Lesson overview
Blood: What does each part of your blood do?
Look at spun blood, then put a stained blood smear under a microscope: find the white blood cells in a field and count the red blood cells in a small square marked in the eyepiece (the graticule), to work out how many red cells there are for each white cell. Then watch models of what each part does, and of a cut that clots.
Suggested sequence
- Lesson 1 · What is in blood? The four components of blood, and red and white blood cells in a smear under the microscope. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · What each part does. What red cells, white cells, platelets and plasma each do. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Clotting. Clotting: why blood clots at a cut, and how. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 7 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 8 questions, 15 min, lesson closed.
Learning goals
Part 1: What is in blood?
- List the components of blood as red blood cells, white blood cells, platelets and plasma (9.4.1)
- Identify red and white blood cells in photomicrographs and diagrams (9.4.2)
- Supplement: identify lymphocytes and phagocytes in photomicrographs and diagrams (S9.4.5)
Part 2: What each part does
- State the functions of red blood cells (transporting oxygen, including the role of haemoglobin), white blood cells (phagocytosis and antibody production), platelets (clotting) and plasma (transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide) (9.4.3)
- Supplement: state the functions of lymphocytes (antibody production) and phagocytes (engulfing pathogens by phagocytosis) (S9.4.6)
Part 3: Clotting
- State the roles of blood clotting as preventing blood loss and the entry of pathogens (9.4.4)
- Supplement: describe the process of clotting as the conversion of fibrinogen to fibrin to form a mesh (S9.4.7)
Misconceptions to listen for
- “Blood is red cells, white cells, oxygen and water.” — Oxygen is carried by the red cells, and water is only part of the plasma. Neither is a component on its own.
- “Haemoglobin is one of the four components.” — Haemoglobin is a protein inside the red blood cells. It is part of a component, not a component itself.
- “Fibrin is one of the four components.” — Fibrin forms only at a cut, from a protein dissolved in the plasma. The component you left out is platelets.
- “X is the plasma, because it is pale.” — The plasma is the large pale yellow layer at the top. The thin band is the white blood cells and platelets.
- “Z is haemoglobin dissolved in water.” — Z is pale yellow. Haemoglobin is red and stays inside the red cells, which have sunk to the bottom.
- “Red cells, because without the stain they have no colour at all.” — Red cells are full of haemoglobin, a red protein, so they keep a pale colour of their own without any stain.
- “White cells, because without the stain they lose their nucleus.” — The stain only colours the nucleus; it does not make it. The nucleus is still there, but it is now almost colourless, like the rest of the cell.
- “Red cells, because without the stain their nucleus cannot be seen.” — Red blood cells have no nucleus at all, stained or not.
- “A nucleus in several joined lobes.” — A nucleus in lobes is the mark of a phagocyte, not a lymphocyte.
- “No nucleus and a paler centre.” — Every white blood cell has a nucleus. No nucleus and a pale centre mark a red blood cell.
Scope
Blood (9.4.1–9.4.7): the components of blood (red blood cells, white blood cells, platelets and plasma), red and white blood cells in photomicrographs and diagrams, the functions of red cells (oxygen and haemoglobin), white cells (phagocytosis and antibody production), platelets (clotting) and plasma (what it carries), and the roles of clotting; for the Supplement, lymphocytes and phagocytes told apart and their functions, and clotting as fibrinogen turned into a mesh of fibrin. The vessels are in “Blood vessels”, the heart in “The heart and double circulation” and antibodies and immunity in “Immunity and vaccination”; blood groups are not covered.