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1 Dec 2025
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AQA A Level Biology - Osmosis Practical Notes
Milkshakemi
@milkshakemi
1 / 4
Setting Up Your Dilution Series
You'll be creating different sucrose concentrations to test osmosis in potato tissue. Think of it like making squash - you start with the strongest solution and add water to make weaker ones.
The key formula here is M₁V₁ = M₂V₂, which helps you work out exactly how much concentrated solution you need. For example, to make 20cm³ of 0.2M solution from 1.0M stock, you'd need 4cm³ of the concentrated stuff plus 16cm³ of distilled water.
Your independent variable is the sucrose concentration (what you're changing), whilst the dependent variable is the mass change of the potato (what you're measuring). Everything else - temperature, time, potato type - stays constant as controlled variables.
Top Tip: Label your test tubes clearly with concentrations (0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M) before you start - trust me, it gets confusing quickly!
Preparing Your Potato Samples
Fresh potatoes are absolutely crucial here - dried-out spuds will mess up your results because their solute concentration changes as water evaporates. You want consistent starting conditions across all samples.
Use a cork borer to cut six uniform cylinders from the same potato, then carefully remove the skin with a scalpel. The skin acts like a waterproof barrier, so leaving it on would prevent proper osmosis from occurring.
Blot each cylinder dry before weighing - any surface water will throw off your initial mass readings. You don't need perfectly identical lengths, but try to keep them fairly uniform.
Key Point: Always zero your balance before weighing, and record masses immediately in a pre-prepared table to avoid mixing up your data.
Running the Experiment
Pour exactly 20cm³ of each solution into separate test tubes, adding the most concentrated solution last to avoid contamination. Pop one potato cylinder into each tube and place them all in a water bath simultaneously.
After 20 minutes, remove the cylinders and place each one on labelled paper towels according to their concentration. This timing is critical - too short and osmosis won't be complete, too long and other factors might interfere.
Blot away surface water before the final weighing - you're measuring water that's moved into or out of the cells, not water clinging to the outside. Any excess moisture will appear as a false mass increase.
Remember: Handle each cylinder gently and work systematically through the concentrations to avoid mix-ups.
Analysing Your Results
Calculate the percentage change in mass using the formula: (change in mass ÷ initial mass) × 100. This standardises your results, making comparisons meaningful even if your potato cylinders weren't identical sizes.
When you plot concentration against percentage change, you'll get a lovely negative correlation - as sucrose concentration increases, mass change decreases. Positive values mean water moved in (hypotonic solution), negative values mean water moved out (hypertonic solution).
The magic happens where the line crosses zero - this is the isotonic point, roughly around 0.3M in most cases. Here, no net water movement occurs because the solute concentration inside the potato cells matches the external solution.
Analysis Tip: This zero-crossing point tells you the actual solute concentration inside potato cells - pretty neat for a simple practical!
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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.
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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
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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
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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
AQA A Level Biology - Osmosis Practical Notes
Milkshakemi
@milkshakemi
Ever wondered how cells control what goes in and out? This osmosis practical uses potato chips and sugar solutions to demonstrate how water moves across cell membranes - and it's actually quite brilliant for understanding this fundamental biological process.
Setting Up Your Dilution Series
You'll be creating different sucrose concentrations to test osmosis in potato tissue. Think of it like making squash - you start with the strongest solution and add water to make weaker ones.
The key formula here is M₁V₁ = M₂V₂, which helps you work out exactly how much concentrated solution you need. For example, to make 20cm³ of 0.2M solution from 1.0M stock, you'd need 4cm³ of the concentrated stuff plus 16cm³ of distilled water.
Your independent variable is the sucrose concentration (what you're changing), whilst the dependent variable is the mass change of the potato (what you're measuring). Everything else - temperature, time, potato type - stays constant as controlled variables.
Top Tip: Label your test tubes clearly with concentrations (0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M) before you start - trust me, it gets confusing quickly!
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Preparing Your Potato Samples
Fresh potatoes are absolutely crucial here - dried-out spuds will mess up your results because their solute concentration changes as water evaporates. You want consistent starting conditions across all samples.
Use a cork borer to cut six uniform cylinders from the same potato, then carefully remove the skin with a scalpel. The skin acts like a waterproof barrier, so leaving it on would prevent proper osmosis from occurring.
Blot each cylinder dry before weighing - any surface water will throw off your initial mass readings. You don't need perfectly identical lengths, but try to keep them fairly uniform.
Key Point: Always zero your balance before weighing, and record masses immediately in a pre-prepared table to avoid mixing up your data.
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Running the Experiment
Pour exactly 20cm³ of each solution into separate test tubes, adding the most concentrated solution last to avoid contamination. Pop one potato cylinder into each tube and place them all in a water bath simultaneously.
After 20 minutes, remove the cylinders and place each one on labelled paper towels according to their concentration. This timing is critical - too short and osmosis won't be complete, too long and other factors might interfere.
Blot away surface water before the final weighing - you're measuring water that's moved into or out of the cells, not water clinging to the outside. Any excess moisture will appear as a false mass increase.
Remember: Handle each cylinder gently and work systematically through the concentrations to avoid mix-ups.
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Analysing Your Results
Calculate the percentage change in mass using the formula: (change in mass ÷ initial mass) × 100. This standardises your results, making comparisons meaningful even if your potato cylinders weren't identical sizes.
When you plot concentration against percentage change, you'll get a lovely negative correlation - as sucrose concentration increases, mass change decreases. Positive values mean water moved in (hypotonic solution), negative values mean water moved out (hypertonic solution).
The magic happens where the line crosses zero - this is the isotonic point, roughly around 0.3M in most cases. Here, no net water movement occurs because the solute concentration inside the potato cells matches the external solution.
Analysis Tip: This zero-crossing point tells you the actual solute concentration inside potato cells - pretty neat for a simple practical!
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What is the Knowunity AI companion?
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Where can I download the Knowunity app?
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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