Cambridge International AS & A Level Biology Revision
Explore Cambridge International AS & A Level Biology revision topics. This qualification is not a GCSE; the existing guide address and saved checklist are retained. Check the official specification for complete requirements.
Qualification code: 9700
Course details
Assessment For assessment details, see the official specification.
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Reviewed course guidance
Revision points, with the explanation beside them
Open a point to read what to know, how to use it in an assessment, a plain-language explanation and a self-check. Answers stay hidden until you choose to reveal them.
Options and source
Cambridge International assessment route
- AS only: Papers 1, 2, 3
- Staged A level: AS Papers 1–3, then A level Papers 4–5
- Linear A level: Papers 1–5 in one series
Syllabus overview: AS-only, staged and linear assessment routes
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There are no fully covered explanations for these selections yet. Partial support may still appear below. Use the official specification and your teacher’s guidance.
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Topic group
Reviewed requirements
- Core
Open revision guidance
What to know
- On a Michaelis–Menten rate-versus-substrate-concentration curve, Vmax is the maximum rate approached at high substrate concentration. Km is the substrate concentration associated with half Vmax in the standard model. When conditions and model are comparable, a lower Km indicates greater apparent affinity between enzyme and substrate.
What to do in an assessment
- Read Vmax from the plateau and half that rate; locate the substrate concentration at that rate to estimate Km. Compare Km values only for comparable conditions and do not confuse Km with Vmax.
In plain language
Vmax is a rate; Km is a substrate concentration. The specification uses Km to compare enzyme affinity.
Self-check
At half of Vmax, enzyme A requires 2 mmol dm⁻³ substrate and enzyme B requires 5 mmol dm⁻³. Which has the lower Km and greater apparent affinity?
Show the answer
A has the lower Km (2 mmol dm⁻³) and therefore the greater apparent affinity under comparable conditions.
Earlier topic checklist
These earlier topic ticks are separate from the reviewed points above and do not count towards that progress.
Biology topic list
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These ticks keep your earlier topic checklist. They do not count towards the new reviewed requirements above. Its numbering may be internal; use the linked references above for the exact reviewed source requirements.
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