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KatieB!!
06/12/2025
Biology
CCEA biology AS level
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6 Dec 2025
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CCEA AS Level Biology: Understanding Molecules
K
KatieB!!
@ktstudying123
1 / 7
The Basics of Carbohydrates
Every carbohydrate you'll ever encounter contains just three elements: carbon, hydrogen, and oxygen. Think of them as nature's energy storage units with the general formula Cx(H2O)y.
Carbohydrates fall into three main groups that get progressively larger. Monosaccharides are single sugars (like glucose), disaccharides are double sugars (like table sugar), and polysaccharides contain 8 or more sugar units (like starch).
Monosaccharides are the sweet-tasting, water-soluble building blocks. Their names depend on how many carbon atoms they contain: triose (3 carbons), pentose (5 carbons), or hexose (6 carbons). The hexose sugars with 6 carbons are the most important ones you'll study.
Quick Tip: Remember the pattern - tri means 3, pent means 5, and hex means 6, just like in geometry!
Glucose - The Energy Currency
Glucose is the superstar of monosaccharides and the one you'll encounter most often. This hexose sugar has 6 carbons and the chemical formula C6H12O6 - you might recognise this from photosynthesis equations.
The clever thing about glucose is its ring structure. Rather than being a straight chain, glucose atoms arrange themselves in a ring with hydroxyl groups attached to the carbon atoms.
What makes this even more interesting is that glucose exists in two forms: α-glucose (alpha) and β-glucose (beta). The only difference is that the -H and -OH groups on carbon 1 are flipped around. These are called isomers - same formula, different arrangement.
Remember: Alpha glucose is "top heavy" with the OH group pointing down, whilst beta glucose has it pointing up on carbon 1.
Fructose and Sugar Testing
Fructose is another important hexose sugar that shares the same chemical formula as glucose (C6H12O6). However, its structure is quite different, which shows you how versatile these molecules can be.
When it comes to testing for sugars, you've got a couple of options. Clinistix are handy strips that turn purple/blue when glucose is present - they're actually used to test for diabetes by detecting glucose in urine.
For any reducing sugar, you'll use Benedict's test. Mix your food sample with Benedict's solution, heat it in a water bath for 5 minutes, and watch for the colour change from blue to red if sugars are present.
Lab Success: Always grind solid food samples with water first to get them into liquid form before testing.
Water - The Universal Solvent
Water makes up 50-90% of most living cells, making it absolutely crucial for life. In H2O, each hydrogen atom forms a covalent bond with oxygen, but the charge isn't distributed evenly.
This uneven charge distribution makes water polar - oxygen gets a slight negative charge whilst hydrogen gets a slight positive charge. Hydrogen bonds form between different water molecules, creating weak but important connections.
Being polar makes water an excellent solvent that can dissolve a huge range of substances. Hydrophilic molecules (like glucose and amino acids) are attracted to water, whilst hydrophobic molecules (like lipids) repel it.
Why This Matters: Most chemical reactions in your cells happen in water, and it's the main transport medium in living organisms - from your bloodstream to plant sap.
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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
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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
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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
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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
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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
CCEA AS Level Biology: Understanding Molecules
K
KatieB!!
@ktstudying123
Ready to dive into the building blocks of life? Carbohydrates are everywhere - from the sugar in your tea to the energy that powers your muscles. Understanding these essential molecules will help you grasp how living things store and use... Show more
The Basics of Carbohydrates
Every carbohydrate you'll ever encounter contains just three elements: carbon, hydrogen, and oxygen. Think of them as nature's energy storage units with the general formula Cx(H2O)y.
Carbohydrates fall into three main groups that get progressively larger. Monosaccharides are single sugars (like glucose), disaccharides are double sugars (like table sugar), and polysaccharides contain 8 or more sugar units (like starch).
Monosaccharides are the sweet-tasting, water-soluble building blocks. Their names depend on how many carbon atoms they contain: triose (3 carbons), pentose (5 carbons), or hexose (6 carbons). The hexose sugars with 6 carbons are the most important ones you'll study.
Quick Tip: Remember the pattern - tri means 3, pent means 5, and hex means 6, just like in geometry!
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Glucose - The Energy Currency
Glucose is the superstar of monosaccharides and the one you'll encounter most often. This hexose sugar has 6 carbons and the chemical formula C6H12O6 - you might recognise this from photosynthesis equations.
The clever thing about glucose is its ring structure. Rather than being a straight chain, glucose atoms arrange themselves in a ring with hydroxyl groups attached to the carbon atoms.
What makes this even more interesting is that glucose exists in two forms: α-glucose (alpha) and β-glucose (beta). The only difference is that the -H and -OH groups on carbon 1 are flipped around. These are called isomers - same formula, different arrangement.
Remember: Alpha glucose is "top heavy" with the OH group pointing down, whilst beta glucose has it pointing up on carbon 1.
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Fructose and Sugar Testing
Fructose is another important hexose sugar that shares the same chemical formula as glucose (C6H12O6). However, its structure is quite different, which shows you how versatile these molecules can be.
When it comes to testing for sugars, you've got a couple of options. Clinistix are handy strips that turn purple/blue when glucose is present - they're actually used to test for diabetes by detecting glucose in urine.
For any reducing sugar, you'll use Benedict's test. Mix your food sample with Benedict's solution, heat it in a water bath for 5 minutes, and watch for the colour change from blue to red if sugars are present.
Lab Success: Always grind solid food samples with water first to get them into liquid form before testing.
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Water - The Universal Solvent
Water makes up 50-90% of most living cells, making it absolutely crucial for life. In H2O, each hydrogen atom forms a covalent bond with oxygen, but the charge isn't distributed evenly.
This uneven charge distribution makes water polar - oxygen gets a slight negative charge whilst hydrogen gets a slight positive charge. Hydrogen bonds form between different water molecules, creating weak but important connections.
Being polar makes water an excellent solvent that can dissolve a huge range of substances. Hydrophilic molecules (like glucose and amino acids) are attracted to water, whilst hydrophobic molecules (like lipids) repel it.
Why This Matters: Most chemical reactions in your cells happen in water, and it's the main transport medium in living organisms - from your bloodstream to plant sap.
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We thought you’d never ask...
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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