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1
Lilia Steadman
29/11/2025
Biology
Unit 8 exchange and transport in animals biology higher edexcel GCSE summary pages
406
•
29 Nov 2025
•
What Makes Breathing Cool: Aerobic vs Anaerobic and Mitochondria's Magic
Lilia Steadman
@liliasteadman_
Gas Exchange and Transport in Animals
This page delves deeper into the processes of gas exchange and transport in animals, focusing on the respiratory system and its adaptations for efficient gas exchange.
The page begins by explaining the need for gas exchange in organisms:
Highlight: Cells require oxygen for aerobic respiration, which produces carbon dioxide as a waste product. These gases, along with other substances, move between cells and the environment through diffusion.
The structure of the thorax is briefly mentioned, introducing the respiratory system components.
The lungs are described as the primary organ for gas exchange:
Definition: Alveoli are millions of tiny air sacs in the lungs where gas exchange takes place.
The process of gas exchange in the alveoli is explained in detail:
- Blood arriving at the alveoli contains high levels of CO₂ and low levels of O₂.
- This creates a concentration gradient that maximizes the diffusion of both gases.
- O₂ diffuses from the air in the alveoli into the blood.
- CO₂ diffuses in the opposite direction to be exhaled.
The page highlights several adaptations of alveoli that make them efficient for gas exchange:
- Moist lining for dissolving gases
- Good blood supply to maintain concentration gradients of O₂ and CO₂
- Very thin walls to minimize the distance gases have to move
The concept of surface area to volume ratios (SA:V) is introduced:
Vocabulary: Surface area to volume ratio (SA:V) is the relationship between an organism's surface area and its volume, which affects its ability to exchange substances with the environment.
The page explains that larger organisms have a smaller surface area compared to their volume, making it difficult to exchange enough substances across their outside surface alone. This is why complex organisms have developed specialized gas exchange systems.
An experiment using pink cubes is described to illustrate the concept of SA:V ratios:
Example: As cube sizes increase, their SA:V ratio decreases. The smallest cube represents unicellular organisms, while the largest represents multicellular organisms, demonstrating why larger organisms need specialized exchange surfaces.
The page concludes by touching on the movement of substances, introducing the concepts of diffusion and active transport:
Definition: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.
Definition: Active transport is the movement of molecules or ions from an area of low concentration to an area of higher concentration, using energy released from respiration.
These processes are crucial for understanding how organisms exchange substances with their environment and maintain cellular functions.
Cellular Respiration and Gas Exchange
Cellular respiration is a fundamental process in living organisms that releases energy for various metabolic functions. This page introduces the concept of cellular respiration and its two main types: aerobic and anaerobic respiration.
Definition: Cellular respiration is an exothermic reaction occurring continuously in living cells to release energy for metabolic processes.
The differences between aerobic and anaerobic respiration are explained:
-
Aerobic respiration:
- Occurs with oxygen
- Involves the complete oxidation of glucose
- Produces carbon dioxide and water
- Generates more energy (ATP) for cells
-
Anaerobic respiration:
- Occurs without oxygen
- Involves incomplete breakdown of glucose
- Produces lactic acid in animals or ethanol and carbon dioxide in yeast and plants
- Generates less energy but serves as a short-term fix when oxygen is unavailable
Highlight: Lactic acid produced during anaerobic respiration can be toxic and cause muscle pain and cramps when it builds up.
The page also presents the chemical equations for both types of respiration:
Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
Anaerobic respiration (in animals): Glucose → Lactic acid + Energy Anaerobic respiration : Glucose → Ethanol + Carbon dioxide + Energy
The role of mitochondria in cellular respiration is briefly mentioned:
Vocabulary: Mitochondria are organelles in eukaryotic cells where aerobic respiration takes place.
The importance of respiration for cellular functions is emphasized, as cells need to respire to gain energy for all life processes.
The page concludes with information on testing for carbon dioxide, a byproduct of respiration:
- Lime water test: Turns from colorless to cloudy white in the presence of CO₂
- Hydrogen carbonate indicator test: Turns from orange to yellow in the presence of CO₂, and from orange to purple in its absence
Example: An experiment using lime water can demonstrate the presence of CO₂ in exhaled air, as it turns cloudy white when exhaled air is bubbled through it.
