for survival of both partners.
Statement II: Commensalism benefits one species without affecting the other.
1. Both statements are true.
2. Both statements are false.
3. Statement I is true but Statement II is false.
4. Statement I is false but Statement II is true.

Explanation: Mutualism may be obligatory or facultative depending on the organisms involved. Commensalism clearly benefits one partner without harming or benefiting the other. Thus, Statement I is false and Statement II is true. Correct answer: Option (4).

Topic: Decomposition; Subtopic: Factors affecting decomposition rate

Keyword Definitions:

• Decomposition: The biological breakdown of organic matter into simpler inorganic compounds like CO₂, water, and minerals.

• Detritus: Dead plant and animal remains that serve as raw material for decomposition.

• Lignin: A complex polymer in plant cell walls that resists microbial decomposition.

• Chitin: A structural polysaccharide found in fungal cell walls and insect exoskeletons, resistant to decomposition.

Lead Question – 2024 (Jhajjhar)
In the light of the above statements, choose the correct answer from the options given below:
Statement I: The rate of decomposition is not related to chemical composition of detritus and climatic factors.
Statement II: In a particular climatic condition, decomposition rate is faster if detritus is rich in lignin and chitin.
1. Both Statement I and Statement II are True
2. Both Statement I and Statement II are False
3. Statement I is True but Statement II is False
4. Statement I is False but Statement II is True

Explanation: The rate of decomposition depends strongly on the detritus composition and climatic factors like temperature and moisture. Decomposition is slower when detritus contains lignin and chitin as these compounds resist microbial breakdown. Hence, Statement I is false and Statement II is also false. Therefore, the correct answer is Option (2).

1. The most active decomposers in soil are:
1. Fungi
2. Bacteria
3. Algae
4. Protozoa

Explanation: Bacteria are the most active decomposers in soil as they rapidly decompose simple organic materials. Fungi act on complex substances like cellulose and lignin, while protozoa and algae have minor roles. Thus, bacteria form the primary decomposer community. Correct answer: Option (2).

2. Which one of the following factors does not directly affect the rate of decomposition?
1. Temperature
2. Soil moisture
3. Solar radiation
4. Chemical nature of detritus

Explanation: Solar radiation does not directly influence decomposition, although it affects temperature indirectly. Decomposition mainly depends on microbial activity, moisture, and chemical nature of detritus. High temperature and moderate moisture accelerate decomposition. Correct answer: Option (3).

3. The humification process results in the formation of:
1. Simple inorganic compounds
2. Ammonia
3. Humus
4. Carbon dioxide

Explanation: Humification is the process of partial decomposition of organic matter leading to the formation of humus — a dark, amorphous, and stable organic substance that enriches soil fertility. It plays a vital role in nutrient cycling. Correct answer: Option (3).

4. The release of nutrients during decomposition is known as:
1. Immobilization
2. Mineralization
3. Humification
4. Degradation

Explanation: During decomposition, inorganic nutrients are released from organic matter through microbial action. This process is called mineralization, making nutrients available to plants. Immobilization is the reverse process where nutrients are absorbed by microbes. Correct answer: Option (2).

5. Which climatic condition favors rapid decomposition?
1. Low temperature and high humidity
2. High temperature and low humidity
3. Moderate temperature and high humidity
4. Low temperature and low humidity

Explanation: Decomposition occurs fastest in warm and moist conditions that favor microbial activity. Tropical regions with moderate temperature and high humidity show the highest rate of organic matter decomposition. Correct answer: Option (3).

6. Which sequence represents correct steps in decomposition?
1. Fragmentation → Leaching → Catabolism → Humification → Mineralization
2. Catabolism → Fragmentation → Leaching → Humification → Mineralization
3. Leaching → Fragmentation → Humification → Catabolism → Mineralization
4. Fragmentation → Catabolism → Leaching → Humification → Mineralization

Explanation: Decomposition follows a definite sequence: fragmentation (breaking into smaller pieces), leaching (soluble materials removed), catabolism (enzyme action), humification (formation of humus), and mineralization (release of inorganic nutrients). Correct answer: Option (1).

7. Assertion-Reason Question:
Assertion (A): Litter decomposition is faster in tropics than in temperate regions.
Reason (R): High temperature and moisture favor microbial activity.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Explanation: The warm and moist conditions of tropical regions promote microbial activity, leading to rapid litter decomposition compared to temperate regions. Hence, both A and R are true, and R correctly explains A. Correct answer: Option (1).

8. Matching Type Question:
Match List I with List II:
A. Fragmentation – I. Leaching of soluble substances
B. Leaching – II. Breakdown into smaller particles
C. Catabolism – III. Enzymatic breakdown
D. Humification – IV. Formation of humus

1. A-II, B-I, C-III, D-IV
2. A-I, B-II, C-III, D-IV
3. A-II, B-III, C-IV, D-I
4. A-IV, B-I, C-II, D-III

Explanation: Fragmentation breaks litter into smaller pieces (II), leaching removes soluble substances (I), catabolism involves enzymatic degradation (III), and humification results in stable humus formation (IV). Correct matching: A-II, B-I, C-III, D-IV. Correct answer: Option (1).

9. Fill in the Blanks:
Decomposition of dead organic matter is largely an __________ process carried out by microbes.
1. Anaerobic
2. Aerobic
3. Photolytic
4. Chemical

Explanation: Most decomposition in soil is an aerobic process, requiring oxygen for microbial respiration and oxidation of organic compounds. Anaerobic decomposition occurs under waterlogged or oxygen-poor conditions, producing methane. Correct answer: Option (2).

10. Choose the Correct Statements:
Statement I: Humus is highly resistant to microbial action.
Statement II: Humus plays no role in nutrient cycling.
1. Both statements are true.
2. Both statements are false.
3. Statement I is true and Statement II is false.
4. Statement I is false and Statement II is true.

Explanation: Humus is resistant to decomposition and forms a stable reservoir of nutrients. It plays a crucial role in nutrient cycling and maintaining soil fertility. Therefore, Statement I is true while Statement II is false. Correct answer: Option (3).

Topic: Productivity in Ecosystem; Subtopic: Net Primary Productivity (NPP)

Keyword Definitions:

• Gross Primary Productivity (GPP): Total rate of photosynthesis including the energy used by plants for respiration.

• Net Primary Productivity (NPP): Energy remaining after respiration, available to herbivores and decomposers.

• Tropical Rain Forest: Dense forest located near the equator with high temperature and rainfall throughout the year.

• Productivity: Rate at which energy is accumulated in the form of biomass per unit area per unit time.

Lead Question – 2024 (Jhajjhar)
Highest annual Net Primary Productivity is observed in:
1. Tropical deciduous forest
2. Temperate evergreen forest
3. Temperate deciduous forest
4. Tropical rain forest

Explanation: The correct answer is Tropical rain forest. These forests, found near the equator, receive abundant rainfall and sunlight, ensuring continuous photosynthesis. The warm, moist conditions support diverse flora that maintains high biomass. Hence, tropical rainforests exhibit the highest NPP, producing vast organic matter that sustains complex food webs year-round.

1. Single Correct Answer MCQ:
Which of the following ecosystems has the lowest Net Primary Productivity?
1. Desert
2. Tropical forest
3. Coral reef
4. Estuary

Explanation: The correct answer is Desert. Deserts have minimal water availability and sparse vegetation, leading to extremely low photosynthetic activity. Limited rainfall, high temperature, and nutrient-poor soils restrict biomass production. As a result, deserts show the lowest NPP among all ecosystems due to their harsh climatic conditions and limited primary producers.

2. Single Correct Answer MCQ:
Which factor directly influences the rate of primary productivity?
1. Soil color
2. Temperature and light intensity
3. Animal population
4. Wind velocity

Explanation: The correct answer is Temperature and light intensity. These environmental factors regulate photosynthesis, which determines primary productivity. Adequate light enables chlorophyll activity, while optimal temperature ensures efficient enzyme function. Together with water and nutrients, they govern the rate of energy conversion from sunlight to biomass.

3. Single Correct Answer MCQ:
Which of the following correctly represents the relationship between GPP, NPP, and respiration (R)?
1. NPP = GPP + R
2. NPP = GPP - R
3. GPP = NPP - R
4. R = NPP + GPP

Explanation: The correct answer is NPP = GPP - R. Plants use a portion of the energy fixed during photosynthesis for respiration. The remaining energy contributes to biomass accumulation. Thus, Net Primary Productivity is the gross energy fixed minus the energy consumed in plant respiration.

4. Single Correct Answer MCQ:
In aquatic ecosystems, primary productivity is highest in:
1. Open ocean
2. Coastal regions
3. Deep sea
4. Polar waters

Explanation: The correct answer is Coastal regions. These areas receive nutrient-rich runoff from land, promoting phytoplankton growth. Shallow waters allow sufficient light penetration, enhancing photosynthesis. Consequently, coastal regions exhibit high primary productivity, supporting diverse marine life and forming the base of aquatic food chains.

5. Assertion–Reason Type:
Assertion (A): Tropical rain forests have high NPP.
Reason (R): They receive low sunlight and limited water throughout the year.
1. Both A and R are true and R explains A
2. Both A and R are true but R does not explain A
3. A is true but R is false
4. A is false but R is true

Explanation: The correct answer is A is true but R is false. Tropical rainforests indeed have high NPP, but this is due to abundant sunlight, moisture, and dense vegetation, not limited water. The false reasoning highlights why high productivity results from favorable, not restrictive, climatic conditions.

6. Matching Type MCQ:
Match the ecosystem with their average productivity (kcal/m²/yr):
A. Tropical forest – I. 9000
B. Desert – II. 90
C. Open ocean – III. 500
D. Coral reef – IV. 2000
Options:
1. A-I, B-II, C-III, D-IV
2. A-IV, B-II, C-III, D-I
3. A-I, B-III, C-IV, D-II
4. A-II, B-I, C-III, D-IV

Explanation: The correct match is A-I, B-II, C-III, D-IV. Tropical forests show maximum productivity, deserts the least, open oceans moderate, and coral reefs very high per unit area. These variations arise due to differences in nutrient supply, light penetration, and vegetation density across ecosystems.

