Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
a What is a protoplast? [1]
b i What is the pressure potential at 90%, 95% and 100% relative cell volume? [1]
ii Calculate the change in pressure potential between 90% and 95% relative cell volume and between 95%
and 100% relative cell volume. [2]
iii Explain why the pressure potential curve is not linear. [2]
iv State the water potential when the cell reaches maximum turgidity. [1]
The graph above shows that as the cell loses water, pressure potential falls and the relative cell volume
decreases (the cell shrinks).
c i What is the minimum value of the pressure potential? [1]
ii In a shrinking cell, what is the relative cell volume when the minimum value of the pressure potential
is reached? [1]
iii What is the term used to describe the state of the cell at this point? [1]
iv What happens to the values of water potential and solute potential at this point? [1]
v State the equation which links ψ p
, ψ s
and ψ. [1]
vi Describe what is happening to the cell between the point identified in c ii and c iii above and 80%
relative cell volume. [5]
d As the cell changes volume, the change in solute potential is much less than the change in pressure potential.
Suggest an explanation for this. [3]
[Total: 20]
12 The diagram shows the concentration in mmol dm –3 of two different ions inside a human red blood cell and
in the plasma outside the cell.
92
ion
blood
plasma
red blood cell
Na +
144
K + 5
15
150
a Explain why these concentrations could not have occurred as a result of diffusion. [1]
b Explain how these concentrations could have been achieved. [2]
c If respiration of red blood cells is inhibited, the concentrations of potassium ions and sodium ions inside
the cells gradually change until they come into equilibrium with the plasma. Explain this observation. [4]
[Total: 7]