Maths
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Responding to change (a2 only)
Infection and response
Homeostasis and response
Energy transfers (a2 only)
Cell biology
Organisms respond to changes in their internal and external environments (a-level only)
Biological molecules
Organisation
Substance exchange
Bioenergetics
Genetic information & variation
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Genetics & ecosystems (a2 only)
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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
World war one
Britain: 1509 -1745
Show all topics
Biology
5 Dec 2025
330
5 pages
Emily Anne @emilyanne
Every single cell in your body is wrapped in a biological membrane - think of it as the... Show more
Understanding biological membranes starts with knowing they're made primarily of phospholipids - molecules with a water-loving head and two water-hating tails. Picture them like tiny magnets that naturally arrange themselves into a double layer with heads facing outward and tails tucked inside.
The fluid mosaic model describes how cell membranes actually work in real life. The "fluid" part means phospholipids can slide around sideways (they're not stuck in place), whilst "mosaic" refers to all the different components scattered throughout like pieces of a puzzle.
Beyond phospholipids, membranes contain cholesterol for stability, transport proteins that act like doorways for molecules, and glycoproteins that help cells recognise each other. Think of it as a busy city with roads (phospholipids), traffic lights (proteins), and street signs (glycoproteins) all working together.
Key Point The fluid mosaic model shows that membranes are dynamic, flexible structures - not rigid walls!
Cell membranes are brilliant at controlling what enters and exits cells through various transport mechanisms. Small, non-polar molecules like oxygen and carbon dioxide can slip straight through the phospholipid bilayer - no help needed.
Diffusion moves substances from high to low concentration without using energy. Simple diffusion happens directly through the membrane, whilst facilitated diffusion requires special proteins to help larger or charged molecules cross over.
Osmosis is specifically about water movement through aquaporins (water channels) from areas of higher water concentration to lower water concentration. Remember, this follows water potential gradients - water always moves towards more negative water potential.
Different transport proteins have specific jobs channel proteins create tunnels for ions and water, whilst carrier proteins physically bind to molecules, change shape, and release them on the other side.
Remember Passive transport (diffusion and osmosis) needs no energy input - it's like rolling downhill!
Sometimes cells need to move substances uphill against concentration gradients, which requires active transport. This process uses ATP (cellular energy) and carrier proteins to pump molecules from low to high concentration areas.
Co-transport is particularly clever - it moves two different molecules simultaneously using a co-transport protein. Common examples include sodium ions with glucose, sodium with amino acids, and hydrogen ions with sucrose.
The beauty of co-transport is that whilst one molecule moves downhill (high to low concentration), it provides energy to move another molecule uphill. It's like using a heavy person going down a seesaw to lift a lighter person up.
These transport mechanisms give cells incredible control over their internal environment. They can accumulate nutrients, remove waste, and maintain the precise conditions needed for life.
Top Tip Active transport always requires ATP energy - think "active = energy needed"!
Biological membranes are absolutely crucial for organelle function throughout the cell. The rough endoplasmic reticulum (RER) connects directly to the nuclear envelope, creating a continuous membrane system for protein transport.
Vesicles constantly fuse with membranes in the Golgi apparatus, allowing cells to package and export molecules. This membrane fusion process is essential for secreting hormones, enzymes, and other vital substances.
Phagocytosis (cell eating) relies entirely on membrane flexibility. White blood cells engulf bacteria by wrapping their membrane around the pathogen, then fusing with lysosomes containing digestive enzymes to destroy the invader.
Even bacterial conjugation depends on membranes forming bridges between cells, allowing antibiotic resistance genes to spread horizontally between bacteria - which explains why antibiotic resistance spreads so effectively.
Real-world Connection Understanding membrane fusion helps explain both immune defence and antibiotic resistance - two major medical challenges!
The electron transport chain in both aerobic respiration and photosynthesis happens across membranes, making them essential for life's energy processes. These membranes contain specialised transport proteins that pump hydrogen ions across, creating the energy gradients needed for ATP production.
