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Cell Biology Homework – Transport across cell membranes Homework Exercise 4 1 The diagram below represents differences in the concentration of molecules inside and outside an animal cell, together with the direction of movement of the molecules. Identify the arrow (A, B, C or D) on the diagram that would represent the diffusion of oxygen into the cell. (1) 2. The diagram below shows the appearance of a cell from an onion. Pieces of onion were placed in three different solutions: a 10% salt solution, 2% salt solution and pure water. The following diagrams show the appearance of the cells after 10 minutes Solution X Cells swell solution Y cells unchanged solution Z cell content shrinks Identify the other two solutions (i) 10% salt solution _______ 2% salt solution pure water Y _______ (2) (ii) Look at the diagrams of the plant cells drawn above and state which cell Is plasmolysed and which cell is turgid. 8 (2) Cell Biology Homework – Transport across cell membranes (iii) Give a definition of osmosis. (3) 3. The diagrams below represent red blood cells in different solutions as they would appear under a microscope. (a)(i) Use the information in the diagrams to predict the percentage water in a red blood cell. (1) (ii) Explain your answer (1) (b) The cells in diagram B are smaller in size. Explain the change in terms of water concentration. (2) (C ) State what would happen to red blood cells bathed in pure water. 9 (1) Cell Biology Homework – Transport across cell membranes 4. A student cut five similar cylinders from the same potato, dried them with a paper towel and weighed them. Each cylinder was placed in a different concentration of sugar solution as shown in the diagram below. After three hours, the student removed the cylinders from the solutions, dried and weighed them as before. The results are shown in the table below. Test Concentration Initial mass Final mass Change in mass Percentage tube of sugar of potato of potato of potato change in mass solution (M) cylinder (g) cylinder (g) cylinder (g) of potato A 0.1 2.0 2.2 +0.2 +10 B 0.2 2.0 2.1 +0.1 +5 C 0.3 2.0 1.8 -0.2 -10 D 0.4 2.0 1.7 -0.3 E 0.5 2.0 1.5 -0.5 -25 (a) Calculate the percentage change in mass of the potato cylinder in 0.4M sugar solution. (1) (b) Name the variable altered in this investigation. (1) (c ) Suggest one way in which the reliability of the results could be improved. (1) (d) Predict the appearance of the cells in potato cylinder E after three hours. (1) (e) At the end of the experiment, identify one tube that would contain turgid cells. (1) 10 Cell Biology Homework – Transport across cell membranes 5. Active transport involves the movement of molecules or ions aross a cell membrane. (a) Which of the digarams below shows the direction of movement of the molecules by active transport into the cell? (1) molecules (b) Name the type of molecule found in the cell membranes that is required for the process of active transport. (1) (c) The movement of molecules in or out of a cell can be by passive or active transport. Describe one difference between passive and active transport. (1) 11