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Blood is made of plasma, red blood cells, white blood cells and platelets. Free GCSE AQA Biology notes with worked examples and 15 questions answered.
Components of Blood is part of Animal tissues, organs and organ systems in GCSE AQA Higher Biology.
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Blood is made of plasma, red blood cells, white blood cells and platelets. Free GCSE AQA Biology notes with worked examples and 15 questions answered.
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Use this lesson to stay inside Animal tissues, organs and organ systems while connecting the detail back to the wider Organisation topic.
Read the core explanations from Components of Blood before testing yourself from memory.
Picture a busy motorway system carrying everything your body needs to survive. That's blood - but it's not just a simple liquid. Blood is actually a tissue made up of different components, each with a specific job. When you look at blood under a microscope, you'll see it's like a soup with different ingredients floating around.
Blood consists of a liquid called plasma with three types of cells suspended in it: red blood cells, white blood cells, and platelets. Think of plasma as the delivery truck, and the cells as the cargo - each type of cargo has a different destination and purpose.
Plasma is the transport medium - it's like the river that carries everything else. It's mostly water (about 90%) but contains hundreds of dissolved substances. Glucose travels in plasma to feed your cells, hormones use plasma as their highway, and waste products like carbon dioxide dissolve in plasma to be carried away.
Red blood cells are the oxygen delivery service. Their unique biconcave shape (like a doughnut that's been squashed) gives them a large surface area for gas exchange. The red colour comes from haemoglobin - an iron-containing protein that binds to oxygen in the lungs and releases it in body tissues.
White blood cells are your body's security force. Unlike red blood cells, they have nuclei and can change shape. Some white blood cells (phagocytes) patrol the bloodstream looking for invaders to engulf and destroy. Others (lymphocytes) remember previous infections and produce specific antibodies to fight them.
Platelets are the emergency repair crew. When you cut yourself, platelets rush to the scene and stick together like biological glue. They're not complete cells - they're fragments of larger cells made in bone marrow. Despite being tiny, they're essential for preventing blood loss.
Each blood component has evolved for a specific job. Understanding their functions helps explain why blood disorders can be so serious - if one component fails, the whole system suffers.
Worked example: Worked Example: Applying Components of Blood
Use this method to answer an exam-style question about what makes blood special?.
Answer: A complete response links mechanism, evidence, and conclusion for components of blood.
Trap: Many students think red blood cells carry carbon dioxide like they carry oxygen. Actually, most CO₂ travels dissolved in plasma as hydrogen carbonate ions, not attached to haemoglobin.
Here's something that catches students out: blood is classified as a tissue, not just a liquid. A tissue is a group of similar cells working together for a common function. Blood fits this definition perfectly - it's a liquid tissue where different cell types cooperate to transport materials and defend the body.
Unlike other tissues (like muscle or nerve tissue), blood is a fluid tissue. The cells aren't stuck together in a fixed structure - they flow freely in the plasma. This allows blood to reach every part of your body through the circulatory system.
Understanding blood components helps explain what goes wrong in blood disorders. Each component's failure causes specific symptoms that match their normal function.
Anaemia occurs when you don't have enough healthy red blood cells or haemoglobin. Result? Less oxygen transport, causing tiredness and breathlessness. Leukaemia affects white blood cell production, compromising immune defence. Haemophilia prevents proper blood clotting due to missing clotting factors in plasma.
Blood component questions are exam favourites because they test both knowledge and application. Here's how to maximise your marks.
Command word focus: 'Describe' questions want you to state what each component does. 'Explain' questions want you to link structure to function - why the biconcave shape helps oxygen transport, why white blood cells need nuclei, etc.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Haemoglobin is an iron-containing protein in red blood cells that binds to oxygen in the lungs and releases it in body tissues. It gives blood its red colour, and red blood cells have no nucleus so there is maximum space for haemoglobin.
Plasma is the pale yellow liquid component of blood that makes up about 55% of blood volume. It is about 90% water and carries dissolved nutrients such as glucose, hormones, antibodies and waste products such as carbon dioxide.
Blood is made of plasma, red blood cells, white blood cells and platelets. Plasma is the liquid that transports substances, red blood cells carry oxygen, white blood cells defend the body against pathogens, and platelets help blood clot at injury sites.
Anaemia is a blood disorder where there are not enough healthy red blood cells or not enough haemoglobin. The result is less oxygen transport, causing tiredness and breathlessness.
Red blood cells carry oxygen around the body. Their biconcave shape gives a large surface area for gas exchange, and they are packed with haemoglobin, which binds to oxygen in the lungs and releases it in body tissues.
Platelets help blood clot at injury sites. They are small cell fragments without nuclei, made from larger cells in bone marrow, that stick together and release chemicals to form a plug, preventing blood loss.
Platelets are fragments of larger cells made in bone marrow. They are not complete cells and have no nucleus, but when a cut happens they stick together and release chemicals to form a plug, preventing blood loss.
Most carbon dioxide travels dissolved in plasma as hydrogen carbonate ions, not attached to haemoglobin. Red blood cells carry oxygen, but waste products like carbon dioxide dissolve in plasma to be carried away.
Plasma makes up about 55% of blood volume. It is a pale yellow liquid that is mostly water, about 90%, and contains dissolved nutrients, hormones, antibodies and waste products.
Blood is a tissue made of a liquid called plasma with three types of cells suspended in it: red blood cells, white blood cells and platelets. Plasma makes up about 55% of blood volume, red blood cells carry oxygen, white blood cells defend against pathogens, and platelets help blood clot.
Red blood cells do not carry most carbon dioxide in the way they carry oxygen. Most CO₂ travels dissolved in plasma as hydrogen carbonate ions, not attached to haemoglobin.
Blood is classed as a tissue because it is a group of cells working together for a common function: transporting materials and defending the body. Unlike muscle or nerve tissue, blood is a fluid tissue, so its cells flow freely in the plasma rather than being stuck in a fixed structure.
Erythrocytes are red blood cells, biconcave cells packed with haemoglobin that carry oxygen, and leukocytes are white blood cells, larger cells with nuclei that defend the body against pathogens. Leukocytes include phagocytes, which engulf bacteria, and lymphocytes, which produce antibodies.
Haemophilia is a blood disorder that prevents proper blood clotting because of missing clotting factors in plasma. It shows how the failure of one blood component causes symptoms that match its normal function.
Leukaemia is a blood disorder affecting white blood cell production, which compromises immune defence. White blood cells normally defend the body against pathogens, so each blood disorder causes symptoms that match the normal function of the component that fails.