FSc Part 1 Biology chapter 3: Enzymes MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

19 exam-style questions on Enzymes, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

19 questions · 2 topics · 10 per test

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What chapter 3 covers

Ten Enzymes questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. An enzyme converts glucose-6-phosphate into fructose-6-phosphate without adding or removing any atoms. It belongs to the class

  1. A
    isomerases
  2. B
    oxidoreductases
  3. C
    lyases
  4. D
    ligases
Show answer

Answer: A. The product has the same formula but a different arrangement, so it is an isomerisation.

2. The part of an enzyme where the substrate binds and the reaction takes place is the

  1. A
    allosteric site
  2. B
    apoenzyme
  3. C
    prosthetic group
  4. D
    active site
Show answer

Answer: D. The active site is a small pocket formed by a few amino acids. The allosteric site is a different site where some regulators bind.

3. Chemically, almost all enzymes are

  1. A
    proteins
  2. B
    lipids
  3. C
    carbohydrates
  4. D
    nucleic acids
Show answer

Answer: A. Enzymes are globular proteins; a few have non-protein parts (cofactors) attached.

4. The induced fit model of enzyme action was proposed by

  1. A
    Emil Fischer
  2. B
    Sanger
  3. C
    Louis Pasteur
  4. D
    Koshland
Show answer

Answer: D. Koshland (1959) proposed that the active site changes shape as the substrate binds. Emil Fischer (1894) proposed the rigid lock and key model.

5. A loosely attached, non-protein organic cofactor, often derived from a vitamin, is called a

  1. A
    prosthetic group
  2. B
    activator
  3. C
    coenzyme
  4. D
    apoenzyme
Show answer

Answer: C. A coenzyme (e.g. NAD) is organic and loosely bound. A prosthetic group is organic but tightly (covalently) bound; activators are inorganic ions.

6. How does the induced fit model differ from the lock and key model?

  1. A
    the enzyme binds the product rather than the substrate, so the reaction stops
  2. B
    the enzyme is used up as the substrate is converted into product
  3. C
    the active site is flexible and moulds itself around the substrate
  4. D
    the substrate turns the enzyme into a different protein for good
Show answer

Answer: C. In induced fit the active site is not rigid; binding of the substrate changes its shape for a tighter fit. The enzyme is unchanged at the end.

7. Enzymes that catalyse the transfer of a group such as –NH2 or phosphate from one molecule to another are

  1. A
    isomerases
  2. B
    lyases
  3. C
    transferases
  4. D
    hydrolases
Show answer

Answer: C. Transferases move functional groups between molecules. Isomerases rearrange atoms within one molecule.

8. Urease breaks down urea quickly but has no effect on thiourea, a molecule of similar shape. This property of the enzyme is called

  1. A
    denaturation
  2. B
    specificity
  3. C
    allosteric activation
  4. D
    feedback inhibition
Show answer

Answer: B. Specificity comes from the exact shape and charge of the active site: only urea fits it properly, so thiourea is not broken down. Denaturation would stop the enzyme working on urea too.

9. Cyanide and heavy metal ions such as mercury are called irreversible inhibitors because they

  1. A
    only work at low temperature and stop acting when warmed
  2. B
    compete with the substrate for the active site and can be displaced by more substrate
  3. C
    act as coenzymes that are used up during the reaction
  4. D
    bind tightly to the enzyme and permanently destroy its activity
Show answer

Answer: D. Irreversible inhibitors form strong (often covalent) bonds with the enzyme so its activity cannot be recovered.

10. At the end of a reaction catalysed by an enzyme, the enzyme is

  1. A
    used up and must be replaced
  2. B
    converted into product
  3. C
    unchanged and can be used again
  4. D
    permanently denatured
Show answer

Answer: C. Enzymes are catalysts: they are released unchanged after each reaction, so a small amount can convert a large amount of substrate.

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Enzymes: questions students ask

How many Enzymes MCQs are there?

19, each with the answer and a short explanation, across 2 topics: Characteristics and mechanism of enzyme action, Factors affecting enzyme action, inhibition and classification. Every chapter test draws ten of them, so you can take it many times.

Is the FSc Part 1 Biology chapter 3 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

Can I read the explanations in Urdu?

Yes. In practice mode and on your results you can switch the explanations to Urdu.

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