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Nikita
29/11/2025
Biology
Kreb’s cycle and link reaction - Alevel Biology Unit 3 WJEC
253
•
29 Nov 2025
•
Understanding Krebs Cycle and Link Reaction for A-Level Biology WJEC
Nikita
@nikitaxo8
The Link Reaction and Krebs Cycle
Your cells are basically tiny power stations, and the link reaction is where things get properly interesting. This process takes pyruvate (from glycolysis) and transforms it through two key steps that you absolutely need to remember.
First, dehydrogenation strips hydrogen from pyruvate, which gets picked up by NAD+ to form NADH + H+. Think of this like removing a crucial component to change the molecule's identity. Then decarboxylation removes a carbon atom, releasing it as CO₂ waste gas.
What's left combines with coenzyme A to create acetyl CoA - a 2-carbon powerhouse that's ready for the next stage. Here's the key point: no ATP is made directly, but you get CO₂, NADH, and that vital acetyl CoA.
The Krebs cycle is where the real magic happens. Acetyl CoA joins with oxaloacetate (4 carbons) to form citrate (6 carbons), kicking off a cycle that's basically a molecular conveyor belt. As citrate moves through various intermediate compounds, it's systematically stripped of carbons (released as CO₂) and hydrogens (captured by NAD and FAD).
Remember: One glucose molecule means the cycle runs twice - once for each pyruvate that entered the link reaction!
Each cycle produces 1 ATP directly, 3 reduced NAD, 1 reduced FAD, and 2 CO₂. Since everything happens twice per glucose molecule, you're looking at 2 ATP, 6 reduced NAD, 2 reduced FAD, and 4 CO₂ in total.
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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.
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David K
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Sudenaz Ocak
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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
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
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Understanding Krebs Cycle and Link Reaction for A-Level Biology WJEC
Nikita
@nikitaxo8
Ever wondered how your body actually extracts energy from the food you eat? The link reaction and Krebs cycle are two crucial stages of cellular respiration that happen inside your mitochondria, transforming simple molecules into the energy currency your cells... Show more
The Link Reaction and Krebs Cycle
Your cells are basically tiny power stations, and the link reaction is where things get properly interesting. This process takes pyruvate (from glycolysis) and transforms it through two key steps that you absolutely need to remember.
First, dehydrogenation strips hydrogen from pyruvate, which gets picked up by NAD+ to form NADH + H+. Think of this like removing a crucial component to change the molecule's identity. Then decarboxylation removes a carbon atom, releasing it as CO₂ waste gas.
What's left combines with coenzyme A to create acetyl CoA - a 2-carbon powerhouse that's ready for the next stage. Here's the key point: no ATP is made directly, but you get CO₂, NADH, and that vital acetyl CoA.
The Krebs cycle is where the real magic happens. Acetyl CoA joins with oxaloacetate (4 carbons) to form citrate (6 carbons), kicking off a cycle that's basically a molecular conveyor belt. As citrate moves through various intermediate compounds, it's systematically stripped of carbons (released as CO₂) and hydrogens (captured by NAD and FAD).
Remember: One glucose molecule means the cycle runs twice - once for each pyruvate that entered the link reaction!
Each cycle produces 1 ATP directly, 3 reduced NAD, 1 reduced FAD, and 2 CO₂. Since everything happens twice per glucose molecule, you're looking at 2 ATP, 6 reduced NAD, 2 reduced FAD, and 4 CO₂ in total.
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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