Osmosis
Water moves through a membrane from dilute to concentrated solutions.
About this topic
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (high water potential) to a more concentrated solution (low water potential). Animal cells in pure water swell and may burst, and in concentrated solutions shrink. Plant cells become turgid in water, held by their cell wall, and plasmolysed in strong solutions.
Osmosis is how roots take up water and is tested by weighing potato chips in different sugar solutions.
Put a potato chip in strong salt solution and it turns limp as water leaves its cells; in pure water it becomes firm as water enters. The same effect explains why slugs shrivel when salted and why drinking seawater dehydrates you. In plant cells, water entering makes the vacuole push against the wall, giving turgor pressure that holds stems upright.
Hospitals use isotonic saline drips, which match the concentration of body fluids, so blood cells neither swell nor shrink. A common mistake is saying water moves toward the more concentrated solute, which is right in effect but confusing; clearer is that water moves from high to low water potential. Also remember that osmosis is only for water and only across a partially permeable membrane.
Key ideas
- Passive transport of water
- Cells shrink in strong solution
- Plant cells become turgid in water
Quick check
Use cases: where Osmosis helps
- Homework: review the key idea behind Osmosis before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Osmosis without notes.
- Visual learning: play with the interactive lab to see how Osmosis changes when you adjust its inputs.
- Teaching a friend: explain Osmosis in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Osmosis?
Water moves through a membrane from dilute to concentrated solutions.
What will I learn in Osmosis?
Passive transport of water. Cells shrink in strong solution. Plant cells become turgid in water.
Is Osmosis part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Osmosis lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Osmosis?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.