Blood is a liquid tissue with four components, each with its own job: red blood cells carry oxygen, white blood cells fight pathogens, platelets help blood clot, and plasma carries everything else. Telling the two kinds of white blood cell apart, their separate jobs and the fibrinogen-to-fibrin step of clotting are Extended.
Blood is made of red blood cells, white blood cells, platelets and plasma. Red blood cells transport oxygen using haemoglobin; white blood cells carry out phagocytosis and antibody production; platelets are involved in clotting; plasma transports blood cells, ions, nutrients, urea, hormones and carbon dioxide. Clotting prevents blood loss and the entry of pathogens.
Start on the blood sample view and rotate it. Then switch to phagocyte, lymphocyte and clotting, and press Play in each to watch the white blood cells and platelets at work.
| Component | What it looks like | Function |
|---|---|---|
| Red blood cells | small, biconcave discs, no nucleus, very numerous | transport oxygen: haemoglobin combines with oxygen in the lungs and releases it in the tissues |
| White blood cells | larger, with a nucleus that stains darkly; far fewer | phagocytosis and antibody production |
| Platelets | tiny cell fragments | clotting (details not required at Core) |
| Plasma | straw-coloured liquid, mostly water | transports blood cells, ions, nutrients (such as glucose and amino acids), urea, hormones and carbon dioxide |
Plasma, not red blood cells, carries most carbon dioxide, along with glucose, urea and hormones. Red blood cells carry oxygen. Do not write that plasma carries oxygen.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the blood sample view, which component is shown as tiny fragments rather than whole cells?
According to the sim, what does the haemoglobin in red blood cells do?
Which of these does plasma carry, according to the sim?
In the phagocyte view, what happens to the bacterium?
Extended. There are two main types of white blood cell. You can tell them apart by the shape of the nucleus.
| Phagocyte | Lymphocyte | |
|---|---|---|
| Nucleus | lobed (several lobes) | large and round, filling most of the cell |
| Cytoplasm | plenty, often granular | very little, a thin ring round the nucleus |
| Function | engulfing pathogens by phagocytosis, then digesting them with enzymes | antibody production |
Lymphocytes make antibodies; they do not engulf pathogens. Phagocytes engulf pathogens; they do not make antibodies. Match the cell to its job.
When a blood vessel is cut, a clot quickly forms a plug. In the clotting view, pale threads appear across the wound and red blood cells collect in them.
Fibrinogen is soluble and always present in plasma; fibrin is the insoluble form that makes the mesh. Write "fibrinogen is converted to fibrin", not the other way round.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which feature identifies a cell in a blood smear as a white blood cell?
Extended: which cell has a large round nucleus and produces antibodies?
Extended: which change happens when blood clots?
State the two roles of blood clotting.
This skill is now recorded on your profile. Keep the chain going.