7. Fill in the Blanks Type:
_________ is the portion of GPP available for consumption by herbivores and decomposers.
1. Gross Primary Productivity
2. Secondary Productivity
3. Net Primary Productivity
4. Community Productivity

Explanation: The correct answer is Net Primary Productivity. It represents the remaining energy after plant respiration, forming the energy base for higher trophic levels. This fraction of GPP sustains all consumers and decomposers in an ecosystem, driving energy flow and nutrient recycling efficiently.

8. Single Correct Answer MCQ:
The energy flow in an ecosystem is:
1. Cyclic
2. Linear and unidirectional
3. Random
4. Reciprocal

Explanation: The correct answer is Linear and unidirectional. Energy enters ecosystems through photosynthesis and flows through trophic levels, ultimately lost as heat. Unlike matter, energy does not recycle but continuously moves from the sun to producers and consumers before dissipating, ensuring ecological balance.

9. Choose the Correct Statements (Statement I & II):
Statement I: Secondary productivity is measured for consumers.
Statement II: It depends on the food assimilated by producers.
1. Both statements are true
2. Both statements are false
3. Statement I is true but Statement II is false
4. Statement I is false but Statement II is true

Explanation: The correct answer is Statement I is true but Statement II is false. Secondary productivity measures the rate of biomass formation in consumers, not producers. It depends on the food energy assimilated from producers, emphasizing the energy transfer efficiency between trophic levels.

10. Single Correct Answer MCQ:
The main source of energy for autotrophs is:
1. Chemical compounds
2. Organic matter
3. Sunlight
4. Heat from the Earth

Explanation: The correct answer is Sunlight. Autotrophs, especially green plants, trap solar energy through photosynthesis to produce glucose from CO₂ and water. This stored energy drives all ecological activities, making sunlight the primary energy source supporting life on Earth.

Topic: Population Growth Models; Subtopic: Logistic Growth Pattern

Keyword Definitions:

• Population: A group of individuals of the same species living in a defined geographical area.

• Carrying Capacity (K): The maximum number of individuals that an environment can support sustainably.

• Exponential Growth: Rapid population increase when resources are unlimited, forming a J-shaped curve.

• Logistic Growth: Population growth that slows as resources become limited, forming an S-shaped curve.

• Asymptote: The plateau phase of logistic growth where birth rate equals death rate.

Lead Question - 2024 (Jhajjhar)
The population growing in a habitat with limited resources will show:
A. Lag phase, followed by phases of acceleration and deceleration and finally an asymptote.
B. The ability to realise its innate potential to grow in number and reach enormous densities in short time.
C. Exponential growth
D. Logistic growth
Choose the correct answer from the option given below:
1. A and B only
2. C and D only
3. A and D only
4. B and C only

Explanation: When resources are limited, a population exhibits logistic growth. It passes through lag, acceleration, deceleration, and asymptote phases, ultimately stabilizing at the carrying capacity. Exponential growth occurs only under ideal conditions with unlimited resources. Thus, the correct answer is A and D only, representing logistic growth characteristics. (Answer: 3)

1. Which of the following curves best represents population growth under limited resources?
1. J-shaped curve
2. S-shaped curve
3. Linear curve
4. Inverted U-shaped curve
Explanation: Under limited resource conditions, population growth follows the logistic pattern forming an S-shaped curve. It includes lag, exponential, and stationary phases where the carrying capacity limits growth. Hence, the correct answer is S-shaped curve. (Answer: 2)

2. During which phase of population growth does natality equal mortality?
1. Lag phase
2. Exponential phase
3. Stationary phase
4. Decline phase
Explanation: At the stationary phase (asymptote) of logistic growth, birth and death rates become equal due to resource limitation. The population stabilizes, maintaining dynamic equilibrium. Hence, the correct answer is Stationary phase. (Answer: 3)

3. Which of the following equations represents logistic growth?
1. dN/dt = rN
2. dN/dt = rN(K - N)/K
3. dN/dt = rN²
4. dN/dt = K/N
Explanation: The logistic growth model is expressed as dN/dt = rN(K − N)/K, where N is population size, r is growth rate, and K is carrying capacity. It describes growth slowing as resources are depleted. Hence, the correct answer is dN/dt = rN(K − N)/K. (Answer: 2)

4. Which phase of population growth shows maximum growth rate?
1. Lag phase
2. Exponential phase
3. Deceleration phase
4. Stationary phase
Explanation: The exponential phase displays the highest growth rate since resources are abundant and environmental resistance is minimal. The population doubles rapidly at this stage. Hence, the correct answer is Exponential phase. (Answer: 2)

5. In logistic growth, population stops increasing when:
1. Birth rate is greater than death rate
2. Resources become abundant
3. Population reaches carrying capacity
4. Predation decreases
Explanation: Logistic growth levels off when population size (N) equals carrying capacity (K). Resource limitation and competition maintain population stability, where natality equals mortality. Hence, the correct answer is Population reaches carrying capacity. (Answer: 3)

6. Population density remains constant when:
1. Natality = Mortality
2. Natality > Mortality
3. Immigration > Emigration
4. Natality < Mortality
Explanation: Population density remains stable when the birth rate equals the death rate, and immigration equals emigration. This condition represents the stationary phase of logistic growth. Hence, the correct answer is Natality = Mortality. (Answer: 1)

7. Assertion-Reason Type:
Assertion (A): Exponential growth can continue indefinitely in natural populations.
Reason (R): Resources in nature are finite.
1. Both A and R are true and R explains A.
2. Both A and R are true but R does not explain A.
3. A is false but R is true.
4. Both A and R are false.
Explanation: Exponential growth cannot continue indefinitely because natural resources are finite. When resources become limited, growth slows and logistic growth follows. Thus, Assertion is false but Reason is true. Correct answer: 3.

8. Matching Type:
Match the following growth phases with their characteristics:
A. Lag phase — (i) Slow initial growth
B. Exponential phase — (ii) Maximum growth rate
C. Deceleration phase — (iii) Growth slows
D. Stationary phase — (iv) Growth stops
1. A-(i), B-(ii), C-(iii), D-(iv)
2. A-(ii), B-(i), C-(iv), D-(iii)
3. A-(iii), B-(ii), C-(iv), D-(i)
4. A-(iv), B-(i), C-(iii), D-(ii)
Explanation: Lag phase shows slow start, exponential phase has maximum growth, deceleration phase slows growth, and stationary phase halts increase. Hence, the correct match is 1.

9. Fill in the Blanks:
In the logistic growth model, the growth rate decreases as population size approaches __________.
1. Carrying capacity
2. Zero
3. Doubling time
4. Half of initial size
Explanation: In logistic growth, as population approaches carrying capacity (K), environmental resistance increases and growth rate declines. Finally, the population stabilizes at K. Hence, the correct answer is Carrying capacity. (Answer: 1)

10. Choose the Correct Statements (Statement I & II):
Statement I: Logistic growth curve is S-shaped.
Statement II: Exponential growth curve is J-shaped.
1. Both statements are true.
2. Both statements are false.
3. Statement I true, Statement II false.
4. Statement I false, Statement II true.
Explanation: Logistic growth under limited resources forms an S-shaped curve, while exponential growth under unlimited resources forms a J-shaped curve. Therefore, both statements are true. Correct answer is 1.

Topic: Population Interactions; Subtopic: Competitive Exclusion Principle

Keyword Definitions:
• Competition: Interaction between species or individuals for limited resources like food or habitat.
• Competitive Exclusion Principle: States that two species competing for identical resources cannot coexist indefinitely.
• Resource Partitioning: Evolutionary process where species use resources differently to reduce competition.
• Ecological Niche: The role and position a species occupies in an ecosystem.
• Population: A group of individuals of the same species living in a particular area.

Lead Question - 2024  (Jhajjhar)
Given below are two statements:
Statement - I : Gause’s competitive exclusion principle states that two closely related species competing for different resources cannot exist indefinitely.
Statement - II : According to Gause’s principle, during competition, the inferior will be eliminated. This may be true if resources are limiting.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are false
(2) Statement I is true but Statement II is false
(3) Statement I is false but Statement II is true
(4) Both Statement I and Statement II are true

Explanation:
The correct answer is (3) Statement I is false but Statement II is true. Gause’s competitive exclusion principle states that two species competing for the same resources cannot coexist indefinitely in the same niche. When resources are limiting, the inferior competitor is eliminated. However, if species utilize different resources, they can coexist. (100 words)

1. Two species that can coexist by occupying different ecological niches demonstrate:
(1) Mutualism
(2) Resource Partitioning
(3) Parasitism
(4) Commensalism
Explanation: The correct answer is (2) Resource Partitioning. When species utilize resources differently (for example, by feeding at different times or places), they reduce direct competition, allowing coexistence. This phenomenon, known as resource partitioning, supports Gause’s principle by showing how species can coexist through ecological differentiation. (100 words)

2. Which of the following best exemplifies the competitive exclusion principle?
(1) Two birds using different parts of the same tree
(2) One bacterial species outcompeting another in the same culture medium
(3) Two fish species living in different ponds
(4) Two plants pollinated by different insects
Explanation: The correct answer is (2) One bacterial species outcompeting another in the same culture medium. Gause demonstrated this principle using Paramecium species, where one species eliminated the other when competing for the same food source under identical conditions. It highlights that no two species can occupy the same niche indefinitely. (100 words)

3. In an ecosystem, if two species coexist without eliminating each other, it is most likely due to:
(1) Competition for the same niche
(2) Resource partitioning
(3) Limited carrying capacity
(4) Equal growth rates
Explanation: The correct answer is (2) Resource partitioning. When species occupy different niches by utilizing different aspects of the environment, competition reduces, enabling coexistence. This adaptation is a key ecological mechanism to avoid exclusion, ensuring survival despite overlapping habitats. (100 words)

