3 Cells
Answers to Practice questions
1 a) A = cell wall; B = flagellum; C = plasmid
[3]
b)
[3]
Name of structure
Description
Rough endoplasmic
reticulum
Synthesises proteins and transports them around
the cell
Lysosome
Contains enzymes that digest substances, such as
worn-out organelles or ingested bacterial cells
Microvilli
Increases the surface area of the cell.
2 a)
[2]
Uses membrane proteins
Requires energy from ATP
Active transport


Facilitated diffusion

X
b) Water potential in hollow/in sucrose solution lower/more negative than potato cells; water
enters solution by osmosis; down a concentration/diffusion/water potential gradient. (For
first marking point, answer must refer to water potential and not concentration.)
[3]
3 a) The water potential of the sodium chloride solution was lower/more negative than the water
potential of the potato cells/tissue; water leaves potato cells; by osmosis; cells smaller/less
turgid/loss of mass; (also acceptable: reverse argument for marking point 1).
[3]
b) Allows comparison; discs differ in mass to start with.
[2]
c) 0.27 M (acceptable: 0.26–0.28 M)
[1]
d) i)
So that the changes in mass were greater; reduces effect of measurement errors;
increases surface area so equilibrium reached sooner.
ii)
[2]
Surface area of discs similar/same; same distance to centre of discs (for water
movement).
[2]
4 a) Fluid = molecules can move around/it is liquid; mosaic = proteins floating among
phospholipids/not just phospholipids/other molecules in it.
b) i)
[2]
Rate of entry into cell levels off at a certain point; this is when all the protein carriers are
occupied.
[2]
© Hodder & Stoughton Limited 2015
3 Cells
Answers to Practice questions
ii)
[2]
Molecule
Description
A
Small, lipid-soluble
B
Water-soluble ion
Can pass through phospholipid bilayer; enters by simple diffusion/does not need protein
carrier/channel. (No marks for identifying A or B.)
c) i)
Increased temperature causes pigment to leak from cells; slowly at first/up to 42°C but
greater after this/suitable named point. Also acceptable as alternative to second point:
no leakage of pigment up to 22°C but increased leakage above this temperature.
ii)
[2]
Heat denatures membrane proteins/described; allows pigment to leak; correct
reference to heat disrupting phospholipids.
[2]
© Hodder & Stoughton Limited 2015