H1 Biology 8876 · Nov 2023BiologyPaper 1Commented

Paper 1 Q12 — Comparing initial rates

Kinetics — initial rate is the gradient at t = 0, read before curves level off

What the examiners said

“A significant proportion of candidates selected the incorrect option C. These candidates had not considered that the initial rate of reaction shown by curve Y was greater than the initial rate shown by curve X.”

Try the question

Two reactions give product-vs-time curves. Curve Y is steeper at the very start but both reach the same final amount of product. Which has the greater initial rate?

Examiner report: “Candidates ignored that curve Y's initial rate (gradient at t=0) was greater than X's.”

Explore — read the gradient at t = 0

Both curves reach the same final product. Toggle the tangents at the start to see that the initial rate is set by the steepness at t = 0, not by where the curve ends.

Show tangent at t=0: on

Same destination, different starting speed. Initial rate compares the tangents at the origin, not the final product or which curve finishes last.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Biology 8876 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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