O Level Biology Ecology Quiz

O-Level Biology Quiz - Ecology (Answer Key)

Section A

1. Producer: An organism (usually a green plant or algae) that synthesizes its own organic nutrients from inorganic substances using light energy via photosynthesis. [1]
2. Primary Source: The Sun. [1]
3. Difference: A food chain is a linear sequence of organisms through which nutrients and energy pass [1]; a food web is a network of interconnected food chains showing the complex feeding relationships in an ecosystem [1]. [2]
4. Organism: Phytoplankton. [1]
5. Non-cyclical: Energy is lost as heat to the environment at each trophic level [1] and cannot be reused by producers; it must be constantly replenished by the sun [1]. [2]
6. Role: Decomposers break down dead organic matter [1], releasing carbon dioxide back into the atmosphere via respiration [1]. [2]
7. Biodiversity: The variety of different species of organisms in a particular habitat or ecosystem [1]. High biodiversity ensures that if one species declines, others can fill the ecological niche, maintaining ecosystem stability [1]. [2]

Section B

8. Calculation: 10 kJ [1]. Explanation: Using the 10% rule, energy decreases by 90% at each level: Grass (10,000) $\rightarrow$ Grasshopper (1,000) $\rightarrow$ Frog (100) $\rightarrow$ Snake (10) [2]. [3]
9. Energy Loss:
   • Lost as heat during respiration [1].
   • Lost in undigested materials/faeces [1].
   • Not all parts of the organism are consumed (e.g., bones, roots) [1]. [3]
10. Comparison: Pyramid of numbers shows the count of individuals [1]; pyramid of biomass shows the total dry mass of organic matter [1]. Inverted when a single large producer (e.g., one oak tree) supports many small primary consumers (e.g., aphids) [1]. [3]
11. Biomagnification: Persistent chemicals (insecticides) are absorbed by producers [1]. They are not metabolized or excreted and accumulate in tissues [1]. As they move up the food chain, the concentration increases at each trophic level [1], reaching toxic levels in top predators [1]. [4]
12. Greenhouse Effect: Combustion releases $\text{CO}_2$ [1]. $\text{CO}_2$ is a greenhouse gas that traps infrared radiation/heat [1] reflecting off the Earth's surface, leading to an increase in global temperature [1]. [3]
13. Carbon Sinks: Forests absorb more $\text{CO}_2$ via photosynthesis than they release via respiration [2]. Deforestation removes these sinks, increasing atmospheric $\text{CO}_2$ [1] and often releasing stored carbon if trees are burned [1]. [4]
14. Sewage/Fish: Sewage increases nutrient levels (nitrates/phosphates) [1] $\rightarrow$ causes algal bloom [1] $\rightarrow$ algae die and are decomposed by aerobic bacteria [1] $\rightarrow$ dissolved oxygen is depleted, causing fish to suffocate/die [1]. [4]

Section C

15. Mangrove Adaptations:
    • Pneumatophores (aerial roots) to absorb oxygen from air in waterlogged soil [2].
    • Salt-excreting glands in leaves or ultrafiltration in roots to manage high salinity [2]. [4]
16. Non-native Predator: The predator may have no natural enemies, leading to rapid population growth [1]. It competes with native predators for the same prey [1], potentially driving them to extinction [1]. Over-predation of native prey can collapse the lower trophic levels [1], destabilizing the entire web [1]. [5]
17. Balance: Photosynthesis removes $\text{CO}_2$ and releases $\text{O}_2$ [2]; Respiration removes $\text{O}_2$ and releases $\text{CO}_2$ [2]. Together they create a cycle that keeps atmospheric concentrations stable. [4]
18. Sustainable Methods:
    • Selective logging: Only harvesting mature trees to allow the canopy to regenerate [2].
    • Ecotourism: Providing economic value to standing forests to prevent clearing for agriculture [2]. [4]
19. Comparison:
    • Coral Reefs: Warming leads to coral bleaching (expulsion of zooxanthellae), destroying the habitat for thousands of species [2.5].
    • Polar: Melting ice caps destroy hunting grounds for apex predators (e.g., polar bears) and alter ocean currents [2.5]. [5]
20. Evaluation: The statement is incorrect [1]. This is known as a "trophic cascade" [1]. Without the top predator, the population of secondary consumers (herbivores) increases rapidly [1]. These herbivores then over-consume the producers [1], leading to a drastic decline in plant biomass [1] and potentially causing ecosystem collapse [1]. [6]