Question 1 Medium
A potato cylinder is placed in pure water. Does its mass increase or decrease?
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Answer: increase
- Pure water is more dilute than the cells.
- Water enters, so the mass rises.
Osmosis: GCSE Combined Science Biology practice questions
A second set of questions on osmosis. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
A red blood cell is placed in pure water. What is likely to happen to it?
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Answer: it bursts
- Water enters by osmosis.
- An animal cell has no wall, so it bursts.
Question 3 Medium
A plant cell is placed in a very concentrated solution. Does water move into the cell or out of the cell?
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Answer: out of the cell
- The solution outside is more concentrated.
- Water moves towards it, so it leaves the cell.
Question 4 Medium
A potato cylinder goes from 8.0 g to 8.4 g. Calculate the percentage change.
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Answer: 5%
- change = 0.4 g.
- 0.4 ÷ 8.0 × 100 = 5%.
Question 5 Hard
A cylinder starts at 4.0 g and ends at 3.2 g. Calculate the percentage change.
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Answer: −20%
- change = −0.8 g.
- −0.8 ÷ 4.0 × 100 = −20%.
Question 6 Hard
A cylinder has no change in mass in a 0.4 M solution. What does this tell you about the cell contents?
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Answer: same concentration
- No net movement means no gradient.
- The cell contents have the same concentration as the solution.
Question 7 Hard
In a very concentrated solution, a plant cell membrane pulls away from the cell wall. Name this.
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Answer: plasmolysis
- The cell has lost a lot of water.
- The effect is plasmolysis.
Question 8 Hard
Why is each cylinder blotted dry before weighing? Give one word to describe the water that is removed.
Show answer
Answer: surface
- Water on the outside would add mass.
- So the surface water is removed.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is osmosis?
Show answer
The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
Check 2
What is a partially permeable membrane?
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A membrane that lets some small molecules, such as water, through but not larger ones.
Check 3
Which way does water move in osmosis?
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From the more dilute solution to the more concentrated solution.
Check 4
What happens to an animal cell in pure water?
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Water enters and the cell swells and may burst.
Check 5
What happens to an animal cell in a very concentrated solution?
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Water leaves and the cell shrinks.
Check 6
What does turgid mean?
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A plant cell that is firm and swollen with water.
Check 7
What does flaccid mean?
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A plant cell that has lost water and is limp.
Check 8
What is plasmolysis?
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When a plant cell loses so much water that the membrane pulls away from the cell wall.
Check 9
Why does a plant cell not burst in pure water?
Show answer
The strong cell wall stops it.
Check 10
What is the independent variable in the potato practical?
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The concentration of the solution.
Check 11
What is the dependent variable in the potato practical?
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The change in mass of the potato cylinder.
Check 12
Why is each potato cylinder blotted dry before it is weighed?
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To remove water on the surface that is not inside the cells.
Check 13
Name two control variables in the potato practical.
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Size of cylinder, volume of solution, time and temperature.
Check 14
What is the equation for percentage change in mass?
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(final mass − start mass) ÷ start mass × 100.
Check 15
What does a percentage change of 0 show about the solution?
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It has the same concentration as the potato cells.
Check 16
How can you find the concentration at which there is no mass change?
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Plot a graph and read off where the line crosses zero change.
Check 17
What is a solution?
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A liquid with a substance dissolved in it.
Check 18
What does dilute mean?
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A solution with only a little dissolved substance, so it is mostly water.
Check 19
What does concentrated mean?
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A solution with a lot of dissolved substance and less water.
Check 20
Which liquid is the most dilute?
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Pure water, because nothing is dissolved in it.
Check 21
What does no net movement mean?
Show answer
Water moves both ways at the same rate, so there is no overall change.
Check 22
Why can an animal cell burst in pure water?
Show answer
It has no cell wall, so nothing stops it swelling as water enters.
Check 23
Why does a plant wilt?
Show answer
Its cells lose water and become flaccid.
Check 24
Why must the potato cylinders be the same size and left for the same time?
Show answer
To make the test fair, so only the concentration changes.
Check 25
What sign does the percentage change have if the mass falls?
Show answer
A negative sign.
Check 26
What solutions are used in the potato osmosis practical?
Show answer
Sucrose solutions of different concentrations, including distilled water.
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