Your blood is far more complex than you might think!... Show more
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Biology
Components of a look and functions
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Your blood is far more complex than you might think!... Show more










Plasma makes up over half your blood volume and acts like your body's delivery service. It transports everything from digested food (glucose and amino acids) from your small intestine to your liver, then distributes nutrients wherever they're needed. It also carries waste products like carbon dioxide and urea to organs that can get rid of them.
Think of plasma as your body's temperature control system too. It moves heat from busy internal organs to your skin where it can escape, keeping you at a steady 37°C.
Red blood cells (erythrocytes) are your oxygen carriers - about 5 million of them packed into every cubic millimetre of blood! They contain haemoglobin, the red pigment that grabs onto oxygen and gives blood its colour. These cells are perfectly designed for their job with a biconcave disc shape that maximises surface area for oxygen exchange.
Key fact: Red blood cells have no nucleus, which leaves more room for haemoglobin molecules - each cell contains 250-300 million haemoglobin molecules!

White blood cells (leucocytes) are your body's security team. Much larger than red blood cells but fewer in number , they can squeeze through tiny blood vessels by changing shape. They defend against infections and play a key role in inflammatory responses when tissues get damaged.
All white blood cells have a nucleus and colourless cytoplasm - some contain granules that can be stained for identification under a microscope.
Platelets are tiny fragments from large bone marrow cells called megakaryocytes. With 150,000-400,000 per mm³ of blood, they're essential for blood clotting.
When you get a cut, platelets spring into action. They break open and release serotonin (which narrows blood vessels to reduce flow) and thromboplastin (an enzyme that kicks off the clotting process).
Remember: Platelets are like your body's emergency repair kit - always ready to plug leaks in your blood vessels!

Blood clotting is a brilliant two-step chemical reaction that saves your life every time you get injured. Here's how it works:
Step 1: Thromboplastin (released from broken platelets) converts prothrombin (inactive protein in plasma) into thrombin (active enzyme). This needs calcium ions to work properly.
Step 2: Thrombin then converts fibrinogen (soluble plasma protein) into fibrin (insoluble protein threads). These fibrin threads form a mesh that traps more platelets and red blood cells, creating a clot.
Special proteins in platelets contract to tighten the clot, forming a protective scab whilst new skin grows underneath. It's like your body's own emergency repair system!
Clinical connection: Babies are given vitamin K injections because it's essential for making prothrombin - without it, they could suffer dangerous internal bleeding.

Understanding blood components becomes clearer when you tackle exam-style questions. Here are some key examples:
Red blood cells and oxygen transport: RBCs lack a nucleus, giving them more space for haemoglobin molecules. However, without a nucleus containing repair instructions, they only live about 120 days. Oxygen diffuses from alveoli into RBCs down concentration gradients, then from RBCs to body cells where it's needed.
Fetal vs adult haemoglobin: Fetal haemoglobin has higher oxygen affinity than adult haemoglobin. This means fetal blood becomes oxygenated when it runs close to mum's blood in the placenta - the fetal haemoglobin "steals" oxygen from adult haemoglobin.
Prothrombin vs fibrinogen: Both are inactive precursors carried in plasma, but prothrombin becomes an enzyme (thrombin) whilst fibrinogen becomes a structural protein (fibrin). Both conversions happen during the clotting cascade.
Exam tip: Always explain the advantage of having inactive precursors - they prevent unwanted clotting until actually needed!

Arteries carry blood away from your heart at high pressure - they need to be tough! Their walls have three layers: an outer collagen layer for strength, a middle layer of elastic fibres and smooth muscle, and a smooth inner lining (endothelium) for easy blood flow.
The thick elastic fibres allow arteries to stretch when your heart pumps, then recoil to keep blood moving. Arteries near your heart have more elastic tissue, whilst those further away have more smooth muscle.
Arterioles are smaller arteries that control blood flow to different organs. When their smooth muscle contracts, they narrow and reduce blood flow - like adjusting taps throughout your body.
Capillaries are where the real action happens! Their walls are just one cell thick, making them perfect for exchanging oxygen, nutrients and waste between blood and tissues. They're so narrow that red blood cells squeeze through single-file.
Think about it: Capillaries have the largest total surface area in your circulatory system - that's why blood slows right down to give time for exchange!

Veins face a tough job - returning low-pressure blood back to your heart, often against gravity. Their structure reflects this challenge with relatively thin walls and large internal spaces (lumens) to maximise blood flow.
Unlike arteries, veins have semi-lunar valves that act like one-way gates. When blood flows towards your heart, valves open. If blood tries to flow backwards, valves slam shut. It's brilliant engineering!
Since blood pressure is low in veins, they rely on help from your skeletal muscles. When you walk or move, muscles compress veins and squeeze blood along - like squeezing a tube of toothpaste.
Venules are smaller veins without valves that collect blood from capillary networks and deliver it to larger veins.
Cool fact: The graph shows an inverse relationship between blood vessel surface area and blood velocity - where surface area is highest (capillaries), velocity is lowest due to friction!



