DHS 2023 H2 Prelim Paper 2

© DHS 2023 9744/02 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 BIOLOGY 9744/02 Paper 2 Structured Questions 15 September 2023 2 hours READ THESE INSTRUCTIONS FIRST: Write your centre number, index number, name and class at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 13 2 11 3 9 4 9 5 12 6 11 7 9 8 9 9 8 10 4 11 5 Total 100 This document consists of 33 printed pages and 3 blank pages.

2 © DHS 2023 9744/02 Section A: Structured Questions Answer all questions. Question 1 Capillaries are the smallest blood vessels in humans. Their very thin walls are made of endothelial cells, across which nutrients and cells may pass selectively. Fig 1.1 shows a cross section of a human capillary, with some blood cells found in its lumen. Fig 1.1 (a) Explain how the cross section of a human capillary in Fig 1.1 supports the cell theory. [2]

3 © DHS 2023 9744/02 [Turn over BLANK PAGE

4 © DHS 2023 9744/02 An experiment was carried out to study the synthesis and movement of proteins within macrophages. Fig 1.2 shows the method used. Fig 1.2 Table 1 shows the results of this experiment. Table 1 Time / minutes Level of radioactivity / arbitrary units Ribosomes Cisternal space of rough endoplasmic reticulum Golgi apparatus 5 60 0 0 10 80 40 0 15 20 50 0 20 15 50 10 25 10 20 30 30 5 20 60 35 5 10 40 40 5 5 20 Total radioactivity 200 195 160 cells were incubated in a medium with radioactive amino acids for 5 minutes cells were washed thoroughly cells were incubated in a medium with non-radioactive amino acids sample of cells were removed every 5 minutes for 40 minutes levels of radioactivity in three different locations were determined

5 © DHS 2023 9744/02 [Turn over (b) Describe and explain the changes in the level of radioactivity in the ribosomes. [4] (c) Suggest why the total radioactivity in the Golgi apparatus was lower than the total radioactivity in the ribosomes. [2]

6 © DHS 2023 9744/02 A macrophage is a type of phagocyte which engulfs bacteria during a bacterial infection . Fig 1.3 shows some processes that occur in a macrophage. Fig 1.3 (d) (i) State two structural features of bacteria that are not found in a macrophage. [2] (ii) Phagocytes such as macrophages contain many lysosomes. With reference to Fig 1.3, explain the functions of lysosomes. [3] Total: [13]

7 © DHS 2023 9744/02 [Turn over Question 2 Sorghum is a staple food in Africa. The major storage protein that it contains, kafirin, is not easily digested by protease enzymes. Upon heating, kafirin can undergo unfolding as shown in Fig 2.1. Fig 2.1 (a) With reference to Fig 2.1, explain what determines the three-dimensional conformation of kafirin. [3] (b) Explain why an enzyme acts only on a specific substrate. [2]

8 © DHS 2023 9744/02 The digestibility of the protein in two varieties of sorghum (Macia and NK8828) was measured when raw, after cooking with and without acid. Digestibility was measured as the percentage of the protein that was broken down to amino acids during digestion. The results are shown in Fig 2.2. Fig 2.2 (c) With reference to Fig 2.2, contrast (i) the digestibility of raw and cooked sorghum, [1] (ii) the digestibility of cooked sorghum with and without acid. [1]

9 © DHS 2023 9744/02 [Turn over (d) Account for the two differences described in (c)(i) and (ii). [4] Total: [11]

10 © DHS 2023 9744/02 Question 3 Fig 3.1 shows water and ion channels that are found in the cell surface membrane of all cells. Fig 3.1a Fig 3.1b (a) Explain why these channels are necessary to allow movement of ions and water molecules across the cell surface membrane. [3] (b) With reference to Fig 3.1, describe how the mechanism of transport differs between the two channels. [1]