Enzymes — Drills · Grade 10 Science

Chapter: Investigating the Chemistry of Life

What these drills covers

By the end of Enzymes you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: enzyme, catalyst, substrate, active site, activation energy, denature, ribozyme.

Problem 1

An enzyme speeds up a reaction by
  1. raising the temperature of the cell
  2. lowering the activation energy
  3. making a non-spontaneous reaction spontaneous
  4. adding energy to the products
Answer and explanation

lowering the activation energy

Enzymes lower the activation energy barrier. They do not change whether a reaction is energetically favourable overall, and they do not heat the cell.

Problem 2

The region of an enzyme that binds the substrate is the
  1. active site
  2. peptide bond
  3. phosphate head
  4. nucleotide
Answer and explanation

active site

The active site is a pocket shaped by the protein's folding; its shape and charge distribution determine which substrate fits.

Problem 3

An enzyme-catalysed reaction forms 24 μmol of product in 3.0 minutes. Report the mean rate in μmol per minute.
Answer and explanation

8 μmol/min

24 μmol / 3.0 min = 8.0 μmol/min. This is a mean rate over the interval, not necessarily the rate at any instant.

Problem 4

Reaction rate rises from 2 to 8 μmol/min when the temperature goes from 15 °C to 35 °C, then falls to 1 μmol/min at 55 °C. By what factor did the rate rise over the first interval?
Answer and explanation

4

8 / 2 = 4. The fall at 55 °C is not a continuation of the same trend; it reflects denaturation.

Problem 5

Adding more substrate increases the rate at first, then stops increasing it. Explain why.
Answer and explanation

At low substrate concentration many active sites are empty, so adding substrate increases the number of productive collisions. Once nearly every active site is occupied, the enzyme molecules are saturated and the rate is limited by how fast each enzyme can process substrate, so further substrate makes no difference. Adding more enzyme would raise the plateau.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Distinguish a competitive inhibitor from a noncompetitive one by where it binds and by what happens when substrate is added.
Answer and explanation

A competitive inhibitor binds the active site itself, so it competes with substrate and its effect is reduced when substrate concentration rises. A noncompetitive inhibitor binds elsewhere on the enzyme and changes the active site's shape, so adding substrate does not relieve the inhibition.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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