Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

4.1.4Ecology & the Environment

Practical: Investigating the Distribution of Organisms — Edexcel International GCSE Biology 4BI1 Revision Notes & Topical Questions

5 min read 5 parts Lesson 5 of 7 Unit quiz

📚 Edexcel International GCSE Biology 4BI1 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 5Sampling with Quadrats

4.1.4 Practical: Investigating the Distribution of Organisms

A quadrat is a square frame that marks out a small, known area so organisms inside can be counted.

1
Lay out two tape measures at right angles to mark out a survey area, for example 10 m by 10 m.
2
Use a random number generator to pick x and y coordinates, then place the quadrat at that point.
3
Count the number of each species of plant inside the quadrat, using a key to identify species you do not know.
4
Repeat for at least 10 quadrats in the area and then do the same in the second survey area.
5
Calculate the mean number per quadrat, or per square metre, for each area and compare them.

Part 2 of 5Interpreting Results

Different areas often hold different organisms because conditions are not the same.

Biodiversity
  • The number of different species in an area gives an indication of its biodiversity;
    • more species means higher biodiversity.
Distribution
  • Where organisms are found, which can be compared between areas or along a transect from one habitat to another.
Abiotic factors
  • Light intensity, temperature, water availability, soil pH and mineral content all affect which species can survive.
Biotic factors
  • Competition, predation and food supply from other organisms also limit where a species lives.
Limit of method
  • Counting species alone does not show how many individuals of each species there are.

Part 3 of 5Reliability and Evaluation

Reliability and Evaluation
Random placement
  • Random coordinates avoid bias, such as choosing the most crowded patches, so the sample is representative.
Enough samples
  • Using at least 10 quadrats per area and a mean reduces the effect of chance and anomalies.
Missed organisms
  • Small plants can hide under leaves, so move foliage carefully and count only if more than half is inside the quadrat.
Fair comparison
  • The same size of quadrat, time of day, season and sampling method must be used in both areas.

Part 4 of 5Worked Example

Question

  • Over 10 quadrats of 1 m² placed in a shaded area, 52 daisy plants were counted in total.
  • Calculate the mean number per quadrat and estimate the number in a 400 m² area.

  1. Mean per quadrat = 52 ÷ 10 = 5.2 plants per m².
  2. Estimated population = 5.2 × 400 = 2080 plants.

Answer

  • About 2080 daisy plants;
    • this is an estimate that assumes the sample is representative.

Part 5 of 5Exam Checklist & Tips

4.1.4 – Key Points for the Exam

  • Quadrat A square frame used to sample a known area.
  • Biodiversity The number of different species in an area.
  • Abiotic factor A non-living factor in the environment, such as light or temperature.
  • Biotic factor A living factor in the environment, such as predation or competition.
  • Random sampling Choosing sample positions by chance to avoid bias.

Common Mistakes

  • Placing quadrats where organisms look most numerous, which creates bias.
  • Using only one or two quadrats and treating the result as typical of the whole area.
  • Mixing up abundance, the number of individuals, with biodiversity, the number of species.
  • Forgetting to keep the quadrat size and sampling method the same in both areas.

Last updated:

\n