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1.3.2Osmosis

AQA GCSE Biology (8461), Higher tier · Cell biology › Transport in cells

Practise Osmosis. 19 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.

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Required practical: Osmosis (method, variables and exam tips)

Quick recall

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Name the structure that stops a plant cell bursting when it is placed in pure water.
cell wall

Sample questions

Written for this site in the style of AQA exam questions. They are not taken from real past papers.

Question 1Easy5 marks
Water moves into and out of cells by osmosis.
(a) Complete the definition of osmosis.
Osmosis is the diffusion of water from a ____________ solution to a ____________ solution through a ____________ membrane.[3]
(b) A plant cell is placed in pure water.
Which statement describes what happens?
Tick (✓) one box.[1]
  • Water moves into the cell by osmosis.
  • Water moves out of the cell by osmosis.
  • Sugar moves into the cell by osmosis.
  • Salt moves out of the cell by osmosis.
(c) Name the structure that stops a plant cell bursting when it is placed in pure water.[1]
Show the answer and mark scheme
(a) Answer: dilute; concentrated; partially permeable
  • dilute
  • concentrated
  • partially permeable
(b) Answer: Water moves into the cell by osmosis.
(c) Answer: cell wall
  • cell wall
Question 2Medium8 marks
A scientist placed samples of red blood cells into three different solutions:
  • solution A – pure water
  • solution B – a salt solution with the same concentration as blood plasma
  • solution C – a concentrated salt solution.
(a) Describe and explain what happens to the red blood cells in solution A.[3]
(b) Predict what happens to the red blood cells in solution C.[1]
(c) Explain why a plant cell placed in pure water does not burst.[2]
(d) Fluids given to patients through a drip into a vein must have the same concentration as blood plasma.
Explain why.[2]
Show the answer and mark scheme
(a)
  • water moves into the cells by osmosis
  • because the water is more dilute than the solution inside the cells
  • the cells swell and burst (because they have no cell wall)
(b)
  • they shrink / shrivel (as they lose water)
(c)
  • a plant cell has a (strong) cell wall
  • which stops the cell expanding any further (the cell becomes turgid)
(d)
  • there is no net movement of water into or out of the blood cells by osmosis
  • so the cells do not burst or shrink
Question 3Hard8 marks
A student wanted to investigate the effect of the concentration of salt solution on the mass of beetroot tissue.
(a) Describe a method the student could use.
Your method should produce valid results.[6]
(b) One cylinder had a starting mass of 3.20 g and a final mass of 2.84 g.
Calculate the percentage change in mass.[2]
Show the answer and mark scheme
(a)
  • use a cork borer to cut cylinders of beetroot and a scalpel and ruler to cut them all to the same length, e.g. 3 cm
  • blot each cylinder dry with paper towel and measure its mass on a balance
  • prepare a range of salt solutions, e.g. 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm3, including distilled water
  • put one cylinder into the same volume of each solution in a labelled boiling tube
  • leave for the same time, e.g. 24 hours, at the same temperature
  • remove the cylinders, blot dry in the same way and measure the mass again
  • calculate the percentage change in mass for each cylinder
  • repeat for each concentration and calculate a mean; plot a graph of percentage change in mass against concentration

Marked with levels of response: the full level descriptors are in the app.

(b) Answer: −11.25% (−11.3%) %
  • (2.84 − 3.20) ÷ 3.20 × 100
  • −11.25 (%) / −11.3 (%)

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