1. 1
   A piece of dialysis tubing (a partially permeable membrane) is filled with concentrated sugar solution, sealed, and placed in a beaker of pure water. After an hour, the tubing has become firm and swollen.

   (a)

   Which process explains the movement of water into the tubing?

   [1 mark]

   • AActive transport
   • BDiffusion of sugar molecules
   • COsmosis
   • DTranspiration

   (b)

   Which region has the higher water potential at the start of the experiment: the pure water in the beaker, or the sugar solution inside the tubing?

   [1 mark]

   • AThe sugar solution inside the tubing
   • BThe pure water in the beaker
   • CBoth have exactly the same water potential
   • DWater potential does not apply to pure water

   (c)

   Describe what would happen to the dialysis tubing if it were instead filled with pure water and placed into a beaker of concentrated sugar solution, and explain why.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student places equal-sized potato chips into three beakers: one containing pure water, one containing a dilute salt solution, and one containing a concentrated salt solution. After an hour, the chip in the concentrated salt solution has become soft and bendy.

   (a)

   What has happened to the cells of this chip?

   [1 mark]

   • AThey have become plasmolysed
   • BThey have become turgid
   • CThey have gained mass by active transport
   • DThey have divided by mitosis

   (b)

   The chip placed in pure water is found to have increased in mass and become firm. What term describes the state of this chip's cells?

   [1 mark]

   • AFlaccid
   • BPlasmolysed
   • CDehydrated
   • DTurgid

   (c)

   Explain why the potato cells in pure water became turgid rather than bursting, even though water continued to enter them by osmosis.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A gardener notices that an unwatered pot plant has wilted, with its leaves and stem drooping, while a nearby well-watered plant of the same species remains upright.

   (a)

   State what is meant by turgor pressure, and explain its importance in supporting plant tissues such as stems.

   [3 marks]

   (b)

   Explain, in terms of water potential and osmosis, why the unwatered plant wilted while the well-watered plant did not.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology class investigates osmosis by placing identical cylinders of potato tissue into five different concentrations of sucrose solution, from pure water to a highly concentrated solution, and measuring the change in mass of each cylinder after 24 hours.

   (a)

   Explain, in terms of water potential, what results the class would expect to see across the five solutions, and explain the cellular changes occurring in the cylinders at each end of the concentration range.

   [6 marks]

   (b)

   One student in the class suggests that measuring the length, rather than the mass, of each potato cylinder would give a less reliable result. Explain why measuring mass is generally considered a more reliable way to detect osmotic movement of water than measuring length, and explain how the class could improve the reliability of their overall investigation.

   [6 marks]

   Total for question 4: 12 marks

End of questions