Compare osmotic effects on animal and plant cells
Use membrane and wall differences to interpret swelling and shrinking.
Section B3.2 · Osmosis
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall plant and animal boundaries and water potential.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why can a plant cell resist osmotic expansion better than a typical animal cell?
What you will learn
- Use membrane and wall differences to interpret swelling and shrinking.
- Apply the idea to a supplied biological example or investigation.
Animal cells lack a supporting wall
Water can enter or leave animal cells through their membranes by osmosis. With higher external water potential, net entry can make a cell swell; sufficiently extreme entry can burst a cell because it lacks the plant cell wall that resists expansion.
In lower external water potential, an animal cell can lose water and shrink. Describe an animal cell as shrunken rather than plasmolysed: plasmolysis refers to plant-cell membrane separation from a wall. These are supplied classroom cell models, not advice for medical treatment.
Separate observations and conditions
Plant and animal cells share osmotic membrane exchange, but their mechanical responses differ because of the wall. A plant cell can become turgid while an animal cell under a strong inward gradient may swell dangerously. Actual outcomes depend on starting state, exposure and membrane integrity.
At equal water potentials the model has no sustained net water transfer. The cell is not empty of water or metabolically dead just because net osmosis is zero. Use the named cell type and supplied evidence in every explanation.
Sources for this lesson
Pause and explain
An animal cell loses water and shrinks. Which description avoids a false wall claim?
Worked example
Two cells face higher external water potential. One has a rigid wall and the other does not. Explain different responses.
Show the worked solution
- Water tends to enter both membranes.
- A plant wall resists expansion and supports turgor.
- Without a wall, an animal cell may swell and under extreme conditions burst.
Answer Shared inward osmosis, different mechanical protection.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Predict the initial response of an animal cell in higher external water potential.
Give me a hint
Water moves inward.
Compare my reasoning
- Net water enters.
- The cell may swell.
Swelling; sufficiently extreme entry may cause bursting.
Look for these in your work
- Do not guarantee bursting for every exposure.
Predict the response in lower external water potential.
Give me a hint
Water moves outward.
Compare my reasoning
- The cell loses water.
- Its volume can decrease.
Osmotic water loss and shrinkage.
Look for these in your work
- Avoid plasmolysis terminology here.
Why does equal water potential not prove water molecules have stopped crossing the membrane?
Give me a hint
Recall opposing random movements.
Compare my reasoning
- Water still crosses both ways.
- Transfers balance on average.
There is no sustained net movement, not no molecular movement.
Look for these in your work
- Distinguish net from individual transfer.
Common mistakes
- Do not label an animal cell plasmolysed.
- A model of cell response is not a medical recommendation.
What can you explain now?
An animal cell loses water and shrinks. Which description avoids a false wall claim?
Compare with the explanation
Osmotic shrinkage.
An animal cell has no wall for the membrane to pull away from.
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Make it stick
Compare a plant wall and an animal membrane under water entry.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.