Scottish Highers Biology Problem Solving: An experiment was carried out to

Question

An experiment was carried out to investigate the evolutionary relatedness of four species of fish by comparing proteins extracted from the fish. The more closely related species are, the more proteins they have in common.

A sample of muscle tissue from each species of fish was heated in a solution to extract proteins.

The protein extracts were analysed by gel electrophoresis which separates proteins according to their mass. A protein standard containing proteins of known masses was also analysed.

The results of the gel electrophoresis are shown in the diagram. Each band represents a protein.

Mass of protein in protein standard (kDa)
Distance travelled (mm)

16                 50
20                 40
26                 30
44                 24
66                 15
108               10

Protein X

(i) Identify two variables related to the protein extraction, not already mentioned, which should be kept constant so that a valid conclusion can be drawn.

1.
2.

(ii) During the preparation the samples were heated. This unfolds the proteins changing their three-dimensional shape.
Name one type of bond that could have been broken to cause this change.

(iii) Draw a line graph to show the distance travelled by the protein bands in the gel against the mass of protein in the protein standard.
(Additional graph paper, if required, can be found on page 33)

Band X travelled 28 mm. Use the graph to identify the mass of the protein in band X.

____________ kDa

(iv) Explain why it was concluded that species 1, 2 and 4 are more closely related to each other than they are to species 3.

An experiment was carried out to investigate the evolutionary relatedness of four species of fish by comparing proteins extracted from the fish - Scottish Highers Biology - Question 10 - 2018

Worked Solution & Example Answer:An experiment was carried out to investigate the evolutionary relatedness of four species of fish by comparing proteins extracted from the fish - Scottish Highers Biology - Question 10 - 2018

Identify two variables related to the protein extraction, not already mentioned, which should be kept constant so that a valid conclusion can be drawn.

Name one type of bond that could have been broken to cause this change.

Draw a line graph to show the distance travelled by the protein bands in the gel against the mass of protein in the protein standard.

Use the graph to identify the mass of the protein in band X.

Explain why it was concluded that species 1, 2 and 4 are more closely related to each other than they are to species 3.

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