4. The principle that states “complete competitors cannot coexist” is known as:
(1) Law of tolerance
(2) Competitive exclusion principle
(3) Limiting factor concept
(4) Law of succession
Explanation: The correct answer is (2) Competitive exclusion principle. It explains that if two species compete for identical ecological requirements, one will eliminate the other. This was experimentally shown by Gause using Paramecium species, establishing that competition drives niche specialization or extinction. (100 words)

5. Assertion-Reason Question:
Assertion (A): Gause’s principle explains the outcome of interspecific competition.
Reason (R): Two species competing for identical resources can coexist indefinitely.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, but R is false
(4) A is false, but R is true
Explanation: The correct answer is (3) A is true, but R is false. Gause’s principle indeed describes interspecific competition outcomes, but species competing for identical resources cannot coexist indefinitely, leading to exclusion or niche differentiation. (100 words)

6. Match the following:
List I - Interaction Type | List II - Example
A. Competition | I. Lichen
B. Mutualism | II. Cuscuta on Hibiscus
C. Parasitism | III. Lion and Tiger
D. Commensalism | IV. Barnacles on Whale
(1) A-III, B-I, C-II, D-IV
(2) A-I, B-II, C-III, D-IV
(3) A-IV, B-II, C-I, D-III
(4) A-II, B-III, C-IV, D-I
Explanation: The correct answer is (1) A-III, B-I, C-II, D-IV. Competition occurs between lion and tiger; mutualism between fungus and algae (lichen); parasitism between Cuscuta and Hibiscus; and commensalism between barnacles and whale. These relationships define major ecological interactions. (100 words)

7. The exclusion of a species due to competition depends mainly on:
(1) Resource abundance
(2) Resource limitation
(3) Abiotic factors only
(4) Mutation rate
Explanation: The correct answer is (2) Resource limitation. Gause’s experiments and ecological theory state that competition leads to exclusion only when resources are limiting. When resources are abundant, species may coexist without direct exclusion pressure. (100 words)

8. Fill in the blanks:
When two species compete for the same limited resources, one will be __________.
(1) Coexisting
(2) Eliminated
(3) Mutated
(4) Dominated
Explanation: The correct answer is (2) Eliminated. The competitive exclusion principle clearly predicts that one species will be driven to extinction when two species compete for the same ecological niche and limiting resources, due to unequal competitive abilities. (100 words)

9. Which ecological principle is best demonstrated by Darwin’s finches of Galapagos Islands?
(1) Coevolution
(2) Adaptive radiation
(3) Resource partitioning
(4) Mutualism
Explanation: The correct answer is (3) Resource partitioning. The finches evolved different beak types to exploit various food sources, reducing competition. This adaptive differentiation exemplifies how species coexist by utilizing different resources, thus avoiding exclusion. (100 words)

10. Choose the correct statements:
Statement I: Competitive exclusion results in niche differentiation.
Statement II: Resource partitioning minimizes interspecific competition.
(1) Both I and II are true
(2) Both I and II are false
(3) I is true but II is false
(4) I is false but II is true
Explanation: The correct answer is (1) Both I and II are true. Niche differentiation often arises from exclusion, leading to coexistence via resource partitioning. It reduces competition and enhances ecological stability among similar species. (100 words)

Topic: Energy Flow in Ecosystems; Subtopic: Primary Productivity and Trophic Levels

Keyword Definitions:

• Gross Primary Productivity (GPP): Total rate of photosynthesis, including energy used for plant respiration.

• Net Primary Productivity (NPP): Energy remaining after plant respiration; available to herbivores and decomposers.

• Trophic Level: A step in the food chain representing energy transfer between organisms.

• Energy Flow: The transfer of energy through different trophic levels, typically 10% is passed to the next level.

• Ecological Efficiency: The percentage of energy transferred from one trophic level to the next, usually about 10%.

Lead Question (September 2024)
In an ecosystem if the Net Primary Productivity (NPP) of first trophic level is 100x (kcal m–2) yr–1, what would be the Gross Primary Productivity (GPP) of the third trophic level of the same ecosystem?
(1) x (kcal m–2) yr–1
(2) 10x (kcal m–2) yr–1
(3) 100x/3x (kcal m–2) yr–1
(4) x/10 (kcal m–2) yr–1

Explanation: The correct answer is (4). Only about 10% of energy is transferred from one trophic level to the next. If the NPP of the first trophic level is 100x, the second will receive 10x and the third only x. Therefore, GPP of the third trophic level equals x/10 (kcal m–2) yr–1, illustrating the energy loss in trophic transfer.

1. Which of the following represents the correct relation between GPP, NPP, and R?
(1) NPP = GPP + R
(2) GPP = NPP + R
(3) R = NPP + GPP
(4) NPP = R – GPP

Explanation: The correct answer is (2). Gross Primary Productivity (GPP) represents total energy captured by autotrophs through photosynthesis. Net Primary Productivity (NPP) is the portion remaining after subtracting the energy used for plant respiration (R). Thus, GPP = NPP + R. It reflects the basic energy flow in all ecosystems.

2. Which ecosystem has the highest Net Primary Productivity (NPP)?
(1) Desert
(2) Open ocean
(3) Tropical rainforest
(4) Tundra

Explanation: The correct answer is (3). Tropical rainforests exhibit the highest Net Primary Productivity because of warm temperature, abundant sunlight, and high rainfall. These favorable conditions enhance photosynthesis, producing the greatest biomass per unit area among terrestrial ecosystems, making them the most productive biomes on Earth.

3. Assertion–Reason Question:
Assertion (A): Only 10% of the energy is transferred from one trophic level to the next.
Reason (R): Most of the energy is lost as heat and through respiration at each trophic transfer.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, but R is false
(4) A is false, but R is true

Explanation: The correct answer is (1). Energy transfer in ecosystems follows the 10% law, where most energy is lost as heat or used in metabolic processes. Hence, only about 10% of energy at each trophic level is available to the next, explaining declining energy and biomass with higher levels.

4. Fill in the Blanks:
The energy available to the next trophic level is about __________ of the energy received from the previous level.
(1) 1%
(2) 5%
(3) 10%
(4) 25%

Explanation: The correct answer is (3). Only around 10% of the energy at one trophic level is transferred to the next. The remaining 90% is lost through respiration, excretion, and heat. This principle explains why food chains rarely exceed four trophic levels and why energy pyramids are always upright.

5. The main source of energy for all ecosystems is:
(1) Green plants
(2) Sunlight
(3) Chemical reactions
(4) Soil nutrients

Explanation: The correct answer is (2). Sunlight provides the primary energy source for almost all ecosystems. Producers like green plants, algae, and some bacteria capture solar energy through photosynthesis to produce food. This stored chemical energy supports all higher trophic levels in the food chain.

6. Choose the Correct Statements:
Statement I: Energy flow in an ecosystem is unidirectional.
Statement II: Energy once lost as heat cannot be reused by the ecosystem.
(1) Both statements are correct
(2) Only Statement I is correct
(3) Only Statement II is correct
(4) Both statements are incorrect

Explanation: The correct answer is (1). Energy flows in one direction—from producers to various consumers and finally to decomposers. Unlike nutrients, energy cannot be recycled. Once released as heat, it dissipates into the environment, confirming the unidirectional nature of energy flow in ecosystems.

7. Which of the following trophic levels receives the least amount of energy?
(1) Producers
(2) Primary consumers
(3) Secondary consumers
(4) Tertiary consumers

Explanation: The correct answer is (4). Tertiary consumers, being at the top of the food chain, receive the least energy. Energy decreases progressively at each trophic level because only about 10% is transferred upward. Hence, higher-level consumers have limited populations and depend heavily on the base energy input.

8. Matching Type Question:
Match the following terms with their correct descriptions:
A. GPP    I. Total energy captured by producers
B. NPP    II. Energy available to herbivores
C. R        III. Energy used in respiration
D. 10% Law    IV. Energy transfer efficiency
(1) A–I, B–II, C–III, D–IV
(2) A–II, B–I, C–IV, D–III
(3) A–III, B–IV, C–I, D–II
(4) A–IV, B–III, C–II, D–I

Explanation: The correct answer is (1). GPP is the total energy captured by autotrophs; NPP is energy remaining for herbivores after respiration (R). The 10% law describes the energy transfer efficiency across trophic levels, fundamental for understanding ecosystem energetics and biomass pyramids.

9. Which of the following is an example of a heterotroph in an ecosystem?
(1) Green plant
(2) Blue-green algae
(3) Goat
(4) Phytoplankton

Explanation: The correct answer is (3). A goat is a heterotroph that depends directly or indirectly on producers for its energy. It consumes plant material (primary producer biomass) and represents a primary consumer in the trophic hierarchy. Heterotrophs include all animals, fungi, and many microorganisms.

10. The ecological pyramid of energy is always:
(1) Inverted
(2) Spindle-shaped
(3) Upright
(4) Irregular

Explanation: The correct answer is (3). The energy pyramid is always upright because energy decreases at successive trophic levels. Producers form the broad base with maximum energy, while tertiary consumers form the narrow apex. This pattern follows the Second Law of Thermodynamics and the 10% energy transfer principle.

Topic: Population Growth Models; Subtopic: Verhulst-Pearl Logistic Growth Equation

Keyword Definitions:

• Population Growth: The change in the number of individuals in a population over time, influenced by birth rate, death rate, immigration, and emigration.

• Carrying Capacity (K): The maximum population size that an environment can support sustainably with available resources.

• Intrinsic Rate of Natural Increase (r): The rate at which a population increases in size under ideal conditions without resource limitations.

• Logistic Growth: Population growth pattern where growth rate decreases as population size approaches carrying capacity.

