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Enzymes: Question 6

Syllabus 5.1

Multiple choice Core 1 mark

Catalase is an enzyme found in liver and potato cells. It speeds up the breakdown of hydrogen peroxide into water and oxygen gas.

A student places a small piece of fresh liver into a test tube and adds a sample of hydrogen peroxide solution. Bubbles of oxygen gas form quickly. Once the bubbling stops, the student pours away the liquid, leaving the same piece of liver in the test tube, and adds a fresh sample of hydrogen peroxide solution. Bubbles of oxygen gas form quickly again, at about the same rate as before.

Which statement best explains why the same piece of liver can break down a second sample of hydrogen peroxide, without any new enzyme being added?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Identify what stayed the same between the two reactions

The same piece of liver, containing the same catalase molecules, is used for both the first and the second sample of hydrogen peroxide. No new liver tissue or enzyme is added between the two tests, and bubbling still occurs at a similar rate the second time.

Step 2: Recall the defining property of a catalyst

Catalase is an enzyme, and all enzymes are biological catalysts. A catalyst speeds up a chemical reaction without being used up or permanently changed by that reaction. This means the same catalase molecules present in the liver piece before the first reaction are still present, and still able to work, after it, so they are ready to act on a fresh sample of hydrogen peroxide.

Why the other options are wrong

  • B: water and oxygen are the products of the reaction catalase speeds up; they are not raw materials that get built back up into new enzyme molecules.
  • C: there is no need for the liver cells to make a new enzyme, because the original catalase was never used up or destroyed.
  • D: the question does not suggest a more concentrated sample was used, and this does not explain why the same piece of liver still works. Only the catalyst-not-used-up property does.

Final answer

The liver piece can be reused because catalase is a catalyst and is not used up by the reaction, option A.