In respiration, the inner mitochondrial membrane houses the electron transport chain, whilst in photosynthesis, it occurs in the thylakoid membranes of chloroplasts. Both processes rely on membranes creating compartments with different ion concentrations.
Without biological membranes, cells couldn't generate ATP efficiently, making complex life impossible. They're involved in virtually every major biological process - from cell division to waste removal to energy production.
Membranes truly are the unsung heroes of biology, quietly enabling life through their sophisticated structure and versatile functions. Master the membrane, and you've mastered a huge chunk of how life actually works.
Big Picture Membranes aren't just cell boundaries - they're the foundation that makes complex life possible!
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.
You can download the app from Google Play Store and Apple App Store.
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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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore key concepts of viral diseases including Measles, HIV/AIDS, and plant viruses. This summary covers transmission methods, symptoms, complications, and available vaccines. Ideal for GCSE Biology students seeking to grasp the fundamentals of viral infections and their impact on health.
BiologyExplore the key differences between animal and plant cells, focusing on cell structure and the processes of diffusion and osmosis. This summary covers essential concepts of passive transport, including the movement of particles and water across cell membranes. Ideal for revision and understanding cellular functions.
BiologyExplore the essential functions and structures of cell membranes, including the fluid mosaic model, phospholipid bilayer, and the role of membrane proteins. This summary covers how membranes regulate substance movement, compartmentalize cellular functions, and facilitate communication within and outside the cell.
BiologyExplore key concepts of cell structure and function in this comprehensive glossary. Understand the roles of organelles, transport mechanisms, and cellular processes essential for A-level biology. Ideal for students seeking clarity on cell anatomy, membrane transport, and the differences between eukaryotic and prokaryotic cells.
BiologyExplore key concepts in cell biology, including DNA structure, protein synthesis, cellular respiration, and genetic engineering. This summary covers essential processes such as glycolysis, fermentation, and enzyme functions, providing a comprehensive overview for students studying cellular structures and functions. Ideal for Nat 5 Biology revision.
BiologyExplore the essential concepts of plant and animal transport systems, including xylem and phloem functions, blood vessel structures, and the role of stem cells in growth and repair. This summary covers key topics such as cellular respiration, the nervous system, and the structure and function of cells, making it a valuable resource for SQA National 5 Biology students.
BiologyApp Store
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
Emily Anne
@emilyanne
Every single cell in your body is wrapped in a biological membrane - think of it as the cell's security system that decides what gets in and what stays out. These membranes aren't just barriers though; they're incredibly sophisticated structures... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Understanding biological membranes starts with knowing they're made primarily of phospholipids - molecules with a water-loving head and two water-hating tails. Picture them like tiny magnets that naturally arrange themselves into a double layer with heads facing outward and tails tucked inside.
The fluid mosaic model describes how cell membranes actually work in real life. The "fluid" part means phospholipids can slide around sideways (they're not stuck in place), whilst "mosaic" refers to all the different components scattered throughout like pieces of a puzzle.
Beyond phospholipids, membranes contain cholesterol for stability, transport proteins that act like doorways for molecules, and glycoproteins that help cells recognise each other. Think of it as a busy city with roads (phospholipids), traffic lights (proteins), and street signs (glycoproteins) all working together.
Key Point: The fluid mosaic model shows that membranes are dynamic, flexible structures - not rigid walls!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cell membranes are brilliant at controlling what enters and exits cells through various transport mechanisms. Small, non-polar molecules like oxygen and carbon dioxide can slip straight through the phospholipid bilayer - no help needed.
Diffusion moves substances from high to low concentration without using energy. Simple diffusion happens directly through the membrane, whilst facilitated diffusion requires special proteins to help larger or charged molecules cross over.
Osmosis is specifically about water movement through aquaporins (water channels) from areas of higher water concentration to lower water concentration. Remember, this follows water potential gradients - water always moves towards more negative water potential.
Different transport proteins have specific jobs: channel proteins create tunnels for ions and water, whilst carrier proteins physically bind to molecules, change shape, and release them on the other side.
