O Level Biology Ecology Quiz

O-Level Biology Quiz - Ecology (Answer Key)

1. Define the term producer in the context of an ecosystem. [1]

• Answer: An organism that makes its own organic food/energy (usually via photosynthesis) from inorganic substances.
• Marking Note: Accept "plants" or "autotrophs" if context implies synthesis from sunlight/CO2.

2. State the primary source of energy for almost all ecosystems on Earth. [1]

• Answer: The Sun / Solar energy.

3. Explain why energy transfer between trophic levels is inefficient. Give two reasons for energy loss. [2]

• Answer:
  1. Energy is lost as heat during respiration/metabolism.
  2. Energy is lost in excretion/egestion (faeces/urine) or uneaten parts (bones/roots).
• Marking Note: Do not accept "energy is recycled." Energy flows and is lost; nutrients cycle.

4. Estimate the amount of energy available to the frog. [2]

• Answer: 100 kJ.
• Working:
  • Grass (10,000 kJ) $\rightarrow$ Grasshopper (10% = 1,000 kJ).
  • Grasshopper (1,000 kJ) $\rightarrow$ Frog (10% = 100 kJ).
• Marking Note: 1 mark for correct calculation steps, 1 mark for final answer.

5. Distinguish between a pyramid of numbers and a pyramid of biomass. [2]

• Answer:
  • Pyramid of numbers shows the count of individuals at each trophic level.
  • Pyramid of biomass shows the total mass (dry mass) of living material at each trophic level.
• Marking Note: Must distinguish between "number of organisms" and "mass/weight."

6. Name the process by which plants absorb carbon dioxide from the atmosphere. [1]

• Answer: Photosynthesis.

7. Identify two processes that release carbon dioxide into the atmosphere. [2]

• Answer:
  1. Respiration (by plants, animals, or decomposers).
  2. Combustion (burning of fossil fuels or biomass).
• Marking Note: Accept "decomposition" as it involves respiration by microbes.

8. Explain the role of decomposers in the carbon cycle. [2]

• Answer: Decomposers (bacteria/fungi) break down dead organic matter/waste. They respire, releasing carbon dioxide back into the atmosphere.
• Marking Note: Must mention breakdown of dead matter AND release of CO2 via respiration.

9. Describe how deforestation contributes to global warming. [2]

• Answer:
  1. Fewer trees mean less carbon dioxide is removed from the atmosphere via photosynthesis.
  2. Burning/clearing trees releases stored carbon as carbon dioxide.
• Marking Note: Both points (reduced uptake and increased release) are often required for full marks in O-Level contexts.

10. State one effect of global warming on marine ecosystems. [1]

• Answer: Coral bleaching / Rising sea levels flooding habitats / Change in species distribution.
• Marking Note: Any valid ecological impact.

11. Define biomagnification. [1]

• Answer: The increase in concentration of a substance (e.g., toxin/pesticide) in the tissues of organisms at successively higher levels in a food chain.
• Marking Note: Key concept: concentration increases up the trophic levels.

12. Explain why insecticides like DDT are more concentrated in top predators than in producers. [2]

• Answer:
  1. The substance is not easily broken down or excreted (it accumulates in fat/tissues).
  2. Predators eat many prey organisms, accumulating the toxin from all of them.
• Marking Note: Must mention accumulation/non-excretion and consumption of multiple prey.

13. Describe one negative impact of plastic waste on marine animals. [1]

• Answer: Ingestion causing blockage/starvation OR Entanglement causing injury/drowning.
• Marking Note: Specific physical harm required.

14. Suggest two methods to reduce the impact of sewage pollution on water bodies. [2]

• Answer:
  1. Treat sewage in wastewater treatment plants before discharge.
  2. Use biological treatment (bacteria) to break down organic matter.
• Marking Note: Accept "reduce fertilizer use" if context is general pollution, but question specifies sewage.

15. What is meant by sustainable development? [1]

• Answer: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
• Marking Note: Accept "using resources at a rate where they can be replaced/nature can recover."

16. Identify predator and prey. [1]

• Answer:
  • Predator: Species A
  • Prey: Species B
• Marking Note: Based on the lag effect and lower numbers typically associated with higher trophic levels, plus the inverse relationship.

17. Explain the trend in the population of Species B (Prey) between Year 2 and Year 3. [2]

• Answer: The population of Species B decreased because the population of Predator (Species A) increased, leading to higher predation rates.
• Marking Note: Must link the decrease in prey to the increase in predators.

18. Describe the process of eutrophication. [3]

• Answer:
  1. Nitrates/minerals cause rapid growth of algae (algal bloom).
  2. Algae block sunlight, causing underwater plants to die.
  3. Decomposers break down dead plants, using up oxygen via respiration, leading to death of aquatic animals (fish kills).
• Marking Note: Sequence: Nutrient increase $\rightarrow$ Algal bloom $\rightarrow$ Light blocked/Plants die $\rightarrow$ Decomposition $\rightarrow$ Oxygen depletion.

19. Explain why biodiversity is important for the stability of an ecosystem. [2]

• Answer:
  1. High biodiversity means more complex food webs.
  2. If one species declines, others can replace its role, preventing ecosystem collapse.
• Marking Note: Concept of resilience/interdependence.

20. State one potential economic disadvantage of a no-fishing zone. [1]

• Answer: Reduced immediate catch/fish supply for local fishermen leading to lower income.
• Marking Note: Must be an economic disadvantage (not ecological).