Lead Question – 2024

The equation of Verhulst-Pearl logistic growth is
dN/dt = rN (K − N)/K
From this equation, K indicates:

(1) Biotic potential
(2) Carrying capacity
(3) Population density
(4) Intrinsic rate of natural increase

Explanation: In the logistic growth equation, K represents the carrying capacity of the environment, which is the maximum number of individuals that can be sustained without degrading resources. As N approaches K, population growth slows and stabilizes. The model balances population growth with environmental limitations. (Answer: 2)

1. In the logistic growth model, population growth is maximum when:
(1) N = 0
(2) N = K
(3) N = K/2
(4) N = r

Explanation: In logistic growth, population growth rate is maximum when population size (N) is half the carrying capacity (K/2). At this point, resources are sufficiently available, and reproduction rate is optimal. When N approaches K, competition increases, reducing the growth rate and stabilizing population size. (Answer: 3)

2. If the carrying capacity (K) of a population is exceeded:
(1) The population grows exponentially
(2) Resources become abundant
(3) Mortality rate increases
(4) Birth rate increases

Explanation: When population size exceeds the carrying capacity, resources become limiting, leading to competition, starvation, and higher mortality rates. As a result, the population size decreases until it stabilizes around K again. This self-regulation ensures long-term population equilibrium. (Answer: 3)

3. In a population following logistic growth, the value of (K − N)/K indicates:
(1) Environmental resistance
(2) Growth rate modifier
(3) Carrying capacity
(4) Mortality rate

Explanation: The term (K − N)/K in the logistic growth equation acts as a growth rate modifier. It reflects how close the population is to its carrying capacity. When N is small, growth is rapid; as N approaches K, the factor decreases, slowing population growth. (Answer: 2)

4. Which of the following conditions is characteristic of exponential growth?
(1) Limited food and space
(2) Constant growth rate and unlimited resources
(3) Decreasing birth rate
(4) High death rate

Explanation: Exponential growth occurs under ideal conditions where resources are unlimited and the environment offers no resistance. The population grows at a constant rate (r) and the size doubles over equal time intervals, forming a J-shaped curve. Eventually, resource limitation shifts growth toward logistic behavior. (Answer: 2)

5. In the logistic model, when N = K, then:
(1) dN/dt = 0
(2) dN/dt = rN
(3) dN/dt = K/2
(4) dN/dt = K

Explanation: When N equals K in the logistic growth equation, the growth rate (dN/dt) becomes zero. This means the population has reached carrying capacity, where birth and death rates balance. The environment cannot support further increase, resulting in a stable population size. (Answer: 1)

6. Which of the following is not a density-dependent factor?
(1) Predation
(2) Disease
(3) Earthquake
(4) Competition

Explanation: Density-dependent factors regulate population size according to its density. Predation, disease, and competition increase with population density. In contrast, natural disasters like earthquakes are density-independent factors, affecting populations regardless of their size or density. (Answer: 3)

7. Assertion-Reason Type:
Assertion (A): Logistic growth curve is sigmoid (S-shaped).
Reason (R): Population growth is initially exponential and later slows as it approaches carrying capacity.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation
(3) A is true, R is false
(4) A is false, R is true

Explanation: Logistic growth curve is S-shaped because population growth starts exponentially when resources are abundant and slows down as resources become limiting. The curve stabilizes at carrying capacity, forming the sigmoid shape. Thus, both Assertion and Reason are true, and R correctly explains A. (Answer: 1)

8. Matching Type Question:
Match the terms with their descriptions:
A. Exponential Growth – (i) J-shaped curve
B. Logistic Growth – (ii) S-shaped curve
C. Carrying Capacity – (iii) Maximum population sustainable
D. Intrinsic Rate (r) – (iv) Rate of increase under ideal conditions
Options:
(1) A–i, B–ii, C–iii, D–iv
(2) A–ii, B–i, C–iv, D–iii
(3) A–iii, B–iv, C–ii, D–i
(4) A–iv, B–ii, C–iii, D–i

Explanation: Exponential growth forms a J-shaped curve, logistic growth forms an S-shaped curve, carrying capacity indicates the maximum population an environment can support, and the intrinsic rate (r) is the ideal growth rate without limiting factors. Therefore, the correct matching is A–i, B–ii, C–iii, D–iv. (Answer: 1)

9. Fill in the Blanks:
In logistic growth, when population size (N) approaches carrying capacity (K), the growth rate __________.
(1) Increases
(2) Decreases
(3) Becomes constant
(4) Doubles

Explanation: In logistic growth, as population size approaches the carrying capacity, environmental resistance increases due to limited resources, resulting in a decrease in growth rate. The population eventually stabilizes around K, maintaining ecological balance and resource sustainability. (Answer: 2)

10. Choose the Correct Statements:
Statement I: Carrying capacity remains constant over time.
Statement II: Environmental changes can alter carrying capacity.
(1) Both statements are true
(2) Both statements are false
(3) Statement I is true, Statement II is false
(4) Statement I is false, Statement II is true

Explanation: Carrying capacity is not constant; it varies with environmental conditions such as resource availability, climate, and habitat changes. Natural events or human activities can increase or decrease K over time. Thus, Statement I is false and Statement II is true. (Answer: 4)

Chapter: Organisms and Populations; Topic: Population Interactions; Subtopic: Competitive Exclusion Principle

Keyword Definitions:
• Competition: Interaction between species or individuals for limited resources like food or habitat.
• Competitive Exclusion Principle: States that two species competing for identical resources cannot coexist indefinitely.
• Resource Partitioning: Evolutionary process where species use resources differently to reduce competition.
• Ecological Niche: The role and position a species occupies in an ecosystem.
• Population: A group of individuals of the same species living in a particular area.

Lead Question - 2024
Given below are two statements:
Statement - I : Gause’s competitive exclusion principle states that two closely related species competing for different resources cannot exist indefinitely.
Statement - II : According to Gause’s principle, during competition, the inferior will be eliminated. This may be true if resources are limiting.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are false
(2) Statement I is true but Statement II is false
(3) Statement I is false but Statement II is true
(4) Both Statement I and Statement II are true

Explanation:
The correct answer is (3) Statement I is false but Statement II is true. Gause’s competitive exclusion principle states that two species competing for the same resources cannot coexist indefinitely in the same niche. When resources are limiting, the inferior competitor is eliminated. However, if species utilize different resources, they can coexist. (100 words)

1. Two species that can coexist by occupying different ecological niches demonstrate:
(1) Mutualism
(2) Resource Partitioning
(3) Parasitism
(4) Commensalism
Explanation: The correct answer is (2) Resource Partitioning. When species utilize resources differently (for example, by feeding at different times or places), they reduce direct competition, allowing coexistence. This phenomenon, known as resource partitioning, supports Gause’s principle by showing how species can coexist through ecological differentiation. (100 words)

2. Which of the following best exemplifies the competitive exclusion principle?
(1) Two birds using different parts of the same tree
(2) One bacterial species outcompeting another in the same culture medium
(3) Two fish species living in different ponds
(4) Two plants pollinated by different insects
Explanation: The correct answer is (2) One bacterial species outcompeting another in the same culture medium. Gause demonstrated this principle using Paramecium species, where one species eliminated the other when competing for the same food source under identical conditions. It highlights that no two species can occupy the same niche indefinitely. (100 words)

3. In an ecosystem, if two species coexist without eliminating each other, it is most likely due to:
(1) Competition for the same niche
(2) Resource partitioning
(3) Limited carrying capacity
(4) Equal growth rates
Explanation: The correct answer is (2) Resource partitioning. When species occupy different niches by utilizing different aspects of the environment, competition reduces, enabling coexistence. This adaptation is a key ecological mechanism to avoid exclusion, ensuring survival despite overlapping habitats. (100 words)

4. The principle that states “complete competitors cannot coexist” is known as:
(1) Law of tolerance
(2) Competitive exclusion principle
(3) Limiting factor concept
(4) Law of succession
Explanation: The correct answer is (2) Competitive exclusion principle. It explains that if two species compete for identical ecological requirements, one will eliminate the other. This was experimentally shown by Gause using Paramecium species, establishing that competition drives niche specialization or extinction. (100 words)

5. Assertion-Reason Question:
Assertion (A): Gause’s principle explains the outcome of interspecific competition.
Reason (R): Two species competing for identical resources can coexist indefinitely.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, but R is false
(4) A is false, but R is true
Explanation: The correct answer is (3) A is true, but R is false. Gause’s principle indeed describes interspecific competition outcomes, but species competing for identical resources cannot coexist indefinitely, leading to exclusion or niche differentiation. (100 words)

6. Match the following:
List I - Interaction Type | List II - Example
A. Competition | I. Lichen
B. Mutualism | II. Cuscuta on Hibiscus
C. Parasitism | III. Lion and Tiger
D. Commensalism | IV. Barnacles on Whale
(1) A-III, B-I, C-II, D-IV
(2) A-I, B-II, C-III, D-IV
(3) A-IV, B-II, C-I, D-III
(4) A-II, B-III, C-IV, D-I
Explanation: The correct answer is (1) A-III, B-I, C-II, D-IV. Competition occurs between lion and tiger; mutualism between fungus and algae (lichen); parasitism between Cuscuta and Hibiscus; and commensalism between barnacles and whale. These relationships define major ecological interactions. (100 words)

7. The exclusion of a species due to competition depends mainly on:
(1) Resource abundance
(2) Resource limitation
(3) Abiotic factors only
(4) Mutation rate
Explanation: The correct answer is (2) Resource limitation. Gause’s experiments and ecological theory state that competition leads to exclusion only when resources are limiting. When resources are abundant, species may coexist without direct exclusion pressure. (100 words)

8. Fill in the blanks:
When two species compete for the same limited resources, one will be __________.
(1) Coexisting
(2) Eliminated
(3) Mutated
(4) Dominated
Explanation: The correct answer is (2) Eliminated. The competitive exclusion principle clearly predicts that one species will be driven to extinction when two species compete for the same ecological niche and limiting resources, due to unequal competitive abilities. (100 words)

9. Which ecological principle is best demonstrated by Darwin’s finches of Galapagos Islands?
(1) Coevolution
(2) Adaptive radiation
(3) Resource partitioning
(4) Mutualism
Explanation: The correct answer is (3) Resource partitioning. The finches evolved different beak types to exploit various food sources, reducing competition. This adaptive differentiation exemplifies how species coexist by utilizing different resources, thus avoiding exclusion. (100 words)

10. Choose the correct statements:
Statement I: Competitive exclusion results in niche differentiation.
Statement II: Resource partitioning minimizes interspecific competition.
(1) Both I and II are true
(2) Both I and II are false
(3) I is true but II is false
(4) I is false but II is true
Explanation: The correct answer is (1) Both I and II are true. Niche differentiation often arises from exclusion, leading to coexistence via resource partitioning. It reduces competition and enhances ecological stability among similar species. (100 words)

Topic: Energy Flow in Ecosystems; Subtopic: Primary Productivity and Trophic Levels

Keyword Definitions:

• Gross Primary Productivity (GPP): Total rate of photosynthesis, including energy used for plant respiration.