Remember: Passive transport (diffusion and osmosis) needs no energy input - it's like rolling downhill!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Sometimes cells need to move substances uphill against concentration gradients, which requires active transport. This process uses ATP (cellular energy) and carrier proteins to pump molecules from low to high concentration areas.
Co-transport is particularly clever - it moves two different molecules simultaneously using a co-transport protein. Common examples include sodium ions with glucose, sodium with amino acids, and hydrogen ions with sucrose.
The beauty of co-transport is that whilst one molecule moves downhill (high to low concentration), it provides energy to move another molecule uphill. It's like using a heavy person going down a seesaw to lift a lighter person up.
These transport mechanisms give cells incredible control over their internal environment. They can accumulate nutrients, remove waste, and maintain the precise conditions needed for life.
Top Tip: Active transport always requires ATP energy - think "active = energy needed"!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Biological membranes are absolutely crucial for organelle function throughout the cell. The rough endoplasmic reticulum (RER) connects directly to the nuclear envelope, creating a continuous membrane system for protein transport.
Vesicles constantly fuse with membranes in the Golgi apparatus, allowing cells to package and export molecules. This membrane fusion process is essential for secreting hormones, enzymes, and other vital substances.
Phagocytosis (cell eating) relies entirely on membrane flexibility. White blood cells engulf bacteria by wrapping their membrane around the pathogen, then fusing with lysosomes containing digestive enzymes to destroy the invader.
Even bacterial conjugation depends on membranes forming bridges between cells, allowing antibiotic resistance genes to spread horizontally between bacteria - which explains why antibiotic resistance spreads so effectively.
Real-world Connection: Understanding membrane fusion helps explain both immune defence and antibiotic resistance - two major medical challenges!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The electron transport chain in both aerobic respiration and photosynthesis happens across membranes, making them essential for life's energy processes. These membranes contain specialised transport proteins that pump hydrogen ions across, creating the energy gradients needed for ATP production.
In respiration, the inner mitochondrial membrane houses the electron transport chain, whilst in photosynthesis, it occurs in the thylakoid membranes of chloroplasts. Both processes rely on membranes creating compartments with different ion concentrations.
Without biological membranes, cells couldn't generate ATP efficiently, making complex life impossible. They're involved in virtually every major biological process - from cell division to waste removal to energy production.
Membranes truly are the unsung heroes of biology, quietly enabling life through their sophisticated structure and versatile functions. Master the membrane, and you've mastered a huge chunk of how life actually works.
Big Picture: Membranes aren't just cell boundaries - they're the foundation that makes complex life possible!
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.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
3
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore key concepts of viral diseases including Measles, HIV/AIDS, and plant viruses. This summary covers transmission methods, symptoms, complications, and available vaccines. Ideal for GCSE Biology students seeking to grasp the fundamentals of viral infections and their impact on health.
BiologyExplore the key differences between animal and plant cells, focusing on cell structure and the processes of diffusion and osmosis. This summary covers essential concepts of passive transport, including the movement of particles and water across cell membranes. Ideal for revision and understanding cellular functions.
BiologyExplore the essential functions and structures of cell membranes, including the fluid mosaic model, phospholipid bilayer, and the role of membrane proteins. This summary covers how membranes regulate substance movement, compartmentalize cellular functions, and facilitate communication within and outside the cell.
BiologyExplore key concepts of cell structure and function in this comprehensive glossary. Understand the roles of organelles, transport mechanisms, and cellular processes essential for A-level biology. Ideal for students seeking clarity on cell anatomy, membrane transport, and the differences between eukaryotic and prokaryotic cells.
BiologyExplore key concepts in cell biology, including DNA structure, protein synthesis, cellular respiration, and genetic engineering. This summary covers essential processes such as glycolysis, fermentation, and enzyme functions, providing a comprehensive overview for students studying cellular structures and functions. Ideal for Nat 5 Biology revision.
BiologyExplore the essential concepts of plant and animal transport systems, including xylem and phloem functions, blood vessel structures, and the role of stem cells in growth and repair. This summary covers key topics such as cellular respiration, the nervous system, and the structure and function of cells, making it a valuable resource for SQA National 5 Biology students.
BiologyApp Store
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
Sociology