Subjects
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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0
Trudie Wallace
29/11/2025
Biology
topic four: bioenergetics
324
•
29 Nov 2025
•
Trudie Wallace
@trudie123.w
Bioenergetics covers the essential energy processes that keep living things... Show more
Ever wondered how plants create their own food? Photosynthesis happens in chloroplasts - tiny green structures in leaves that contain chlorophyll, the pigment that absorbs sunlight.
The process converts carbon dioxide and water into glucose and oxygen using light energy. The word equation is: carbon dioxide + water → glucose + oxygen. Since it requires energy input, photosynthesis is an endothermic reaction.
Carbon dioxide enters through stomata (tiny pores in leaves), whilst water travels up from roots through xylem vessels. Once glucose is made, plants use it for five key purposes: making oils and fats, cellular respiration for energy, creating starch for storage, building cellulose to strengthen cell walls, and combining with nitrates to make amino acids.
Quick Tip: Remember that photosynthesis needs light, CO₂, water, and chlorophyll - if any are missing, the process slows down!
Four main factors control how fast photosynthesis occurs: light intensity, temperature, carbon dioxide concentration, and chlorophyll levels. Understanding these helps explain why plants grow differently in various conditions.
As temperature increases, photosynthesis speeds up because particles have more energy and collide more frequently. However, beyond the optimum temperature (around 45°C), enzymes denature and the rate crashes to zero as proteins lose their shape.
Chlorophyll can be reduced by disease (like tobacco mosaic virus), environmental stress, or lack of nutrients. With light intensity and CO₂ levels, rates increase until something else becomes the limiting factor - that's when the graph levels off.
Farmers exploit these factors by using greenhouses with artificial lighting, CO₂ pumps, heaters, and fertilisers. It's expensive but allows year-round crop production in any climate.
Remember: Only one factor limits photosynthesis at a time - even if you increase light, without enough CO₂, the rate won't improve!
Cellular respiration is the opposite of photosynthesis - it's an exothermic reaction that releases energy from glucose continuously in all living cells. This energy powers everything from building proteins to keeping your body temperature stable.
Aerobic respiration is the most efficient method, occurring in mitochondria when oxygen is available. The equation is: glucose + oxygen → carbon dioxide + water. It completely breaks down glucose, releasing maximum energy.
Anaerobic respiration happens without oxygen during intense exercise like sprinting. In humans, glucose breaks down incompletely to form lactic acid. This is much less efficient but provides emergency energy when oxygen can't keep up with demand.
In plants and yeast, anaerobic respiration produces ethanol and carbon dioxide instead - that's how we get alcohol in beer and wine, plus the air bubbles that make bread rise!
Key Point: Your body prefers aerobic respiration because it's 19 times more efficient than anaerobic respiration!
When you exercise hard, your muscles demand loads more energy for contraction. Your body responds by increasing breathing rate and heart rate to pump more oxygen around - but sometimes it's still not enough.
During intense activity, muscles switch to anaerobic respiration, producing lactic acid as a waste product. This builds up in your muscles, causing that burning sensation you feel during tough workouts.
After exercise, your body needs to clear this lactic acid by reacting it with oxygen - this is called oxygen debt. That's why you keep breathing heavily even after you've stopped exercising. The more lactic acid built up, the more oxygen you'll need.
Your blood carries the lactic acid to your liver, where it gets converted back to glucose using oxygen. This explains why recovery time depends on how intensely you've been exercising - more intensity means more lactic acid to clear up.
Fun Fact: Elite athletes have more efficient oxygen delivery systems, so they build up less lactic acid and recover faster than untrained people!
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.
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
Trudie Wallace
@trudie123.w
Bioenergetics covers the essential energy processes that keep living things alive - photosynthesis and respiration. These processes work together like a perfect cycle: plants capture light energy to make glucose, whilst all living organisms break down glucose to release energy... Show more
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Ever wondered how plants create their own food? Photosynthesis happens in chloroplasts - tiny green structures in leaves that contain chlorophyll, the pigment that absorbs sunlight.
The process converts carbon dioxide and water into glucose and oxygen using light energy. The word equation is: carbon dioxide + water → glucose + oxygen. Since it requires energy input, photosynthesis is an endothermic reaction.
Carbon dioxide enters through stomata (tiny pores in leaves), whilst water travels up from roots through xylem vessels. Once glucose is made, plants use it for five key purposes: making oils and fats, cellular respiration for energy, creating starch for storage, building cellulose to strengthen cell walls, and combining with nitrates to make amino acids.
Quick Tip: Remember that photosynthesis needs light, CO₂, water, and chlorophyll - if any are missing, the process slows down!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Four main factors control how fast photosynthesis occurs: light intensity, temperature, carbon dioxide concentration, and chlorophyll levels. Understanding these helps explain why plants grow differently in various conditions.
As temperature increases, photosynthesis speeds up because particles have more energy and collide more frequently. However, beyond the optimum temperature (around 45°C), enzymes denature and the rate crashes to zero as proteins lose their shape.
Chlorophyll can be reduced by disease (like tobacco mosaic virus), environmental stress, or lack of nutrients. With light intensity and CO₂ levels, rates increase until something else becomes the limiting factor - that's when the graph levels off.
Farmers exploit these factors by using greenhouses with artificial lighting, CO₂ pumps, heaters, and fertilisers. It's expensive but allows year-round crop production in any climate.
Remember: Only one factor limits photosynthesis at a time - even if you increase light, without enough CO₂, the rate won't improve!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cellular respiration is the opposite of photosynthesis - it's an exothermic reaction that releases energy from glucose continuously in all living cells. This energy powers everything from building proteins to keeping your body temperature stable.
Aerobic respiration is the most efficient method, occurring in mitochondria when oxygen is available. The equation is: glucose + oxygen → carbon dioxide + water. It completely breaks down glucose, releasing maximum energy.
Anaerobic respiration happens without oxygen during intense exercise like sprinting. In humans, glucose breaks down incompletely to form lactic acid. This is much less efficient but provides emergency energy when oxygen can't keep up with demand.
In plants and yeast, anaerobic respiration produces ethanol and carbon dioxide instead - that's how we get alcohol in beer and wine, plus the air bubbles that make bread rise!
Key Point: Your body prefers aerobic respiration because it's 19 times more efficient than anaerobic respiration!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
When you exercise hard, your muscles demand loads more energy for contraction. Your body responds by increasing breathing rate and heart rate to pump more oxygen around - but sometimes it's still not enough.
During intense activity, muscles switch to anaerobic respiration, producing lactic acid as a waste product. This builds up in your muscles, causing that burning sensation you feel during tough workouts.
After exercise, your body needs to clear this lactic acid by reacting it with oxygen - this is called oxygen debt. That's why you keep breathing heavily even after you've stopped exercising. The more lactic acid built up, the more oxygen you'll need.
Your blood carries the lactic acid to your liver, where it gets converted back to glucose using oxygen. This explains why recovery time depends on how intensely you've been exercising - more intensity means more lactic acid to clear up.
Fun Fact: Elite athletes have more efficient oxygen delivery systems, so they build up less lactic acid and recover faster than untrained people!
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
Sociology