A-LEVEL BIOLOGY PAPER 2

AQA A-LEVEL BIOLOGY PAPER 2 Answer all questions in the spaces provided. Do not write outside the 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 . 1 Suggest and explain how the interaction between the muscles labelled in Figure 1 could cause the pupil to constrict (narrow). [2 marks] 3 . 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 write outside the box Do not refer to colour vision in your answer. [3 marks] . 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 πr2. Use π = 3.14 in your calculation. Show your working. [2 marks] Answer % Question 1 continues on the next page Turn over ► 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] Do not write outside the box 5 Testosterone is a steroid hormone that belongs to a group of male sex hormones called androgens. Do not write outside the box . Steroid hormones are hydrophobic. Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane. [2 marks] . 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] Question 2 continues on the next page 6 . 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. Do not write outside the box [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 . What can you conclude from the data in Table 1? [3 marks] 7 Figure 2 shows one type of calorimeter. Do not write outside the box 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. . 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 2 Question 3 continues on the next page Turn over ► 8 . A 2 g sample of biomass was fully combusted in a calorimeter. The volume of water in the calorimeter was 100 cm3 The increase in temperature recorded was 15.7 °C 4.18 J of energy are needed to increase the temperature of 1 cm3 of water by 1 C Use this information to calculate the heat energy released in kJ per g of biomass. Do not write outside the box Show your working. [2 marks] Answer kJg–1 Plants and algae produce fuels called biofuels. Scientists have used Chlorella to produce biofuel. Chlorella is a genus of single-celled photosynthetic alga. Chlorella can be grown in open ponds and fermenters. 0 3 . In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why. [2 marks] 1 2 9 0 3 . The light absorbed by chlorophyll is used in the light-dependent reaction. Name the two products of the light-dependent reaction that are required for the light-independent reaction. Do not write outside the box [2 marks] 1 2 . Chlorella cells can divide rapidly. A culture of 2000 Chlorella cells was set up in a fermenter. The cells divided every 90 minutes. You can assume that there were no limiting factors and that no cells died during the 24 hours. Calculate the number of cells in the culture after 24 hours. Give your answer in standard form. Show your working. [2 marks] Answer Turn over for the next question 10 Figure 3 shows the banding pattern of a single sarcomere. Do not write outside the box Figure 3 . Explain the banding pattern shown in Figure 3. [3 marks]