• Net Primary Productivity (NPP): Energy remaining after plant respiration; available to herbivores and decomposers.

• Trophic Level: A step in the food chain representing energy transfer between organisms.

• Energy Flow: The transfer of energy through different trophic levels, typically 10% is passed to the next level.

• Ecological Efficiency: The percentage of energy transferred from one trophic level to the next, usually about 10%.

Lead Question (September 2024)
In an ecosystem if the Net Primary Productivity (NPP) of first trophic level is 100x (kcal m–2) yr–1, what would be the Gross Primary Productivity (GPP) of the third trophic level of the same ecosystem?
(1) x (kcal m–2) yr–1
(2) 10x (kcal m–2) yr–1
(3) 100x/3x (kcal m–2) yr–1
(4) x/10 (kcal m–2) yr–1

Explanation: The correct answer is (4). Only about 10% of energy is transferred from one trophic level to the next. If the NPP of the first trophic level is 100x, the second will receive 10x and the third only x. Therefore, GPP of the third trophic level equals x/10 (kcal m–2) yr–1, illustrating the energy loss in trophic transfer.

1. Which of the following represents the correct relation between GPP, NPP, and R?
(1) NPP = GPP + R
(2) GPP = NPP + R
(3) R = NPP + GPP
(4) NPP = R – GPP

Explanation: The correct answer is (2). Gross Primary Productivity (GPP) represents total energy captured by autotrophs through photosynthesis. Net Primary Productivity (NPP) is the portion remaining after subtracting the energy used for plant respiration (R). Thus, GPP = NPP + R. It reflects the basic energy flow in all ecosystems.

2. Which ecosystem has the highest Net Primary Productivity (NPP)?
(1) Desert
(2) Open ocean
(3) Tropical rainforest
(4) Tundra

Explanation: The correct answer is (3). Tropical rainforests exhibit the highest Net Primary Productivity because of warm temperature, abundant sunlight, and high rainfall. These favorable conditions enhance photosynthesis, producing the greatest biomass per unit area among terrestrial ecosystems, making them the most productive biomes on Earth.

3. Assertion–Reason Question:
Assertion (A): Only 10% of the energy is transferred from one trophic level to the next.
Reason (R): Most of the energy is lost as heat and through respiration at each trophic transfer.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, but R is false
(4) A is false, but R is true

Explanation: The correct answer is (1). Energy transfer in ecosystems follows the 10% law, where most energy is lost as heat or used in metabolic processes. Hence, only about 10% of energy at each trophic level is available to the next, explaining declining energy and biomass with higher levels.

4. Fill in the Blanks:
The energy available to the next trophic level is about __________ of the energy received from the previous level.
(1) 1%
(2) 5%
(3) 10%
(4) 25%

Explanation: The correct answer is (3). Only around 10% of the energy at one trophic level is transferred to the next. The remaining 90% is lost through respiration, excretion, and heat. This principle explains why food chains rarely exceed four trophic levels and why energy pyramids are always upright.

5. The main source of energy for all ecosystems is:
(1) Green plants
(2) Sunlight
(3) Chemical reactions
(4) Soil nutrients

Explanation: The correct answer is (2). Sunlight provides the primary energy source for almost all ecosystems. Producers like green plants, algae, and some bacteria capture solar energy through photosynthesis to produce food. This stored chemical energy supports all higher trophic levels in the food chain.

6. Choose the Correct Statements:
Statement I: Energy flow in an ecosystem is unidirectional.
Statement II: Energy once lost as heat cannot be reused by the ecosystem.
(1) Both statements are correct
(2) Only Statement I is correct
(3) Only Statement II is correct
(4) Both statements are incorrect

Explanation: The correct answer is (1). Energy flows in one direction—from producers to various consumers and finally to decomposers. Unlike nutrients, energy cannot be recycled. Once released as heat, it dissipates into the environment, confirming the unidirectional nature of energy flow in ecosystems.

7. Which of the following trophic levels receives the least amount of energy?
(1) Producers
(2) Primary consumers
(3) Secondary consumers
(4) Tertiary consumers

Explanation: The correct answer is (4). Tertiary consumers, being at the top of the food chain, receive the least energy. Energy decreases progressively at each trophic level because only about 10% is transferred upward. Hence, higher-level consumers have limited populations and depend heavily on the base energy input.

8. Matching Type Question:
Match the following terms with their correct descriptions:
A. GPP    I. Total energy captured by producers
B. NPP    II. Energy available to herbivores
C. R        III. Energy used in respiration
D. 10% Law    IV. Energy transfer efficiency
(1) A–I, B–II, C–III, D–IV
(2) A–II, B–I, C–IV, D–III
(3) A–III, B–IV, C–I, D–II
(4) A–IV, B–III, C–II, D–I

Explanation: The correct answer is (1). GPP is the total energy captured by autotrophs; NPP is energy remaining for herbivores after respiration (R). The 10% law describes the energy transfer efficiency across trophic levels, fundamental for understanding ecosystem energetics and biomass pyramids.

9. Which of the following is an example of a heterotroph in an ecosystem?
(1) Green plant
(2) Blue-green algae
(3) Goat
(4) Phytoplankton

Explanation: The correct answer is (3). A goat is a heterotroph that depends directly or indirectly on producers for its energy. It consumes plant material (primary producer biomass) and represents a primary consumer in the trophic hierarchy. Heterotrophs include all animals, fungi, and many microorganisms.

10. The ecological pyramid of energy is always:
(1) Inverted
(2) Spindle-shaped
(3) Upright
(4) Irregular

Explanation: The correct answer is (3). The energy pyramid is always upright because energy decreases at successive trophic levels. Producers form the broad base with maximum energy, while tertiary consumers form the narrow apex. This pattern follows the Second Law of Thermodynamics and the 10% energy transfer principle.

Topic: Population Growth Models; Subtopic: Verhulst-Pearl Logistic Growth Equation

Keyword Definitions:

• Population Growth: The change in the number of individuals in a population over time, influenced by birth rate, death rate, immigration, and emigration.

• Carrying Capacity (K): The maximum population size that an environment can support sustainably with available resources.

• Intrinsic Rate of Natural Increase (r): The rate at which a population increases in size under ideal conditions without resource limitations.

• Logistic Growth: Population growth pattern where growth rate decreases as population size approaches carrying capacity.

Lead Question – 2024

The equation of Verhulst-Pearl logistic growth is
dN/dt = rN (K − N)/K
From this equation, K indicates:

(1) Biotic potential
(2) Carrying capacity
(3) Population density
(4) Intrinsic rate of natural increase

Explanation: In the logistic growth equation, K represents the carrying capacity of the environment, which is the maximum number of individuals that can be sustained without degrading resources. As N approaches K, population growth slows and stabilizes. The model balances population growth with environmental limitations. (Answer: 2)

1. In the logistic growth model, population growth is maximum when:
(1) N = 0
(2) N = K
(3) N = K/2
(4) N = r

Explanation: In logistic growth, population growth rate is maximum when population size (N) is half the carrying capacity (K/2). At this point, resources are sufficiently available, and reproduction rate is optimal. When N approaches K, competition increases, reducing the growth rate and stabilizing population size. (Answer: 3)

2. If the carrying capacity (K) of a population is exceeded:
(1) The population grows exponentially
(2) Resources become abundant
(3) Mortality rate increases
(4) Birth rate increases

Explanation: When population size exceeds the carrying capacity, resources become limiting, leading to competition, starvation, and higher mortality rates. As a result, the population size decreases until it stabilizes around K again. This self-regulation ensures long-term population equilibrium. (Answer: 3)

3. In a population following logistic growth, the value of (K − N)/K indicates:
(1) Environmental resistance
(2) Growth rate modifier
(3) Carrying capacity
(4) Mortality rate

Explanation: The term (K − N)/K in the logistic growth equation acts as a growth rate modifier. It reflects how close the population is to its carrying capacity. When N is small, growth is rapid; as N approaches K, the factor decreases, slowing population growth. (Answer: 2)

4. Which of the following conditions is characteristic of exponential growth?
(1) Limited food and space
(2) Constant growth rate and unlimited resources
(3) Decreasing birth rate
(4) High death rate

Explanation: Exponential growth occurs under ideal conditions where resources are unlimited and the environment offers no resistance. The population grows at a constant rate (r) and the size doubles over equal time intervals, forming a J-shaped curve. Eventually, resource limitation shifts growth toward logistic behavior. (Answer: 2)

5. In the logistic model, when N = K, then:
(1) dN/dt = 0
(2) dN/dt = rN
(3) dN/dt = K/2
(4) dN/dt = K

Explanation: When N equals K in the logistic growth equation, the growth rate (dN/dt) becomes zero. This means the population has reached carrying capacity, where birth and death rates balance. The environment cannot support further increase, resulting in a stable population size. (Answer: 1)

