A-LevelBiologyCell membranes and transport9700/21 · Oct/Nov 2019 · Q36 Marks
A student carried out an experiment to investigate the effect of increasing the concentration of sucrose solution on the mass of potato tissue. • Potato tissue was cut into cylinders of equal length and diameter. • The mass of each cylinder was recorded. • Each cylinder was put into a solution of sucrose, as shown in Fig. 3.1. [Figure 3.1] • After one hour each cylinder was removed, blotted dry and reweighed. • The percentage change in mass of each cylinder was calculated. • The experiment was repeated three times. • The mean percentage change in mass of the potato cylinders in each sucrose solution was calculated. Fig. 3.2 shows the results of this investigation. [Figure 3.2]
- (a)With reference to Fig. 3.2, describe the effect of increasing the concentration of sucrose solution on the mass of the potato cylinders.[3]
- (b)Explain why there was a change in mass for the potato cylinders in 0.6moldm⁻³ sucrose solution.[3]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.
- [3] (a) between 0 – 0.2 mol dm-³ the mass of the potato increases or between 0.2 – 1.0 mol dm³ the mass of the potato decreases ; no change in mass at 0.2 mol dm-³; from approximately 0.2 mol dm³ increasing concentration gives a greater decrease ; comparative data quote including two concentrations and two percentage changes; units for concentration of sucrose and reference to percentage change in mass must appear once to award this point
- [3] (b) three from decrease in mass because water (molecules) leave the cells ; by osmosis; down a water potential gradient / from higher water potential to lower water potential or solution has a more negative water potential than the potato tissue ; ref. to plasmolysis / loss of turgidity;
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