Competency-Based Question Bank: Ecosystem

Section A: Competency-Based Multiple Choice Questions (Application & Analysis)

1. Analyze the Pyramid: An ecological pyramid of biomass is inverted. In which ecosystem would you most likely find this? a) Rainforest b) Grassland c) Pond / Ocean d) Desert Answer: c) Pond / Ocean Explanation: In aquatic ecosystems, the producers (phytoplankton) are microscopic and have a short lifespan/high turnover. Their standing biomass at any point is low compared to the long-lived zooplankton and fish that feed on them.

2. Evaluate the Energy Flow: According to the 10% law, if the producers in an ecosystem capture 10,000 Joules of solar energy (as NPP), how much energy will be available to the Secondary Consumers (Trophic Level 3)? a) 1000 J b) 100 J c) 10 J d) 1 J Answer: b) 100 J Explanation:

• Producers (T1): 10,000 J
• Primary Consumers (T2): 10% of 10,000 = 1,000 J
• Secondary Consumers (T3): 10% of 1,000 = 100 J

3. Decomposition Factors: A fallen log in a tropical rainforest decomposes much faster than a similar log in a northern coniferous forest (Taiga). What is the primary reason for this difference? a) The rainforest log has more lignin. b) The rainforest soil is acidic. c) The rainforest has higher temperature and moisture, favoring microbial activity. d) The Taiga has more detritivores. Answer: c) The rainforest has higher temperature and moisture... Explanation: Decomposition is largely an enzymatic process carried out by microbes. Warmth and humidity are the optimal conditions for these enzymes and for microbial growth.

4. Assertion (A): Energy flow in an ecosystem is unidirectional. Reason (R): Energy dissipated as heat at each trophic level cannot be captured again by the producers. 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 but R is false. d) A is false but R is true. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: Energy enters as sunlight and leaves as heat. It cannot be recycled like nutrients (Carbon, Nitrogen, etc.). This makes the flow strictly one-way.

5. Identify the Trophic Level: In a food chain: Grass -> Grasshopper -> Frog -> Snake -> Hawk, which organism represents the Secondary Carnivore? a) Grasshopper b) Frog c) Snake d) Hawk Answer: c) Snake Explanation:

• Grass (Producer)
• Grasshopper (Primary Consumer / Herbivore)
• Frog (Secondary Consumer / Primary Carnivore)
• Snake (Tertiary Consumer / Secondary Carnivore)

6. Productivity Analysis: Why is the Net Primary Productivity (NPP) always less than the Gross Primary Productivity (GPP)? a) Because herbivores eat some of the plants. b) Because a significant amount of energy is used by the plants for their own respiration (R). c) Because decomposers break down the biomass. d) Because of the 10% law. Answer: b) Because a significant amount of energy is used by the plants for their own respiration (R). Explanation: GPP is total photosynthesis. Plants must burn some of this sugar to survive (Respiration). NPP = GPP - R.

7. Nutrient Cycling: Which of the following is a key difference between the Phosphorus Cycle and the Carbon Cycle? a) Carbon cycle is sedimentary; Phosphorus cycle is gaseous. b) Phosphorus cycle lacks a significant atmospheric (gaseous) component. c) Carbon cycle does not involve decomposers. d) Phosphorus is not required by living organisms. Answer: b) Phosphorus cycle lacks a significant atmospheric (gaseous) component. Explanation: The reservoir for Carbon is the atmosphere (CO2). The reservoir for Phosphorus is rock/soil. It is a sedimentary cycle.

8. Succession Logic: In a primary succession on bare rock, which group of organisms typically acts as the "Pioneer Species"? a) Herbs b) Shrubs c) Lichens d) Trees Answer: c) Lichens Explanation: Lichens can grow on bare rock and secrete acids to dissolve the rock, starting the process of soil formation (weathering) required for other plants.

9. Ecosystem Service: Robert Costanza and his colleagues estimated the value of ecosystem services. Which service contributed the most (~50%) to the total price tag? a) Recreation b) Nutrient Cycling c) Soil Formation d) Climate Regulation Answer: c) Soil Formation Explanation: Soil is the foundation of all terrestrial life. Its natural formation is a slow, complex service that is invaluable and expensive to replicate.

10. Decomposition Process: Which step of decomposition involves the breakdown of detritus into smaller particles by earthworms? a) Leaching b) Catabolism c) Fragmentation d) Humification Answer: c) Fragmentation Explanation: Detritivores (like earthworms) physically chew and break down leaves into smaller bits, increasing surface area for microbes.

11. Food Web Stability: Why is a complex food web more stable than a simple food chain? a) It has more energy. b) It provides alternative food sources if one species declines. c) It has fewer predators. d) It has more producers. Answer: b) It provides alternative food sources if one species declines. Explanation: In a web, if one prey species dies out, the predator can switch to another prey, preventing ecosystem collapse. A simple chain has single points of failure.