6. Which of the following is not a density-dependent factor?
(1) Predation
(2) Disease
(3) Earthquake
(4) Competition

Explanation: Density-dependent factors regulate population size according to its density. Predation, disease, and competition increase with population density. In contrast, natural disasters like earthquakes are density-independent factors, affecting populations regardless of their size or density. (Answer: 3)

7. Assertion-Reason Type:
Assertion (A): Logistic growth curve is sigmoid (S-shaped).
Reason (R): Population growth is initially exponential and later slows as it approaches carrying capacity.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation
(3) A is true, R is false
(4) A is false, R is true

Explanation: Logistic growth curve is S-shaped because population growth starts exponentially when resources are abundant and slows down as resources become limiting. The curve stabilizes at carrying capacity, forming the sigmoid shape. Thus, both Assertion and Reason are true, and R correctly explains A. (Answer: 1)

8. Matching Type Question:
Match the terms with their descriptions:
A. Exponential Growth – (i) J-shaped curve
B. Logistic Growth – (ii) S-shaped curve
C. Carrying Capacity – (iii) Maximum population sustainable
D. Intrinsic Rate (r) – (iv) Rate of increase under ideal conditions
Options:
(1) A–i, B–ii, C–iii, D–iv
(2) A–ii, B–i, C–iv, D–iii
(3) A–iii, B–iv, C–ii, D–i
(4) A–iv, B–ii, C–iii, D–i

Explanation: Exponential growth forms a J-shaped curve, logistic growth forms an S-shaped curve, carrying capacity indicates the maximum population an environment can support, and the intrinsic rate (r) is the ideal growth rate without limiting factors. Therefore, the correct matching is A–i, B–ii, C–iii, D–iv. (Answer: 1)

9. Fill in the Blanks:
In logistic growth, when population size (N) approaches carrying capacity (K), the growth rate __________.
(1) Increases
(2) Decreases
(3) Becomes constant
(4) Doubles

Explanation: In logistic growth, as population size approaches the carrying capacity, environmental resistance increases due to limited resources, resulting in a decrease in growth rate. The population eventually stabilizes around K, maintaining ecological balance and resource sustainability. (Answer: 2)

10. Choose the Correct Statements:
Statement I: Carrying capacity remains constant over time.
Statement II: Environmental changes can alter carrying capacity.
(1) Both statements are true
(2) Both statements are false
(3) Statement I is true, Statement II is false
(4) Statement I is false, Statement II is true

Explanation: Carrying capacity is not constant; it varies with environmental conditions such as resource availability, climate, and habitat changes. Natural events or human activities can increase or decrease K over time. Thus, Statement I is false and Statement II is true. (Answer: 4)

Topic: Water Pollution; Subtopic: Dissolved Oxygen & Biochemical Oxygen Demand (BOD)

Keyword Definitions:

• Dissolved Oxygen (DO): Amount of oxygen present in water available for aquatic organisms, critical for survival of fish and microorganisms.

• Biochemical Oxygen Demand (BOD): Measure of oxygen required by microorganisms to decompose organic matter in water, indicating pollution level.

• Aquatic Life: Organisms living in water, including fish, invertebrates, and plants.

• Water Body Health: Overall quality and ecosystem functionality of rivers, lakes, and ponds determined by chemical, physical, and biological parameters.

• Organic Matter: Plant or animal-derived materials present in water, which can increase microbial activity and oxygen consumption.

• Inverse Relationship: A correlation where an increase in one factor causes decrease in another.

• Indicator: Parameter that reflects the quality or condition of an environment, used for monitoring.

• Pollution: Introduction of harmful substances or excess organic matter into the environment affecting ecosystem balance.

• Oxygen Depletion: Reduction of DO in water, leading to stress or death of aquatic organisms.

• Microbial Activity: Metabolic processes of microorganisms that consume oxygen to degrade organic compounds.

• Water Quality Assessment: Process of analyzing chemical, biological, and physical parameters to determine suitability of water for life and use.

Lead Question - 2023 (Manipur):

Select the correct statements regarding dissolved oxygen and biochemical oxygen demand:

A: BOD is inversely related to dissolved oxygen
B: Low dissolved oxygen and high BOD lead to loss of aquatic life
C: High BOD leads to high dissolved oxygen
D: Both BOD and dissolved oxygen are indicators of health of a water body
E: Both BOD and dissolved oxygen are affected by amount of organic matter in the water body

Choose the most appropriate answer from the options given below:

1. (A), (B), (C), (E) only
2. (A), (B), (D), (E) only
3. (A), (B), (C), (D) only
4. (B), (C), (D), (E) only

Explanation: Correct option is (A), (B), (D), (E) only. BOD is inversely proportional to dissolved oxygen; high BOD depletes oxygen, stressing aquatic life. Both BOD and DO serve as indicators of water body health and are influenced by organic matter content. Monitoring these parameters helps in assessing pollution, ecosystem stability, and water quality management for sustainable aquatic environments.

Guessed MCQs:

1. Single Correct Answer MCQ: Which factor increases BOD in water?
(A) High organic matter
(B) High dissolved oxygen
(C) Low microbial activity
(D) Low temperature
Explanation: High organic matter is correct. Presence of excess plant or animal debris provides substrate for microorganisms, increasing metabolic activity and oxygen consumption, raising BOD. Elevated BOD can deplete dissolved oxygen, stressing aquatic life. Monitoring BOD helps evaluate pollution levels. This parameter is central to water quality assessment and ecosystem health management, ensuring aquatic biodiversity and ecological balance.

2. Single Correct Answer MCQ: Low dissolved oxygen in water causes:
(A) Increased fish population
(B) Loss of aquatic life
(C) Reduced BOD
(D) Decreased microbial activity
Explanation: Loss of aquatic life is correct. Dissolved oxygen is essential for respiration of aquatic organisms. Low DO, often due to high BOD or pollution, stresses or kills fish, invertebrates, and plants. Monitoring DO is crucial for assessing water quality and ecosystem health. This shows the interdependence of chemical and biological parameters in maintaining aquatic life and preventing eutrophication or hypoxic conditions.

3. Single Correct Answer MCQ: BOD measures:
(A) Oxygen available for fish
(B) Oxygen consumed by microorganisms to decompose organic matter
(C) Total dissolved oxygen
(D) Salinity of water
Explanation: Oxygen consumed by microorganisms is correct. BOD indicates the amount of dissolved oxygen required by aerobic microbes to degrade organic substances in water. High BOD signals organic pollution, potentially reducing DO and harming aquatic life. It is a critical parameter for evaluating water quality and pollution load. Monitoring BOD ensures sustainable aquatic ecosystem management and highlights effects of human activities on water bodies.

4. Single Correct Answer MCQ: Which statement about DO is true?
(A) High DO indicates polluted water
(B) DO is essential for aquatic organisms
(C) DO is not affected by temperature
(D) Low DO favors fish survival
Explanation: DO is essential for aquatic organisms is correct. Dissolved oxygen supports respiration of fish, invertebrates, and microorganisms. Its concentration is influenced by temperature, organic matter, and photosynthesis. Low DO can cause hypoxia, leading to fish kills. DO monitoring is vital for water quality assessment and ecosystem health. Maintaining adequate DO ensures biodiversity and prevents ecological imbalance in freshwater and marine systems.

5. Single Correct Answer MCQ: High organic pollution in water results in:
(A) Low BOD
(B) High DO
(C) High BOD
(D) Low temperature
Explanation: High BOD is correct. Organic pollutants serve as substrate for microorganisms, increasing oxygen consumption to decompose matter. Elevated BOD lowers dissolved oxygen, threatening aquatic life. Monitoring BOD identifies pollution levels and ecological risk. Understanding this relationship aids in water treatment, environmental management, and maintaining ecosystem services, ensuring water bodies remain sustainable for human and aquatic use while preventing eutrophication.

6. Single Correct Answer MCQ: Which of the following is an indicator of water body health?
(A) BOD
(B) Dissolved Oxygen
(C) Both A and B
(D) Temperature only
Explanation: Both A and B is correct. BOD and DO together provide a comprehensive picture of water quality. BOD reflects organic pollution and microbial activity, while DO indicates oxygen availability for aquatic organisms. Regular monitoring helps assess ecosystem health, detect pollution, and guide remedial actions. This dual parameter approach ensures sustainable aquatic environments, supporting biodiversity and maintaining ecological balance.

7. Assertion-Reason MCQ:
Assertion (A): Low DO and high BOD lead to aquatic life loss.
Reason (R): Microorganisms consume oxygen to decompose organic matter, reducing available oxygen for aquatic animals.
(A) Both A and R are true, and R is the correct explanation of A
(B) Both A and R are true, but R is not the correct explanation of A
(C) A is true, R is false
(D) A is false, R is true
Explanation: Option (A) is correct. High BOD increases microbial oxygen consumption, depleting DO. Aquatic animals rely on DO for respiration. Reduced oxygen levels result in stress or death of fish and other organisms. This demonstrates the interconnectedness of chemical and biological water parameters. Monitoring BOD and DO helps prevent ecosystem collapse and maintain healthy aquatic environments.

8. Matching Type MCQ: Match the following:
1. BOD    A. Oxygen required by microbes
2. DO    B. Oxygen available for aquatic life
3. Organic pollution    C. Increases microbial activity
(A) 1-A, 2-B, 3-C
(B) 1-B, 2-A, 3-C
(C) 1-C, 2-A, 3-B
(D) 1-A, 2-C, 3-B
Explanation: Correct option is 1-A, 2-B, 3-C. BOD measures oxygen consumed by microorganisms (1-A). DO represents oxygen available for aquatic organisms (2-B). Organic pollution provides substrate, increasing microbial activity and BOD (3-C). Understanding these relationships is essential for water quality assessment, ecological monitoring, and ensuring sustainable aquatic environments. These parameters guide pollution control and ecosystem management strategies effectively.

