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6 Dec 2025
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Understanding Diffusion and Osmosis: Key Concepts and Diagrams
Maitreyi Taduri
@maitreyi_t
1 / 4
Understanding Diffusion
Think of diffusion like the smell of your favourite takeaway spreading through your house - particles naturally move from where there's loads of them to where there's fewer. Diffusion is simply particles spreading out from areas of high concentration to low concentration.
Your body relies on diffusion every single day. When you breathe, oxygen moves into your bloodstream whilst carbon dioxide moves out through gas exchange in your lungs. Your kidneys also use diffusion to filter out waste like urea from your blood.
Three main factors control how fast diffusion happens. A steeper concentration gradient means faster diffusion because more particles are on the move. Higher temperature makes particles zip around faster, causing more collisions. Finally, a larger surface area lets more particles pass through at once.
Quick Tip: Remember the acronym CST - Concentration gradient, Surface area, and Temperature all speed up diffusion when increased!
Osmosis Explained Simply
Osmosis is like diffusion's picky cousin - it only moves water molecules across special barriers called partially permeable membranes. Water always flows from where there's more of it to where there's less of it.
Here's the tricky bit that catches many students out: a dilute solution has high water concentration, whilst a concentrated solution has low water concentration. Think of it like squash - the more concentrated the squash, the less actual water there is!
Scientists describe solutions using three key terms. An isotonic solution has the same concentration as inside a cell, so water movement balances out. A hypertonic solution is more concentrated than the cell's contents. A hypotonic solution is less concentrated than what's inside the cell.
Memory Trick: Hyper = Higher concentration, Hypo = Lower concentration. The "tonic" part always refers to what's outside the cell!
How Osmosis Affects Living Cells
Animal cells are quite fragile when it comes to osmosis. Put them in pure water (hypotonic) and they'll swell up like balloons until they burst - not ideal! Place them in very salty water (hypertonic) and they shrivel up like raisins as water rushes out.
Plant cells handle osmosis much better thanks to their tough cell walls. When water rushes in, the cell becomes turgid (firm and rigid) - this is what keeps plants standing upright! Your houseplant's leaves stay perky because of turgor pressure.
However, if a plant cell loses too much water, it becomes flaccid (floppy) and eventually undergoes plasmolysis. This is when the cell membrane pulls away from the cell wall - basically the plant equivalent of severe dehydration.
Real-Life Connection: This is why plants wilt when you forget to water them and why putting salt on slugs is so effective (though rather cruel)!
Investigating Osmosis in the Lab
You can actually see osmosis in action using a simple potato experiment that's become a classic in biology labs. It's dead easy to set up and gives you proper scientific results you can analyse.
The method involves cutting potato cylinders and dunking them in different sugar or salt concentrations for 24 hours. You'll measure their mass before and after to see if water moved in or out. Pure water makes them gain mass, whilst concentrated solutions make them lose mass.
The clever bit is calculating percentage change in mass rather than just looking at raw numbers. This lets you compare results fairly and plot a proper graph. When you plot concentration against percentage change, you'll get a lovely curve that shows exactly how osmosis works.
The point where the line crosses zero tells you the concentration inside the potato cells - that's where no net water movement happens because it's isotonic!
Exam Tip: Always dry your potato cylinders properly before weighing - surface water will mess up your results and cost you marks!
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Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
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This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
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The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
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In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding Diffusion and Osmosis: Key Concepts and Diagrams
Maitreyi Taduri
@maitreyi_t
Ever wonder how your body gets oxygen to your cells or how plants stay upright? It's all down to two crucial biological processes that happen constantly around and inside you. Diffusion and osmosisare the invisible forces that keep life... Show more
Understanding Diffusion
Think of diffusion like the smell of your favourite takeaway spreading through your house - particles naturally move from where there's loads of them to where there's fewer. Diffusion is simply particles spreading out from areas of high concentration to low concentration.
Your body relies on diffusion every single day. When you breathe, oxygen moves into your bloodstream whilst carbon dioxide moves out through gas exchange in your lungs. Your kidneys also use diffusion to filter out waste like urea from your blood.
Three main factors control how fast diffusion happens. A steeper concentration gradient means faster diffusion because more particles are on the move. Higher temperature makes particles zip around faster, causing more collisions. Finally, a larger surface area lets more particles pass through at once.
Quick Tip: Remember the acronym CST - Concentration gradient, Surface area, and Temperature all speed up diffusion when increased!
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Osmosis Explained Simply
Osmosis is like diffusion's picky cousin - it only moves water molecules across special barriers called partially permeable membranes. Water always flows from where there's more of it to where there's less of it.
Here's the tricky bit that catches many students out: a dilute solution has high water concentration, whilst a concentrated solution has low water concentration. Think of it like squash - the more concentrated the squash, the less actual water there is!
Scientists describe solutions using three key terms. An isotonic solution has the same concentration as inside a cell, so water movement balances out. A hypertonic solution is more concentrated than the cell's contents. A hypotonic solution is less concentrated than what's inside the cell.
Memory Trick: Hyper = Higher concentration, Hypo = Lower concentration. The "tonic" part always refers to what's outside the cell!
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How Osmosis Affects Living Cells
Animal cells are quite fragile when it comes to osmosis. Put them in pure water (hypotonic) and they'll swell up like balloons until they burst - not ideal! Place them in very salty water (hypertonic) and they shrivel up like raisins as water rushes out.
Plant cells handle osmosis much better thanks to their tough cell walls. When water rushes in, the cell becomes turgid (firm and rigid) - this is what keeps plants standing upright! Your houseplant's leaves stay perky because of turgor pressure.
However, if a plant cell loses too much water, it becomes flaccid (floppy) and eventually undergoes plasmolysis. This is when the cell membrane pulls away from the cell wall - basically the plant equivalent of severe dehydration.
Real-Life Connection: This is why plants wilt when you forget to water them and why putting salt on slugs is so effective (though rather cruel)!
Sign up to see the contentIt's free!
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Improve your grades
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Investigating Osmosis in the Lab
You can actually see osmosis in action using a simple potato experiment that's become a classic in biology labs. It's dead easy to set up and gives you proper scientific results you can analyse.
The method involves cutting potato cylinders and dunking them in different sugar or salt concentrations for 24 hours. You'll measure their mass before and after to see if water moved in or out. Pure water makes them gain mass, whilst concentrated solutions make them lose mass.
The clever bit is calculating percentage change in mass rather than just looking at raw numbers. This lets you compare results fairly and plot a proper graph. When you plot concentration against percentage change, you'll get a lovely curve that shows exactly how osmosis works.
The point where the line crosses zero tells you the concentration inside the potato cells - that's where no net water movement happens because it's isotonic!
Exam Tip: Always dry your potato cylinders properly before weighing - surface water will mess up your results and cost you marks!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
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Is Knowunity really free of charge?
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Most popular content: Diffusion and Osmosis
Most popular content in Biology
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English - inspector calls quotes and analysis
Quotes from every main character
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user