12. Calculate: If a Sparrow eats a worm that ate a leaf, what trophic level does the Sparrow occupy? a) T1 b) T2 c) T3 d) T4 Answer: c) T3 Explanation:

• Leaf (Producer/T1)
• Worm (Primary Consumer/T2)
• Sparrow (Secondary Consumer/T3)

13. Stratification: The vertical distribution of different species occupying different levels in a forest is called: a) Standing Crop b) Stratification c) Succession d) Trophic Structure Answer: b) Stratification Explanation: Stratification refers to layers like the canopy, understory, shrub layer, and ground layer, each occupied by specific organisms.

14. Process ID: The process by which humus is further degraded by some microbes to release inorganic nutrients is called: a) Humification b) Mineralization c) Leaching d) Fragmentation Answer: b) Mineralization Explanation: This is the final step where organic matter is converted back into inorganic minerals (like Nitrate, Phosphate) available for plant uptake.

15. Concept Application: Which of the following ecosystems would likely have the highest Gross Primary Productivity (GPP)? a) Open Ocean b) Desert c) Tropical Rainforest d) Tundra Answer: c) Tropical Rainforest Explanation: Rainforests have abundant light, water, and warm temperatures year-round, leading to maximum photosynthesis rates.

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Section B: Case-Study & Source-Based Questions

Case Study 1: The Pond Ecosystem

A group of students visited a nearby pond. They observed:

1. Algae floating on the surface.
2. Small microscopic animals eating the algae.
3. Small fish eating the microscopic animals.
4. Large fish eating the small fish.
5. Dead leaves and fish settling at the bottom, where bacteria were abundant.

16. Identify: Which group represents the "Zooplankton"? a) Algae b) Microscopic animals c) Small fish d) Bacteria Answer: b) Microscopic animals Explanation: Zooplankton are microscopic animals that drift in water and feed on phytoplankton (algae).

17. Analyze: What would happen if all the bacteria (decomposers) at the bottom died? a) The water would become clearer. b) Nutrient cycling would stop, leading to a shortage of minerals for the algae. c) The fish would grow larger. d) Primary productivity would increase. Answer: b) Nutrient cycling would stop, leading to a shortage of minerals for the algae. Explanation: Decomposers recycle nutrients. Without them, minerals remain locked in dead bodies, starving the producers (algae), and the ecosystem collapses.

18. Trophic Structure: The "Large Fish" occupies which trophic level? a) T2 b) T3 c) T4 d) T5 Answer: c) T4 Explanation:

• T1: Algae
• T2: Microscopic animals
• T3: Small Fish
• T4: Large Fish

Case Study 2: The Energy Trap

Consider a field of corn. The sun provides 1,000,000 Joules of light energy. The corn plants capture only 1% of this into chemical energy (GPP). They use 20% of GPP for respiration. A swarm of locusts eats the corn.

19. Calculate: What is the NPP available to the locusts? a) 10,000 J b) 8,000 J c) 1,000 J d) 800 J Answer: b) 8,000 J Explanation:

• GPP = 1% of 1,000,000 = 10,000 J
• Respiration (R) = 20% of 10,000 = 2,000 J
• NPP = GPP - R = 10,000 - 2,000 = 8,000 J

20. Efficiency: If birds eat the locusts, roughly how much energy will be stored in the bird biomass? (Apply 10% law to the energy the locusts assimilated). a) 8000 J b) 800 J c) 80 J d) 8 J Answer: b) 800 J Explanation:

• Available to Locusts: 8,000 J
• Energy assimilated/stored by Locusts (available to birds) approx 10% of ingested: 800 J.
• (Note: The question implies applying the 10% transfer rule from the plant level to the locust level for the next transfer).

21. Concept: The light energy that plants can use (400-700nm) is called: a) UV Radiation b) PAR (Photosynthetically Active Radiation) c) Infrared d) Total Solar Irradiance Answer: b) PAR (Photosynthetically Active Radiation) Explanation: This is the visible spectrum range essential for chlorophyll excitation.

Case Study 3: Succession on a Volcano

After a volcanic eruption, a new island is formed of bare lava rock. Initially, there is no life. Over time, life appears in a specific order.

22. Sequence: Choose the correct order of succession: a) Grasses -> Lichens -> Shrubs -> Trees b) Lichens -> Mosses -> Herbs/Grasses -> Shrubs -> Forest c) Trees -> Shrubs -> Grasses -> Lichens d) Mosses -> Trees -> Lichens -> Grasses Answer: b) Lichens -> Mosses -> Herbs/Grasses -> Shrubs -> Forest Explanation: Succession starts with pioneers (Lichens) that create soil, followed by simple plants (Mosses/Herbs), then larger plants (Shrubs), and finally Trees (Climax).

23. Mechanism: How do Lichens help the next stage (Mosses) to establish? a) They provide shade. b) They secrete acids that dissolve rock to form soil (weathering). c) They attract birds. d) They fix nitrogen only. Answer: b) They secrete acids that dissolve rock to form soil. Explanation: Soil formation is the critical step for rooting plants like mosses.

