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A Level H2 Biology Ecology Quiz

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A Level H2 Biology AI Generated Generated by Gemma 4 31B Updated 2026-06-03

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A-Level Biology H2 Quiz - Ecology

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 60

Duration: 60 Minutes
Total Marks: 60 Marks

Instructions:

Answer all questions in the spaces provided.
Use precise biological terminology.
For calculation questions, show all working.

Section A: Energy Flow and Nutrient Cycling (Questions 1-7)

Define the term trophic level and explain why the number of trophic levels in a food chain is typically limited. [3]

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Compare the efficiency of energy transfer between primary producers and primary consumers versus the transfer between secondary and tertiary consumers. [3]

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Describe the process of eutrophication in a freshwater lake, specifically explaining the role of aerobic bacteria in the decline of fish populations. [4]

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Explain the importance of decomposers in the nitrogen cycle, specifically focusing on the process of ammonification. [3]

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With reference to the carbon cycle, explain how the process of carbon sequestration in peat bogs helps mitigate the greenhouse effect. [3]

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Distinguish between gross primary productivity (GPP) and net primary productivity (NPP). [2]

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Explain why a pyramid of numbers may not always be pyramid-shaped, whereas a pyramid of energy always is. [4]

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Section B: Population Dynamics (Questions 8-14)

Describe the characteristics of an r-selected species and explain why these traits are advantageous in unstable environments. [3]

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Explain the difference between density-dependent and density-independent factors that regulate population growth, providing one example of each. [4]

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A population of rabbits shows a logistic growth curve. Explain the biological significance of the inflection point on this curve. [3]

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Describe the relationship between a predator and prey population using the concept of coupled oscillations. [4]

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Define carrying capacity ( $K$ ) and discuss two factors that could cause $K$ to fluctuate over time in a forest ecosystem. [4]

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Explain how intraspecific competition differs from interspecific competition in terms of its impact on the niche width of a species. [3]

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Describe the competitive exclusion principle and explain how niche partitioning allows two species to coexist in the same habitat. [4]

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Section C: Biodiversity and Environmental Issues (Questions 15-20)

Explain the difference between alpha diversity and beta diversity in the context of a tropical rainforest. [3]

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Discuss how the introduction of an invasive species can lead to a decrease in the biodiversity of a native ecosystem. [4]

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Explain the concept of edge effects and how the fragmentation of a habitat increases the vulnerability of interior-dwelling species. [4]

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Describe how an increase in global atmospheric $\text{CO}_2$ concentrations can lead to ocean acidification and explain the impact on calcifying organisms. [4]

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Compare the stability of a monoculture plantation versus a polyculture forest in terms of their resilience to pest outbreaks. [3]

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Explain the role of keystone species in maintaining the structure of a community and provide an example of what happens when a keystone species is removed. [4]

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Answers

Answer Key - A-Level Biology H2 Quiz: Ecology

1. Trophic Level & Limitations [3]

Definition: The position an organism occupies in a food chain. [1]
Limitation: Energy is lost at each level (approx. 90%) via respiration, excretion, and uneaten parts. [1]
Result: Insufficient energy remains to support higher trophic levels. [1]

2. Energy Transfer Efficiency [3]

Efficiency is generally similar (approx. 10%) across levels. [1]
However, primary producers often have higher biomass, but the transfer to primary consumers is limited by indigestible matter (e.g., cellulose). [1]
Tertiary consumers often have very small populations due to the cumulative loss of energy. [1]

3. Eutrophication [4]

Nutrient runoff (nitrates/phosphates) $\rightarrow$ algal bloom. [1]
Algae block sunlight $\rightarrow$ submerged plants die. [1]
Aerobic bacteria decompose dead organic matter. [1]
Bacteria use up dissolved oxygen $\rightarrow$ hypoxia $\rightarrow$ fish suffocate/die. [1]

4. Ammonification [3]

Decomposers (bacteria/fungi) break down organic nitrogen (proteins/nucleic acids) from dead organisms/waste. [1]
This converts organic nitrogen into ammonium ions ( $\text{NH}_4^+$ ). [1]
This makes nitrogen available for nitrifying bacteria to convert into nitrates for plant uptake. [1]

5. Carbon Sequestration [3]

Peat bogs have anaerobic/waterlogged conditions. [1]
This inhibits the activity of decomposers (bacteria). [1]
Carbon remains trapped in dead organic matter instead of being released as $\text{CO}_2$ , reducing the greenhouse effect. [1]

