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Science · Grades 10–12

Enzymes and interpreting rate data

Enzymes increase reaction rate by providing a pathway with a lower activation-energy barrier.

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Understand the idea

Catalysis

Enzymes increase reaction rate by providing a pathway with a lower activation-energy barrier.

Read the conditions

Temperature, pH, substrate concentration and enzyme concentration can affect the measured rate.

Examples and reasoning

Which quantity is lowered by an enzyme-catalysed pathway?

activation energy

activation energy

An enzyme acts on a molecule that binds at its active site. That molecule is called the

substrate

substrate

Check your understanding

  1. Which statement is most accurate?

    1. All proteins are enzymes.
    2. All catalysts are enzymes.
    3. Many enzymes are proteins, and some RNA molecules are catalytic.
    4. All enzymes are simple sugars.

  2. An enzyme changes shape at high temperature and its rate falls. Which is a possible explanation?

    1. The active site no longer supports binding or catalysis effectively.
    2. The substrate becomes an element.
    3. The enzyme creates unlimited energy.
    4. All atoms vanish.

  3. Hypothetical rates at pH 4, 6, 8 are 2, 9, 3 units/min. At which tested pH is the rate highest?

  4. Do measurements at pH 4, 6 and 8 prove that pH 6 is the exact optimum?

Answers and marking notes

Answers and marking notes
  1. Many enzymes are proteins, and some RNA molecules are catalytic.

    Many enzymes are proteins, and some RNA molecules are catalytic.

  2. The active site no longer supports binding or catalysis effectively.

    The active site no longer supports binding or catalysis effectively.

  3. 6

    The largest measured rate is 9 at pH 6.

  4. No. An untested pH between the sampled values might give a greater rate; more measurements are needed.

    No. An untested pH between the sampled values might give a greater rate; more measurements are needed.

Further reading and review references

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Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.