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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
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Biology
20 Dec 2025
194
4 pages
Ever wondered how we discovered that all living things are made of tiny building blocks called cells? From... Show more
Your smartphone camera can zoom in pretty close, but imagine magnifying something thousands of times to see the invisible world around you! That's exactly what microscopes made possible, revealing individual cells that make up every living thing on Earth.
Back in the 16th and 17th centuries, early scientists developed the first light microscopes. By the mid-1800s, these instruments were powerful enough to see individual cells clearly. This breakthrough led to the development of cell theory - one of biology's most important discoveries.
Cell theory states three fundamental principles both plant and animal tissues are composed of cells, cells are the basic unit of all life, and cells only develop from existing cells. This might seem obvious now, but it was revolutionary at the time!
Did you know? Robert Hooke coined the term "cell" in 1665 because the cork compartments he observed reminded him of tiny prison cells!
The story of cell theory perfectly shows how science progresses. As technology improved and new evidence emerged, scientists continuously refined their understanding, sometimes proving earlier theories completely wrong.
Between 1665 and 1860, brilliant scientists made groundbreaking observations that built our understanding of cells piece by piece. Robert Hooke first spotted cell walls in cork, whilst Anton van Leeuwenhoek became the first person to observe living cells swimming in pond water using his handcrafted microscopes.
The universal cell theory emerged in 1837-38 when Matthias Schleiden and Theodor Schwann independently concluded that all living things are composed of cells. This was a massive leap forward in biological understanding.
Later discoveries proved that new cells only come from existing cells through cell division, not from spontaneous generation as many believed. Louis Pasteur finally put the spontaneous generation theory to rest in 1860 with his famous sterile broth experiments.
Remember These discoveries happened over 200 years - science takes time, patience, and lots of failed experiments!
Modern compound light microscopes use two lenses (objective and eyepiece) working together to achieve high magnification whilst reducing distortion. The specimen sits on a slide with light shining from underneath.
Here's the problem with looking at cells they're mostly transparent! Without staining techniques, you'd struggle to see much detail because cells don't naturally absorb much light, creating very low contrast images.
Stains work by binding to different parts of cells, making structures visible under the microscope. Positive stains like crystal violet are attracted to negatively charged parts of cells, whilst negative stains stay outside cells, creating a dark background that makes unstained cells stand out.
Differential staining is particularly clever - it helps distinguish between different types of organisms or structures. The Gram stain technique separates bacteria into gram-positive (purple) and gram-negative (red) groups. This isn't just academic - gram-positive bacteria respond to penicillin, whilst gram-negative bacteria don't!
Exam tip Learn the Gram stain steps crystal violet → iodine → alcohol wash → safranin counterstain. This sequence often appears in exam questions!
The acid-fast technique specifically identifies Mycobacterium bacteria (which causes tuberculosis) by using special dyes that resist acid washing. These practical techniques remain essential in medical diagnosis today.
Working with microscopic specimens involves various preparation techniques, each suited to different sample types. Dry mounts work well for solid specimens like pollen or hair, whilst wet mounts are perfect for living organisms in water.
Squash slides help spread out soft tissue samples, and smear slides create thin, even coatings - essential for blood samples. Professional slide preparation involves fixing (preserving), sectioning (cutting thin slices), staining, and mounting specimens.
Safety matters enormously in microscopy work. Many stains are toxic or irritating, so proper risk assessments are essential before starting any practical work. Schools use CLEAPSS guidelines to ensure student safety.
Safety first Always follow your teacher's instructions when handling stains and chemicals - they're there to protect you!
Understanding these techniques gives you the foundation for advanced microscopy work. Whether you're identifying bacteria, examining plant cells, or studying tissue samples, these principles remain unchanged from those pioneering scientists centuries ago.
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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Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the various types of microscopes including Optical, Transmission Electron Microscopes (TEMs), and Scanning Electron Microscopes (SEMs). This summary covers key concepts such as magnification, resolution, and the advantages and disadvantages of each microscope type. Ideal for A-level biology students studying cell structure and microscopy techniques.
BiologyExplore the intricate structures and functions of eukaryotic cells, including organelles like the nucleus, mitochondria, and chloroplasts. This summary covers key concepts in cellular biology, microscopy techniques, and the differences between prokaryotic and eukaryotic cells. Ideal for students studying cell biology and related fields.
BiologyExplore the essentials of microscopy, including types of microscopes, magnification, and resolution. This summary covers the history of light and electron microscopes, detailing their functions and applications in scientific observation. Ideal for students seeking a clear understanding of microscopy concepts.
BiologyExplore the fundamentals of microscopy, including the use of light and electron microscopes, specimen preparation, viewing techniques, and magnification calculations. This practical guide covers essential skills for studying cells and sub-cellular structures, making it ideal for biology students. Includes step-by-step instructions and examples for effective scientific drawing and measurement conversions.
BiologyExplore the fundamentals of microscopy and cellular biology, including the functions of cell organelles, practical methods for observing cheek cells, and the differences between light and electron microscopes. This summary covers key concepts such as magnification, resolution, and measurement units essential for GCSE students.
BiologyExplore the various types of microscopes, including light, electron, and confocal microscopes, along with their magnification capabilities, resolutions, and applications in biology. This summary covers key concepts such as cell theory, staining techniques, and the history of microscopy, making it essential for OCR A AS and A Level Biology students. Understand how to measure magnification and resolution effectively.
