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Understanding Excretion in Biology - Edexcel IGCSE Insights
E
Emma
@mmaang_xwhbmttsgscnr
1 / 3
Human Excretion Basics
Ever wondered why holding your breath feels uncomfortable or why you need the loo after drinking loads of water? It's all about excretion - your body's clever way of getting rid of toxic waste products before they can harm you.
Your body produces waste through normal metabolic reactions, and if these wastes build up, they become seriously dangerous. Carbon dioxide makes your blood acidic (messing with enzymes), whilst other waste products can make your body fluids too concentrated, causing cells to shrivel up like raisins.
Three main organs handle different types of waste: your lungs remove CO2, your skin loses water and mineral ions through sweat, and your kidneys deal with urea, excess water, and mineral ions. The kidneys are the real stars here - they're responsible for both excretion and osmoregulation (keeping your blood's water content just right).
Quick Tip: Remember that excretion involves waste that's already been absorbed by your body, unlike egestion (poo) which is just undigested food passing through!
Kidney Structure and How Filtering Works
Your urinary system is basically a sophisticated waste management facility. Two bean-shaped kidneys filter your blood, connecting to your bladder via tubes called ureters. The bladder stores urine until you're ready to release it through the urethra.
Each kidney contains about a million tiny filtering units called nephrons. These microscopic structures have several key parts: the glomerulus (a cluster of capillaries), Bowman's capsule (which surrounds the glomerulus), convoluted tubules, the loop of Henle, and the collecting duct.
The magic happens through ultrafiltration at the glomerulus. High blood pressure forces small molecules like water, urea, and glucose out of the blood and into Bowman's capsule, creating glomerular filtrate. Think of it like a really fine sieve - big stuff like red blood cells and proteins stay in the blood.
Next comes selective reabsorption in the proximal convoluted tubule, where 100% of glucose gets actively transported back into your blood (because your body needs it for respiration). People with diabetes can't reabsorb all their glucose, which is why doctors test urine for glucose to diagnose the condition.
Remember: Your kidneys filter about 180 litres of blood daily, but you only produce 1-2 litres of urine - that's some serious reabsorption happening!
Water Control and ADH
Your kidneys are brilliant at adjusting how much water you lose, and it's all controlled by a hormone called ADH (antidiuretic hormone). Think of ADH as your body's water conservation manager.
When your blood becomes too concentrated (maybe you're dehydrated), your hypothalamus detects this and tells your pituitary gland to release more ADH. This hormone travels to your kidneys and makes the collecting ducts more permeable to water, so more water gets reabsorbed back into your blood. Result? You produce less, more concentrated (darker) urine.
When you've had loads to drink, the opposite happens - less ADH is released, the collecting ducts become less permeable, and you produce more dilute, pale yellow urine. It's a perfect example of negative feedback keeping everything balanced.
Your urine composition tells a story about your body's state. Normal urine contains water, urea, and excess mineral ions. The colour and concentration depend on factors like how much you've drunk, the temperature (hot weather means more sweating, so darker urine), and how much you've exercised.
Fun Fact: Only the collecting duct cells respond to ADH because they're the only ones with ADH receptors - it's like having the right key for a specific lock!
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This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
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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
Understanding Excretion in Biology - Edexcel IGCSE Insights
E
Emma
@mmaang_xwhbmttsgscnr
Your kidneys are incredible biological filters that work 24/7 to keep you alive by removing toxic waste and controlling your body's water balance. Understanding how excretion works will help you grasp one of biology's most impressive homeostatic systems.
Human Excretion Basics
Ever wondered why holding your breath feels uncomfortable or why you need the loo after drinking loads of water? It's all about excretion - your body's clever way of getting rid of toxic waste products before they can harm you.
Your body produces waste through normal metabolic reactions, and if these wastes build up, they become seriously dangerous. Carbon dioxide makes your blood acidic (messing with enzymes), whilst other waste products can make your body fluids too concentrated, causing cells to shrivel up like raisins.
Three main organs handle different types of waste: your lungs remove CO2, your skin loses water and mineral ions through sweat, and your kidneys deal with urea, excess water, and mineral ions. The kidneys are the real stars here - they're responsible for both excretion and osmoregulation (keeping your blood's water content just right).
Quick Tip: Remember that excretion involves waste that's already been absorbed by your body, unlike egestion (poo) which is just undigested food passing through!
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Kidney Structure and How Filtering Works
Your urinary system is basically a sophisticated waste management facility. Two bean-shaped kidneys filter your blood, connecting to your bladder via tubes called ureters. The bladder stores urine until you're ready to release it through the urethra.
Each kidney contains about a million tiny filtering units called nephrons. These microscopic structures have several key parts: the glomerulus (a cluster of capillaries), Bowman's capsule (which surrounds the glomerulus), convoluted tubules, the loop of Henle, and the collecting duct.
The magic happens through ultrafiltration at the glomerulus. High blood pressure forces small molecules like water, urea, and glucose out of the blood and into Bowman's capsule, creating glomerular filtrate. Think of it like a really fine sieve - big stuff like red blood cells and proteins stay in the blood.
Next comes selective reabsorption in the proximal convoluted tubule, where 100% of glucose gets actively transported back into your blood (because your body needs it for respiration). People with diabetes can't reabsorb all their glucose, which is why doctors test urine for glucose to diagnose the condition.
Remember: Your kidneys filter about 180 litres of blood daily, but you only produce 1-2 litres of urine - that's some serious reabsorption happening!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Water Control and ADH
Your kidneys are brilliant at adjusting how much water you lose, and it's all controlled by a hormone called ADH (antidiuretic hormone). Think of ADH as your body's water conservation manager.
When your blood becomes too concentrated (maybe you're dehydrated), your hypothalamus detects this and tells your pituitary gland to release more ADH. This hormone travels to your kidneys and makes the collecting ducts more permeable to water, so more water gets reabsorbed back into your blood. Result? You produce less, more concentrated (darker) urine.
When you've had loads to drink, the opposite happens - less ADH is released, the collecting ducts become less permeable, and you produce more dilute, pale yellow urine. It's a perfect example of negative feedback keeping everything balanced.
Your urine composition tells a story about your body's state. Normal urine contains water, urea, and excess mineral ions. The colour and concentration depend on factors like how much you've drunk, the temperature (hot weather means more sweating, so darker urine), and how much you've exercised.
Fun Fact: Only the collecting duct cells respond to ADH because they're the only ones with ADH receptors - it's like having the right key for a specific lock!
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
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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