CAIE A Level Biology 9700 · Classification, biodiversity and conservation

Classification, biodiversity and conservation: explain question

Explain6 marksChallenge

A student investigated plant biodiversity in two grassland areas, X and Y. In each area, 20 quadrats of area 0.25 m² were placed using random coordinates. The table shows the number of individuals of each plant species recorded across all quadrats in each area.

Species	Area X count	Area Y count
A	45	120
B	38	15
C	42	12
D	35	8
E	40	5
Total	200	160

The formula for Simpson's index of diversity (D) is: $D = 1 - \sum (\frac{n}{N})^2$ , where $n$ is the number of individuals of a species and $N$ is the total number of individuals.

The student calculated D for area X as 0.82 and for area Y as 0.45.

Explain why the student used random sampling and what these D values indicate about biodiversity in the two areas.

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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