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Amelia
18/10/2025
Biology
Diffusion
551
•
18 Oct 2025
•
Understanding Facilitated Diffusion and Transport Across Cell Membranes for A Level Biology
Amelia
@ameliafox64
Protein Channels and Carrier Proteins in Facilitated Diffusion
This page delves into the specific mechanisms of facilitated diffusion, focusing on protein channels and carrier proteins that enable the transport of molecules across cell membranes.
Protein Channels
Protein channels are integral membrane proteins that form hydrophilic passages across the cell membrane. These channels are highly specific and selective in their function.
Key features of protein channels:
- Form water-filled, hydrophilic channels across the membrane
- Allow specific water-soluble ions to pass through
- Open selectively in the presence of specific ions
- Remain closed when the particular ion is not present
Highlight: The selectivity of protein channels ensures that only specific ions can pass through, maintaining cellular homeostasis.
Carrier Proteins
Carrier proteins are another type of transmembrane protein involved in facilitated diffusion. They undergo conformational changes to transport molecules across the membrane.
Characteristics of carrier proteins:
- Span the entire membrane and are highly specific
- Change shape when a specific molecule binds to them
- Release the molecule to the inside of the cell
- Require no energy input, as molecules move down the concentration gradient using their kinetic energy
Example: The glucose transporter GLUT4 is a carrier protein that facilitates the entry of glucose into muscle and fat cells.
Vocabulary: Transmembrane channels are specific points on the plasma membrane where facilitated diffusion occurs through protein channels or carrier proteins.
Understanding the mechanisms of protein channels and carrier proteins is crucial for A Level Biology students, particularly when studying transport across cell membranes and preparing for AQA exam questions on this topic.
Diffusion and Facilitated Diffusion
Diffusion is a fundamental process in biology, involving the movement of particles from areas of high concentration to low concentration. This page explores the key principles of diffusion and introduces the concept of facilitated diffusion.
Principles of Diffusion
Diffusion is characterized by the random motion of particles due to their kinetic energy. This process is passive, requiring no additional energy input. The cell surface membrane's partial permeability plays a crucial role in regulating diffusion.
Definition: Diffusion is the net movement of molecules or ions from a region of higher concentration to one of lower concentration until evenly distributed.
Substances that can diffuse through cell membranes include:
- Lipid-soluble molecules
- Non-polar molecules
- Small molecules like oxygen and carbon dioxide
Highlight: The rate of diffusion is influenced by several factors, including concentration gradient, temperature, surface area, molecule size, and diffusion distance.
Facilitated Diffusion
Facilitated diffusion allows water-soluble, charged ions, and polar molecules to cross the plasma membrane. This process is essential for substances that cannot pass through the hydrophobic fatty acid tails of the membrane.
Vocabulary: Facilitated diffusion utilizes protein channels and carrier proteins to transport molecules across the cell membrane.
Key characteristics of facilitated diffusion:
- It is a passive process
- Occurs down the concentration gradient
- Relies on the kinetic energy of molecules
- Takes place at specific points on the plasma membrane
Example: Glucose, a polar molecule, requires facilitated diffusion to enter cells efficiently.
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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
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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
Understanding Facilitated Diffusion and Transport Across Cell Membranes for A Level Biology
Amelia
@ameliafox64
Facilitated diffusion is a crucial process in A Level Biology, involving the movement of molecules across cell membranes. This passive transport mechanism allows specific substances to cross the plasma membrane through protein channels and carrier proteins, playing a vital... Show more
Protein Channels and Carrier Proteins in Facilitated Diffusion
This page delves into the specific mechanisms of facilitated diffusion, focusing on protein channels and carrier proteins that enable the transport of molecules across cell membranes.
Protein Channels
Protein channels are integral membrane proteins that form hydrophilic passages across the cell membrane. These channels are highly specific and selective in their function.
Key features of protein channels:
- Form water-filled, hydrophilic channels across the membrane
- Allow specific water-soluble ions to pass through
- Open selectively in the presence of specific ions
- Remain closed when the particular ion is not present
Highlight: The selectivity of protein channels ensures that only specific ions can pass through, maintaining cellular homeostasis.
Carrier Proteins
Carrier proteins are another type of transmembrane protein involved in facilitated diffusion. They undergo conformational changes to transport molecules across the membrane.
Characteristics of carrier proteins:
- Span the entire membrane and are highly specific
- Change shape when a specific molecule binds to them
- Release the molecule to the inside of the cell
- Require no energy input, as molecules move down the concentration gradient using their kinetic energy
Example: The glucose transporter GLUT4 is a carrier protein that facilitates the entry of glucose into muscle and fat cells.
Vocabulary: Transmembrane channels are specific points on the plasma membrane where facilitated diffusion occurs through protein channels or carrier proteins.
Understanding the mechanisms of protein channels and carrier proteins is crucial for A Level Biology students, particularly when studying transport across cell membranes and preparing for AQA exam questions on this topic.
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Improve your grades
Join milions of students
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Diffusion and Facilitated Diffusion
Diffusion is a fundamental process in biology, involving the movement of particles from areas of high concentration to low concentration. This page explores the key principles of diffusion and introduces the concept of facilitated diffusion.
Principles of Diffusion
Diffusion is characterized by the random motion of particles due to their kinetic energy. This process is passive, requiring no additional energy input. The cell surface membrane's partial permeability plays a crucial role in regulating diffusion.
Definition: Diffusion is the net movement of molecules or ions from a region of higher concentration to one of lower concentration until evenly distributed.
Substances that can diffuse through cell membranes include:
- Lipid-soluble molecules
- Non-polar molecules
- Small molecules like oxygen and carbon dioxide
Highlight: The rate of diffusion is influenced by several factors, including concentration gradient, temperature, surface area, molecule size, and diffusion distance.
Facilitated Diffusion
Facilitated diffusion allows water-soluble, charged ions, and polar molecules to cross the plasma membrane. This process is essential for substances that cannot pass through the hydrophobic fatty acid tails of the membrane.
Vocabulary: Facilitated diffusion utilizes protein channels and carrier proteins to transport molecules across the cell membrane.
Key characteristics of facilitated diffusion:
- It is a passive process
- Occurs down the concentration gradient
- Relies on the kinetic energy of molecules
- Takes place at specific points on the plasma membrane
Example: Glucose, a polar molecule, requires facilitated diffusion to enter cells efficiently.
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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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