6. GPP vs NPP [2]

GPP: Total rate at which energy is captured by producers via photosynthesis. [1]
NPP: GPP minus energy lost through respiration ( $\text{NPP} = \text{GPP} - \text{R}$ ). [1]

7. Pyramids of Numbers vs Energy [4]

Numbers: Can be inverted (e.g., one large producer tree supporting thousands of insects). [2]
Energy: Always upright because energy is lost as heat at each transfer (Second Law of Thermodynamics). [1]
Energy cannot be created; thus, the base must always be the largest. [1]

8. r-selected Species [3]

Traits: Small size, early maturity, many offspring, little to no parental care. [1]
Advantage: Rapid colonization of new/unstable habitats. [1]
High growth rate allows them to exploit resources before competition increases. [1]

9. Population Regulation Factors [4]

Density-dependent: Impact increases as population density rises (e.g., disease, competition for food). [2]
Density-independent: Impact is unrelated to density (e.g., volcanic eruption, severe frost). [2]

10. Inflection Point [3]

The point where the growth rate is at its maximum. [1]
Transition from the exponential growth phase to the decelerating growth phase. [1]
Indicates that environmental resistance (limiting factors) is beginning to significantly slow growth. [1]

11. Coupled Oscillations [4]

Prey population increases $\rightarrow$ more food for predators $\rightarrow$ predator population increases. [1]
High predator density $\rightarrow$ over-predation $\rightarrow$ prey population crashes. [1]
Lack of prey $\rightarrow$ predators starve $\rightarrow$ predator population crashes. [1]
Reduced predation $\rightarrow$ prey population recovers, restarting the cycle. [1]

12. Carrying Capacity (K) [4]

Definition: The maximum population size an environment can sustain indefinitely. [1]
Factor 1: Food availability (e.g., seasonal fruiting). [1.5]
Factor 2: Space/Nesting sites (e.g., deforestation). [1.5]

13. Intraspecific vs Interspecific Competition [3]

Intraspecific: Between members of the same species; more intense because niches are identical. [1]
Interspecific: Between different species; less intense if niches overlap only partially. [1]
Intraspecific competition often leads to stronger selection for niche specialization. [1]

14. Competitive Exclusion & Niche Partitioning [4]

Competitive Exclusion: Two species competing for the exact same resource cannot coexist; one will be eliminated. [2]
Niche Partitioning: Species evolve to use different parts of the resource (e.g., different feeding heights in a tree). [1]
This reduces competition and allows coexistence. [1]

15. Alpha vs Beta Diversity [3]

Alpha: Diversity within a specific site or local area (e.g., number of species in one plot). [1]
Beta: The variation in species composition between two different sites. [1]
High beta diversity indicates high turnover of species across a landscape. [1]

16. Invasive Species [4]

Lack of natural predators in the new environment allows rapid population growth. [1]
Outcompete native species for food/space. [1]
May prey on native species that have no evolved defenses. [1]
Leads to extinction of native species and simplified food webs. [1]

17. Edge Effects [4]

Fragmentation creates more "edges" relative to the "core" area. [1]
Edges have different microclimates (more wind, light, lower humidity). [1]
Interior species are sensitive to these changes and cannot survive at the edge. [1]
Effective habitat size is reduced more than the actual physical area loss. [1]

18. Ocean Acidification [4]

$\text{CO}_2$ dissolves in seawater $\rightarrow$ forms carbonic acid ( $\text{H}_2\text{CO}_3$ ). [1]
This dissociates, increasing $\text{H}^+$ concentration (lowering pH). [1]
$\text{H}^+$ reacts with carbonate ions ( $\text{CO}_3^{2-}$ ) to form bicarbonate ( $\text{HCO}_3^-$ ). [1]
Reduces availability of $\text{CO}_3^{2-}$ , making it harder for corals/molluscs to build $\text{CaCO}_3$ shells. [1]

19. Monoculture vs Polyculture [3]

Monoculture: Low genetic diversity; if a pest evolves to attack one plant, all are susceptible. [1]
Polyculture: High diversity; some species may be resistant, slowing the spread of the pest. [1]
Polyculture is more resilient and stable. [1]

20. Keystone Species [4]

Definition: A species that has a disproportionately large effect on its environment relative to its abundance. [1]
Example: Sea otters controlling sea urchin populations. [1]
Removal: Urchins overgraze kelp forests $\rightarrow$ loss of habitat for many other species. [1]
Result: Total collapse of the ecosystem structure/biodiversity. [1]