SAJC H2 Prelim P4 2023 Mark scheme for sharing

2022 9744 Preliminary Examination H2 Biology Mark Scheme (SAJC) 1 1 You will investigate the water potential of potato cells. When pieces of potato are put into a sucrose solution, water will move by osmosis into and out of the potato cells. The overall direction of water movement depends on the difference between the water potential of the potato cells and the water potential of the sucrose solution. • If the overall movement of water is out of the potato cells, the sucrose solution will become less concentrated. • If the overall movement of water is into the potato cells, the sucrose solution will become more concentrated. Fig. 1.1 shows how the change in concentration of the sucrose solution after 15 minutes can be assessed. A blue dye is added to the sucrose solution around the potato pieces at the end of the 15 minutes. The blue dye does not affect the concentration of the sucrose solution. After mixing, a drop of the blue sucrose solution is added to the original sucrose solution in a separate test-tube. The movement of the blue drop is then observed. Fig. 1.1 • If the sucrose solution has become less concentrated, then the density of the sucrose solution will have decreased. • If the sucrose solution has become more concentrated, then the density of the sucrose solution will have increased.

2022 9744 Preliminary Examination H2 Biology Mark Scheme (SAJC) 2 (a) (i) When two solutions of different density are added to one another without mixing, the denser solution will sink to the bottom and the less dense solution will rise to the top. Complete Fig. 1.2 by drawing an arrow on each test-tube, as shown in the key, to predict how you expect the drop of blue solution to move. Fig. 1.2 1 All three directions correct ; in order from left to right , ,  [1]   

2022 9744 Preliminary Examination H2 Biology Mark Scheme (SAJC) 3 You are provided with: • 5 potato cylinders, in a Petri dish labelled P • 150cm3 1.00 mol dm-3 sucrose solution S, in a container labelled S • 250cm3 distilled water W, in a container labelled W • 20cm3 blue dye M, in a container labelled M. If M comes into contact with your skin, wash it off immediately under cold water. It is recommended that you wear suitable eye protection. You will carry out a serial dilution of the 1.00 mol dm -3 sucrose solution, S, to reduce the concentration by half between each successive dilution. You will need to prepare four concentrations of sucrose solution in addition to the 1.00 mol dm-3 sucrose solution, S. After the serial dilution is completed, you will need to have 50.0 cm3 of each concentration available to use. (ii) Complete Table 1.1 to show how you will make the concentrations of the sucrose solutions needed. ……………………………………………………………………………..……………………..[3] Table 1.1 sucrose solution concentration of sucrose solution / mol dm-3 1.00 0.50 0.25 0.125 0.0