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
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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
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Biology
2 Dec 2025
14
3 pages
Sara @bluesquidz88
Your body is constantly working to remove waste products and maintain the perfect balance of water and chemicals... Show more
Think of excretion as your body's waste management system - it's not just about getting rid of undigested food, but removing toxic waste products from your blood. The liver acts like your body's chemical processing plant, handling multiple jobs simultaneously.
The liver consists of lobules made from rows of hepatocytes (liver cells) that exchange materials with blood. These specialised cells work alongside macrophages that remove old red blood cells from circulation.
Deamination is one of the liver's most important functions - it breaks down excess amino acids, producing ammonia (NH₃) which gets converted to less toxic urea. The liver also produces essential blood components like red blood cells, plasma proteins, and bile for fat digestion.
Your liver stores vital nutrients including glycogen, iron, and vitamins A, D, and B12. It also detoxifies harmful substances like drugs and alcohol through enzyme action, particularly using alcohol dehydrogenase to break down ethanol.
Key Point When hepatocytes become damaged faster than they can be replaced, scar tissue forms and reduces liver function - this can lead to liver failure.
Your kidneys are remarkable filtering machines that process about 180 litres of blood daily! Each kidney contains around a million tiny filtering units called nephrons that work together to clean your blood and control water balance.
The filtration process starts in the glomerulus and Bowman's capsule. Blood pressure forces fluid through three filtering layers capillary walls with tiny pores, a basement membrane that blocks large molecules, and podocytes that create narrow slits allowing only small particles through.
Glomerular filtrate is essentially blood plasma minus the large components - no red blood cells, white blood cells, or proteins make it through. The glomerular filtration rate measures how much blood gets filtered per minute, helping doctors assess kidney health.
Selective reabsorption happens next, where useful substances like glucose, sodium ions, and water get actively transported back into your blood. This process requires energy (ATP) and involves sodium pumps that create concentration gradients, allowing water to follow passively.
Remember The afferent arteriole is wider than the efferent arteriole - this size difference maintains the high pressure needed for effective filtration.
The loop of Henle creates a brilliant counter-current system that allows your kidneys to produce concentrated urine when needed. This ingenious design lets you conserve water during dehydration or produce dilute urine when you've had plenty to drink.
In the descending limb, water moves out but sodium stays in, making the filtrate more concentrated. The ascending limb does the opposite - sodium gets pumped out (using energy) whilst water stays put, diluting the filtrate again.
This creates a concentration gradient in the medulla, with the deepest part having the highest salt concentration. When filtrate reaches the collecting duct, the final decision about water retention happens based on your body's needs.
ADH (antidiuretic hormone) from your pituitary gland controls this final step. When you're dehydrated, your hypothalamus detects this change and triggers ADH release, making the collecting duct more permeable to water so you produce concentrated urine and conserve fluid.
Clinical Connection Understanding this system explains why diabetes insipidus (lack of ADH) causes excessive urination, whilst kidney disease affects the body's ability to regulate water and waste removal.
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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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
Sara
@bluesquidz88
Your body is constantly working to remove waste products and maintain the perfect balance of water and chemicals in your blood. This process, called excretion, involves several key organs working together like a sophisticated filtration system.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Think of excretion as your body's waste management system - it's not just about getting rid of undigested food, but removing toxic waste products from your blood. The liver acts like your body's chemical processing plant, handling multiple jobs simultaneously.
The liver consists of lobules made from rows of hepatocytes (liver cells) that exchange materials with blood. These specialised cells work alongside macrophages that remove old red blood cells from circulation.
Deamination is one of the liver's most important functions - it breaks down excess amino acids, producing ammonia (NH₃) which gets converted to less toxic urea. The liver also produces essential blood components like red blood cells, plasma proteins, and bile for fat digestion.
Your liver stores vital nutrients including glycogen, iron, and vitamins A, D, and B12. It also detoxifies harmful substances like drugs and alcohol through enzyme action, particularly using alcohol dehydrogenase to break down ethanol.
Key Point: When hepatocytes become damaged faster than they can be replaced, scar tissue forms and reduces liver function - this can lead to liver failure.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Your kidneys are remarkable filtering machines that process about 180 litres of blood daily! Each kidney contains around a million tiny filtering units called nephrons that work together to clean your blood and control water balance.
The filtration process starts in the glomerulus and Bowman's capsule. Blood pressure forces fluid through three filtering layers: capillary walls with tiny pores, a basement membrane that blocks large molecules, and podocytes that create narrow slits allowing only small particles through.
Glomerular filtrate is essentially blood plasma minus the large components - no red blood cells, white blood cells, or proteins make it through. The glomerular filtration rate measures how much blood gets filtered per minute, helping doctors assess kidney health.
Selective reabsorption happens next, where useful substances like glucose, sodium ions, and water get actively transported back into your blood. This process requires energy (ATP) and involves sodium pumps that create concentration gradients, allowing water to follow passively.
Remember: The afferent arteriole is wider than the efferent arteriole - this size difference maintains the high pressure needed for effective filtration.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The loop of Henle creates a brilliant counter-current system that allows your kidneys to produce concentrated urine when needed. This ingenious design lets you conserve water during dehydration or produce dilute urine when you've had plenty to drink.
In the descending limb, water moves out but sodium stays in, making the filtrate more concentrated. The ascending limb does the opposite - sodium gets pumped out (using energy) whilst water stays put, diluting the filtrate again.
This creates a concentration gradient in the medulla, with the deepest part having the highest salt concentration. When filtrate reaches the collecting duct, the final decision about water retention happens based on your body's needs.
ADH (antidiuretic hormone) from your pituitary gland controls this final step. When you're dehydrated, your hypothalamus detects this change and triggers ADH release, making the collecting duct more permeable to water so you produce concentrated urine and conserve fluid.
Clinical Connection: Understanding this system explains why diabetes insipidus (lack of ADH) causes excessive urination, whilst kidney disease affects the body's ability to regulate water and waste removal.
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.
0
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Quotes from every main character
English LiteratureApp 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