Enzyme activity peaks at optimal pH, maximizing effective collisions

Steps:

• Examine graph: rate of enzyme activity highest at pH 8, indicating optimal conditions.
• Recall enzyme kinetics: activity reflects frequency of effective collisions between enzyme and substrate.
• Compare pH values: collisions greatest where activity peaks (pH 8), lowest at extremes.
• Evaluate options: select statement matching peak activity data.

Why D is correct:

• Per collision theory, enzyme activity rate is proportional to effective collision frequency; highest rate at pH 8 means greatest collisions there.

Why the others are wrong:

• A: Denaturation implies irreversible loss, but graph shows activity variation, not confirmed denaturation.
• B: pH affects enzyme shape, not substrate kinetic energy, which depends on temperature (constant here).
• C: Lowest collisions align with minimal activity, likely at pH 4 extreme, not confirmed as absolute low.

Final answer: D