CLEP Biology Ecosystems and Energy Flow 3 — Questions and Answers
Question 1: If a grassland ecosystem has 10,000 kcal available at the producer level, approximately how many kcal are available to secondary consumers, assuming 10% efficiency at each transfer?
- 1,000 kcal
- 100 kcal (Correct answer)
- 10 kcal
- 1 kcal
Correct answer: 100 kcal
At 10% efficiency, 10,000 kcal → 1,000 kcal (primary consumers) → 100 kcal (secondary consumers).
Question 2: Mutualistic mycorrhizal fungi associated with plant roots primarily benefit the plant by:
- Fixing atmospheric nitrogen directly for the plant
- Increasing the plant's ability to absorb water and phosphorus (Correct answer)
- Protecting the plant from herbivore damage
- Converting soil ammonia into nitrates
Correct answer: Increasing the plant's ability to absorb water and phosphorus
Mycorrhizal fungi greatly extend the root surface area, enhancing uptake of water and minerals, especially phosphorus, in exchange for plant carbohydrates.
Question 3: Which of the following best illustrates a bottom-up trophic cascade?
- Removal of wolves leads to overgrazing by deer, reducing plant cover
- Fertilizer runoff increases algae growth, which supports more fish (Correct answer)
- Overfishing of tuna allows jellyfish populations to explode
- Disease kills top predators, releasing prey from predation pressure
Correct answer: Fertilizer runoff increases algae growth, which supports more fish
A bottom-up cascade starts at the producer level; nutrient addition boosts primary producers, increasing biomass at each successive trophic level.
Question 4: In the phosphorus cycle, which reservoir contains the largest amount of phosphorus on Earth?
- Ocean water
- Soil organic matter
- Rocks and sediments (Correct answer)
- Living biomass
Correct answer: Rocks and sediments
Most of Earth's phosphorus is locked in rocks and marine sediments, making it unavailable until released by weathering over geological timescales.
Question 5: An ecological pyramid of numbers can be inverted (wider at the top) when:
- Parasites are counted and each host supports many parasites (Correct answer)
- Energy transfer efficiency exceeds 20% between trophic levels
- The ecosystem is aquatic rather than terrestrial
- Producers reproduce faster than consumers
Correct answer: Parasites are counted and each host supports many parasites
A single large host organism can harbor thousands of parasites, so an inverted numbers pyramid occurs when parasites constitute the highest trophic level.
Question 6: Which statement about ecosystem respiration is correct?
- Only autotrophs contribute to ecosystem respiration
- Ecosystem respiration includes both autotroph and heterotroph respiration (Correct answer)
- Ecosystem respiration only occurs during nighttime hours
- Ecosystem respiration decreases carbon dioxide in the atmosphere
Correct answer: Ecosystem respiration includes both autotroph and heterotroph respiration
Ecosystem respiration is the sum of all aerobic respiration by producers, consumers, and decomposers, releasing CO₂ back into the atmosphere.
Question 7: The ratio of Net Primary Productivity to Gross Primary Productivity (NPP/GPP) tends to be lowest in which environment?
- Cold tundra ecosystems
- Warm tropical ecosystems (Correct answer)
- Temperate forests in summer
- Deep ocean benthic zones
Correct answer: Warm tropical ecosystems
In warm tropical ecosystems, high temperatures accelerate plant respiration rates, consuming a larger fraction of GPP, resulting in a lower NPP/GPP ratio.
CLEP Biology Ecosystems and Energy Flow 3
If a grassland ecosystem has 10,000 kcal available at the producer level, approximately how many kcal are available to secondary consumers, assuming 10% efficiency at each transfer?