BECE Photosynthesis and Ecosystems 3 — Questions and Answers
Question 1: In the carbon cycle, which process returns carbon dioxide to the atmosphere from living organisms?
- Photosynthesis
- Nitrogen fixation
- Cellular respiration (Correct answer)
- Transpiration
Correct answer: Cellular respiration
Cellular respiration in all living organisms breaks down glucose, releasing CO₂ back into the atmosphere.
Question 2: What term describes organisms such as bacteria and fungi that break down dead organic matter?
- Producers
- Primary consumers
- Decomposers (Correct answer)
- Omnivores
Correct answer: Decomposers
Decomposers break down dead organic material, recycling nutrients back into the soil for use by producers.
Question 3: Which of the following ecosystems stores the most carbon per unit area?
- Desert
- Grassland
- Tropical rainforest (Correct answer)
- Tundra
Correct answer: Tropical rainforest
Tropical rainforests have the highest density of plant biomass, making them the largest terrestrial carbon stores per unit area.
Question 4: An ecosystem loses its top predator. What is the most likely immediate effect?
- Producer populations decline
- Decomposer populations disappear
- Herbivore populations increase unchecked (Correct answer)
- Sunlight availability decreases
Correct answer: Herbivore populations increase unchecked
Without top predators, herbivore populations grow unchecked, which can lead to overgrazing and ecosystem destabilization.
Question 5: Which nutrient cycle involves both the processes of fixation and denitrification?
- Carbon cycle
- Water cycle
- Nitrogen cycle (Correct answer)
- Phosphorus cycle
Correct answer: Nitrogen cycle
The nitrogen cycle includes nitrogen fixation (N₂ → usable forms) and denitrification (nitrates → N₂ gas).
Question 6: What percentage of energy is typically transferred from one trophic level to the next?
- 1%
- 10% (Correct answer)
- 50%
- 90%
Correct answer: 10%
Only about 10% of energy is passed to the next trophic level; the rest is lost as heat through metabolic processes.
Question 7: A pond ecosystem has algae, water fleas, small fish, and large fish. If algae are drastically reduced by pollution, which population is FIRST to be directly affected?
- Large fish
- Small fish
- Water fleas (Correct answer)
- Decomposers
Correct answer: Water fleas
Water fleas are primary consumers that feed directly on algae, so they would be the first population to suffer from reduced algae.
BECE Photosynthesis and Ecosystems 3
In the carbon cycle, which process returns carbon dioxide to the atmosphere from living organisms?