AQA A LEVEL BIOLOGY PAPER 1 2020 QUESTION PAPER

Answer all questions in the spaces provided. box

0 1 Figure 1 shows a cell from the lining of the ileum specialised for absorption of

products of digestion.

SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports

glucose and sodium ions (Na+) into the cell.

Figure 1

0 1 . 1 The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP

hydrolase enzyme.

Explain the function of this ATP hydrolase.

[2 marks]

0 1 . 2 The movement of Na+ out of the cell allows the absorption of glucose into the

cell lining the ileum.

Explain how.

[2 marks]

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box 0 1 . 3 Describe and explain two features you would expect to find in a cell specialised for

absorption.

[2 marks]

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Question 1 continues on the next page

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box Figure 2 is a diagram of one SGLT1 carrier protein.

Figure 2

0 1 . 4 Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into

the cell-surface membrane.

Do not draw more than eight phospholipids.

[2 marks]

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box 0 1 . 5 Figure 2 shows the SGLT1 polypeptide with NH2 at one end and COOH at the

other end.

Describe how amino acids join to form a polypeptide so there is always NH2 at

one end and COOH at the other end.

You may use a diagram in your answer.

[2 marks]

Space for diagram:

Turn over for the next question

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box 0 2 To study lipid digestion, a scientist placed a tube into the gut of a healthy

20-year-old man. The end of the tube passed through the stomach but did not reach

as far as the ileum.

The scientist fed the man a meal containing triglycerides through the tube.

The scientist also used the tube to remove samples from the man’s gut at intervals

after the meal.

The scientist measured the type of lipid found in the samples. Some of her results are

shown in Table 1.

Table 1

Sample Time of collection

after meal / min

Concentration of

fatty acids / mg cm−3

Concentration of

triglycerides / mg cm−3

A 45 2.7 0.6

B 75 3.3 0.0

0 2 . 1 Use your knowledge of lipid digestion to explain the differences in the results for

samples A and B shown in Table 1.

You should assume that no absorption had occurred.

[3 marks]

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box 0 2 . 2 After collecting the samples, the scientist immediately heated them to

70 °C for 10 minutes.

Explain why.

[2 marks]

0 2 . 3 Describe the role of micelles in the absorption of fats into the cells lining the ileum.

[3 marks]

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box 0 3 Figure 3 shows pressure and blood flow during the cardiac cycle in a dog.

Figure 3

0 3 . 1 At P on Figure 3, the pressure in the left ventricle is increasing. At this time, the rate

of blood flow has not yet started to increase in the aorta.

Use evidence from Figure 3 to explain why.

[2 marks]

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box 0 3 . 2 At Q on Figure 3 there is a small increase in pressure and in rate of blood flow in the

aorta.

Explain how this happens and its importance.

[2 marks]

0 3 . 3 A student correctly plotted the right ventricle pressure on the same grid as the left

ventricle pressure in Figure 3.

Describe one way in which the student’s curve would be similar to and one way it

would be different from the curve shown in Figure 3.

[2 marks]

Similarity

Difference

0 3 . 4 Use information from Figure 3 to calculate the heart rate of this dog.