Cell membranes are like the bouncers of the cellular world,... Show more
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04/12/2025
Biology
2.1.5 OCR A LEVEL BIOLOGY- ( cell membrane)
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Cell Membrane Functions and Structure
Your cells are basically tiny factories that need proper security systems to function properly. The plasma membrane acts as a selective barrier, keeping your cell's contents safe whilst allowing essential molecules to pass through when needed.
Inside your cells, internal membranes create separate compartments around organelles like mitochondria and the nucleus. Think of these like different departments in a factory - each area can focus on specific jobs without interference from other processes.
The fluid mosaic model explains how membranes are built. Picture a double layer of phospholipids (like a sandwich) with various proteins floating around like icebergs. Cholesterol molecules squeeze between the phospholipids to keep everything stable and control how fluid the membrane stays.
Key Point: The membrane isn't rigid like a wall - it's more like a flexible boundary that can adapt whilst maintaining control over what passes through.
Membrane Components and Cell Recognition
Glycoproteins and glycolipids are basically the cell's ID cards - they stick out from the membrane surface with unique carbohydrate chains that help other cells recognise whether you're friend or foe. This is why your immune system can tell the difference between your own cells and invading bacteria.
These recognition molecules also work as binding sites for hormones and drugs. When you take medicine like salbutamol for asthma, it specifically targets receptors on your airway muscles, causing them to relax and helping you breathe easier.
Membrane proteins are the real workhorses, forming channels and pumps that move substances across the membrane. Some create pores for molecules that can't dissolve in the fatty phospholipid layer, whilst others actively transport materials against concentration gradients.
Temperature and solvents like alcohol can seriously mess with membrane structure. As temperature rises, membranes become leakier, and eventually proteins can denature, causing the whole system to break down.
Key Point: Cell signalling depends entirely on the right shapes fitting together - like biological lock and key systems that coordinate your entire body's activities.
Transport Across Membranes
Moving stuff across membranes happens in two main ways, and understanding this difference will save you marks in exams. Passive transport doesn't need any cellular energy - molecules simply follow their natural tendency to spread out from crowded areas to less crowded ones.
Diffusion works for small or fat-soluble molecules that can slip through the phospholipid bilayer directly. Facilitated diffusion uses protein channels or carriers to help larger molecules cross, whilst osmosis specifically refers to water movement down its concentration gradient.
Several factors speed up diffusion rates: higher temperatures give molecules more energy to move faster, steeper concentration gradients create stronger driving forces, and larger surface areas provide more space for crossing.
Active transport is completely different - it burns ATP energy to pump molecules uphill against their concentration gradients. This is like pushing water uphill instead of letting it flow downhill naturally, requiring special pump proteins that change shape to move molecules across.
Key Point: Remember that passive transport is like rolling downhill (no energy needed), whilst active transport is like cycling uphill (requires energy input).
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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
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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
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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
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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
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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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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.
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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
OCR A-Level Biology: Understanding the Cell Membrane
Cell membranes are like the bouncers of the cellular world, controlling what gets in and out of your cells. Understanding how these vital barriers work is absolutely crucial for your biology exams, and once you grasp the basics, the rest... Show more
Cell Membrane Functions and Structure
Your cells are basically tiny factories that need proper security systems to function properly. The plasma membrane acts as a selective barrier, keeping your cell's contents safe whilst allowing essential molecules to pass through when needed.
Inside your cells, internal membranes create separate compartments around organelles like mitochondria and the nucleus. Think of these like different departments in a factory - each area can focus on specific jobs without interference from other processes.
The fluid mosaic model explains how membranes are built. Picture a double layer of phospholipids (like a sandwich) with various proteins floating around like icebergs. Cholesterol molecules squeeze between the phospholipids to keep everything stable and control how fluid the membrane stays.
Key Point: The membrane isn't rigid like a wall - it's more like a flexible boundary that can adapt whilst maintaining control over what passes through.
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Membrane Components and Cell Recognition
Glycoproteins and glycolipids are basically the cell's ID cards - they stick out from the membrane surface with unique carbohydrate chains that help other cells recognise whether you're friend or foe. This is why your immune system can tell the difference between your own cells and invading bacteria.
These recognition molecules also work as binding sites for hormones and drugs. When you take medicine like salbutamol for asthma, it specifically targets receptors on your airway muscles, causing them to relax and helping you breathe easier.
Membrane proteins are the real workhorses, forming channels and pumps that move substances across the membrane. Some create pores for molecules that can't dissolve in the fatty phospholipid layer, whilst others actively transport materials against concentration gradients.
Temperature and solvents like alcohol can seriously mess with membrane structure. As temperature rises, membranes become leakier, and eventually proteins can denature, causing the whole system to break down.
Key Point: Cell signalling depends entirely on the right shapes fitting together - like biological lock and key systems that coordinate your entire body's activities.
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Transport Across Membranes
Moving stuff across membranes happens in two main ways, and understanding this difference will save you marks in exams. Passive transport doesn't need any cellular energy - molecules simply follow their natural tendency to spread out from crowded areas to less crowded ones.
Diffusion works for small or fat-soluble molecules that can slip through the phospholipid bilayer directly. Facilitated diffusion uses protein channels or carriers to help larger molecules cross, whilst osmosis specifically refers to water movement down its concentration gradient.
Several factors speed up diffusion rates: higher temperatures give molecules more energy to move faster, steeper concentration gradients create stronger driving forces, and larger surface areas provide more space for crossing.
Active transport is completely different - it burns ATP energy to pump molecules uphill against their concentration gradients. This is like pushing water uphill instead of letting it flow downhill naturally, requiring special pump proteins that change shape to move molecules across.
Key Point: Remember that passive transport is like rolling downhill (no energy needed), whilst active transport is like cycling uphill (requires energy input).
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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