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Question 14

A student investigated the activity of the enzyme catechol oxidase in potato tissue.

When potato tissue is exposed to air, catechol oxidase catalyses a reaction between colourless catechol compounds in potato tissue and oxygen to form a dark pigment.

catechol compounds+oxygen→catechol oxidasedark pigment \text{catechol compounds} + \text{oxygen} \xrightarrow{\text{catechol oxidase}} \text{dark pigment} catechol compounds+oxygencatechol oxidase​dark pigment

The student measured the time taken for the dark pigment to appear in two potato cultivars (X\text{X}X and Y\text{Y}Y).

Method

  1. Cut a 1 cm1\text{ cm}1 cm cube of potato tissue from cultivar X\text{X}X.
  2. Put the cube on a plate and leave the plate at 25 ∘C25\text{ }^\circ\text{C}25 ∘C.
  3. Measure the time for the dark pigment to appear.
  4. Repeat steps 1 to 3 two more times.
  5. Repeat steps 1 to 4 with potato tissue from cultivar Y\text{Y}Y.

The student obtained the results shown below, but did not record the data in a results table.

  • Cultivar X\text{X}X: 12 min 40 s12\text{ min } 40\text{ s}12 min 40 s, 14 min 00 s14\text{ min } 00\text{ s}14 min 00 s, 11 min 20 s11\text{ min } 20\text{ s}11 min 20 s
  • Cultivar Y\text{Y}Y: 5 min 10 s5\text{ min } 10\text{ s}5 min 10 s, 6 min 40 s6\text{ min } 40\text{ s}6 min 40 s, 6 min 10 s6\text{ min } 10\text{ s}6 min 10 s
1.

Design a suitable results table in your answer, entering the results and their mean values calculated to 1 decimal place.

[3]
2.

Suggest and explain why the results for cultivar X\text{X}X are different from the results for cultivar Y\text{Y}Y.

[2]
3.

The student repeated the investigation but made one change to the method used to prepare the potato tissue, observing shorter times for the pigment to appear. Suggest this change (do not suggest using a different volume or mass) and explain why the dark pigment appeared in a shorter time.

[3]
4.

Which change in procedure will provide a successful measure of catechol oxidase activity?

  • Option A: Measure the increase in oxygen concentration in the air around the cube of potato tissue on a plate.
  • Option B: Measure the intensity of dark colour by comparing potato tissue with a colour chart showing a range of potato tissues of known pigment concentration.
  • Option C: Measure the intensity of colour produced from dark potato tissue in a biuret test.
  • Option D: Measure the percentage of light transmitted through a cube of dark potato tissue using a colorimeter.
[1]

Proteins Questions

  1. A Level
  2. /Biology
  3. /Proteins

Practise AQA A Level Biology Proteins with exam-style questions for A Level Biology. 22 questions covering General properties of proteins and Many proteins are enzymes, matched to the AQA A Level Biology (7402) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.

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