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Anna
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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
What Makes Breathing Cool: Aerobic vs Anaerobic and Mitochondria's Magic
Lilia Steadman
@liliasteadman_
Cellular respiration is a vital process in living organisms that releases energy for metabolic functions. This summary explores the differences between aerobic and anaerobic respiration, the role of mitochondria in cellular respiration, and how carbon dioxide affects lime... Show more
Gas Exchange and Transport in Animals
This page delves deeper into the processes of gas exchange and transport in animals, focusing on the respiratory system and its adaptations for efficient gas exchange.
The page begins by explaining the need for gas exchange in organisms:
Highlight: Cells require oxygen for aerobic respiration, which produces carbon dioxide as a waste product. These gases, along with other substances, move between cells and the environment through diffusion.
The structure of the thorax is briefly mentioned, introducing the respiratory system components.
The lungs are described as the primary organ for gas exchange:
Definition: Alveoli are millions of tiny air sacs in the lungs where gas exchange takes place.
The process of gas exchange in the alveoli is explained in detail:
- Blood arriving at the alveoli contains high levels of CO₂ and low levels of O₂.
- This creates a concentration gradient that maximizes the diffusion of both gases.
- O₂ diffuses from the air in the alveoli into the blood.
- CO₂ diffuses in the opposite direction to be exhaled.
The page highlights several adaptations of alveoli that make them efficient for gas exchange:
- Moist lining for dissolving gases
- Good blood supply to maintain concentration gradients of O₂ and CO₂
- Very thin walls to minimize the distance gases have to move
The concept of surface area to volume ratios (SA:V) is introduced:
Vocabulary: Surface area to volume ratio (SA:V) is the relationship between an organism's surface area and its volume, which affects its ability to exchange substances with the environment.
The page explains that larger organisms have a smaller surface area compared to their volume, making it difficult to exchange enough substances across their outside surface alone. This is why complex organisms have developed specialized gas exchange systems.
An experiment using pink cubes is described to illustrate the concept of SA:V ratios:
Example: As cube sizes increase, their SA:V ratio decreases. The smallest cube represents unicellular organisms, while the largest represents multicellular organisms, demonstrating why larger organisms need specialized exchange surfaces.
The page concludes by touching on the movement of substances, introducing the concepts of diffusion and active transport:
Definition: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.
Definition: Active transport is the movement of molecules or ions from an area of low concentration to an area of higher concentration, using energy released from respiration.
These processes are crucial for understanding how organisms exchange substances with their environment and maintain cellular functions.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cellular Respiration and Gas Exchange
Cellular respiration is a fundamental process in living organisms that releases energy for various metabolic functions. This page introduces the concept of cellular respiration and its two main types: aerobic and anaerobic respiration.
Definition: Cellular respiration is an exothermic reaction occurring continuously in living cells to release energy for metabolic processes.
The differences between aerobic and anaerobic respiration are explained:
-
Aerobic respiration:
- Occurs with oxygen
- Involves the complete oxidation of glucose
- Produces carbon dioxide and water
- Generates more energy (ATP) for cells
-
Anaerobic respiration:
- Occurs without oxygen
- Involves incomplete breakdown of glucose
- Produces lactic acid in animals or ethanol and carbon dioxide in yeast and plants
- Generates less energy but serves as a short-term fix when oxygen is unavailable
Highlight: Lactic acid produced during anaerobic respiration can be toxic and cause muscle pain and cramps when it builds up.
The page also presents the chemical equations for both types of respiration:
Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
Anaerobic respiration (in animals): Glucose → Lactic acid + Energy Anaerobic respiration : Glucose → Ethanol + Carbon dioxide + Energy
The role of mitochondria in cellular respiration is briefly mentioned:
Vocabulary: Mitochondria are organelles in eukaryotic cells where aerobic respiration takes place.
The importance of respiration for cellular functions is emphasized, as cells need to respire to gain energy for all life processes.
The page concludes with information on testing for carbon dioxide, a byproduct of respiration:
- Lime water test: Turns from colorless to cloudy white in the presence of CO₂
- Hydrogen carbonate indicator test: Turns from orange to yellow in the presence of CO₂, and from orange to purple in its absence
Example: An experiment using lime water can demonstrate the presence of CO₂ in exhaled air, as it turns cloudy white when exhaled air is bubbled through it.
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?
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
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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
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