CAIE A Level Biology 9700 · Classification, biodiversity and conservation

Classification, biodiversity and conservation: explain question

Explain6 marksChallenge

Two grassland sites, A and B, were sampled using random quadrats. The table shows the total number of individuals of each plant species recorded across all quadrats.

Site A		Site B
Species	Count	Species	Count
Grass sp. 1	45	Grass sp. 1	120
Grass sp. 2	38	Grass sp. 2	10
Clover sp.	22	Clover sp.	5
Daisy sp.	20	Daisy sp.	3
Buttercup sp.	15	Buttercup sp.	2
Total N = 140		Total N = 140

Simpson's index of diversity (D) is given by the formula:

D = 1 - \sum \left(\frac{n}{N}\right)^2

where $n$ is the number of individuals of a species and $N$ is the total number of individuals.

For site A, $D = 0.77$ ; for site B, $D = 0.26$ .

Explain what these $D$ values indicate about the biodiversity of the two sites. Also discuss why random sampling is important when collecting data such as these for calculating Simpson's index.

How this question is marked

6 marks, so the mark scheme is looking for about 6 separate creditworthy points. Making the same point twice in different words earns it once.

Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.

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