A Level H1 Biology Ecology Quiz

A-Level Biology H1 Quiz - Ecology – Answer Key

Total marks: 40

Section A

1. Definition: The role and position an organism has in its environment, including its interactions with other organisms and its use of resources. [1]
Example: (any valid, e.g.) A barn owl occupies the niche of a nocturnal predator of small mammals. [1]
(Accept other suitable definitions and examples.)

2. (a) Any two abiotic factors: temperature, light intensity, water availability, pH, salinity, wind, etc. [1 mark each, 2 total]
(b) Explanation linking the chosen factor to population limits. Example: Low temperature can slow enzyme activity in poikilotherms, reducing metabolic rate and reproductive success, thus limiting population growth. [2]
(Award 1 mark for stating the limiting mechanism, 1 mark for linking it to population size.)

3. Energy passes through the ecosystem from producers to consumers and is eventually lost as heat; energy cannot be recycled back to the sun or producers. [1] Therefore, the flow is always one-way from the sun/producers upwards. [1]
(Accept: energy enters as sunlight, is transferred along food chains, and is ultimately dissipated as heat.)

4. Biomass [1]

5. Gas: carbon dioxide (or methane, water vapour). [1 for name] Effect: it traps heat/infrared radiation in the atmosphere, leading to warming. [1 for correct effect]
(If only name given, no mark for effect; total 1 mark.)

Section B

6. (a) Algae [1]
(b) Water flea (or any primary consumer from food web) [1]

7. (a) P: Nitrogen fixation [1]
Q: Nitrification [1]
(b) Nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonium compounds (NH₄⁺) by nitrogen-fixing bacteria (e.g., Rhizobium) or by lightning. [1 for any correct description]
(c) Nitrifying bacteria oxidise ammonium compounds to nitrites and then to nitrates, making nitrogen available to plants. [1]

8. Any two of the following (1 mark each):

• Deforestation reduces the number of trees, which absorb CO₂ for photosynthesis, leading to higher atmospheric CO₂.
• Burning of forests releases stored carbon as CO₂.
• Decomposition of dead plant material releases CO₂ back to the atmosphere.
• Destruction of forest soils releases carbon from organic matter.
  (Accept other valid points.)

9. Carrying capacity [1]

10. Any one advantage, e.g.: Biological control agents are specific to the pest and do not harm other organisms; pests do not develop resistance as quickly; it does not leave chemical residues. [1]

Section C

11. (a) 200 individuals (or as indicated on graph) [1]
(b) Any two limiting factors: food shortage, predation, disease, competition, limited space/ nesting sites, etc. [2]

12. (a) The CO₂ concentration has steadily increased over the years 1960–2020. [1] The rate of increase appears to be accelerating/ greater in recent decades. [1]
(Accept: overall upward trend with specific data reference.)
(b) Any valid reason: increased burning of fossil fuels, deforestation reducing CO₂ uptake, industrial processes, increased vehicle emissions, etc. [1 for reason, 1 for explanation linking to CO₂ release.]

13. Biodiversity is the variety of living organisms in an ecosystem, including genetic diversity, species diversity, and ecosystem diversity. [1]

14. Any valid method: Simpson’s diversity index, quadrat sampling with species identification, transect line sampling, mark–release–recapture (for animals), etc. [1]

15. Any benefit: provides resources (food, medicine), ecosystem services (pollination, water purification), cultural/aesthetic value, stability of ecosystems, etc. [1]

Section D

16. Discuss impacts; 4 marks. Award for:

• Increased sea temperature causes coral bleaching (loss of symbiotic zooxanthellae), leading to coral death and reef degradation.
• Ocean acidification (due to more CO₂ dissolving) reduces calcification, weakening coral skeletons.
• Rising sea levels may alter light availability for photosynthesis.
• Changes in storm intensity can physically damage reefs.
• Loss of coral reefs reduces biodiversity, fish habitats, and coastal protection.
  (Award 1 mark for each distinct, well-explained impact up to 4.)

17. Greenhouse gases (e.g., CO₂, methane) absorb and re-emit infrared radiation emitted by the Earth’s surface. [1] This traps heat in the atmosphere, reducing heat loss to space. [1] The enhanced greenhouse effect (due to increased gas concentrations from human activities) leads to greater warming, i.e., global warming. [1]

18. A trophic level is the position an organism occupies in a food chain, determined by its feeding relationship. [1]

19. Energy is lost at each trophic level (e.g., through respiration, heat, undigested material), so only a small percentage (about 10%) is transferred to the next level. [1] After a few transfers, insufficient energy remains to support another level, limiting the length to about 4–5.

20. Any realistic action: reduce energy use, use public transport, recycle, adopt a plant-based diet, reduce meat consumption, use energy-efficient appliances, plant trees, etc. [1]

(Total: 40 marks)