By the end of this lesson
- Identify the four blood components.
- Relate each component to its role.
- Interpret a separated blood sample.
BIG QUESTION
How can one liquid transport materials, defend against disease and repair a damaged vessel?
Blood is a tissue whose specialised cells and cell fragments are suspended in plasma.
Plasma is the transport medium
plasmaThe liquid part of the blood, which transports carbon dioxide, digested food, urea, hormones and heat. is the pale liquid carrying blood cells and dissolved substances. It is mostly water with proteins, ions and transported solutes.
Its fluid state links exchange surfaces, organs and body cells.
Cells and fragments divide the work
red blood cellA biconcave blood cell with no nucleus, packed with haemoglobin, that carries oxygen from the lungs to body tissues. carry oxygen using haemoglobin. white blood cellA blood cell that defends the body against pathogens, either by phagocytosis (phagocytes) or by making antibodies (lymphocytes). defend against pathogens; different types carry out different responses.
plateletA small fragment of a cell in the blood that helps blood to clot at a wound. are small cell fragments that help initiate clotting after vessel damage.
A centrifuge separates by density
Centrifuged blood forms a lower red-cell layer, a thin buffy coat of white cells and platelets, and an upper plasma layer.
Layer size can describe composition, but diagnosis requires clinical standards and is beyond a classroom comparison.
Blood components
Structure supports each role.
| Component | Structure | Main role |
|---|---|---|
| Plasma | Watery liquid. | Transports cells, solutes and heat. |
| Red blood cell | Biconcave, haemoglobin-rich cell. | Oxygen transport. |
| White blood cell | Nucleated immune cell. | Defence against pathogens. |
| Platelet | Small cell fragment. | Blood clotting. |
Language that earns precision
- plasma
- Liquid component of blood.
- red blood cell
- Haemoglobin-containing cell specialised for oxygen transport.
- white blood cell
- Immune cell involved in defence.
- platelet
- Cell fragment involved in clotting.
Common misconceptions
Claim: Plasma is just water.
Correction: It contains proteins, ions and many transported substances.
Claim: All white blood cells make antibodies.
Correction: Lymphocytes can produce antibodies; phagocytes have a different role.
Claim: Platelets are complete cells.
Correction: They are small cell fragments.
Match the answer to the command word
Use all four named components.
Do not merge platelets with white blood cells.
Recall, apply, then justify
Name the four main blood components and give one function of each.
Hint
One matched role per component.
Suggested marking points
- Plasma transports dissolved substances/cells/heat.
- Red blood cells carry oxygen.
- White blood cells defend against pathogens.
- Platelets help blood clot.
Explain why blood is described as a tissue.
Hint
Several specialised parts cooperate.
Suggested marking points
- It contains different specialised cells/cell fragments in plasma.
- The components work together in transport, defence and repair.
Explain the layers formed when blood is centrifuged.
Planning hint
Use component density.
What a strong design includes
- Components separate according to density.
- Dense red blood cells form the lower layer.
- Plasma forms the upper liquid layer.
- White cells and platelets form a thin intermediate buffy coat.
- Layer proportions reflect blood composition.