Enzymes — Class 11 Biology Quiz
Eight medium-difficulty conceptual multiple-choice questions on enzymes (Class 11 Biology chapter). Each item tests core ideas, applications, and common misconceptions.
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Quiz Questions & Answers
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Question 1: Which statement best captures the fundamental role of enzymes in biological reactions?
They change the equilibrium of reactions to produce more products.
They provide energy to drive endergonic reactions directly.
They lower activation energy to speed up reactions without being consumed.
They permanently bind substrates and become part of products.
Question 2: Why does increasing substrate concentration eventually stop increasing the rate of an enzyme-catalyzed reaction?
Product formation stops because equilibrium is reached instantly.
Substrate molecules begin inhibiting each other at high concentration.
All enzyme active sites become saturated so adding more substrate has no further effect.
The enzyme denatures immediately when substrate is abundant.
Question 3: Which change is most likely to permanently abolish an enzyme's activity?
Competitive inhibitor present at low concentration.
Covalent modification that disrupts the enzyme's tertiary structure irreversibly.
A mild reversible pH shift within physiological range.
Temporary substrate depletion.
Question 4: A noncompetitive inhibitor reduces Vmax but does not change Km. What does this imply about the inhibitor's interaction?
It only binds to the enzyme-substrate complex to speed turnover.
It increases Km by decreasing substrate affinity.
It binds an allosteric site and decreases catalytic efficiency regardless of substrate binding.
It competes with substrate for the active site.
Question 5: Which scenario best illustrates induced fit in enzyme action?
Enzyme and substrate are rigid and fit perfectly without change.
Substrate binding causes the active site to change shape, optimizing contacts for catalysis.
Enzyme is cleaved into products during the reaction.
Substrate changes shape after product release only.
Question 6: Which statement corrects the myth: 'All enzymes work best at human body temperature'?
Temperature has no effect on enzyme activity.
Optimal temperature varies: enzymes from different organisms adapt to their environmental temperatures.
All enzymes become inactive above 37 degrees Celsius.
Human enzymes are identical to bacterial enzymes in temperature response.
Question 7: How does an enzyme increase the rate of a reaction without altering the reaction's ΔG (free energy change)?
By lowering the activation energy barrier while leaving the relative energies of reactants and products unchanged.
By converting endergonic reactions into exergonic ones.
By increasing product stability to shift equilibrium.
By adding energy from ATP into the reaction automatically.
Question 8: Which experimental observation would best identify an enzyme as a holoenzyme versus an apoenzyme?
Activity is present only after adding a specific prosthetic group or cofactor to the inactive protein.
Activity increases when temperature is lowered slightly.
Substrate binds but no product is formed due to competitive inhibition.
Enzyme activity is unchanged after removing metal ions.