How does the heart pump blood around the body, and how are the blood vessels adapted to their jobs?
The structure of the heart and the double circulatory system, the roles of the arteries, veins and capillaries, how the heart rate is controlled, and the structure and function of the lungs in gas exchange.
A focused answer to AQA GCSE Biology 4.2.2, covering the structure of the heart, the double circulatory system, the three types of blood vessel, control of heart rate, and the structure of the lungs for gas exchange.
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What this dot point is asking
AQA wants you to describe the structure of the heart and the double circulatory system, explain how arteries, veins and capillaries are adapted to their roles, describe how natural and artificial pacemakers control heart rate, and explain how the lungs are adapted for gas exchange.
The heart and double circulation
The heart has four chambers. The right atrium receives deoxygenated blood from the body and passes it to the right ventricle, which pumps it to the lungs through the pulmonary artery. Oxygenated blood returns from the lungs via the pulmonary vein to the left atrium, then the left ventricle, which pumps it around the body through the aorta. The left ventricle has a thicker muscular wall because it pumps blood much further (around the whole body) and so at higher pressure than the right ventricle, which only pumps to the nearby lungs.
The three blood vessels
- Arteries: carry blood away from the heart at high pressure. They have thick, muscular and elastic walls to withstand the pressure, and a relatively small lumen.
- Veins: carry blood back to the heart at low pressure. They have thinner walls, a large lumen, and valves to stop the blood flowing backwards.
- Capillaries: tiny vessels with walls only one cell thick. This short diffusion distance lets substances such as oxygen, glucose and carbon dioxide be exchanged between the blood and the surrounding cells.
The lungs and gas exchange
Air passes down the trachea, then the bronchi, then the bronchioles, to tiny air sacs called alveoli. Here oxygen diffuses from the air in the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli to be breathed out.
Try this
Q1. Explain why the wall of the left ventricle is thicker than the right ventricle. [2 marks]
- Cue. The left ventricle pumps blood around the whole body at higher pressure, so it needs more muscle.
Q2. Give two ways alveoli are adapted for gas exchange. [2 marks]
- Cue. Large surface area and thin walls (also moist lining and good blood supply).
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksCompare the structure of an artery, a vein and a capillary, and explain how each is adapted to its function.Show worked answer →
A 4-mark question rewards each vessel's structure linked to its job.
An artery carries blood away from the heart at high pressure, so it has a thick, muscular, elastic wall to withstand and maintain the pressure, and a relatively small lumen. A vein carries blood back to the heart at low pressure, so it has a thinner wall, a larger lumen, and valves to prevent the blood flowing backwards. A capillary is where exchange happens, so it has a wall only one cell thick, giving a short diffusion distance for substances such as oxygen, glucose and carbon dioxide to pass between the blood and the cells.
Markers reward the structure of each vessel linked correctly to high pressure (artery), low pressure with valves (vein), and exchange (capillary).
AQA 20214 marksExplain how the structure of the heart and the double circulatory system allow oxygen to be delivered efficiently to the body's cells.Show worked answer →
A 4-mark explain question rewards the double circulation linked to efficient delivery.
In a double circulatory system the blood passes through the heart twice per circuit: the right side pumps deoxygenated blood to the lungs to pick up oxygen, and the left side pumps the now oxygenated blood around the body. After passing through the lungs the blood pressure has dropped, so returning it to the heart and pumping it again restores a high pressure, which delivers oxygen to the body cells quickly. The left ventricle has a thicker muscular wall because it must pump blood at high pressure all the way around the body.
Markers reward blood passing through the heart twice, the two pumps (lungs and body), the higher pressure giving faster delivery, and the thicker left ventricle wall.
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Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)