24. Classification: This type of succession, starting on bare rock where no soil existed, is called: a) Secondary Succession b) Primary Succession c) Climax Succession d) Aquatic Succession Answer: b) Primary Succession Explanation: Primary starts from scratch (no soil). Secondary starts where soil already exists (e.g., after a fire).

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Section C: Creating, Designing & Critical Thinking

25. Designing an Ecosystem: You are designing a self-sustaining Terrarium (sealed glass jar ecosystem).

• Components: List 4 essential biotic components you must include for it to survive for months.
• Justification: Explain the role of each.
• Constraint: Why can you NOT include a large herbivore (like a rabbit)? Answer:
• Components:
  1. Green Plant (e.g., Fern/Moss) - Producer (O2 + Food).
  2. Small Invertebrate (e.g., Springtail/Isopod) - Consumer (CO2).
  3. Bacteria/Fungi - Decomposer (Recycle nutrients).
  4. Soil/Substrate - Reservoir for water/nutrients.
• Constraint: A rabbit has a high metabolic rate and energy requirement (Endotherm). A small jar cannot produce enough biomass (GPP) to sustain it, and its waste would overwhelm the decomposers (Toxic buildup).

26. Troubleshooting Decomposition: Scenario: A compost pit in your garden is not breaking down. The waste is just sitting there, smelling bad (anaerobic), but not turning into compost.

• Diagnosis: What factor might be missing or wrong?
• Solution: Propose two actions to fix the compost pit. Answer:
• Diagnosis: The bad smell indicates Anaerobic conditions (lack of oxygen) and possibly too much moisture (waterlogging). Aerobic decomposers cannot work.
• Solution:
  1. Turn the pile: Use a shovel to mix the waste, introducing Oxygen (Aeration).
  2. Add Browns: Add dry leaves or cardboard to absorb excess moisture and balance the Carbon:Nitrogen ratio.

27. Visualizing Energy Flow: Draw a Pyramid of Energy for a 4-step food chain.

• Data: Producers = 10,000 J.
• Task: Label each Trophic level (T1, T2, T3, T4) and write the estimated energy value inside each bar.
• Constraint: Explain why this pyramid cannot be inverted. Answer:
• Drawing:
  • Base (T1 - Producers): 10,000 J
  • Level 2 (T2 - Primary Consumers): 1,000 J
  • Level 3 (T3 - Secondary Consumers): 100 J
  • Top (T4 - Tertiary Consumers): 10 J
• Constraint: It cannot be inverted because of the 2nd Law of Thermodynamics. Energy is always lost as heat when transferred or transformed. T2 can never have more energy than T1.

28. Ethical/Economic Analysis: "Nature provides services worth trillions of dollars for free."

• Task: Choose one ecosystem service (e.g., Pollination or Water Purification).
• Scenario: Imagine this service stopped working naturally. Describe the economic cost and technological difficulty of replacing it artificially. Answer:
• Service: Pollination.
• Scenario: If bees disappear, we would need "Artificial Pollination".
• Cost/Difficulty: This would require hiring thousands of laborers to hand-paint pollen onto every single flower (e.g., Apple/Almond orchards) or developing microscopic drones. The cost would be billions of dollars, making fruits/nuts luxury items unaffordable for most.

29. Formulating a Hypothesis: Observation: In a forest, the biomass of trees is huge, but the biomass of top carnivores (tigers) is very small.

• Question: Why can't the forest support as many tigers as it does deer?
• Hypothesis: Formulate a hypothesis based on thermodynamic efficiency. Answer:
• Hypothesis: Energy transfer between trophic levels is inefficient (~10%). By the time energy reaches the top trophic level (Tigers), 99.9% of the original solar energy captured by trees has been lost as heat/metabolism by the intermediate levels (Deer). Therefore, the ecosystem does not have enough energy budget to support a large biomass of top predators.

30. Comparison Strategy: Compare Primary Succession and Secondary Succession.

• Criteria: 1. Starting condition. 2. Speed. 3. Pioneer species.
• Example: Give one real-world example for each. Answer:
• Primary Succession:
  1. Start: Bare rock/No Soil.
  2. Speed: Very Slow (1000s of years).
  3. Pioneer: Lichens.
  • Example: New volcanic island.
• Secondary Succession:
  1. Start: Soil is present (Disturbed land).
  2. Speed: Fast (50-200 years).
  3. Pioneer: Grasses/Weeds.
  • Example: Burnt forest or abandoned farm.

31. Critical Thinking: "The Climax Community is stable."

• Analyze: What does "stable" mean in this context? Does it mean nothing changes, or that it is in equilibrium with the environment? What happens if the climate changes permanently? Answer:
• Meaning: "Stable" means it is in equilibrium with the current environment. The species composition remains relatively constant as long as the environment remains unchanged. It is a dynamic balance (homeostasis).
• Climate Change: If the climate changes permanently (e.g., global warming drying out a rainforest), the Climax Community will destabilize and change. It will undergo a new succession to find a new equilibrium suited to the new climate (e.g., turning into a Savanna).