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IGCSEBiology
Trial Class

Original practice · 5 questions · 16 marks · about 18 minutes

Enzymes and Rate Graphs Practice Questions

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Use these questions to practise moving from graph description to molecular explanation. The most valuable answers link kinetic energy or active-site shape to successful collisions.

Before you open the answers

  • Attempt every question without notes.
  • Show working for calculations and write complete biological statements.
  • Use the suggested time as a guide, not a strict limit on the first attempt.

These are original practice questions. They do not reproduce an official Cambridge paper or official mark scheme.

  1. Question 1

    Paper 4 Both 2 marks Difficulty 1/5

    Define an enzyme and state what happens to it during the reaction.

    Show model answer and marking guidance
    1. An enzyme is a protein that acts as a biological catalyst.
    2. It speeds up the reaction without being used up or permanently changed by the reaction.

    Watch for: Calling an enzyme a living organism.

  2. Question 2

    Paper 4 Extended 4 marks Difficulty 3/5

    Explain why the rate of an enzyme-controlled reaction increases from 15 °C to 40 °C.

    Show model answer and marking guidance
    1. Molecules gain kinetic energy.
    2. Enzyme and substrate molecules move faster.
    3. They collide more frequently.
    4. More successful collisions or enzyme–substrate complexes form per unit time.

    Watch for: Mentioning denaturation while the temperature remains below the optimum.

  3. Question 3

    Paper 4 Both 3 marks Difficulty 2/5

    Explain why a high temperature can permanently reduce enzyme activity.

    Show model answer and marking guidance
    1. High temperature changes the enzyme’s three-dimensional or active-site shape.
    2. The substrate is no longer complementary and cannot bind effectively.
    3. Fewer enzyme–substrate complexes form, so the enzyme is denatured and rate falls.

    Watch for: Writing that the enzyme is killed.

  4. Question 4

    Paper 5/6 Both 2 marks Difficulty 2/5

    Starch disappears after 80 s. Calculate the reaction rate in s⁻¹.

    Show model answer and marking guidance
    1. Rate = 1 ÷ time.
    2. Rate = 1 ÷ 80 = 0.0125 s⁻¹.

    Watch for: Using time itself as the rate.

  5. Question 5

    Paper 5/6 Both 5 marks Difficulty 4/5

    A student investigates the effect of pH on amylase. Describe a method that would produce reliable results.

    Show model answer and marking guidance
    1. Use a range of buffer solutions with known pH values.
    2. Keep temperature, enzyme and starch concentrations and volumes constant.
    3. Mix amylase and starch and sample at fixed intervals into iodine.
    4. Record the time when iodine no longer turns blue-black and calculate rate as 1 ÷ time.
    5. Repeat each pH and calculate a mean.

    Watch for: Changing pH without using a buffer or controlling temperature.

Mark the set consistently

Award a point only when the idea is clearly present in the written answer. Correct any missed point in a complete sentence, then test the same skill on a different question several days later.

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