A graph plots potential energy (y-axis) against the progress of a reaction (x-axis). The substrate S starts at a higher energy level than the product P. Two curves join S to P: curve X rises to a tall peak, and curve Y rises to a much lower peak. Which statement about the graph is correct?
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An enzyme speeds up a reaction by lowering its activation energy, the peak the substrate must climb, so Y is the catalysed path. Since S and P are unchanged, the overall energy released is the same.
- A.
Enzymes lower the activation energy barrier, so the lower peak Y belongs to the catalysed reaction.
- B.
Both curves start at S and end at P, so the energy difference between them is the same with or without the enzyme.
- D.
When the product has less energy than the substrate, energy is released and the reaction is exothermic.
NCERT: Class 11 Biology, Chapter 9