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GCSE Biology 06 — Ecosystems

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Topics include Ecological Organisation & Interdependence, Fieldwork Techniques & Sampling, Biodiversity & Conservation, Trophic Levels, Biomass & Energy Transfer, Nutrient Cycles: Carbon & Water, The Nitrogen Cycle, Water Pollution & Eutrophication, and Air Pollution & Climate Change.

Biology EN
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Ecological Organisation & Interdependence

The structural hierarchy of ecosystems and the complex interactions between organisms, including competition, predation, and symbiosis.

Key points

  • Levels of Organisation: Individual → Population (one species) → Community (all species) → Ecosystem (community + abiotic factors).
  • Factors affecting communities:
    * Abiotic (non-living): Light intensity, temperature, moisture levels, soil pH.
    * Biotic (living): Food availability, new pathogens, competition, predation.
  • Interdependence: Changes in one population affect others (e.g., predator-prey cycles). Removal of a keystone species can cause a trophic cascade.
  • Biotic Interactions:
    * Competition: Intraspecific (same species) vs Interspecific (different species).
    * Parasitism: One benefits, one harmed (e.g., fleas, tapeworms).
    * Mutualism: Both benefit (e.g., mycorrhizal fungi on roots, nitrogen-fixing bacteria).
  • Adaptations: Traits aiding survival (Structural, Behavioural, Functional). Extremophiles (e.g., bacteria in deep-sea vents) perform chemosynthesis without light.

Worked example

Question

Explain how the introduction of a new predator might affect a stable community.

Solution

1. Direct Effect: The predator will eat specific prey species, reducing their population size.
2. Indirect Effect: Reduced prey numbers may increase the population of the producers that the prey ate (less grazing).
3. Competition: The new predator might outcompete native predators for food, reducing native predator numbers.
4. Conclusion: This disrupts the interdependence balance, potentially reducing biodiversity.

Common pitfalls

  • Confusing 'population' (one species) with 'community' (all species).
  • Thinking abiotic factors are 'biological' (e.g., thinking predation is abiotic).
  • Assuming all competition is between different species (intraspecific competition is often fiercer).

Prerequisites

  • Basic definition of species
  • Concept of a food chain
Further resources