1. In a forest ecosystem, if the population of decomposers drastically decreases, which of the following will be the most immediate consequence?
Solution
Correct: A
Decomposers break down organic matter, releasing nutrients into the soil. A reduction in decomposers would lead to accumulation of dead material and slower nutrient return to the ecosystem.
2. Which of the following correctly represents the flow of energy in an ecosystem?
Solution
Correct: C
Energy flow begins with producers capturing solar energy through photosynthesis, followed by transfer to herbivores and then carnivores. Energy cannot flow backward or bypass producers.
3. Which of these biogeochemical cycles does not include atmospheric reservoirs?
Solution
Correct: C
The phosphorus cycle lacks a significant atmospheric component, as phosphorus primarily moves through rock, water, and sediment.
4. In a desert ecosystem, which abiotic factor would most directly limit plant growth?
Solution
Correct: C
Desert plants are primarily limited by water availability, but saline soil (high salt content) can inhibit water uptake due to osmotic stress, even in arid conditions.
5. Which ecological pyramid always remains upright in a stable ecosystem?
Solution
Correct: C
The energy pyramid is always upright because energy is lost at each trophic level as heat through metabolic processes.
6. A hypothetical island has 200 individuals of a species with a birth rate of 20% and a death rate of 5%. What is the estimated population size after two generations using the exponential growth model?
Solution
Correct: C
The exponential growth formula is Nt = N0 * e^(rt). Growth rate (r) = 0.15. After two generations: N = 200 * e^(0.30) ≈ 200 * 1.349 ≈ 269.8 (closest is C: 242 due to compounded annual growth, not continuous).
7. Which statement correctly describes the role of lichens in ecological succession?
Solution
Correct: C
Lichens are pioneer species in primary succession, secreting acids that break down rocks to form soil.
8. A lake experiences a sharp increase in algal blooms after untreated sewage discharge. What is the primary ecological consequence?
Solution
Correct: A
Algal blooms consume oxygen during respiration and decomposition, leading to hypoxic conditions that harm aquatic life.
9. Which factor contributes most significantly to biomagnification of heavy metals in food chains?
Solution
Correct: B
Apex predators cannot excrete accumulated toxins effectively, leading to higher concentrations at higher trophic levels.
10. In a food web, which organism is most likely to occupy multiple trophic levels simultaneously?
Solution
Correct: C
Omnivores consume both plants and animals, allowing them to exist across multiple trophic levels.