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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
What this skill means
Quadrats are square frames placed on the ground to sample organisms in a defined area. Random sampling uses randomly generated coordinates to place quadrats. Systematic sampling places quadrats at regular intervals along a transect line to study how distribution changes across a habitat.
Quadrat sampling is the standard ecological method at IGCSE level. You need to know how to use both random and systematic (transect) sampling, calculate population estimates, and evaluate the reliability of sampling methods.
Random Sampling
Random sampling is used to estimate the population size of a species in a uniform habitat:
Lay out two long tape measures at right angles to form x and y axes along two edges of the area
Generate pairs of random numbers (using a random number generator, not by choosing positions) to use as coordinates
Place the quadrat at each set of coordinates
Count the number of the target species (or estimate percentage cover for plants that are hard to count individually)
Repeat with at least 10 quadrats (more gives a more reliable estimate)
Calculate the mean number per quadrat
Scale up: estimated population = mean per quadrat × (total area ÷ area of one quadrat)
Systematic Sampling with a Transect
A belt transect is used to study how species distribution changes across a habitat (e.g. From a pond edge to dry land, or from under a tree canopy into open grassland):
Lay a tape measure in a straight line across the area of interest
Place quadrats at regular intervals along the line (e.g. Every 2 metres)
Record the species present and their abundance (count or percentage cover) in each quadrat
Present the results as a bar chart or kite diagram showing how abundance changes with distance
This is not random: you are deliberately placing quadrats along an environmental gradient to detect patterns.
Evaluating Sampling Methods
Common evaluation points:
Sample size: more quadrats give a more reliable estimate but take more time
Quadrat size: must be appropriate for the organisms being studied (1 m² for plants, smaller for small invertebrates)
Random placement: without truly random coordinates, human bias may lead to quadrats being placed in "convenient" spots, giving unrepresentative results
Seasonal variation: results may differ depending on time of year (some species are more visible in certain seasons)
Mobile organisms: quadrats work best for non-mobile organisms (plants); mobile animals may move in or out of the quadrat during counting
Use this before submitting your answer
A complete answer is specific enough for another person to repeat or assess.
✓Use random numbers to position quadrats (not personal choice).
✓Use at least 10 quadrats for a reliable estimate.
✓Record species counts or percentage cover consistently.
✓Calculate mean per quadrat before scaling up.
✓Population estimate formula: mean per quadrat × (total area ÷ quadrat area).
✓For transects, place quadrats at regular intervals along the line.
✓State the quadrat size used (e.g. 0.25 m² or 1 m²).
Try the skill in a question (2 marks)
A student uses 10 quadrats (each 0.5 m × 0.5 m = 0.25 m²) in a field of 200 m². The mean number of dandelions per quadrat is 6. Estimate the total dandelion population. [2]
Show the answer and marking guidance
Population = mean per quadrat × (total area ÷ quadrat area) = 6 × (200 ÷ 0.25)
= 6 × 800 = 4800 dandelions
Original practice content written for this site. It is not an official Cambridge question.