A Level H2 Biology Ecology Quiz

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A-Level Biology H2 Quiz - Ecology

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 55

Duration: 60 Minutes
Total Marks: 55

Instructions:

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

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Section A: Ecosystem Dynamics and Energy Flow (Questions 1-7)

1. Define the term ecosystem and distinguish between a community and a population. [3]
   
   
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2. Explain why the energy available to higher trophic levels in a food chain is significantly lower than that available to primary producers. [3]
   
   
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3. With reference to the concept of trophic efficiency, explain why most terrestrial food chains are limited to 4 or 5 trophic levels. [3]
   
   
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4. Describe the process of eutrophication, starting from the runoff of nitrogenous fertilizers into a freshwater lake. [4]
   
   
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5. Compare the roles of detritivores and saprobes in the nutrient cycling of an ecosystem. [3]
   
   
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6. Explain how the process of mineralization contributes to the availability of nitrates for plant uptake. [2]
   
   
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7. Discuss the impact of a significant decrease in the population of primary consumers on the biomass of primary producers and tertiary consumers. [4]
   
   
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Section B: Population Dynamics and Interactions (Questions 8-14)

8. Distinguish between density-dependent and density-independent factors that regulate population growth. Provide one example for each. [4]
   
   
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9. Describe the characteristics of a population exhibiting logistic growth and explain the significance of the carrying capacity ($K$). [3]
   
   
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10. A population of rabbits shows an exponential growth phase. Explain the conditions necessary for this type of growth to occur. [2]
    
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11. Explain the difference between interspecific competition and intraspecific competition. Which is generally more intense and why? [3]
    
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12. Describe the relationship between a remora fish and a shark. How does this differ from a mutualistic relationship? [3]
    
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13. In a predator-prey relationship, explain why the population of the predator typically lags behind the population of the prey. [3]
    
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14. Explain the concept of a niche and describe how competitive exclusion occurs when two species occupy the same niche. [4]
    
    
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Section C: Biodiversity and Environmental Issues (Questions 15-20)

15. Define biodiversity and explain why high genetic diversity within a species is critical for its survival during environmental change. [3]
    
    
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16. Explain how the process of speciation can occur in a population that has been geographically isolated. [4]
    
    
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17. Discuss the effect of increased atmospheric $\text{CO}_2$ concentrations on the distribution of plant species in alpine regions. [3]
    
    
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18. Describe how the introduction of an invasive species can lead to a decrease in the overall biodiversity of a native ecosystem. [3]
    
    
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19. Explain the relationship between habitat fragmentation and the "edge effect," and how this impacts the survival of interior-forest species. [4]
    
    
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20. Evaluate the effectiveness of ex-situ conservation (e.g., seed banks) compared to in-situ conservation (e.g., nature reserves) in maintaining biodiversity. [4]
    
    
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Answer Key - A-Level Biology H2 Quiz: Ecology

1. Ecosystem: A biological community of interacting organisms and their physical environment. (1) Population: 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 a particular area. (1)

2. Energy is lost at each trophic level (1). Loss occurs via heat during respiration (1), excretion of undigested material (faeces), or death of organisms without being consumed (1).

3. Trophic efficiency is typically low (~10%) (1). Only a small fraction of energy is incorporated into the biomass of the next level (1). Eventually, the energy remaining is insufficient to support another viable population of tertiary/quaternary consumers (1).

4. Runoff leads to high nutrient levels (nitrates/phosphates) in water (1) $\rightarrow$ Algal bloom (rapid growth of algae) (1) $\rightarrow$ Algae block sunlight, killing submerged plants $\rightarrow$ Decomposition of dead plants/algae by aerobic bacteria (1) $\rightarrow$ Depletion of dissolved oxygen (hypoxia) $\rightarrow$ Death of fish and other aquatic animals (1).

5. Detritivores: Animals that ingest dead organic matter (e.g., earthworms) (1). Saprobes: Organisms (fungi/bacteria) that secrete enzymes externally to digest organic matter (1). Both break down complex organic molecules into simpler inorganic nutrients (mineralization) (1).

6. Decomposers break down organic nitrogen (proteins/amino acids) from dead matter (1) into inorganic ammonium ions ($\text{NH}_4^+$), which are then nitrified into nitrates ($\text{NO}_3^-$) for plant uptake (1).

7. Primary Producers: Biomass increases because there is less grazing pressure/herbivory (2). Tertiary Consumers: Biomass decreases because the food source (secondary consumers, who rely on primary consumers) declines, leading to starvation or migration (2).

8. Density-dependent: Factors whose effect varies with population density (e.g., competition for food, disease, predation) (2). Density-independent: Factors that affect populations regardless of density (e.g., volcanic eruption, sudden frost, floods) (2).

9. Logistic Growth: Growth starts exponentially but slows as the population approaches the carrying capacity (1). Carrying Capacity ($K$): The maximum population size that a particular environment can sustain indefinitely given the available resources (2).

10. Abundant resources (food, space) (1) and absence of limiting factors such as predators or disease (1).

11. Interspecific: Competition between different species (1). Intraspecific: Competition between individuals of the same species (1). Intraspecific is more intense because individuals have identical niches and requirements for the same limited resources (1).

12. Commensalism: Remora benefits (transport, food scraps), shark is neither helped nor harmed (2). Mutualism: Both species benefit from the interaction (1).

13. Predator population depends on prey density (1). When prey increases, predators have more food, leading to higher birth rates (1). However, as predators increase, they over-consume prey, causing the prey population to crash, followed by a crash in the predator population due to starvation (1).

14. Niche: The specific role and set of environmental conditions a species requires to survive (2). Competitive Exclusion: Two species competing for the same limiting resource cannot coexist; the more efficient competitor will outcompete the other, leading to the extinction or migration of the weaker species (2).

15. Biodiversity: The variety of life in a particular habitat or ecosystem (1). Genetic Diversity: Provides a wider range of alleles/phenotypes (1). This increases the probability that some individuals possess traits that allow them to survive a new disease or changing climate, preventing total population extinction (2).

16. Geographic isolation prevents gene flow between populations (1). Different selective pressures in the two environments lead to different mutations/adaptations (1). Over time, genetic divergence occurs (1). Eventually, the populations become reproductively isolated and cannot interbreed even if reunited (1).

17. Higher $\text{CO}_2$ may initially increase photosynthetic rates (1). However, warming temperatures allow lower-altitude species to migrate upwards (1), potentially outcompeting specialized alpine species or shrinking their available habitat (1).

18. Invasive species often lack natural predators in the new environment (1). They may outcompete native species for resources or prey directly on them (1), leading to the decline or extinction of native species and reduced overall biodiversity (1).

19. Fragmentation: Breaking large habitats into smaller patches (1). Edge Effect: Changes in abiotic factors (light, wind, humidity) at the boundary of the patch (1). Impact: Interior species are sensitive to these changes and lose "core" habitat, increasing vulnerability to predators or dehydration (2).

20. Ex-situ: Effective for preventing immediate extinction of critically endangered species; allows controlled breeding (2). However, it removes species from their natural evolutionary context and may lead to loss of behavioral traits (1). In-situ: Maintains the entire ecosystem and ecological interactions; allows continued co-evolution (2). However, it is harder to protect from poaching or sudden disasters (1).