Blood Components and Their Functions
What Is Blood Made Of?
Lesson duration is: 40 minItems in this lesson
What Is Blood Made Of?
Open with the idea that blood is a tissue, not just a red liquid. The lesson will explain how its four main components work together to keep the body functioning.
Learning goal
I can describe the main components of blood and explain what each one does.
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What words come to mind when you hear blood?
Use this to surface prior ideas such as oxygen, cells, veins, heart, clotting, infection or plasma. Briefly connect student responses to the lesson goal: blood is a mixture with different parts doing different jobs.
Blood Is a Living Mixture
Blood is made of different parts mixed together.
Plasma is the liquid part
Red blood cells carry oxygen
White blood cells help protect the body
Platelets help blood clot
These components move around the body in blood vessels.
Emphasise that each component has a different structure and function. This links to a key biology idea: structure supports function.
Four Parts, One Job
Blood works because its components do different jobs at the same time.
Together they transport materials, defend the body, and prevent too much blood loss.
This slide sets up the central idea of cooperation before moving into each component separately.
Plasma
Plasma is the liquid portion of blood.
It makes up about 55% of blood
It is mostly water
It carries dissolved substances around the body
If helpful, note that plasma appears pale yellow. Avoid going beyond the stated lesson scope into detailed plasma proteins unless needed.
Plasma as a Transport System
Plasma transports:
nutrients
hormones
proteins
waste products
Connect this to the idea of transport in multicellular organisms: cells need materials delivered and wastes removed.
Why Plasma Matters
Without plasma, blood cells could not move easily through vessels.
Plasma acts as the transport medium that carries both cells and dissolved substances to different parts of the body.
Students may think plasma only carries nutrients. Reinforce that it also carries wastes and the blood cells themselves.
What is plasma's main job in blood?
Fight germs
Carry oxygen
Transport materials
Form clots
Checks the key contrast between the four components. Distractors match the other blood components' roles.
Plasma check
Plasma is the liquid portion of blood. It makes up about 55% of blood and carries dissolved substances such as nutrients and waste products around the body.
All blanks come directly from the plasma slides. 'Waste products' matters because students often remember only nutrients.
Red Blood Cells
Red blood cells make up about 45% of blood.
They contain haemoglobin
Haemoglobin carries oxygen
They move oxygen from the lungs to body cells
Use UK spelling: haemoglobin. Link oxygen transport to respiration in cells if students have met that idea before.
Built for Oxygen Delivery
Red blood cells have a biconcave shape.
This helps them move through tiny blood vessels and gives a large surface area for carrying oxygen.
A common misconception is that the shape is just for movement. Mention that the shape also supports efficient gas transport.
From Lungs to Cells
Lungs take in oxygen → red blood cells pick it up → blood carries it around the body → cells receive oxygen for their activities
This is a useful causal chain slide. Keep the focus on transport rather than the full details of gas exchange.
Why does a red blood cell have a biconcave shape?
To fight bacteria
To make hormones
To carry oxygen well
To form a clot
The taught reason is efficient oxygen transport, supported by large surface area and movement through tiny vessels.
Red blood cells check
Red blood cells contain haemoglobin, a protein that carries oxygen. They move it from the lungs to body cells.
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This anchors the causal chain from lungs to cells using the exact lesson vocabulary and UK spelling.
White Blood Cells
White blood cells are part of the body's defence system.
They recognise harmful germs
They help protect the body from infection
They help the body respond to disease
Students do not need the different types of white blood cell here. Keep the focus on their role in protection.
How They Protect Us
When germs enter the body, white blood cells help to find and destroy them.
This reduces the chance of infection spreading.
Use bacteria as the example because it is visually clear and matches the source material.
Defence in the Bloodstream
White blood cells are far fewer in number than red blood cells, but they are essential.
Their job is not transport. Their main role is to protect the body.
This contrast helps students separate functions clearly: red blood cells transport oxygen, white blood cells defend.
What is the main role of white blood cells?
Carry nutrients
Protect the body
Carry oxygen
Stop bleeding
Reinforces the contrast that white blood cells are part of the body's defence system, not a transport system.
How do white blood cells help us stay healthy?
Expected ideas: white blood cells find and destroy germs, reduce the spread of infection, and protect the body from disease.
Platelets
Platelets help blood clot when a blood vessel is damaged.
They rush to the wound
They stick together
They help stop bleeding
Clarify that platelets are cell fragments, but only if needed; the key idea here is clotting.
How a Clot Forms
Damage to a blood vessel → platelets gather at the site → platelets stick together → bleeding slows and a clot begins to form
Keep this as a simple stepwise account. Avoid detailed clotting factors unless students ask.
Why Platelets Matter
Clotting is important because it prevents too much blood loss and starts the healing process.
Without enough platelets, bleeding may not stop easily.
Link clearly to protection: platelets protect by preventing blood loss, not by fighting germs.
What happens first when a blood vessel is damaged?
A clot breaks down
Platelets gather
White cells attack
Oxygen is released
Tests the clotting sequence from the platelet slides.
Platelets check
When a blood vessel is damaged, platelets rush to the wound and stick together. This helps stop bleeding and starts healing.
Focuses on the simple clotting sequence and its purpose.
Working Together
Each blood component has a special role:
plasma transports materials
red blood cells carry oxygen
white blood cells fight infection
platelets help blood clot
This slide synthesises the lesson before showing what happens when a component is missing or reduced.
When Blood Components Fail
If one part of blood cannot do its job properly, the whole body is affected.
Blood health depends on all four components working together.
Set up the final examples as consequences of failed function, which is a core biology way of thinking.
Examples of Failure
Too few red blood cells can cause anaemia and tiredness
Weak white blood cell defence can lead to infections
Too few platelets can mean bleeding does not stop easily
Keep the examples brief and tied directly to function. Do not expand into diagnosis or treatment.
A person bleeds for a long time after a cut. Which part may be low?
Plasma
Platelets
Red blood cells
White blood cells
Application of function to failure. The likely misconception is choosing red blood cells because they are the most familiar blood cells.
Blood components together
Too few red blood cells can cause anaemia and tiredness. Weak white blood cell defence can lead to infection. Too few platelets can mean bleeding does not stop easily.
This final check ties each failed function to its consequence.
What is one thing you learned about blood today?
Reflection only. Invite students to name one component and one linked function they now understand clearly.
Which part of this lesson helped you understand best?
Reflection only. Encourage students to mention a specific idea such as the diagram, the clotting steps, or the lungs-to-cells chain.
Which blood component still feels hardest to remember?
Reflection only. Use responses to identify misconceptions or parts to revisit, such as plasma versus red blood cells or white blood cells versus platelets.
Glossary
blood - a living tissue that contains plasma, red blood cells, white blood cells, and platelets
plasma - the liquid part of blood that transports dissolved substances and blood cells
red blood cells - blood cells that carry oxygen around the body
haemoglobin - a protein in red blood cells that carries oxygen
white blood cells - blood cells that help protect the body from infection
platelets - small cell fragments that help blood clot
clot - a mass formed when blood thickens to help stop bleeding
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