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
Show all topics
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
Show all topics
Combined Science
2 Dec 2025
249
6 pages
Ever wondered how scientists can see inside tiny cells or why water is so essential for life? This... Show more
Getting a clear view of cells isn't as simple as just making them bigger - you need the right tools for the job. Magnification tells you how much bigger an image appears compared to the real thing, whilst resolution determines how much detail you can actually see.
The basic formula you'll need to remember is Magnification = Image size ÷ Actual size. This pops up in exams regularly, so get comfortable with rearranging it.
Light microscopes are your everyday lab heroes - cheap, easy to use, and brilliant for observing living cells. They magnify up to 2000x with decent resolution, but that's where they hit their limit. Electron microscopes are the superstars, with scanning types creating stunning 3D surface images and transmission types revealing incredible internal detail at over 1,000,000x magnification.
Quick Tip Remember that electron microscopes kill samples and only show black and white images - any colours you see have been added by computer afterwards!
Laser scanning confocal microscopes offer the best of both worlds, creating 3D images of living cells by focusing at specific depths, though the final image is actually a computer interpretation of laser data.
Most cells are practically invisible without a bit of help - that's where staining becomes your best friend. Different stains target specific parts of cells acetic orcein turns chromosomes dark red, iodine makes starch granules blue-black, and Sudan red highlights lipids.
Cell ultrastructure refers to all the tiny details you can spot with an electron microscope. Each organelle has its own specific job - think of them as specialised departments in a cellular factory.
The nucleus acts as the control centre, housing DNA and coordinating everything through nuclear pores. Mitochondria power the cell through respiration, whilst ribosomes manufacture proteins. The rough endoplasmic reticulum provides a massive surface area for protein production, and the Golgi apparatus modifies and packages these proteins for export.
Exam Focus Learn the protein production pathway - it's a classic exam question that follows the same sequence every time!
Plant cells get extra features like chloroplasts for photosynthesis and cell walls for structural support. Remember, successful microscopy requires proper sample preparation, appropriate staining, and careful interpretation of what you observe.
Not all cells are created equal - there are two fundamental types you need to know. Prokaryotic cells (like bacteria) are smaller, simpler, and lack a proper nucleus or membrane-bound organelles. Eukaryotic cells (like yours!) are larger, more complex, and packed with specialised compartments.
The cytoskeleton acts like the cell's scaffolding system, made of microtubules and microfilaments that maintain shape and enable movement. Centrioles organise this network and help move chromosomes during cell division.
Here's the protein production assembly line that you absolutely must know mRNA exits the nucleus → ribosomes on rough ER build the protein → vesicles transport it to the Golgi apparatus → Golgi modifies and repackages the protein → final vesicle carries it to the cell membrane → protein gets released outside the cell.
Memory Aid Think of it as a postal system - the nucleus writes the letter, ribosomes print it, Golgi packages it, and vesicles deliver it!
Flagella and cilia are like cellular whips and brushes respectively - flagella help cells swim whilst cilia move fluids across surfaces (like clearing mucus from your lungs).
Water might seem boring, but it's actually one of the most remarkable molecules on Earth. Each water molecule is polar, meaning it has a slightly negative oxygen end and slightly positive hydrogen ends - like a tiny magnet.
These opposite charges create hydrogen bonds between water molecules, giving water its unique superpowers. These bonds are weak individually but incredibly powerful when working together.
Thermal stability means water changes temperature slowly, helping your body maintain a steady internal environment. When water freezes, it forms an open lattice structure that makes ice less dense than liquid water - that's why ice floats and protects aquatic life beneath.
Real-world Connection Your body uses water's high latent heat of vaporisation when you sweat - it takes loads of energy to evaporate water, cooling you down efficiently!
Water's other amazing properties include cohesion (molecules sticking together, creating surface tension), being an excellent solvent for transport, staying transparent for underwater photosynthesis, and being incompressible for hydraulic support systems.
Life is built from polymers - long chains made from smaller units called monomers. Think of monomers as LEGO bricks that snap together to create complex structures.
The three major biological polymers are nucleic acids (DNA and RNA), polysaccharides (like starch), and proteins. Each has its own specific monomer type that determines the polymer's properties.
Nucleotides are the monomers of nucleic acids, each containing a phosphate group, pentose sugar, and organic base. The five bases are adenine, cytosine, guanine, thymine, and uracil (A, C, G, T, U).
Key Difference DNA uses A, C, G, T whilst RNA swaps thymine for uracil - so RNA uses A, C, G, U instead.
Condensation reactions join monomers together by removing water molecules and forming covalent bonds. Hydrolysis does the opposite - it breaks these bonds by adding water back in. These processes are fundamental to building and breaking down biological molecules throughout your body.
Carbohydrates are made entirely from carbon, hydrogen, and oxygen, following the general formula (CH₂O)ₓ. They're your body's preferred fuel source and come in three main types.
Monosaccharides are single sugar units that taste sweet and dissolve easily in water. Glucose is the superstar here, existing as either α-glucose or β-glucose - same formula, different arrangement of atoms. This tiny structural difference has huge consequences for the polymers they create.
Pentose sugars like ribose and deoxyribose contain five carbons and are crucial components of nucleic acids. Ribose forms part of RNA whilst deoxyribose (missing one oxygen atom) forms part of DNA.
Formula Focus Remember that glucose has the molecular formula C₆H₁₂O₆ - this appears frequently in exam questions!
When two monosaccharides join through condensation, they form a disaccharide via a glycosidic bond. Maltose forms when two glucose molecules link together, releasing a water molecule in the process. Understanding these reactions is essential for grasping how complex carbohydrates like starch and cellulose are constructed.
