Lesson focus: The heart produces one-way blood flow through two linked circuits.
Trace blood through chambers, valveA flap that stops blood flowing backwards. and named vessels and explain ventricular differences.
Build on earlier learning
Structure–function chainsApply structure–function chains to tissues, valves and chambers of the heart.
Practical
Examining a heart
- Identify the front of the heart and the four chambers from the outside.
- Compare the thickness of the left and right ventricle walls.
- Locate the valves and the blood vessels that leave the heart.
Record: A labelled drawing and a comparison of the ventricle walls with the reason for the difference.
Safety: Use the scalpel away from your hand on a board; wash hands afterwards.
You will be successful when you can…
- Identify four chambers and major vessels.
- Trace blood through heart, lungs and body.
- Explain valves as one-way controls.
- Explain why the left ventricle wall is thicker.
Words that carry the science
- atrium
- Upper chamber receiving blood into the heart.
- ventricle
- Lower chamber pumping blood out of the heart.
- valve
- Structure preventing backflow.
- artery
- Blood vessel carrying blood away from the heart.
- vein
- Blood vessel carrying blood towards the heart.
Trace one-way flow through a double circulation
01Follow direction, not colour
Body → vena cava → right atriumOne of the two top chambers of the heart, which receive blood. → right ventricleOne of the two bottom chambers of the heart, which pump blood out. → pulmonary arteryA blood vessel that carries blood away from the heart. → lungs. Lung capillaries exchange gases.
Lungs → pulmonary veinA blood vessel that carries blood back towards the heart. → left atrium → left ventricle → aorta → body. Arteries are defined by flow away from the heart, not by oxygen content.
02Valves make pumping effective
valveA flap that stops blood flowing backwards. open when pressure is higher behind them and close when pressure would reverse flow. They do not actively pump blood.
03Walls match pressure demand
The left ventricle supplies the whole systemic circuit and has a thicker muscular wall than the right ventricle. The right ventricle pumps only to nearby lungs at lower pressure.
Double circulation
Blood passes through the heart twice on each trip round the body: once to go to the lungs, and once to go to the rest of the body.
Oxygenated Deoxygenated. The heart is drawn as if you are facing the person, so its right side is on the left.
Stage 1 of 8
Trace one red blood cell
Start in the vena cava and return to the body.
- Vena cava → right atrium → right ventricle.
- Pulmonary artery → lung capillaries, where oxygen enters blood.
- Pulmonary veins → left atrium → left ventricle.
- Aorta → body arteries → capillaries.
How to make the reasoning visible: Name chambers and vessels in order; do not skip the lung circuit.
Circulation pathway
Complete direction and oxygen status.
| Structure | Direction | Typical oxygen status | Role |
|---|---|---|---|
| Vena cava | Body → right atrium | Lower | Returns systemic blood |
| Pulmonary artery | Right ventricle → lungs | Lower | Carries blood to gas exchange |
| Pulmonary veins | Lungs → left atrium | Higher | Returns oxygenated blood |
| Aorta | Left ventricle → body | Higher | Distributes systemic blood |
Why is the pulmonary artery still an artery?
Why is the left ventricular wall thicker?
Use the table. Trace the path of blood from the lungs to the body.
Check your understanding
Answer from memory, then check against the suggested answer.
Which chamber pumps to lungs?
Which vessel leaves the left ventricle?
What do valves prevent?
Which side of the heart pumps blood to the body?
What do veins do?
Predict how a leaky valve reduces effective output.
Why can a weakened left ventricle reduce oxygen delivery even if lungs exchange gases normally?
Why does the left ventricle have a thicker wall than the right ventricle?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Describe the route of blood from the body, through the lungs and back to the body.
(6)Total for this question: 6 marks
Command word: For a route question, use arrows or ordered sentences and check every vessel direction.