Temperature's effect on enzyme activity in starch digestion

Steps:

• Enzymes like amylase speed up starch breakdown to maltose, with activity rising from low temperatures.
• Activity peaks at an optimal temperature (around 40–50°C) where the reaction rate is highest.
• Above the optimum, enzymes denature, slowing the reaction.
• Remaining starch concentration decreases to a minimum at the optimum, then rises, forming a U-shaped curve.

Why A is correct:

• Graph A shows starch concentration decreasing then increasing, matching the enzyme activity curve defined by the lock-and-key model where temperature affects enzyme-substrate fit up to denaturation.

Why the others are wrong:

• B: Linear decrease ignores denaturation, violating enzyme kinetics.
• C: Steady decrease suggests no optimum, contradicting biological enzyme behavior.
• D: Increase only implies inhibition at all temperatures, not realistic for digestion.

Final answer: A