Maths
Chemistry
Biology
English Language
History
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
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
Cells
Show all topics
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
6 Dec 2025
91
5 pages
Lacie Wade @laciewade_btht
Ever wondered what makes you… well, you? It all starts with cells - the tiny building blocks that... Show more
Not all cells are created equal! There are two main types you need to know about. Prokaryotic cells (like bacteria) are the rebels - they don't bother with a nucleus and just let their DNA float around freely in the cytoplasm. Eukaryotic cells (animals, plants, and fungi) are more organised, keeping their DNA safely locked away in a nucleus.
Every cell has specific parts called organelles that work like tiny factories. The cytoplasm is the jelly-like substance where most chemical reactions happen, whilst the cell membrane acts like a bouncer, controlling what gets in and out. Mitochondria are your cell's powerhouses, creating energy through respiration.
Plant cells get some extra kit that animal cells don't have. They've got chloroplasts for photosynthesis (making food from sunlight), a tough cell wall made of cellulose for support, and a large permanent vacuole that keeps the cell firm and upright.
Quick Tip Remember that ribosomes are found in both prokaryotic and eukaryotic cells - they're essential for making proteins!
Here's something mind-blowing every human cell contains 46 chromosomes arranged in 23 pairs. These chromosomes are packed with DNA, which contains all the instructions for making you!
Mitosis is how your body grows and repairs itself. When you cut your finger or grow taller, mitosis is hard at work. The process is quite clever - first, each chromosome makes an identical copy of itself, then they line up in the middle of the cell like they're ready for a dance-off.
The cell then pulls one copy of each chromosome to opposite ends and splits down the middle. The end result? Two identical daughter cells with exactly the same genetic information as the parent cell. This ensures that every new cell in your body has the complete set of instructions it needs to function properly.
Remember Mitosis produces diploid cells (cells with two sets of chromosomes) - this is crucial for maintaining your genetic makeup!
Meiosis is mitosis's more adventurous cousin. Instead of creating identical copies, meiosis mixes things up to create gametes (sex cells like sperm and eggs) in reproductive organs. This is why you're not identical to your siblings!
The process starts similarly to mitosis - chromosomes copy themselves. But here's where it gets interesting similar chromosomes pair up and actually swap sections of DNA with each other. It's like trading cards, creating new combinations of genetic information.
Unlike mitosis, meiosis involves two divisions, not just one. The first division separates the chromosome pairs, and the second division separates the copied chromosomes. This produces four genetically different cells, each with only 23 chromosomes instead of 46.
Key Point Meiosis creates genetic diversity - it's nature's way of ensuring every individual is unique!
The cell cycle is like a cellular to-do list with six stages. Cells grow, copy their DNA, double-check for errors, divide through mitosis, split their cytoplasm, and then either rest or prepare for another round. It's a highly organised process that keeps your body functioning smoothly.
Stem cells are the ultimate shape-shifters - they haven't decided what they want to be when they grow up yet! Embryonic stem cells are the most flexible and can become any type of cell in the body. Adult stem cells are more limited but still crucial for repair and maintenance.
In plants, stem cells hang out in areas called meristems (like root tips and shoot tips). Unlike human stem cells, plant stem cells can differentiate into any cell type throughout the plant's entire life - pretty impressive!
Fun Fact Your bone marrow contains stem cells that constantly produce new blood cells - you make millions every day!
Cell differentiation transforms boring stem cells into specialists. Once a cell differentiates, it can perform specific jobs - muscle cells contract, nerve cells carry signals, and blood cells transport oxygen. Your body's systems work together the muscular system creates movement, the circulatory system transports substances, and the respiratory system handles oxygen exchange.
Cells need to move substances in and out constantly. Diffusion is the lazy method - molecules naturally move from crowded areas to less crowded ones, like oxygen moving from your lungs into your blood. Osmosis is just diffusion for water molecules through partially permeable membranes.
Sometimes cells need to work against the flow. Active transport uses energy to move substances from low to high concentration areas, like swimming upstream. This is essential when cells need to concentrate important molecules against the natural gradient.
Real-World Example When you're dehydrated, your kidneys use active transport to conserve water and maintain the right balance in your body!
