A-level BIOLOGY Paper 1 2020

7402/1 S - The Marketplace for Revision Notes & Study Guides 2 Answer all questions in the spaces provided. Do not write outside the 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 . 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] . The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how. [2 marks] *02* Downloaded by: ibrahim03naqvi | S - The Marketplace for Revision Notes & Study Guides 3 0 1 . 3 Describe and explain two features you would expect to find in a cell specialised for absorption. [2 marks] 1 2 Question 1 continues on the next page Turn over ► Do not write outside the box S - The Marketplace for Revision Notes & Study Guides 4 Figure 2 is a diagram of one SGLT1 carrier protein. Do not write outside the box 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] S - The Marketplace for Revision Notes & Study Guides 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. Do not write outside the box You may use a diagram in your answer. [2 marks] Space for diagram: Turn over for the next question Turn over ► S - The Marketplace for Revision Notes & Study Guides 6 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 . Use your knowledge of lipid digestion to explain the differences in the results for samples A and B shown in Table 1. Do not write outside the box You should assume that no absorption had occurred. [3 marks] *06* Downloaded by: ibrahim03naqvi | S - The Marketplace for Revision Notes & Study Guides 7 . After collecting the samples, the scientist immediately heated them to 70 °C for 10 minutes. Explain why. [2 marks] Do not write outside the box . Describe the role of micelles in the absorption of fats into the cells lining the ileum. [3 marks]