Enzymes lower activation energy without altering overall reaction energy change

Steps:

• Examine graph: X labels higher energy barrier path, indicating slower uncatalysed reaction.
• Identify Y: Lower energy barrier path, showing faster catalysed reaction due to enzyme.
• Determine Z: Vertical difference between reactant and product energy levels, representing net energy change.
• Match to options: Uncatalysed for X, catalysed for Y, overall energy for Z fits enzyme effect.

Why D is correct:

• Enzymes reduce activation energy (Y vs. X) but preserve ΔG, the overall energy change to product level, per Gibbs free energy definition.

Why the others are wrong:

• A: Reverses X and Y; catalysed reaction has lower, not higher, barrier.
• B: Reverses X and Y; "gained by product" assumes endergonic reaction, ignoring exergonic possibility.
• C: Reverses X and Y; "released during reaction" mislabels Z as process energy, not net change.

Final answer: D