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24 Dec 2025
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A Level Biology: Understanding Cells and Organelles
D
DA
@dharina21
Endoplasmic Reticulum and Protein Processing
Think of the endoplasmic reticulum (ER) as your cell's production line - but there are actually two types doing different jobs. The rough ER is covered in ribosomes, giving it that "rough" appearance, and it's brilliant at making and processing proteins.
Meanwhile, the smooth ER has no ribosomes attached and focuses on creating lipids and carbohydrates. It's also your cell's storage facility for these important molecules.
Ribosomes are tiny protein-making machines that either float freely in the cytoplasm or attach to the rough ER. Eukaryotic cells (like yours) have larger 80S ribosomes, whilst prokaryotic cells (like bacteria) have smaller 70S ribosomes.
Quick Tip: Remember "Rough = Ribosomes = pRotein production" - the alliteration makes it stick!
Cellular Defence and Plant Support
Lysosomes act like your cell's security team and cleaning crew rolled into one. These round organelles contain powerful enzymes called lysozymes that can destroy harmful invaders or break down worn-out cell parts.
Plant cells have some unique features that animal cells don't need. The cell wall provides rigid support - it's made of cellulose in plants and algae, but chitin in fungi. This structure prevents the cell from bursting under pressure.
The vacuole in plant cells is like a massive water balloon that keeps the plant upright and healthy. It's filled with cell sap and surrounded by a membrane called the tonoplast.
Cell Membrane and Control Centre
Every cell needs boundaries and a control system to survive. The cell membrane acts like a selective bouncer, made of lipids and proteins that carefully regulate what enters and exits your cells.
The nucleus is definitely the cell's command centre, containing all your DNA and genetic material. It's surrounded by a double membrane called the nuclear envelope, which has pores that allow important molecules like RNA to pass through. Inside, the nucleolus specifically makes ribosomes.
Remember: The nucleus controls everything - think of it as the cell's brain making all the important decisions.
Energy Production and Photosynthesis
Mitochondria are your cellular power plants, producing ATP through aerobic respiration. These oval organelles have a folded inner membrane called cristae, which creates loads of surface area for energy production. The matrix inside contains all the enzymes needed for this vital process.
Plant cells have an extra energy advantage with chloroplasts. These green organelles contain stacks of thylakoids called grana, where the first stage of photosynthesis happens. The fluid-filled stroma surrounding them handles the second stage.
The Golgi apparatus works like a postal service, processing and packaging proteins and lipids from the ER. It adds "address labels" to molecules and sorts them into the correct destinations around the cell.
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This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
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The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
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In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
A Level Biology: Understanding Cells and Organelles
D
DA
@dharina21
Your cells are like incredibly organised factories, with each part having a specific job to keep everything running smoothly. Understanding these cellular components and how they work together is essential for grasping how life functions at the most basic level.
Endoplasmic Reticulum and Protein Processing
Think of the endoplasmic reticulum (ER) as your cell's production line - but there are actually two types doing different jobs. The rough ER is covered in ribosomes, giving it that "rough" appearance, and it's brilliant at making and processing proteins.
Meanwhile, the smooth ER has no ribosomes attached and focuses on creating lipids and carbohydrates. It's also your cell's storage facility for these important molecules.
Ribosomes are tiny protein-making machines that either float freely in the cytoplasm or attach to the rough ER. Eukaryotic cells (like yours) have larger 80S ribosomes, whilst prokaryotic cells (like bacteria) have smaller 70S ribosomes.
Quick Tip: Remember "Rough = Ribosomes = pRotein production" - the alliteration makes it stick!
Cellular Defence and Plant Support
Lysosomes act like your cell's security team and cleaning crew rolled into one. These round organelles contain powerful enzymes called lysozymes that can destroy harmful invaders or break down worn-out cell parts.
Plant cells have some unique features that animal cells don't need. The cell wall provides rigid support - it's made of cellulose in plants and algae, but chitin in fungi. This structure prevents the cell from bursting under pressure.
The vacuole in plant cells is like a massive water balloon that keeps the plant upright and healthy. It's filled with cell sap and surrounded by a membrane called the tonoplast.
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Cell Membrane and Control Centre
Every cell needs boundaries and a control system to survive. The cell membrane acts like a selective bouncer, made of lipids and proteins that carefully regulate what enters and exits your cells.
The nucleus is definitely the cell's command centre, containing all your DNA and genetic material. It's surrounded by a double membrane called the nuclear envelope, which has pores that allow important molecules like RNA to pass through. Inside, the nucleolus specifically makes ribosomes.
Remember: The nucleus controls everything - think of it as the cell's brain making all the important decisions.
Energy Production and Photosynthesis
Mitochondria are your cellular power plants, producing ATP through aerobic respiration. These oval organelles have a folded inner membrane called cristae, which creates loads of surface area for energy production. The matrix inside contains all the enzymes needed for this vital process.
Plant cells have an extra energy advantage with chloroplasts. These green organelles contain stacks of thylakoids called grana, where the first stage of photosynthesis happens. The fluid-filled stroma surrounding them handles the second stage.
The Golgi apparatus works like a postal service, processing and packaging proteins and lipids from the ER. It adds "address labels" to molecules and sorts them into the correct destinations around the cell.
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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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