The Organism in the EnvironmentEdexcel IGCSE Biology: Flashcards

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Define population.

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Define population.: All the organisms of one species living in a particular habitat at a particular time.
Define community.: All the populations of different species living and interacting in a habitat.
Define ecosystem.: A community of organisms interacting with each other and with the non-living (abiotic) parts of their environment.
What is a habitat?: The place where an organism lives.
What is a quadrat used for?: To sample the number or type of organisms in a defined area of a habitat, allowing population size to be estimated.
Why must quadrats be placed randomly?: To avoid bias and get a representative, reliable estimate of population size or species distribution.
How is total population size estimated from quadrat data?: Calculate the mean number of individuals per quadrat, then multiply by (total habitat area divided by quadrat area).
What is biodiversity?: The variety of different species living in an area.
What is a transect, and what does it show?: A line along which quadrats are placed at intervals, used to show how species distribution changes across an area.
Give three examples of abiotic factors.: Light intensity, temperature and water/moisture availability (also pH and oxygen/CO2 concentration).
Give three examples of biotic factors.: Predation, competition and disease (also food availability).
What is competition?: The struggle between organisms for a limited resource, such as food, light, space or mates.
How does an increase in predator numbers typically affect prey population size?: It reduces the prey population size, as more prey individuals are caught and eaten.
Give an example of how an abiotic factor can cause a biotic effect.: A drought (abiotic) reduces plant growth, which reduces food availability for herbivores (a biotic knock-on effect).