A Levels Biology (9700)•9700/11/M/J/24

Explanation
Enzyme kinetics graph axes identification
Steps:
- Enzyme-catalyzed reaction graphs typically plot rate of reaction (y-axis) against a variable factor (x-axis) like substrate concentration, pH, or temperature.
- Rate of reaction measures product formation or substrate depletion over time, always on y-axis in such plots.
- Common trends: hyperbolic for substrate concentration, bell-shaped for pH, sigmoidal then declining for temperature.
- Match option to standard pH effect on enzymes, which shows optimal pH with declining rates on either side.
Why C is correct:
- Enzyme activity follows a bell curve versus pH due to optimal ionization of active site residues, as per enzyme-substrate complex stability principles.
Why the others are wrong:
- A: Reverses axes; rate depends on substrate concentration, not vice versa.
- B: Enzyme concentration linearly increases rate, not a temperature plot; axes mismatched.
- D: Reverses axes and confuses pH with substrate; pH is environmental, not substrate quantity.
Final answer: C
Topic: Factors that affect enzyme action
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