How does blood move around the body, and how is the heart and each blood vessel adapted?
The components of the blood and their functions, the structure of the heart with its chambers and valves, the double circulatory system, the structure and adaptations of arteries, veins and capillaries, and the effect of lifestyle on heart health.
A focused CCEA GCSE Double Award Science (Biology Unit B2) answer on the circulatory system, covering the components of blood, the structure of the heart and its valves, the double circulation, the adaptations of arteries, veins and capillaries, and lifestyle effects on heart health.
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What this dot point is asking
CCEA Double Award wants the components of blood and their jobs, the structure of the heart and how the double circulation works, the adaptations of the three blood vessels, and how lifestyle affects heart health. Tie every structure to the pressure or substance it deals with.
The blood
The heart and double circulation
The heart has four chambers: two thin-walled atria at the top that receive blood, and two thick-walled ventricles below that pump it out. Valves between the chambers and in the vessels stop blood flowing backwards.
The right ventricle pumps deoxygenated blood a short way to the lungs at lower pressure, so it has a thinner wall. The left ventricle pumps oxygenated blood all around the body at high pressure, so it has a much thicker, more muscular wall.
The blood vessels
The three vessels are adapted to the pressure and the job:
- Arteries carry blood away from the heart at high pressure. They have thick, muscular, elastic walls and a narrow lumen.
- Veins carry blood back to the heart at low pressure. They have thinner walls, a wide lumen, and valves to stop backflow.
- Capillaries are tiny vessels with walls one cell thick, allowing oxygen, glucose and waste to exchange with the cells by diffusion.
Lifestyle and heart health
Coronary heart disease happens when the coronary arteries (which supply the heart muscle) become narrowed by fatty deposits, reducing the blood and oxygen supply to the heart. Risk is raised by a diet high in saturated fat, smoking, lack of exercise and being overweight. A healthy lifestyle - balanced diet, regular exercise and not smoking - lowers the risk.
Examples in context
Example 1. Why a heart attack damages the heart. If a coronary artery is blocked, part of the heart muscle is starved of oxygen and dies, causing a heart attack. This shows why the coronary arteries are vital and why fatty deposits there are so dangerous.
Example 2. Why capillaries are so thin. A capillary wall is just one cell thick, so oxygen and glucose only have to diffuse a very short distance into the cells, and carbon dioxide diffuses out. The huge number of capillaries gives a large surface area for exchange.
Try this
Q1. Which blood component helps the blood to clot? [1 mark]
- Cue. Platelets.
Q2. Why do veins have valves? [1 mark]
- Cue. To stop the low-pressure blood flowing backwards.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA-style4 marksCompare the structure of an artery and a vein, and explain how each suits its function.Show worked answer →
Two structural differences linked to function for four marks.
An artery has thick, muscular, elastic walls to withstand and smooth out the high pressure of blood pumped from the heart.
A vein has thinner walls and a wider lumen because the blood is at lower pressure.
A vein has valves to stop the low-pressure blood flowing backwards; an artery does not need them.
Markers reward each structure tied clearly to the pressure of the blood it carries.
CCEA-style3 marksExplain why the left ventricle has a thicker muscular wall than the right ventricle.Show worked answer →
Link the wall to the job for three marks.
The left ventricle pumps blood all around the body (the systemic circulation).
This needs a high pressure to reach every organ, so the muscle wall is thick and powerful.
The right ventricle only pumps blood a short distance to the lungs at lower pressure, so its wall is thinner. Markers want the left side pumping further at higher pressure.
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Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)