MYP Biology sample question: Diffusion and osmosis

A student places potato cylinders in sugar solutions of different concentrations and measures the change in mass after 30 minutes. A cylinder in distilled water gained mass.

1. (a)Define osmosis.[2]
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   • • The net movement of water molecules from a dilute solution to a more concentrated solution (1)
   • • through a partially permeable membrane (1)
2. (b)Explain why the cylinder in distilled water gained mass.[2]
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   • • The solution inside the cells is more concentrated than the distilled water (1)
   • • so water moved into the cells by osmosis (1)
3. (c)Describe how the results could be used to estimate the concentration inside the potato cells.[1]
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   • • Plot percentage change in mass against concentration; the concentration where the line crosses zero change in mass is the estimate (1)

Say that water moves, not the sugar. Describe direction using more dilute to more concentrated.