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Unit 2 - Quadrat Sampling

Ecology is the study of organisms in their habitats. The distribution of the organisms in a particular habitat can be affected by such physical factors as light, shelter from the wind and temperature. In order to try to make a scientific analysis of the organisms and their distribution in a habitat, quadrat sampling and line transects are useful tools. This GCSE Biology quiz is all about quadrat sampling.

Quadrats provide quantitative data either as numbers of individuals or as percentages. They are generally square, wire frames that are 50 cm by 50 cm and they can be used to estimate or count plants and slow moving animals. Their main limitation is that, due to their size, quadrats can only really be used to study the ecology of habitats where trees and bushes are widely spread or completely absent.

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Quadrat sampling consists of randomly placing a quadrat on the ground in the area to be sampled. The position of the quadrat must not be chosen by the experimenter. Numbers and types of plants and animals can then be estimated for the whole habitat by counting them in the individual quadrats. The method is very useful as it is quick and easy to do but needs to be used with care to give valid results. When using quadrat sampling, either actual numbers can be counted or the percentage area covered by each species of plant is estimated. The results can then be scaled up to the area of the area being studied. If the total area of habitat is 200 square metres and the total area sampled using quadrats was 10 square metres, the quadrat count just needs multiplying by 20 to give a result for the full habitat.

Where the environment is not uniform, analysis along a line transect can also be carried out to establish gradual changes (across a field that is boggy at one side but dry at the other for example). A relationship between the number of organisms and the environmental conditions can be worked out using this method.

Try this quiz to see how much you know about using quadrat sampling when studying the ecology of habitats.

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  1. What is the name for sampling along a line across the area of interest in the field?
    This helps ecologists measure gradual changes from one side of a habitat to the other
  2. Which of these is an abiotic factor?
    Some plants are adapted to growing in low light conditions - they have large leaves and high levels of chlorophyll
  3. What are abiotic factors?
    Examples are temperature and humidity
  4. Lichens can be found growing on quite exposed walls and on rocks. This is because they are adapted to withstand...
    They can survive long periods without water. They are called composite organisms because they are a symbiotic combination of fungus with an algae or cyanobacteria
  5. What are biotic factors?
    Biotic factors include competition and predation
  6. Which of the following factors could limit the distribution of moss?
    That's because mosses are adapted to a moist environment
  7. In a field, why would there be very few daisies under a tree?
    The ground under a tree is also low in moisture and nutrients as the tree removes both for its own use
  8. What do we call the place where an organism lives?
    Each habitat has a unique set of plants and animals that are adapted for life there
  9. What do we call the square frame, usually 0.5m by 0.5m, used in sampling organisms?
    It is placed randomly in the field
  10. How would you estimate the population of daisies in a field?
    Just throwing a quadrat and hoping for the best is not random sampling. Scientists divide the field into coordinates and use a random number generator to select the sampling sites

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