Turn over 15 6 The fluid mosaic model of cell membranes was first proposed in 1972. One piece of evidence that was used to support the idea of a phospholipid bilayer was the arrangement of phospholipid molecules on a surface between air and water. (a) (i) Complete the diagram to show the arrangement of four phospholipid molecules at this surface. (2) air water (ii) Which of the molecules found in cell membranes have hydrophilic regions? (1) A channel proteins only B only phospholipids and channel proteins C phospholipids, channel proteins and cholesterol D phospholipids only (b) The vacuoles in beetroot cells contain molecules of betalain, a red pigment. Betalains are large polar molecules. These molecules can leave beetroot cells if the vacuole membrane and the cell surface membrane are damaged. Explain why betalain molecules cannot move through intact cell membranes. 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The effect of detergent on the permeability of beetroot cell membranes was investigated. Sections of beetroot were placed in test tubes containing detergent solution. The colour of the detergent solution at the end of the investigation was measured. The graph shows the results of this investigation. Colour intensity of detergent solution / a.u. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Concentration of detergent solution (%) 0.5 0.4 0.3 0.2 0.1 0.0 (i) The colour of the 0.5% detergent solution was 0.25 a.u. Plot this result on the graph. (1) *(ii) Two students made predictions about the effect of increasing the concentration of detergent. The sketch graphs show the results they expected. 0.5 0.4 0.3 0.2 0.1 0.0 Colour intensity of detergent solution / a.u. Concentration of detergent solution (%) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.5 0.4 0.3 0.2 0.1 0.0 Colour intensity of detergent solution / a.u. Concentration of detergent solution (%) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Graph A Graph B Turn over 17 Explain how to carry out an investigation to test these predictions. 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(Total for Question 6 = 13 marks)