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Biological molecules

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Question 25

A student investigated the activity of the enzyme polyphenol oxidase in apple tissue.

When apple tissue is cut and exposed to air, polyphenol oxidase catalyses a reaction between colourless polyphenol compounds in the apple tissue and oxygen to form brown melanin pigments.

polyphenol compounds+oxygen→polyphenol oxidasemelanin (brown pigment) \text{polyphenol compounds} + \text{oxygen} \xrightarrow{\text{polyphenol oxidase}} \text{melanin (brown pigment)} polyphenol compounds+oxygenpolyphenol oxidase​melanin (brown pigment)

The student measured the time taken for a brown pigment to cover a standardized area on sliced tissue from two apple cultivars (A\text{A}A and B\text{B}B).

Method

  1. Cut a 1 cm31\text{ cm}^31 cm3 cube of apple tissue from cultivar A\text{A}A.
  2. Put the cube on a plate and leave it at 22 ∘C22\text{ }^\circ\text{C}22 ∘C.
  3. Measure the time taken for the brown pigment to appear.
  4. Repeat steps 1 to 3 two more times.
  5. Repeat steps 1 to 4 with apple tissue from cultivar B\text{B}B.

The student obtained the following results, but did not record them in a results table:

  • Cultivar A\text{A}A: 8 min 30 s8\text{ min } 30\text{ s}8 min 30 s, 9 min 10 s9\text{ min } 10\text{ s}9 min 10 s, 7 min 50 s7\text{ min } 50\text{ s}7 min 50 s
  • Cultivar B\text{B}B: 3 min 40 s3\text{ min } 40\text{ s}3 min 40 s, 4 min 10 s4\text{ min } 10\text{ s}4 min 10 s, 4 min 40 s4\text{ min } 40\text{ s}4 min 40 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 A\text{A}A are different from the results for cultivar B\text{B}B.

[2]
3.

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

[3]
4.

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

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

Biological molecules Questions

  1. A Level
  2. /Biology
  3. /Biological molecules