The shape of the lesson
By the end of the lesson, learners can
- Four components: Start on the blood sample view and rotate it.
- Phagocytes and lymphocytes: Extended.
- How blood clots: When a blood vessel is cut, a clot quickly forms a plug.
- Red blood cells: oxygen, using haemoglobin; no nucleus.
- White blood cells: phagocytes engulf (lobed nucleus); lymphocytes make antibodies (large round nucleus).
- Platelets: clotting; Extended: soluble fibrinogen to insoluble fibrin mesh.
- Plasma: blood cells, ions, nutrients, urea, hormones, carbon dioxide.
One picture every idea returns to
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.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Carry, defend, seal.. 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. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Four components | Start on the blood sample view and rotate it. Project tab 7 of the lab (Blood: cells, phagocytosis, antibodies and clotting) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Phagocytes and lymphocytes | Extended. | Pairs |
| 21 to 30 min | Teach and check: How blood clots | When a blood vessel is cut, a clot quickly forms a plug. | Think-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 21 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in How blood clots, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| 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. |
| Lymphocytes make antibodies; they do not engulf pathogens. | Phagocytes engulf pathogens; they do not make antibodies. Match the cell to its job. |
| 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. |
Blood: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
List the four components of blood and state one function of each.
Explain how red blood cells transport oxygen from the lungs to respiring tissues.
Name three substances, other than blood cells, carried by plasma, and for each state where it is carried from or to.
Extended. A student looks at a stained blood smear. Describe how she could distinguish (a) red blood cells from white blood cells, and (b) phagocytes from lymphocytes, and state the function of each type of white blood cell.
Extended. Describe the process of blood clotting and explain why it is important.
A blood test gives the following counts for a patient.
| Component | Patient / per mm3 | Normal range / per mm3 |
|---|---|---|
| red blood cells | 3 200 000 | 4 500 000 to 5 500 000 |
| white blood cells | 7 000 | 4 000 to 11 000 |
| platelets | 260 000 | 150 000 to 400 000 |
(a) Which count is outside the normal range? (b) Suggest one symptom the patient may have and explain it.
Answer key and marking notes
- Red blood cells: transport oxygen (using haemoglobin).
- White blood cells: phagocytosis or antibody production.
- Platelets: clotting.
- Plasma: transports blood cells, ions, nutrients, urea, hormones and carbon dioxide (any one).
- Red blood cells contain haemoglobin.
- In the lungs, where there is a lot of oxygen, haemoglobin combines with oxygen.
- In respiring tissues, where there is little oxygen, the haemoglobin releases the oxygen, which diffuses into the cells.
- Glucose (nutrients): from the small intestine to all cells.
- Urea: from the liver to the kidneys.
- Carbon dioxide: from respiring cells to the lungs. (Also accept hormones from glands to target organs, or ions.)
- (a) Red blood cells have no nucleus (and are smaller, more numerous biconcave discs); white blood cells have a nucleus.
- (b) Phagocytes have a lobed nucleus; lymphocytes have a large, round nucleus that fills most of the cell.
- Phagocytes engulf pathogens by phagocytosis.
- Lymphocytes produce antibodies.
- At a wound, platelets help trigger clotting.
- The soluble plasma protein fibrinogen is converted into insoluble fibrin.
- Fibrin forms a mesh of threads that traps red blood cells, forming a clot (which dries into a scab).
- The clot prevents blood loss and prevents pathogens entering the body through the wound.
- (a) The red blood cell count is below the normal range.
- (b) Tiredness, lack of energy or breathlessness.
- Fewer red blood cells means less haemoglobin, so less oxygen is carried to the tissues and less energy is released by aerobic respiration.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
The diagram shows four components of a stained blood smear. Which labelled structure is a red blood cell?
- AA
- BB
- CC
- DD
What is the function of platelets?
- Aclotting the blood at a wound
- Bcarrying oxygen to the tissues
- Cproducing antibodies against pathogens
- Dtransporting hormones and urea
Which list contains only substances that are transported dissolved in blood plasma?
- Aglucose, urea, hormones
- Boxygen, haemoglobin, glucose
- Curea, platelets, oxygen
- Dhormones, antibodies, starch
A person has far fewer platelets than normal. Which problem are they most likely to have?
- ABleeding for a long time from small cuts
- BBecoming breathless because less oxygen is carried
- CBeing unable to make antibodies against pathogens
- DHaving blood plasma that cannot carry glucose
People who live at high altitude, where the air contains less oxygen, have more red blood cells than people at sea level. How does this help them?
- AMore haemoglobin is available to carry oxygen to the tissues
- BMore antibodies are made to fight disease in the cold
- CThe blood clots more quickly to prevent blood loss
- DMore plasma is available to dissolve carbon dioxide
(Extended) Look again at the blood smear diagram. Which labelled cell produces antibodies?
- AC
- BB
- CA
- DD
(Extended) Which substance forms the mesh of threads that traps red blood cells in a clot?
- Ainsoluble fibrin
- Bsoluble fibrinogen
- Chaemoglobin
- Dantibodies
(Extended) Which sequence describes how a phagocyte destroys a bacterium?
- AMoves towards it, engulfs it into a vacuole, digests it with enzymes
- BReleases antibodies, the bacteria clump, the antibodies digest them
- CEngulfs it, makes fibrin around it, releases it into the plasma
- DDigests it outside the cell, absorbs it, releases antibodies
Quiz key
A has no nucleus and a paler centre, the shape of a biconcave disc seen from above, so it is a red blood cell. B and C both contain a stained nucleus, so they are white blood cells. D are tiny cell fragments, platelets.
Platelets are cell fragments that take part in clotting, which seals wounds. Oxygen is carried by red blood cells using haemoglobin. Antibodies are made by white blood cells (lymphocytes). Hormones and urea are carried dissolved in plasma.
Glucose, urea and hormones are all carried dissolved in plasma. Oxygen is carried mainly by haemoglobin inside red blood cells, and haemoglobin is in the cells, not dissolved in plasma. Platelets are cell fragments carried by plasma, not dissolved in it. Starch is digested to glucose before absorption, so it is not found in the blood.
Platelets are needed for clotting, so with few platelets blood clots slowly and small cuts bleed for a long time, also giving pathogens longer to enter. Breathlessness from poor oxygen transport would come from too few red blood cells or too little haemoglobin. Antibodies are made by lymphocytes. Plasma carries glucose whatever the platelet count.
Red blood cells contain haemoglobin, which combines with oxygen in the lungs. More red blood cells means more haemoglobin, so enough oxygen can still be carried to the tissues when the air holds less. Antibodies come from white blood cells, clotting depends on platelets, and plasma is the liquid part of blood, not made of red blood cells.
C has a large, round nucleus that fills most of the cell, so it is a lymphocyte, which produces antibodies. B has a lobed nucleus, so it is a phagocyte, which engulfs pathogens instead. A is a red blood cell, which carries oxygen, and D are platelets, which help blood clot.
At a wound, the soluble plasma protein fibrinogen is converted into insoluble fibrin, which forms the mesh. Fibrinogen is the soluble starting protein, which is why it can circulate in plasma without forming clots. Haemoglobin carries oxygen inside red blood cells, and antibodies bind to pathogens.
A phagocyte moves towards the bacterium, flows around it and engulfs it into a vacuole, then digests it with enzymes: phagocytosis. Releasing antibodies is the job of lymphocytes, and antibodies do not digest bacteria. Fibrin forms in clotting, not in phagocytosis. Phagocytes digest bacteria inside the cell after engulfing them, not outside.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.