Community Q&A
A-Level Biology May/June 2025 Q9(a): The biodiversity of an area can be assessed using a variety of sampling methods. Outlin…
A-Level Biology · Paper 9700/42 · May/June 2025 · Question 9(a) · [4 marks]
The biodiversity of an area can be assessed using a variety of sampling methods. Outline how a frame quadrat could be used to assess the biodiversity of plants in a field.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
- accepted ✓
To assess the biodiversity of plants in a field, a grid is first established using two perpendicular tape measures to form axes. A random number generator is then used to produce coordinates for where to place the quadrat, ensuring the sampling is not biased.
A frame quadrat of a known, standard area, for example 1m², is placed at the generated coordinates. Within the quadrat, a species identification key is used to identify all the different plant species present. The number of individuals of each species is then counted to determine abundance.
This process is repeated a large number of times across the field to ensure the sample is representative of the entire area. The data on species richness and abundance can then be used to calculate a quantitative measure of biodiversity, such as Simpson's Index of Biodiversity.
How the marks are awarded
- MP1 — The answer states that a quadrat of a 'known / standard, area' is used, which is a fundamental requirement for quantitative sampling.
- MP2 — Credit is given for describing a valid method of random sampling, which involves setting out a grid and using a random number generator to produce coordinates for quadrat placement.
- MP3 — A mark is awarded for outlining the data collection process, specifically mentioning the use of a 'key' to identify species and the counting of 'individuals of each species' (abundance).
- MP4 — The final mark is earned by stating the need for a 'large sample size / repeats' for reliability and/or mentioning that the results are used to 'calculate Simpson's Index of Biodiversity'.
Common mistakes
- Describing systematic sampling with a transect, which is used to investigate changes across a habitat, not to assess the biodiversity of a whole area randomly.
- Stating that quadrats are placed 'randomly' without describing a valid method, such as throwing the quadrat over one's shoulder, which is not truly random.
- Forgetting to mention how species will be identified, such as by using a key, which is a critical step in determining species richness.
- Only mentioning counting the number of species (richness) and not the number of individuals of each species (abundance/evenness), which is required for calculating an index of diversity.
Examiner tip: For any question asking to outline a practical procedure, structure your answer as a logical sequence of steps: setup, data collection, ensuring reliability, and data analysis.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
Your answer
Sign in to answer this question.