A-Level Biology May/June 2025 Q5(c)(ii): Invasive alien species are thought to have contributed to extinctions recorded in the G…

1 answer

• ▲0
  accepted ✓

  Invasive alien species can have numerous negative effects on the ecosystem into which they are introduced. These effects can lead to a reduction in biodiversity and cause extinctions.

  • Competition: Invasive species often compete with native species for resources such as food, water, or territory. As they may occupy the same or a similar niche, this increased competition can lead to the decline and eventual extinction of the native species. (M1)

  • Predation: The introduced species may be a predator that preys on native organisms. Native prey may not have evolved defence mechanisms against this new predator, making them highly vulnerable and leading to a rapid decrease in their population size. (M1)

  • Disease: Invasive species can introduce new diseases and parasites to an ecosystem. Native species may have no immunity to these pathogens, which can result in epidemics that devastate their populations. (M1)

  • Habitat Alteration: Some invasive species can significantly change or damage the physical habitat. For example, invasive plants can outcompete native flora, altering the plant community and thereby affecting all other organisms that depend on it. Invasive animals might cause soil erosion through burrowing. (M1)

  ---

  How the marks are awarded

  • M1 — Awarded for stating that invasive species compete with native species for resources or occupy the same niche, as mentioned in the first bullet point.
  • M1 — Awarded for explaining that invasive species can act as predators, preying on native organisms, as detailed in the second bullet point.
  • M1 — Awarded for the point that invasive species can introduce new diseases or parasites to which native species lack immunity.
  • M1 — Awarded for identifying that invasive species can cause damage to or change the physical habitat, altering the environment for other species.

  Common mistakes

  • Using vague, non-scientific language like 'they upset the balance' or 'they are bad for the environment' without specifying the ecological mechanism (e.g., competition, predation).
  • Confusing ecological terms, for instance, describing predation (eating another organism) as a form of competition.
  • Only providing one or two well-explained points and then repeating them in different words, which prevents earning marks for distinct points.
  • Failing to link the effect to native species. For example, stating 'they introduce disease' is weaker than 'they introduce disease to which native species have no immunity'.

  Examiner tip: For 'discuss' questions asking for effects or reasons, structure your answer by providing several distinct, clearly explained points to maximise your marks.

  ---

  AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →

  @markscheme_answers

Your answer

Sign in to answer this question.