COMMAND WORD · BIOLOGY
Inspect a plan, a set of data or a statement, say what holds and what does not, and back each judgement.
X is a merit or a fault because of Y.
Original question
A plan tests an enzyme at 20 °C and 22 °C, with three repeats, and concludes there is no optimum. Criticise the plan.
Annotated answer
XThe repeats, and the narrow temperature range. Merit or faultThe repeats are a merit. The range is a fault. YRepeats show scatter at those two temperatures, but 20 °C to 22 °C cannot show whether an optimum exists elsewhere.
The labels match the frame. Read them in order. This is one accurate route, not the only one.
Credit a merit when there is one. Criticism here is not only fault-finding.
Writing “the experiment should be improved” without inspecting anything.
Based on a sample question
Mark points shown after marking
Students measured the pigment released from beetroot discs at six temperatures, as a measure of membrane permeability. The graph shows each mean with its spread.
The students concluded that membrane permeability increases across the whole temperature range. Criticise this conclusion.
(5)Total for this question: 5 marks
X is the low-temperature region, and also the later rise. The spreads at 20, 30 and 40 °C overlap, so the evidence Y does not support a steady increase across that part of the range. The means at 60 and 70 °C sit clear of those earlier spreads, so a rise at the higher temperatures is still supported. The graph says nothing about temperatures that were not tested. “It is a bad conclusion” inspects nothing. A spread that does not overlap is not a statistical test.
Unit 3 sample paper. Question 3 (b)(v) asks you to criticise the conclusion that membrane permeability increases as temperature increases, using the table and the graph. Sample assessment, not a live paper.
Sample paper WBI13/01, question 3 (b)(v) (5 marks), 2017 sample assessment. Question page · Mark scheme page
