List the four main components of blood
Distinguish red cells, white cells, platelets and the liquid plasma.
Section B9.4 · Blood
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall cells and tissues.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which blood component is liquid?
What you will learn
- Blood is a tissue with a liquid component
- A model is not a measured blood count
Blood is a tissue with a liquid component
Blood consists of red blood cells, white blood cells, platelets and plasma. Plasma is the liquid in which the cells and platelets are carried. Red and white cells are cells; platelets are small cell fragments involved in clotting. Calling all four components whole cells would incorrectly include plasma and platelets.
The names describe different parts of the same circulating tissue. Red blood cells mainly transport oxygen, white blood cells contribute to defence, and platelets help clotting. Plasma transports the cellular components and dissolved materials. These functions help distinguish the components but do not replace listing their names when the question asks for composition.
A model is not a measured blood count
The original component cards are a classification aid, not a sample with measured proportions. Do not calculate blood percentages from the number of icons on a drawing. A supplied smear can show cells and fragments, while its preparation does not display intact circulating plasma as a clearly labelled liquid volume.
Use precise wording: white blood cells is a broad category containing different types, not the name for every purple object in an image. Platelets are much smaller fragments than typical white cells. Stains help make structures visible but their colour alone is not sufficient identification evidence; the next lessons connect diagrams with genuine photomicrographs.
Sources for this lesson
Pause and explain
Which list contains all four main components?
Worked example
A student lists red cells, white cells and platelets as all of blood. Complete the list and classify the missing component.
Show the worked solution
- The cells and fragments circulate in a liquid.
- That liquid component is plasma.
Answer Add plasma, the liquid component carrying blood cells, platelets and dissolved materials.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
List the four main blood components.
Give me a hint
Include the liquid as well as cells and fragments.
Compare my reasoning
- Name red blood cells and white blood cells.
- Add platelets and plasma.
Red blood cells, white blood cells, platelets and plasma.
Look for these in your work
- Include both cell categories
- Include platelets and plasma
Classify red cells, white cells, platelets and plasma as cells, fragments or liquid.
Give me a hint
Platelets are fragments rather than complete cells.
Compare my reasoning
- Red and white blood cells are cells.
- Platelets are fragments; plasma is liquid.
Red/white cells: cells; platelets: cell fragments; plasma: liquid.
Look for these in your work
- Classify the cells
- Separate fragments from liquid
A sketch shows ten red-cell icons and two white-cell icons. Can it establish their percentages in a real sample?
Give me a hint
A classification sketch is not a counted representative specimen.
Compare my reasoning
- Icon numbers may be chosen for clarity.
- Measured representative sampling would be needed.
No; schematic icon counts do not establish real blood-component percentages.
Look for these in your work
- State the diagram limit
- Identify the need for measured evidence
Common mistakes
- Calling plasma a blood cell.
- Calling platelets complete white blood cells.
What can you explain now?
Which list contains all four main components?
Compare with the explanation
Red blood cells, white blood cells, platelets and plasma
All four distinct components are included.
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Make it stick
Name and classify all four components without looking at the cards.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.