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
Ever wondered how scientists can see inside tiny cells or why water is so essential for life? This guide breaks down the fascinating world of microscopy and the fundamental molecules that make life possible, from the tools that reveal cellular... Show more
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Getting a clear view of cells isn't as simple as just making them bigger - you need the right tools for the job. Magnification tells you how much bigger an image appears compared to the real thing, whilst resolution determines how much detail you can actually see.
The basic formula you'll need to remember is: Magnification = Image size ÷ Actual size. This pops up in exams regularly, so get comfortable with rearranging it.
Light microscopes are your everyday lab heroes - cheap, easy to use, and brilliant for observing living cells. They magnify up to 2000x with decent resolution, but that's where they hit their limit. Electron microscopes are the superstars, with scanning types creating stunning 3D surface images and transmission types revealing incredible internal detail at over 1,000,000x magnification.
Quick Tip: Remember that electron microscopes kill samples and only show black and white images - any colours you see have been added by computer afterwards!
Laser scanning confocal microscopes offer the best of both worlds, creating 3D images of living cells by focusing at specific depths, though the final image is actually a computer interpretation of laser data.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Most cells are practically invisible without a bit of help - that's where staining becomes your best friend. Different stains target specific parts of cells: acetic orcein turns chromosomes dark red, iodine makes starch granules blue-black, and Sudan red highlights lipids.
Cell ultrastructure refers to all the tiny details you can spot with an electron microscope. Each organelle has its own specific job - think of them as specialised departments in a cellular factory.
The nucleus acts as the control centre, housing DNA and coordinating everything through nuclear pores. Mitochondria power the cell through respiration, whilst ribosomes manufacture proteins. The rough endoplasmic reticulum provides a massive surface area for protein production, and the Golgi apparatus modifies and packages these proteins for export.
Exam Focus: Learn the protein production pathway - it's a classic exam question that follows the same sequence every time!
Plant cells get extra features like chloroplasts for photosynthesis and cell walls for structural support. Remember, successful microscopy requires proper sample preparation, appropriate staining, and careful interpretation of what you observe.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Not all cells are created equal - there are two fundamental types you need to know. Prokaryotic cells (like bacteria) are smaller, simpler, and lack a proper nucleus or membrane-bound organelles. Eukaryotic cells (like yours!) are larger, more complex, and packed with specialised compartments.
The cytoskeleton acts like the cell's scaffolding system, made of microtubules and microfilaments that maintain shape and enable movement. Centrioles organise this network and help move chromosomes during cell division.
Here's the protein production assembly line that you absolutely must know: mRNA exits the nucleus → ribosomes on rough ER build the protein → vesicles transport it to the Golgi apparatus → Golgi modifies and repackages the protein → final vesicle carries it to the cell membrane → protein gets released outside the cell.
Memory Aid: Think of it as a postal system - the nucleus writes the letter, ribosomes print it, Golgi packages it, and vesicles deliver it!
Flagella and cilia are like cellular whips and brushes respectively - flagella help cells swim whilst cilia move fluids across surfaces (like clearing mucus from your lungs).
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Water might seem boring, but it's actually one of the most remarkable molecules on Earth. Each water molecule is polar, meaning it has a slightly negative oxygen end and slightly positive hydrogen ends - like a tiny magnet.
These opposite charges create hydrogen bonds between water molecules, giving water its unique superpowers. These bonds are weak individually but incredibly powerful when working together.
Thermal stability means water changes temperature slowly, helping your body maintain a steady internal environment. When water freezes, it forms an open lattice structure that makes ice less dense than liquid water - that's why ice floats and protects aquatic life beneath.
Real-world Connection: Your body uses water's high latent heat of vaporisation when you sweat - it takes loads of energy to evaporate water, cooling you down efficiently!
Water's other amazing properties include cohesion (molecules sticking together, creating surface tension), being an excellent solvent for transport, staying transparent for underwater photosynthesis, and being incompressible for hydraulic support systems.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Life is built from polymers - long chains made from smaller units called monomers. Think of monomers as LEGO bricks that snap together to create complex structures.
The three major biological polymers are nucleic acids (DNA and RNA), polysaccharides (like starch), and proteins. Each has its own specific monomer type that determines the polymer's properties.
Nucleotides are the monomers of nucleic acids, each containing a phosphate group, pentose sugar, and organic base. The five bases are adenine, cytosine, guanine, thymine, and uracil (A, C, G, T, U).
Key Difference: DNA uses A, C, G, T whilst RNA swaps thymine for uracil - so RNA uses A, C, G, U instead.
Condensation reactions join monomers together by removing water molecules and forming covalent bonds. Hydrolysis does the opposite - it breaks these bonds by adding water back in. These processes are fundamental to building and breaking down biological molecules throughout your body.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Carbohydrates are made entirely from carbon, hydrogen, and oxygen, following the general formula (CH₂O)ₓ. They're your body's preferred fuel source and come in three main types.
Monosaccharides are single sugar units that taste sweet and dissolve easily in water. Glucose is the superstar here, existing as either α-glucose or β-glucose - same formula, different arrangement of atoms. This tiny structural difference has huge consequences for the polymers they create.
Pentose sugars like ribose and deoxyribose contain five carbons and are crucial components of nucleic acids. Ribose forms part of RNA whilst deoxyribose (missing one oxygen atom) forms part of DNA.
Formula Focus: Remember that glucose has the molecular formula C₆H₁₂O₆ - this appears frequently in exam questions!
When two monosaccharides join through condensation, they form a disaccharide via a glycosidic bond. Maltose forms when two glucose molecules link together, releasing a water molecule in the process. Understanding these reactions is essential for grasping how complex carbohydrates like starch and cellulose are constructed.
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.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
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
Physics
Sociology