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.
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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
Your blood is far more complex than you might think! It's made up of different components that each have crucial jobs - from carrying oxygen to fighting infections to stopping you from bleeding to death when you get a cut.

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Plasma makes up over half your blood volume and acts like your body's delivery service. It transports everything from digested food (glucose and amino acids) from your small intestine to your liver, then distributes nutrients wherever they're needed. It also carries waste products like carbon dioxide and urea to organs that can get rid of them.
Think of plasma as your body's temperature control system too. It moves heat from busy internal organs to your skin where it can escape, keeping you at a steady 37°C.
Red blood cells (erythrocytes) are your oxygen carriers - about 5 million of them packed into every cubic millimetre of blood! They contain haemoglobin, the red pigment that grabs onto oxygen and gives blood its colour. These cells are perfectly designed for their job with a biconcave disc shape that maximises surface area for oxygen exchange.
Key fact: Red blood cells have no nucleus, which leaves more room for haemoglobin molecules - each cell contains 250-300 million haemoglobin molecules!

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White blood cells (leucocytes) are your body's security team. Much larger than red blood cells but fewer in number , they can squeeze through tiny blood vessels by changing shape. They defend against infections and play a key role in inflammatory responses when tissues get damaged.
All white blood cells have a nucleus and colourless cytoplasm - some contain granules that can be stained for identification under a microscope.
Platelets are tiny fragments from large bone marrow cells called megakaryocytes. With 150,000-400,000 per mm³ of blood, they're essential for blood clotting.
When you get a cut, platelets spring into action. They break open and release serotonin (which narrows blood vessels to reduce flow) and thromboplastin (an enzyme that kicks off the clotting process).
Remember: Platelets are like your body's emergency repair kit - always ready to plug leaks in your blood vessels!

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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Blood clotting is a brilliant two-step chemical reaction that saves your life every time you get injured. Here's how it works:
Step 1: Thromboplastin (released from broken platelets) converts prothrombin (inactive protein in plasma) into thrombin (active enzyme). This needs calcium ions to work properly.
Step 2: Thrombin then converts fibrinogen (soluble plasma protein) into fibrin (insoluble protein threads). These fibrin threads form a mesh that traps more platelets and red blood cells, creating a clot.
Special proteins in platelets contract to tighten the clot, forming a protective scab whilst new skin grows underneath. It's like your body's own emergency repair system!
Clinical connection: Babies are given vitamin K injections because it's essential for making prothrombin - without it, they could suffer dangerous internal bleeding.

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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Understanding blood components becomes clearer when you tackle exam-style questions. Here are some key examples:
Red blood cells and oxygen transport: RBCs lack a nucleus, giving them more space for haemoglobin molecules. However, without a nucleus containing repair instructions, they only live about 120 days. Oxygen diffuses from alveoli into RBCs down concentration gradients, then from RBCs to body cells where it's needed.
Fetal vs adult haemoglobin: Fetal haemoglobin has higher oxygen affinity than adult haemoglobin. This means fetal blood becomes oxygenated when it runs close to mum's blood in the placenta - the fetal haemoglobin "steals" oxygen from adult haemoglobin.
Prothrombin vs fibrinogen: Both are inactive precursors carried in plasma, but prothrombin becomes an enzyme (thrombin) whilst fibrinogen becomes a structural protein (fibrin). Both conversions happen during the clotting cascade.
Exam tip: Always explain the advantage of having inactive precursors - they prevent unwanted clotting until actually needed!

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Arteries carry blood away from your heart at high pressure - they need to be tough! Their walls have three layers: an outer collagen layer for strength, a middle layer of elastic fibres and smooth muscle, and a smooth inner lining (endothelium) for easy blood flow.
The thick elastic fibres allow arteries to stretch when your heart pumps, then recoil to keep blood moving. Arteries near your heart have more elastic tissue, whilst those further away have more smooth muscle.
Arterioles are smaller arteries that control blood flow to different organs. When their smooth muscle contracts, they narrow and reduce blood flow - like adjusting taps throughout your body.
Capillaries are where the real action happens! Their walls are just one cell thick, making them perfect for exchanging oxygen, nutrients and waste between blood and tissues. They're so narrow that red blood cells squeeze through single-file.
Think about it: Capillaries have the largest total surface area in your circulatory system - that's why blood slows right down to give time for exchange!

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Veins face a tough job - returning low-pressure blood back to your heart, often against gravity. Their structure reflects this challenge with relatively thin walls and large internal spaces (lumens) to maximise blood flow.
Unlike arteries, veins have semi-lunar valves that act like one-way gates. When blood flows towards your heart, valves open. If blood tries to flow backwards, valves slam shut. It's brilliant engineering!
Since blood pressure is low in veins, they rely on help from your skeletal muscles. When you walk or move, muscles compress veins and squeeze blood along - like squeezing a tube of toothpaste.
Venules are smaller veins without valves that collect blood from capillary networks and deliver it to larger veins.
Cool fact: The graph shows an inverse relationship between blood vessel surface area and blood velocity - where surface area is highest (capillaries), velocity is lowest due to friction!

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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