Populations & Sustainability — A-Level Biology Revision

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What is Populations & Sustainability?

Ecology at A-Level involves studying populations, communities, and the ecosystems they inhabit. Key concepts include how populations are structured, how they grow, and the factors that limit their size, such as carrying capacity. Sustainability focuses on managing ecosystems to ensure the long-term survival of species and the maintenance of biodiversity, often exploring human impacts and conservation efforts.

Board notes: Population dynamics, succession, and conservation are core components of all A-Level Biology specifications (AQA, Edexcel, OCR). The specific case studies used to illustrate these concepts, such as the management of a particular ecosystem, may differ between the boards.

Worked example

Common mistakes

• 1Confusing density-dependent and density-independent limiting factors. Density-dependent factors, like competition and predation, have a greater effect as population density increases. Density-independent factors, such as natural disasters or climate change, affect populations regardless of their density.
• 2Misinterpreting population growth curves. The initial exponential growth (J-shaped curve) is often slowed by limiting factors, leading to a logistic growth pattern (S-shaped curve) where the population size stabilises around the carrying capacity.
• 3Not understanding the process of succession. Succession is the predictable and orderly change in the composition or structure of an ecological community over time. Primary succession occurs on newly formed land, while secondary succession occurs on land that has been previously occupied.

Populations & Sustainability exam questions

Exam-style questions for Populations & Sustainability with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is carrying capacity?

  Carrying capacity (K) is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available.

• What is the difference between a community and an ecosystem?

  A community is all the different populations of different species living and interacting in an area. An ecosystem includes the community of living organisms (biotic factors) along with the non-living components of their environment (abiotic factors).