Q.14 For an enzyme catalyzed reaction, the plot that correctly represents the relationship between the rate and temperature is
Effect of Temperature on Enzyme-Catalyzed Reactions
Enzymes are biological catalysts whose activity is highly sensitive to temperature. Unlike simple chemical reactions, enzyme-catalyzed reactions show a distinct optimum temperature, beyond which the reaction rate decreases due to enzyme denaturation.
The given question asks:
For an enzyme-catalyzed reaction, which plot correctly represents the relationship between rate and temperature?
Let’s analyze the correct answer step by step by understanding enzyme behavior and then evaluating each option.
Correct Answer: (D) ✅
Why Option (D) is Correct
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At low temperatures, enzyme molecules have low kinetic energy → fewer effective collisions → low reaction rate.
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As temperature increases, kinetic energy increases → reaction rate increases.
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At the optimum temperature, the enzyme shows maximum activity.
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Beyond this point, increased temperature disrupts hydrogen bonds and tertiary structure → enzyme denaturation.
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Denaturation causes a sharp decrease in reaction rate.
This creates a bell-shaped (inverted U-shaped) curve, which is exactly what Option (D) represents.
Explanation of All Options
Option (A): Exponentially Increasing Curve ❌
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This graph suggests the reaction rate keeps increasing indefinitely with temperature.
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Such behavior is true for non-biological chemical reactions (Arrhenius behavior).
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Enzymes do not behave this way because they denature at high temperatures.
❌ Incorrect for enzyme-catalyzed reactions
Option (B): Sudden Sharp Increase at High Temperature ❌
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Indicates an abnormal acceleration at higher temperatures.
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Enzyme activity does not suddenly spike; instead, it declines after the optimum temperature.
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Ignores enzyme denaturation effects.
❌ Incorrect representation
Option (C): U-Shaped Curve ❌
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Suggests reaction rate decreases initially and then increases again.
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This trend has no biochemical basis for enzyme activity.
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Enzymes do not regain activity once denatured.
❌ Incorrect
Option (D): Rise to Maximum Followed by Decline ✅
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Correctly shows:
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Increase in rate due to higher kinetic energy
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Maximum rate at optimum temperature
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Decrease due to enzyme denaturation
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✅ Correct and scientifically accurate
Key Concept to Remember
📌 Enzyme-catalyzed reactions always show an optimum temperature, unlike ordinary chemical reactions.
Final Answer
✔ Correct Option: (D)
