What is blood made of, and how does the heart pump it around the body?
The components of the blood and their functions, the structure of the heart with its chambers and valves, the path of blood through the heart, and how the heartbeat pumps blood around the double circulation.
A focused CCEA GCSE Biology answer on blood and the heart, covering the components of blood and their functions, the chambers and valves of the heart, the path of blood through it, and how the heart pumps blood around the double circulation.
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What this dot point is asking
CCEA wants you to name the four components of the blood and their functions, label the chambers and valves of the heart, describe the path of blood through the heart, and explain how the heartbeat pumps blood around the double circulation.
The components of blood
The structure of the heart
The path of blood through the heart
Deoxygenated blood from the body enters the right atrium, passes to the right ventricle, and is pumped through the pulmonary artery to the lungs. Oxygenated blood returns through the pulmonary vein to the left atrium, passes to the left ventricle, and is pumped through the aorta to the body.
Examples in context
- Example 1. Why red blood cells are perfectly suited to their job
- Red blood cells have no nucleus, leaving more room for haemoglobin, and a biconcave disc shape giving a large surface area for oxygen to diffuse in and out. In the lungs, where oxygen is high, haemoglobin binds oxygen to form oxyhaemoglobin; in the tissues, where oxygen is low, it releases the oxygen. This neat match of structure to function makes the red blood cell a classic CCEA example of a specialised cell.
- Example 2. How a clot seals a wound
- When a blood vessel is cut, platelets gather at the wound and trigger a series of reactions that turn the soluble protein fibrinogen into insoluble fibrin. The fibrin forms a mesh that traps red blood cells and forms a clot, which seals the wound, stops blood loss and prevents pathogens entering. This shows the protective role of platelets and why people who cannot clot properly (as in haemophilia) are at serious risk from small cuts.
- Example 3. Why the heart is described as a double pump
- The two sides of the heart work at the same time but do different jobs. The right side receives deoxygenated blood from the body and pumps it the short distance to the lungs at lower pressure. The left side receives oxygenated blood from the lungs and pumps it the long distance around the whole body at high pressure. Because the two sides are separated by a wall of muscle (the septum), oxygenated and deoxygenated blood never mix. Thinking of the heart as two pumps side by side explains why it fits a double circulatory system and why the left ventricle is the most muscular chamber. CCEA often asks you to relate the structure of each side to the pressure it must produce.
Try this
Q1. Name the part of blood that carries oxygen. [1 mark]
- Cue. Red blood cells (using haemoglobin).
Q2. Which chamber of the heart pumps blood to the lungs? [1 mark]
- Cue. The right ventricle.
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 20204 marksName the four components of blood and state the function of each.Show worked answer →
Four marks for four components, each with its job.
Red blood cells carry oxygen, using the pigment haemoglobin which combines with oxygen to form oxyhaemoglobin.
White blood cells defend the body against disease by engulfing pathogens (phagocytes) and producing antibodies (lymphocytes).
Platelets are cell fragments that help the blood to clot at a wound, sealing it and stopping blood loss and entry of pathogens.
Plasma is the liquid part that carries the cells, dissolved food, carbon dioxide, urea, hormones and heat around the body.
Markers reward each component named with a correct function. A common slip is forgetting plasma carries dissolved substances, not just water.
CCEA 20195 marksDescribe the path taken by blood as it flows through the heart from the body and out to the lungs.Show worked answer →
Five marks for the ordered path through the right side of the heart.
Deoxygenated blood from the body enters the right atrium through the vena cava.
The right atrium contracts and pushes blood through a valve into the right ventricle.
The right ventricle contracts and pumps the blood through another valve into the pulmonary artery.
The pulmonary artery carries the deoxygenated blood to the lungs.
In the lungs the blood picks up oxygen and returns to the left side of the heart through the pulmonary vein.
Markers reward vena cava, right atrium, right ventricle, pulmonary artery, lungs, in the correct order, with valves preventing backflow.
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Sources & how we know this
- CCEA GCSE Biology specification — CCEA (2017)