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177
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27 Dec 2025
•
GCSE Biology: AQA Gas Exchange and Transport
L
Lexi Jury
@lexi.jury
1 / 3
Diffusion and Active Transport
Think of diffusion like perfume spreading across a room - particles naturally move from where there's loads of them to where there's fewer. This happens in gases and solutions, always going from high to low concentration.
Several factors speed up diffusion: a bigger concentration difference works faster, higher temperatures get particles moving quicker, and more surface area gives more space for particles to pass through. Your cell membranes act like selective bouncers - they let tiny molecules like oxygen, water, and glucose through, but block big ones like starch and proteins.
Active transport is diffusion's rebellious cousin - it moves particles against the concentration gradient (from low to high concentration). This takes energy from respiration, like pushing a boulder uphill.
Root hair cells are perfect examples of active transport in action. They stick out into soil and use energy to absorb minerals even when there's more inside the cell than in the soil. In your gut, active transport kicks in when nutrient levels in your intestines drop below those in your blood.
💡 Remember: Diffusion is passive (no energy needed), active transport requires energy from respiration!
Exchange Surfaces
Single cells have it easy - they can get everything they need through simple diffusion across their membrane. But as organisms get bigger, their surface area to volume ratio becomes a problem, like trying to feed a crowd through a single door.
That's where exchange surfaces come in. These specialised structures have clever adaptations: thin membranes create short diffusion pathways, large surface areas allow more substances to pass through, and good blood supplies keep things moving efficiently.
Your lungs and alveoli are brilliant examples. The alveoli are tiny air sacs with an enormous surface area, thin walls for quick gas exchange, and loads of blood capillaries. They're also moist, which helps dissolve gases for easier transport.
Villi in your small intestine work similarly, increasing the absorption of digested food. These finger-like projections have a single layer of surface cells and an excellent blood supply. They even use active transport when needed to grab every last nutrient.
💡 Key insight: All exchange surfaces share the same three features - thin walls, large surface area, and good blood supply!
Specialised Exchange Surfaces
Leaf structure is perfectly designed for gas exchange during photosynthesis. Carbon dioxide diffuses through tiny holes called stomata (mostly on the leaf's underside) into air spaces, then into cells where photosynthesis happens. Oxygen and water vapour diffuse back out the same way.
The leaf's flat shape massively increases the surface area for efficient gas exchange. Guard cells control the stomata size - they'll close them if water loss gets too rapid, preventing the plant from wilting like a deflated balloon.
Fish gills showcase some of nature's cleverest engineering. Water enters through the fish's mouth and flows over the gills in the opposite direction to blood flow. This counter-current system maintains a steep concentration gradient, maximising oxygen uptake.
Gills are made of thin plates called gill filaments, covered in even tinier structures called lamellae. This creates an absolutely massive surface area packed with blood capillaries. The thin surface layers minimise diffusion distance, making the whole system incredibly efficient.
💡 Smart design: Counter-current flow in gills ensures the oxygen concentration in water is always higher than in blood - maximum efficiency guaranteed!
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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!
Sudenaz Ocak
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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
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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
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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
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
GCSE Biology: AQA Gas Exchange and Transport
L
Lexi Jury
@lexi.jury
Your cells are constantly moving substances in and out - but how do they actually do this? Understanding diffusion, active transport, and exchange surfaces is crucial for grasping how living things survive and thrive.
Diffusion and Active Transport
Think of diffusion like perfume spreading across a room - particles naturally move from where there's loads of them to where there's fewer. This happens in gases and solutions, always going from high to low concentration.
Several factors speed up diffusion: a bigger concentration difference works faster, higher temperatures get particles moving quicker, and more surface area gives more space for particles to pass through. Your cell membranes act like selective bouncers - they let tiny molecules like oxygen, water, and glucose through, but block big ones like starch and proteins.
Active transport is diffusion's rebellious cousin - it moves particles against the concentration gradient (from low to high concentration). This takes energy from respiration, like pushing a boulder uphill.
Root hair cells are perfect examples of active transport in action. They stick out into soil and use energy to absorb minerals even when there's more inside the cell than in the soil. In your gut, active transport kicks in when nutrient levels in your intestines drop below those in your blood.
💡 Remember: Diffusion is passive (no energy needed), active transport requires energy from respiration!
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Exchange Surfaces
Single cells have it easy - they can get everything they need through simple diffusion across their membrane. But as organisms get bigger, their surface area to volume ratio becomes a problem, like trying to feed a crowd through a single door.
That's where exchange surfaces come in. These specialised structures have clever adaptations: thin membranes create short diffusion pathways, large surface areas allow more substances to pass through, and good blood supplies keep things moving efficiently.
Your lungs and alveoli are brilliant examples. The alveoli are tiny air sacs with an enormous surface area, thin walls for quick gas exchange, and loads of blood capillaries. They're also moist, which helps dissolve gases for easier transport.
Villi in your small intestine work similarly, increasing the absorption of digested food. These finger-like projections have a single layer of surface cells and an excellent blood supply. They even use active transport when needed to grab every last nutrient.
💡 Key insight: All exchange surfaces share the same three features - thin walls, large surface area, and good blood supply!
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Join milions of students
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Specialised Exchange Surfaces
Leaf structure is perfectly designed for gas exchange during photosynthesis. Carbon dioxide diffuses through tiny holes called stomata (mostly on the leaf's underside) into air spaces, then into cells where photosynthesis happens. Oxygen and water vapour diffuse back out the same way.
The leaf's flat shape massively increases the surface area for efficient gas exchange. Guard cells control the stomata size - they'll close them if water loss gets too rapid, preventing the plant from wilting like a deflated balloon.
Fish gills showcase some of nature's cleverest engineering. Water enters through the fish's mouth and flows over the gills in the opposite direction to blood flow. This counter-current system maintains a steep concentration gradient, maximising oxygen uptake.
Gills are made of thin plates called gill filaments, covered in even tinier structures called lamellae. This creates an absolutely massive surface area packed with blood capillaries. The thin surface layers minimise diffusion distance, making the whole system incredibly efficient.
💡 Smart design: Counter-current flow in gills ensures the oxygen concentration in water is always higher than in blood - maximum efficiency guaranteed!
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Most popular content: Transport Proteins
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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