BiologyApp 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
Ever wondered how we discovered that all living things are made of tiny building blocks called cells? From the first glimpse of cork cells in 1665 to today's advanced staining techniques, microscopy has completely transformed our understanding of life itself.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Your smartphone camera can zoom in pretty close, but imagine magnifying something thousands of times to see the invisible world around you! That's exactly what microscopes made possible, revealing individual cells that make up every living thing on Earth.
Back in the 16th and 17th centuries, early scientists developed the first light microscopes. By the mid-1800s, these instruments were powerful enough to see individual cells clearly. This breakthrough led to the development of cell theory - one of biology's most important discoveries.
Cell theory states three fundamental principles: both plant and animal tissues are composed of cells, cells are the basic unit of all life, and cells only develop from existing cells. This might seem obvious now, but it was revolutionary at the time!
Did you know? Robert Hooke coined the term "cell" in 1665 because the cork compartments he observed reminded him of tiny prison cells!
The story of cell theory perfectly shows how science progresses. As technology improved and new evidence emerged, scientists continuously refined their understanding, sometimes proving earlier theories completely wrong.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Between 1665 and 1860, brilliant scientists made groundbreaking observations that built our understanding of cells piece by piece. Robert Hooke first spotted cell walls in cork, whilst Anton van Leeuwenhoek became the first person to observe living cells swimming in pond water using his handcrafted microscopes.
The universal cell theory emerged in 1837-38 when Matthias Schleiden and Theodor Schwann independently concluded that all living things are composed of cells. This was a massive leap forward in biological understanding.
Later discoveries proved that new cells only come from existing cells through cell division, not from spontaneous generation as many believed. Louis Pasteur finally put the spontaneous generation theory to rest in 1860 with his famous sterile broth experiments.
Remember: These discoveries happened over 200 years - science takes time, patience, and lots of failed experiments!
Modern compound light microscopes use two lenses (objective and eyepiece) working together to achieve high magnification whilst reducing distortion. The specimen sits on a slide with light shining from underneath.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Here's the problem with looking at cells: they're mostly transparent! Without staining techniques, you'd struggle to see much detail because cells don't naturally absorb much light, creating very low contrast images.
Stains work by binding to different parts of cells, making structures visible under the microscope. Positive stains like crystal violet are attracted to negatively charged parts of cells, whilst negative stains stay outside cells, creating a dark background that makes unstained cells stand out.
Differential staining is particularly clever - it helps distinguish between different types of organisms or structures. The Gram stain technique separates bacteria into gram-positive (purple) and gram-negative (red) groups. This isn't just academic - gram-positive bacteria respond to penicillin, whilst gram-negative bacteria don't!
Exam tip: Learn the Gram stain steps: crystal violet → iodine → alcohol wash → safranin counterstain. This sequence often appears in exam questions!
The acid-fast technique specifically identifies Mycobacterium bacteria (which causes tuberculosis) by using special dyes that resist acid washing. These practical techniques remain essential in medical diagnosis today.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Working with microscopic specimens involves various preparation techniques, each suited to different sample types. Dry mounts work well for solid specimens like pollen or hair, whilst wet mounts are perfect for living organisms in water.
Squash slides help spread out soft tissue samples, and smear slides create thin, even coatings - essential for blood samples. Professional slide preparation involves fixing (preserving), sectioning (cutting thin slices), staining, and mounting specimens.
Safety matters enormously in microscopy work. Many stains are toxic or irritating, so proper risk assessments are essential before starting any practical work. Schools use CLEAPSS guidelines to ensure student safety.
Safety first: Always follow your teacher's instructions when handling stains and chemicals - they're there to protect you!
Understanding these techniques gives you the foundation for advanced microscopy work. Whether you're identifying bacteria, examining plant cells, or studying tissue samples, these principles remain unchanged from those pioneering scientists centuries ago.
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.
5
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the various types of microscopes including Optical, Transmission Electron Microscopes (TEMs), and Scanning Electron Microscopes (SEMs). This summary covers key concepts such as magnification, resolution, and the advantages and disadvantages of each microscope type. Ideal for A-level biology students studying cell structure and microscopy techniques.
BiologyExplore the intricate structures and functions of eukaryotic cells, including organelles like the nucleus, mitochondria, and chloroplasts. This summary covers key concepts in cellular biology, microscopy techniques, and the differences between prokaryotic and eukaryotic cells. Ideal for students studying cell biology and related fields.
BiologyExplore the essentials of microscopy, including types of microscopes, magnification, and resolution. This summary covers the history of light and electron microscopes, detailing their functions and applications in scientific observation. Ideal for students seeking a clear understanding of microscopy concepts.
BiologyExplore the fundamentals of microscopy, including the use of light and electron microscopes, specimen preparation, viewing techniques, and magnification calculations. This practical guide covers essential skills for studying cells and sub-cellular structures, making it ideal for biology students. Includes step-by-step instructions and examples for effective scientific drawing and measurement conversions.
BiologyExplore the fundamentals of microscopy and cellular biology, including the functions of cell organelles, practical methods for observing cheek cells, and the differences between light and electron microscopes. This summary covers key concepts such as magnification, resolution, and measurement units essential for GCSE students.
BiologyExplore the various types of microscopes, including light, electron, and confocal microscopes, along with their magnification capabilities, resolutions, and applications in biology. This summary covers key concepts such as cell theory, staining techniques, and the history of microscopy, making it essential for OCR A AS and A Level Biology students. Understand how to measure magnification and resolution effectively.
BiologyApp 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
Sociology