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
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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
Lacie Wade
@laciewade_btht
Ever wondered what makes you… well, you? It all starts with cells - the tiny building blocks that make up every living thing. From bacteria to plants to humans, understanding how cells work, divide, and specialise is key to grasping... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Not all cells are created equal! There are two main types you need to know about. Prokaryotic cells (like bacteria) are the rebels - they don't bother with a nucleus and just let their DNA float around freely in the cytoplasm. Eukaryotic cells (animals, plants, and fungi) are more organised, keeping their DNA safely locked away in a nucleus.
Every cell has specific parts called organelles that work like tiny factories. The cytoplasm is the jelly-like substance where most chemical reactions happen, whilst the cell membrane acts like a bouncer, controlling what gets in and out. Mitochondria are your cell's powerhouses, creating energy through respiration.
Plant cells get some extra kit that animal cells don't have. They've got chloroplasts for photosynthesis (making food from sunlight), a tough cell wall made of cellulose for support, and a large permanent vacuole that keeps the cell firm and upright.
Quick Tip: Remember that ribosomes are found in both prokaryotic and eukaryotic cells - they're essential for making proteins!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Here's something mind-blowing: every human cell contains 46 chromosomes arranged in 23 pairs. These chromosomes are packed with DNA, which contains all the instructions for making you!
Mitosis is how your body grows and repairs itself. When you cut your finger or grow taller, mitosis is hard at work. The process is quite clever - first, each chromosome makes an identical copy of itself, then they line up in the middle of the cell like they're ready for a dance-off.
The cell then pulls one copy of each chromosome to opposite ends and splits down the middle. The end result? Two identical daughter cells with exactly the same genetic information as the parent cell. This ensures that every new cell in your body has the complete set of instructions it needs to function properly.
Remember: Mitosis produces diploid cells (cells with two sets of chromosomes) - this is crucial for maintaining your genetic makeup!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Meiosis is mitosis's more adventurous cousin. Instead of creating identical copies, meiosis mixes things up to create gametes (sex cells like sperm and eggs) in reproductive organs. This is why you're not identical to your siblings!
The process starts similarly to mitosis - chromosomes copy themselves. But here's where it gets interesting: similar chromosomes pair up and actually swap sections of DNA with each other. It's like trading cards, creating new combinations of genetic information.
Unlike mitosis, meiosis involves two divisions, not just one. The first division separates the chromosome pairs, and the second division separates the copied chromosomes. This produces four genetically different cells, each with only 23 chromosomes instead of 46.
Key Point: Meiosis creates genetic diversity - it's nature's way of ensuring every individual is unique!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The cell cycle is like a cellular to-do list with six stages. Cells grow, copy their DNA, double-check for errors, divide through mitosis, split their cytoplasm, and then either rest or prepare for another round. It's a highly organised process that keeps your body functioning smoothly.
Stem cells are the ultimate shape-shifters - they haven't decided what they want to be when they grow up yet! Embryonic stem cells are the most flexible and can become any type of cell in the body. Adult stem cells are more limited but still crucial for repair and maintenance.
In plants, stem cells hang out in areas called meristems (like root tips and shoot tips). Unlike human stem cells, plant stem cells can differentiate into any cell type throughout the plant's entire life - pretty impressive!
Fun Fact: Your bone marrow contains stem cells that constantly produce new blood cells - you make millions every day!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cell differentiation transforms boring stem cells into specialists. Once a cell differentiates, it can perform specific jobs - muscle cells contract, nerve cells carry signals, and blood cells transport oxygen. Your body's systems work together: the muscular system creates movement, the circulatory system transports substances, and the respiratory system handles oxygen exchange.
Cells need to move substances in and out constantly. Diffusion is the lazy method - molecules naturally move from crowded areas to less crowded ones, like oxygen moving from your lungs into your blood. Osmosis is just diffusion for water molecules through partially permeable membranes.
Sometimes cells need to work against the flow. Active transport uses energy to move substances from low to high concentration areas, like swimming upstream. This is essential when cells need to concentrate important molecules against the natural gradient.
Real-World Example: When you're dehydrated, your kidneys use active transport to conserve water and maintain the right balance in your body!
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
App 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