9. Fill in the Blanks / Completion MCQ: High _________ leads to oxygen depletion and aquatic stress.
(A) BOD
(B) DO
(C) pH
(D) Temperature
Explanation: BOD is correct. Elevated BOD indicates high organic load in water, increasing microbial oxygen consumption. This reduces DO, stressing or killing aquatic life. Measuring BOD is critical for water quality monitoring and pollution assessment. Controlling BOD through waste treatment and ecosystem management maintains ecological balance, ensures oxygen availability, and protects biodiversity in freshwater and marine environments, highlighting the link between organic pollution and aquatic health.

10. Choose the correct statements MCQ:
Statement I: BOD is inversely related to DO.
Statement II: Both BOD and DO indicate water body health.
(A) Both I and II are correct
(B) Only I is correct
(C) Only II is correct
(D) Neither I nor II is correct
Explanation: Option (A) is correct. High BOD leads to oxygen consumption, decreasing DO, demonstrating an inverse relationship. Both BOD and DO are critical indicators of water quality and ecosystem health. Monitoring these parameters enables detection of pollution, guides remediation, and ensures sustainability of aquatic life. This relationship is foundational in environmental biology, showing how chemical and biological factors interact to maintain water body health and prevent ecological degradation.

Topic: Environmental Issues; Subtopic: Deforestation, Reforestation, Greenhouse Effect, Eutrophication

Keyword Definitions:

• Deforestation: The process of clearing or removing forested land for other uses like agriculture or urbanization.

• Reforestation: Planting trees in areas where forests have been removed to restore ecological balance.

• Greenhouse effect: Warming of Earth's surface and atmosphere due to accumulation of greenhouse gases like CO₂, CH₄, N₂O.

• Eutrophication: Enrichment of water bodies with nutrients causing excessive growth of algae, leading to oxygen depletion.

• Algal bloom: Rapid growth of algae due to nutrient enrichment, often linked to eutrophication.

• Carbon dioxide: Greenhouse gas contributing to global warming.

• Oxygen depletion: Reduction in dissolved oxygen in water bodies due to decomposition of organic matter.

• Climate change: Long-term alteration in Earth's climate due to natural or anthropogenic causes.

• Anthropogenic activities: Human actions affecting the environment, such as deforestation, industrialization.

• Ecological balance: Equilibrium between living organisms and their environment.

• Biogeochemical cycles: Cycles of nutrients like carbon, nitrogen, and phosphorus through ecosystems.

Lead Question - 2023 (Manipur)

Match List - I with List - II

List-I List-II

(A) Deforestation (I) Responsible for heating of Earth's surface and atmosphere

(B) Reforestation (II) Conversion of forested areas to non-forested areas

(C) Greenhouse effect (III) Natural ageing of lake by nutrient enrichment of its water

(D) Eutrophication (IV) Process of restoring a forest that once existed but was removed

Options:

1. IV III II I

2. I II III IV

3. III I II IV

4. II IV I III

Explanation:

Deforestation (B) refers to the conversion of forested areas into non-forested areas (II). Reforestation (B) is the process of restoring forests (IV). Greenhouse effect (C) is responsible for heating of Earth's surface and atmosphere (I) due to accumulation of gases like CO₂. Eutrophication (D) is nutrient enrichment leading to aging of lakes (III). Hence, the correct matching sequence is (A)-(II), (B)-(IV), (C)-(I), (D)-(III). Correct answer is 4.

1. Single Correct Answer MCQ:

Which gas primarily contributes to the greenhouse effect?

1. Oxygen

2. Carbon dioxide

3. Nitrogen

4. Argon

Explanation:

Carbon dioxide (CO₂) is the major greenhouse gas released from burning fossil fuels and deforestation. It traps heat in the atmosphere, leading to warming. Oxygen, nitrogen, and argon do not significantly contribute to greenhouse warming. Correct answer is 2.

2. Single Correct Answer MCQ:

Which process helps in restoring lost forests?

1. Afforestation

2. Deforestation

3. Urbanization

4. Industrialization

Explanation:

Reforestation or afforestation involves planting trees to restore lost or degraded forests, improving ecological balance. Deforestation removes forests, urbanization and industrialization degrade land. Correct answer is 1.

3. Single Correct Answer MCQ:

Eutrophication primarily affects:

1. Air quality

2. Water bodies

3. Soil fertility

4. Desert ecosystems

Explanation:

Eutrophication enriches water bodies with nutrients, causing excessive algae growth and oxygen depletion. It is a major water pollution problem, not directly affecting air, soil, or deserts. Correct answer is 2.

4. Single Correct Answer MCQ:

Deforestation leads to:

1. Decreased CO₂ levels

2. Global warming

3. Improved biodiversity

4. Enhanced water retention

Explanation:

Deforestation removes trees that absorb CO₂, leading to increased greenhouse gases and global warming. Biodiversity declines and water retention reduces. Correct answer is 2.

5. Single Correct Answer MCQ:

Primary cause of eutrophication is:

1. Industrial smoke

2. Nutrient runoff from agriculture

3. Deforestation

4. Excessive rainfall

Explanation:

Agricultural runoff rich in nitrogen and phosphorus causes eutrophication, leading to algal blooms and oxygen depletion. Industrial smoke, deforestation, or rainfall are indirect factors. Correct answer is 2.

6. Single Correct Answer MCQ:

Which of the following is NOT a greenhouse gas?

1. Methane

2. Carbon dioxide

3. Oxygen

4. Nitrous oxide

Explanation:

Oxygen is not a greenhouse gas. Methane, carbon dioxide, and nitrous oxide trap heat in the atmosphere, contributing to global warming. Correct answer is 3.

7. Assertion-Reason MCQ:

Assertion (A): Reforestation reduces greenhouse effect.

Reason (R): Trees absorb CO₂ during photosynthesis.

1. Both A and R are true and R explains A

2. Both A and R are true but R does not explain A

3. A is true but R is false

4. Both A and R are false

Explanation:

Reforestation increases tree cover, which absorbs carbon dioxide through photosynthesis, reducing greenhouse gases and mitigating global warming. Both statements are true, and the reason explains the assertion. Correct answer is 1.

8. Matching Type MCQ:

Match environmental terms with effects:

A. Greenhouse gases — (i) Global warming

B. Nutrient runoff — (ii) Eutrophication

C. Deforestation — (iii) Biodiversity loss

D. Reforestation — (iv) CO₂ absorption

1. A-(i), B-(ii), C-(iii), D-(iv)

2. A-(ii), B-(iii), C-(iv), D-(i)

3. A-(iii), B-(iv), C-(i), D-(ii)

4. A-(iv), B-(i), C-(ii), D-(iii)

Explanation:

Greenhouse gases cause global warming (i), nutrient runoff causes eutrophication (ii), deforestation leads to biodiversity loss (iii), and reforestation absorbs CO₂ (iv). Correct answer is 1.

9. Fill in the Blanks MCQ:

The excessive growth of algae in lakes due to nutrient enrichment is called _______.

1. Deforestation

2. Eutrophication

3. Greenhouse effect

4. Reforestation

Explanation:

Eutrophication is the process of nutrient enrichment in water bodies, causing algal blooms and oxygen depletion. It is a key water pollution issue. Correct answer is 2.

10. Choose the correct statements MCQ:

Statement I: Deforestation contributes to global warming.

Statement II: Reforestation can mitigate climate change.

1. Statement I only

2. Statement II only

3. Both statements are true

4. Both statements are false

Explanation:

Deforestation increases CO₂, causing global warming, while reforestation absorbs CO₂, mitigating climate change. Both statements are correct. Correct answer is 3.

Topic: Population Ecology; Subtopic: Population Growth and Birth Rate

Keyword Definitions:

• Population: Group of individuals of the same species living in a defined area.

• Birth rate: Number of offspring produced per individual per unit time.

• Snail: A molluscan organism with slow mobility and external shell.

• Reproduction: Biological process by which new individuals are produced.

• Population growth: Increase in the number of individuals in a population over time.

• Pond ecosystem: Aquatic habitat supporting biotic and abiotic interactions.

• Exponential growth: Rapid population increase under ideal conditions.

• Per capita rate: Rate per individual organism.

• Time period: Duration over which population change is measured.

• Doubling: Time required for population to double in size.

• Ecological calculation: Quantitative assessment of population parameters.

Lead Question - 2023 (Manipur)

There are 250 snails in a pond and within a year their number increases to 2500 by reproduction. What should be their birth rate (in per snail per year)?

1. 10

2. 9

3. 25

4. 15

Explanation:

The initial population is 250 snails, final population after one year is 2500. The birth rate per snail is calculated as total increase divided by initial population: (2500-250)/250 = 2250/250 = 9. Therefore, each snail reproduces 9 offspring per year on average. This calculation illustrates population growth and the use of per capita birth rate in ecology. Correct answer is 2.

1. Single Correct Answer MCQ:

If a population increases from 1000 to 4000 in a year, what is the birth rate per individual?

1. 2

2. 3

3. 4

4. 5

Explanation:

Population increase = 4000-1000 = 3000; per capita birth rate = 3000/1000 = 3 offspring per individual per year. Correct answer is 2.

2. Single Correct Answer MCQ:

A population with 500 individuals grows to 1500 in a year. The birth rate per individual is:

1. 1

2. 2

3. 3

4. 4

Explanation:

Population increase = 1500-500 = 1000; per capita birth rate = 1000/500 = 2. Correct answer is 2.

3. Single Correct Answer MCQ:

Which factor directly affects per capita birth rate in a population?

1. Food availability

2. Predation

3. Number of offspring produced per individual

4. Migration

Explanation:

Per capita birth rate is defined as the average number of offspring produced per individual. Food, predation, and migration influence population indirectly. Correct answer is 3.

4. Single Correct Answer MCQ:

If a population remains constant, what is the birth rate per individual?

1. Zero

2. One

3. Equal to death rate

4. Undefined

Explanation:

In a stable population, births equal deaths. Hence, per capita birth rate matches death rate to maintain population size. Correct answer is 3.

5. Single Correct Answer MCQ:

Which population growth model assumes unlimited resources?

