CAIE A Level Biology 9700 · Classification, biodiversity and conservation

Classification, biodiversity and conservation: explain question

Explain4 marksStandard

A student uses the mark-release-recapture method with the Lincoln index to estimate the population size of a species of snail in a park. The formula for the Lincoln index is $N = \frac{n_1 \times n_2}{m}$ , where:

$n_1$ = number of snails captured and marked in the first sample,
$n_2$ = number of snails captured in the second sample,
$m$ = number of marked snails in the second sample.

Explain the importance of random sampling in this method.

How this question is marked

4 marks, so the mark scheme is looking for about 4 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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