Fieldwork and sampling — Edexcel GCSE Biology
Core practical using quadrats and belt transects, and how to estimate the number of organisms in an area from raw data.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Quadrats and belt transects are field-work techniques for investigating how organisms relate to their environment. Quadrats are placed randomly, using coordinates from a random number generator, to avoid bias. A belt transect places quadrats at regular intervals along a tape measure to show how a species changes along an environmental gradient, such as light intensity.
Population size is estimated by sampling, because you cannot count every organism in a large area. Use the equation: estimated population = mean number per quadrat × (total area ÷ area of one quadrat). Many randomly placed quadrats give a more reliable estimate, and percentage cover is used for plants that are hard to count, such as grass.
Exam questions
3 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
7 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecosystems and material cycles on one page, so you can see where this subtopic fits.
Open the mind mapPractical sheet
Method, variables, risks and a results table, with questions to answer.
Print it
Free PDFs to print or save.
Quick check questions
How do you stop bias when placing quadrats?
Show answer
Use random numbers to choose the coordinates.
What does a belt transect show?
Show answer
How the distribution of organisms changes along an environmental gradient.
Write the equation for estimating a population from quadrat data.
Show answer
Mean per quadrat × (total area ÷ area of one quadrat).
Why use many quadrats?
Show answer
To give a more representative and reliable sample, and reduce the effect of anomalies.
Frequently asked questions
How do you use a quadrat to estimate population size?
Place many quadrats randomly in the area and count the chosen species in each one. Find the mean number per quadrat, then multiply it by the total area divided by the area of one quadrat. For example, a mean of 4 daisies in 0.25 m² quadrats across a 100 m² field gives 1600 daisies.
Why should quadrats be placed randomly?
Quadrats should be placed randomly to avoid bias, so the samples represent the whole area. Mark out the area with two tape measures at right angles and use a random number generator to pick coordinates. Taking many quadrats also gives a more reliable estimate and reduces the effect of anomalies.
How do you carry out a belt transect?
Lay a tape measure in a straight line across the habitat, for example from under a tree out into open grass. Place a quadrat at regular intervals, such as every 2 m, and count the organisms in it. At each point measure an environmental factor, such as light intensity with a light meter, then plot a graph.
What is percentage cover?
Percentage cover is the percentage of a quadrat that is covered by a species. It is used for plants that are difficult to count individually, such as grass, instead of counting the number of organisms. It can be estimated in random quadrats or along a transect, and a mean calculated from the results.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026