Secondary 4 Combined Science Biology Ecology Quiz

Answer Key - Secondary 4 Combined Science Biology Quiz: Ecology

1. Definition of Ecosystem

• A community of interacting organisms and their physical (abiotic) environment. [1]

2. Primary Energy Source

• The Sun / Solar energy. [1]

3. Population vs. Community

• Population: A group of organisms of the same species living in the same area at the same time. [1]
• Community: All the populations of different species living and interacting in the same area. [1]

4. Abiotic Factor

• Example: Dissolved oxygen / Temperature / pH. [1]
• Explanation: If dissolved oxygen is too low, fish may suffocate or migrate to other areas. [1]

5. Role of Decomposer

• They break down dead organic matter/waste. [1]
• This recycles essential nutrients (e.g., nitrogen, phosphorus) back into the soil/water for producers to use. [1]

6. Trophic Level Limit

• Energy is lost at each trophic level (approx. 90% loss). [1]
• Energy is lost as heat during respiration, excretion, or as unconsumed parts. [1]
• Eventually, there is insufficient energy remaining to support another viable population of predators. [1]

7. Food Chain vs. Food Web

• Food chain: A linear sequence of organisms through which energy is transferred. [1]
• Food web: A complex network of interconnected food chains showing multiple feeding relationships. [1]

8. Energy Calculation

• Producer: 10,000 kJ $\rightarrow$ Primary Consumer: 1,000 kJ $\rightarrow$ Secondary Consumer: 100 kJ. [1]
• Answer: 100 kJ. [1]

9. Energy Loss

• Heat loss during respiration. [1]
• Energy lost in feces/excretion or undigested material. [1]

10. Carbon Removal

• Photosynthesis. [1]

11. Combustion

• Burning of fossil fuels or biomass. [1]
• Releases stored carbon (in the form of $\text{CO}_2$) back into the atmosphere. [1]

12. Nitrogen Bacteria

• Nitrifying bacteria: Convert ammonia into nitrates. [1] OR Nitrogen-fixing bacteria: Convert atmospheric nitrogen into nitrates. [1]
• This makes nitrogen available for plant uptake. [1]

13. Water Cycle Closed System

• The total amount of water on Earth remains constant. [1]
• Water only changes state (liquid, gas, solid) and moves between reservoirs; it does not leave the planet. [1]

14. Primary Consumer Decrease

• Producers: Population may increase due to reduced grazing pressure. [1]
• Secondary Consumers: Population may decrease due to lack of food/starvation. [1]
• Result: Imbalance in the ecosystem/disruption of the food web. [1]

15. Biodiversity

• The variety of different species of organisms within a particular habitat or ecosystem. [1]

16. Importance of Biodiversity

• Increases ecosystem resilience (better ability to recover from disasters). [1]
• Ensures a more stable food web (alternative food sources if one species declines). [1]

17. Eutrophication Process

• Fertilizers wash into the lake $\rightarrow$ increase in nutrient levels (nitrates/phosphates). [1]
• This causes an algal bloom (rapid growth of algae on the surface). [1]
• Algae block sunlight, killing plants below $\rightarrow$ bacteria decompose dead plants/algae using up dissolved oxygen. [1]
• Low oxygen levels (hypoxia) lead to the death of fish and other aquatic animals. [1]

18. Non-native Species

• Positive: May provide a new food source for local predators or fill an empty niche. [1]
• Negative: May outcompete native species for resources or prey on native species without natural predators. [2]

19. Sustainable Deforestation Methods

• Selective logging (cutting only mature trees). [1]
• Reforestation/Afforestation (planting new trees to replace those cut). [1]

20. Carbon Farming Limitation

• Often involves "monoculture" (planting only one species of tree). [1]
• This reduces habitat variety and species richness. [1]
• It cannot replace the complex biodiversity of a natural forest. [1]