AQA A-LEVEL BIOLOGY PAPER 2 2020 QUESTON PAPER

Answer all questions in the spaces provided. box

0 1 The iris in the human eye is a muscular structure. The iris changes the size of the

pupil.

Figure 1 shows the muscles in the iris.

Figure 1

0 1 . 1 Suggest and explain how the interaction between the muscles labelled in Figure 1

could cause the pupil to constrict (narrow).

[2 marks]

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box 0 1 . 2 The fovea of the eye of an eagle has a high density of cones. An eagle focuses the

image of its prey onto the fovea.

Explain how the fovea enables an eagle to see its prey in detail.

Do not refer to colour vision in your answer.

[3 marks]

0 1 . 3 The retina of the human eye has an area of approximately 1.094 × 103 mm2

The circular fovea in a human eye has a diameter of 3 × 103 µm

Calculate the area of the fovea as a percentage of the area of the retina.

The area of a circle is πr

2

. Use π = 3.14 in your calculation.

Show your working.

[2 marks]

Answer %

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box 0 1 . 4 The retina of an owl has a high density of rod cells.

Explain how this enables an owl to hunt its prey at night.

Do not refer to rhodopsin in your answer.

[3 marks]

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box 0 2 Testosterone is a steroid hormone that belongs to a group of male sex hormones

called androgens.

0 2 . 1 Steroid hormones are hydrophobic.

Explain why steroid hormones can rapidly enter a cell by passing through its

cell-surface membrane.

[2 marks]

0 2 . 2 In the cytoplasm, testosterone binds to a specific androgen receptor (AR).

An AR is a protein.

Suggest and explain why testosterone binds to a specific AR.

[2 marks]

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box 0 2 . 3 The binding of testosterone to an AR changes the shape of the AR. This AR molecule

now enters the nucleus and stimulates gene expression.

Suggest how the AR could stimulate gene expression.

[2 marks]

The gene that codes for the AR has a variable number of CAG repeats.

Some studies have shown an association between the number of CAG repeats and

the risk of developing prostate cancer.

Table 1 shows the results of a statistical test from one study.

Table 1

Number of CAG repeats

in the AR gene Probability (P) value

⩽ 16 0.02

⩽ 17 0.30

⩽ 18 0.07

⩽ 19 0.09

⩾ 20 0.06

0 2 . 4 What can you conclude from the data in Table 1?

[3 marks]

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box 0 3 Figure 2 shows one type of calorimeter.

Figure 2

A calorimeter can be used to determine the chemical energy store of biomass.

A known mass of biomass is fully combusted in a calorimeter. The heat energy

released from this combustion increases the temperature of the water in the

calorimeter. The increase in the temperature of a known volume of water is recorded.

0 3 . 1 Other than the thermometer, explain how two features of the calorimeter shown in

Figure 2 would enable a valid measurement of the total heat energy released.

[2 marks]

1

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