1. Logistic growth

2. Exponential growth

3. Linear growth

4. Declining growth

Explanation:

Exponential growth occurs when resources are unlimited, leading to rapid population increase. Logistic growth considers carrying capacity. Correct answer is 2.

6. Single Correct Answer MCQ:

In the given problem, which type of growth is illustrated?

1. Exponential growth

2. Logistic growth

3. Declining growth

4. Linear growth

Explanation:

Population grows from 250 to 2500 in a year without limiting factors, showing exponential growth. Correct answer is 1.

7. Assertion-Reason MCQ:

Assertion (A): Birth rate per individual is calculated as total population increase divided by initial population.

Reason (R): It gives the average number of offspring produced per individual in a time period.

1. Both A and R are true and R explains A

2. Both A and R are true but R does not explain A

3. A is true but R is false

4. Both A and R are false

Explanation:

Correct calculation of per capita birth rate uses total increase divided by initial population. This gives average offspring per individual, making both statements true and R explains A. Correct answer is 1.

8. Matching Type MCQ:

Match population parameters with definitions:

A. Birth rate — (i) Average offspring per individual

B. Death rate — (ii) Individuals dying per unit time

C. Growth rate — (iii) Change in population size per unit time

D. Carrying capacity — (iv) Maximum sustainable population

1. A-(i), B-(ii), C-(iii), D-(iv)

2. A-(ii), B-(i), C-(iv), D-(iii)

3. A-(iii), B-(iv), C-(i), D-(ii)

4. A-(iv), B-(iii), C-(ii), D-(i)

Explanation:

Birth rate = average offspring per individual, Death rate = deaths per time, Growth rate = change in population, Carrying capacity = max sustainable population. Correct option is 1.

9. Fill in the Blanks MCQ:

Per capita birth rate = (___________) / Initial population.

1. Total population after time period

2. Total population increase

3. Total population decrease

4. Final population

Explanation:

Per capita birth rate is calculated as total population increase divided by initial population to get average offspring per individual. Correct answer is 2.

10. Choose the correct statements MCQ:

Statement I: Per capita birth rate is useful for comparing reproductive potential of populations.

Statement II: A birth rate of 0 indicates no reproduction.

1. Statement I only

2. Statement II only

3. Both statements are true

4. Both statements are false

Explanation:

Both statements are correct: per capita birth rate allows comparison of reproductive potential across populations, and 0 birth rate means no new individuals are produced. Correct answer is 3.

Topic: Community Ecology; Subtopic: Keystone Species & Species Interactions

• Keystone Species: Species that has a disproportionately large effect on its community relative to its abundance.

• Alien Species: Species introduced outside its native range.

• Exotic Species: Non-native species introduced intentionally or accidentally to a new ecosystem.

• Endemic Species: Species native and restricted to a particular geographic region.

• Relative Abundance: The proportion of a species compared to total individuals in a community.

• Community: Group of interacting populations of different species in a common location.

• Species Interactions: Relationships between species such as competition, predation, or mutualism.

• Predator: Organism that hunts and consumes another species (prey).

• Population Control: Regulation of species numbers by biotic and abiotic factors.

• Ecological Balance: Stable state of interactions and abundance in an ecosystem.

• Biodiversity: Variety of species, genetic variation, and ecosystem types in a region.

Lead Question - 2023 (Manipur)

The species of plants that plays a vital role in controlling the relative abundance of other species in a community is called _______.

• 1. Alien species

• 2. Endemic species

• 3. Exotic species

• 4. Keystone species

Explanation: A keystone species significantly affects the structure and composition of its community. Its presence regulates the relative abundance of other species, maintains ecological balance, and supports biodiversity. Alien or exotic species are non-native, and endemic species are native but do not necessarily control community structure. Keystone species are critical for ecosystem stability. Correct answer: 4. Keystone species. Their removal often leads to cascading effects, loss of species diversity, and altered ecosystem function, highlighting their pivotal ecological role.

1. Which of the following is a keystone predator?

• a) Sea otter

• b) Deer

• c) Grass

• d) Oak tree

Explanation: Sea otters maintain kelp forest ecosystems by preying on sea urchins, preventing overgrazing. Deer and plants influence ecosystems but are not keystone predators. Oak trees provide habitat but do not control species abundance. Correct answer: a.

2. Endemic species are:

• a) Native to a specific region and found nowhere else

• b) Introduced species

• c) Species with global distribution

• d) Keystone species

Explanation: Endemic species occur naturally in a limited geographic region and nowhere else. They are different from alien or exotic species which are introduced. Keystone species control community dynamics but may or may not be endemic. Correct answer: a.

3. Alien species can cause:

• a) Ecosystem disruption

• b) Increased native biodiversity

• c) No ecological impact

• d) Natural succession acceleration

Explanation: Alien or invasive species can outcompete natives, disrupt food webs, and reduce biodiversity. While some may integrate harmlessly, often they alter ecosystem structure. Correct answer: a.

4. Keystone species affect community by:

• a) Regulating species abundance

• b) Competing for sunlight only

• c) Increasing soil nutrients

• d) Producing oxygen

Explanation: Keystone species regulate the relative abundance of other species, influencing trophic interactions and community composition. Competing for sunlight, nutrient cycling, or oxygen production are functions of other species. Correct answer: a.

5. Which plant type often acts as keystone species?

• a) Foundation species providing habitat

• b) Annual herbs

• c) Epiphytes

• d) Introduced ornamental plants

Explanation: Foundation plants like mangroves or kelp create habitat, influence community structure, and act as keystone species. Annual herbs, epiphytes, and introduced ornamentals generally do not control community abundance. Correct answer: a.

6. Removal of a keystone species leads to:

• a) Cascading ecological effects

• b) No change in community

• c) Increase in ecosystem stability

• d) Immediate extinction of all species

Explanation: Keystone species maintain community balance; their removal triggers cascading effects, altered species abundances, and potential local extinctions. Ecosystem stability is reduced, but not all species go extinct immediately. Correct answer: a.

7. Assertion (A): Keystone species are crucial for biodiversity.
Reason (R): They regulate the populations of other species and maintain community structure.

• a) Both A and R are true, and R is correct explanation of A

• b) Both A and R are true, but R is not correct explanation of A

• c) A is true, R is false

• d) A is false, R is true

Explanation: Keystone species maintain ecosystem function and regulate community structure, directly supporting biodiversity. Both assertion and reason are correct, and the reason explains the assertion. Correct answer: a.

8. Match the following:

• Column I: 1. Keystone species 2. Alien species 3. Endemic species 4. Exotic species

• Column II: a. Introduced non-native species b. Species critical for community balance c. Native and restricted species d. Species disrupting ecosystems

Choices:
a) 1-b, 2-d, 3-c, 4-a
b) 1-a, 2-b, 3-d, 4-c
c) 1-d, 2-a, 3-b, 4-c
d) 1-c, 2-b, 3-a, 4-d

Explanation: Keystone species (1-b) maintain community balance. Alien species (2-d) can disrupt ecosystems. Endemic species (3-c) are native and restricted. Exotic species (4-a) are introduced and non-native. Correct answer: a.

9. Fill in the blank: A species that regulates community structure and species abundance is called ____________.

• a) Keystone species

• b) Alien species

• c) Endemic species

• d) Exotic species

Explanation: A keystone species has a pivotal role in controlling species abundance and maintaining community structure. Alien or exotic species are non-native and may disrupt ecosystems. Endemic species are native but do not necessarily regulate community composition. Correct answer: a.

10. Choose the correct statements:

Statement I: Keystone species maintain species diversity in ecosystems.
Statement II: Alien species always increase biodiversity.

• a) Both I and II are correct

• b) Only I is correct

• c) Only II is correct

• d) Both I and II are incorrect

Explanation: Keystone species maintain diversity by regulating species abundances. Alien species often disrupt native communities and may reduce biodiversity. Therefore, only Statement I is correct. Correct answer: b.

Topic: Plant-Animal Interactions; Subtopic: Pollination Biology

• Mutualism: Symbiotic interaction where both species benefit from the relationship.

• Commensalism: Interaction where one species benefits without affecting the other.

• Amensalism: Interaction where one species is harmed while the other is unaffected.

• Competition: Interaction where both species compete for the same limited resource.

• Pollen: Male gametophyte of seed plants used for fertilization.

• Nectar: Sweet liquid produced by flowers to attract pollinators.

• Pollination: Transfer of pollen from anther to stigma facilitating fertilization.

• Pollinator: Organism that carries pollen between flowers.

• Floral reward: Resource like nectar or pollen offered to attract pollinators.

• Co-evolution: Mutual evolutionary influence between interacting species.

• Plant-Animal Interaction: Relationship between plants and animals that affects reproduction or survival.

Lead Question - 2023 (Manipur)

Plants offer rewards to animals in the form of pollen and nectar and the animals facilitate the pollination process. This is an example of:

• 1. Amensalism

• 2. Competition

• 3. Commensalism

• 4. Mutualism

Explanation: This is a classic example of mutualism where both organisms benefit. Plants gain efficient pollination while animals receive nectar or pollen as a food resource. It is distinct from commensalism where one benefits without affecting the other, competition where both compete for resources, and amensalism where one is harmed. Correct answer: 4. Mutualism. This interaction exemplifies co-evolution and highlights the importance of plant-animal interactions in ecosystem reproduction and biodiversity maintenance.

1. Nectar primarily attracts which type of pollinators?

• a) Birds and insects

• b) Soil bacteria

• c) Carnivorous mammals

• d) Fungi

Explanation: Nectar is a sugary floral reward designed to attract pollinators like birds and insects. It provides an energy source, and in return, these pollinators facilitate pollen transfer between flowers. Soil bacteria, carnivorous mammals, and fungi do not interact with nectar in this pollination context. Correct answer: a.

2. Which type of pollination involves animals transferring pollen?

• a) Zoophily

• b) Anemophily

• c) Hydrophily

• d) Self-pollination