Page 19 - Q & A STPM 2022 Biology

Biology STPM Chapter 3 Membrane Structure and Transport

Question 11
The diagram below shows a plant cell placed in distilled water. A, B, C and D
represent the direction of pressures exerted on and inside the cell.
Which one of the following represents the cell wall pressure?
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A

Water molecule Semester
D Solute molecule 1
C Tonoplast
Cell membrane

B

Answer : D
Water enters the plant cell by osmosis. As a result, pressure on the cell wall
increases inside the cell, making the cell turgid. The cell wall develops an equal
and opposite pressure to stop water movement into the cell.

Section B Structured Questions

Question 12
The diagram below shows the two adjacent cells. Their values ψ and ψ are
S
P
given in kPa.
Cell A Cell B
ψ = -2000 ψ = -1600
S S
ψ = 1000 ψ = 800
P P
(a) Define osmosis in terms of water potential. (2 marks)
(b) State the direction of water flow between the two cells. (2 marks)
(c) Give one reason for your answer above. (1 mark)
(d) Calculate the values of the pressure potential, ψ and the water potential,
P
ψ of cell A and cell B, when equilibrium is reached. Assume the changes
in solute potential are negligible. (3 marks)

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