AQA GCSE Biology · Ecology
Field investigations required practical
Measure the population size of a common species in a habitat, and use sampling to investigate how a factor affects its distribution.
Random quadrats give a fair estimate of how many of a plant there are in a whole field. A transect shows how the number changes along a line, for example moving out of a tree’s shade.
Equipment
- Quadrat (0.5 m × 0.5 m)
- Two tape measures (to make a grid, or for a transect line)
- Random number generator (or random number table)
- Light meter
- Clipboard and recording sheet
Variables
- Independent you change
- Distance from the tree (along the transect)
- Dependent you measure
- Number of daisies in each quadrat
- Control you keep the same
- Same quadrat size
- Same species counted
- Same counting rule for plants on the edge
- Sampled on the same day
Method
- 1
Random sampling: lay two tape measures at right angles along two edges of the field.
- 2
Use random numbers as coordinates and place the quadrat there, so the sample isn’t biased.
- 3
Count the daisies inside the quadrat. Repeat for at least 10 quadrats.
- 4
Transect: run a tape measure from the base of the tree out into the open field.
- 5
Place a quadrat every 2 m along the line, count the daisies and measure the light intensity.
- 6
Work out the mean per quadrat and estimate the population of the whole field.
Worked example
A transect from a tree trunk out into the field.
| Distance from tree (m) | Light intensity (lux) | Daisies per quadrat |
|---|---|---|
| 0 | 1 200 | 0 |
| 2 | 2 600 | 1 |
| 4 | 5 100 | 3 |
| 6 | 8 400 | 6 |
| 8 | 10 900 | 8 |
| 10 | 11 300 | 9 |
Working
Random quadrats: 3, 5, 0, 2, 4, 6, 1, 3, 2, 4 daisies → mean = 30 ÷ 10 = 3.0 per quadrat
Quadrat area = 0.5 × 0.5 = 0.25 m², so 3.0 ÷ 0.25 = 12 daisies per m²
Field = 20 m × 30 m = 600 m², so population ≈ 12 × 600 = 7 200 daisies
Conclusion
There are about 7 200 daisies in the field. Along the transect, more daisies grow further from the tree, where light intensity is higher, because daisies need light for photosynthesis.
Risks
- Allergies, stings or thornsWear gloves and check for allergies to plants or insects.
- Water, slopes or uneven groundStay in safe areas and work in pairs.
- Animal waste on the groundWash hands afterwards.
Common mistakes
- Choosing where to put the quadrat. Throwing it or picking spots gives a biased sample; use random coordinates.
- Forgetting to scale up correctly. Convert the mean per quadrat to per m² first, then multiply by the total area.
- Using random sampling to study change across a habitat. Use a transect to see how distribution changes along a line.
Better results
- Sample more quadrats so the mean is more representative.
- Decide a rule for plants on the edge of the quadrat (e.g. count those touching the top and left edges only).
- Take several transects in different places and calculate a mean at each distance.
Launching November 2026
7 exam questions on this practical.
Practise the method, the variables, the maths and what the results mean, then revise the Ecology flashcards. It opens to students soon: join the waitlist and we’ll email you once, when it does.