Lesson overview
The heart and double circulation: Why does blood pass through a mammal’s heart twice?
Start one heartbeat by hand in a model heart cut open between the lungs and the body: watch the valves open and shut and the pressures rise and fall, then compare the walls of the chambers. Follow one red blood cell round the body, choosing its next place each time, and compare the single circulation of a fish. Learn the parts of the heart, how arteries and veins carry blood away and back, and why two circulations are better than one.
Suggested sequence
- Lesson 1 · A pump, pipes and valves. The circulatory system: blood vessels, a pump and valves for one-way flow; arteries carry blood away from the heart and veins bring it back; the parts of the heart and its coronary arteries. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 2 · One beat, step by step. One beat, step by step: the atria contract, then the ventricles; the atrioventricular and semilunar valves; the thick and thin walls of the chambers; the septum. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Twice through the heart. Twice through the heart: the double circulation of a mammal, the single circulation of a fish and the advantages of a double circulation. 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. 9 questions, 15 min, lesson closed.
Learning goals
Part 1: A pump, pipes and valves
- Describe the circulatory system as a system of blood vessels with a pump and valves to ensure one-way flow of blood (9.1.1)
- Identify in diagrams and images the structures of the mammalian heart: muscular wall, septum, left and right ventricles, left and right atria, one-way valves and coronary arteries (9.2.1)
- State that blood is pumped away from the heart in arteries and returns to the heart in veins (9.2.2)
Part 2: One beat, step by step
- Supplement: identify in diagrams and images the atrioventricular and semilunar valves in the mammalian heart (S9.2.7)
- Supplement: explain the relative thickness of the muscle walls of the left and right ventricles, and of the atria compared with the ventricles (S9.2.8)
- Supplement: explain the importance of the septum in separating oxygenated and deoxygenated blood (S9.2.9)
- Supplement: describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and the action of the valves (S9.2.10)
Part 3: Twice through the heart
- Supplement: describe the single circulation of a fish (S9.1.2)
- Supplement: describe the double circulation of a mammal (S9.1.3)
- Supplement: explain the advantages of a double circulation (S9.1.4)
Misconceptions to listen for
- “The rubber flap matches the septum, because both hold a liquid back.” — The septum is a fixed wall between the two sides of the heart; it never opens. A flap that opens one way and shuts the other is a valve.
- “The pipes match the heart, because the water passes through them.” — Blood passes through the heart too, but the heart is the pump. The tubes that carry the blood all round the body are the blood vessels.
- “The electric pump matches the valves.” — Valves only open and shut. The heart's muscle makes the blood move, as the pump does.
- “C, because it is on the left of the drawing.” — The diagram is seen from the front, so the heart's left side is on the right of the page. C is the right ventricle.
- “B, the space at the top right.” — B is an atrium, with a thin wall. The ventricles are the lower spaces.
- “A, the space at the top left.” — A is an atrium too, on the heart's right side. The left ventricle is a lower space, on the heart's left side.
- “A vein carries the blood down to the leg, and an artery brings it back.” — That swaps them. Arteries carry blood away from the heart, and veins bring it back.
- “The vena cava comes first, because it is the largest vessel.” — Size does not decide. The vena cava brings blood back into the heart, so it is a vein and comes last.
- “A is the left atrium because it is on the left.” — The diagram is seen from the front, so the heart's right side is on the left of the page.
- “H is a vein bringing blood back into the heart.” — H runs over the outside of the muscle: it is a coronary artery, which supplies the heart muscle itself.
Scope
The circulatory system as blood vessels with a pump and valves for one-way flow (9.1.1); the single circulation of a fish, the double circulation of a mammal and its advantages (9.1.2–9.1.4); the structures of the mammalian heart (9.2.1); arteries carry blood away from the heart and veins return it (9.2.2); the atrioventricular and semilunar valves (9.2.7); the relative thickness of the walls (9.2.8); the septum (9.2.9); the contraction of the atria and the ventricles and the action of the valves (9.2.10). Heart rate, exercise and coronary heart disease are in Exercise and heart health, the blood vessels themselves in Blood vessels, and blood in Blood. The pressures and times in the experiment are illustrative values for an adult at rest.