What are the parts of blood, and how does coronary heart disease affect the heart?
The components of blood and their functions, and the cause and treatment of coronary heart disease.
A focused answer to the WJEC GCSE Science Double Award Unit 1 topic on blood, covering the four components of blood and their functions, and the cause, effects and treatment of coronary heart disease.
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What this dot point is asking
WJEC Double Award Unit 1 wants you to name the components of blood and their functions, and describe the cause, effects and treatment of coronary heart disease.
The components of blood
- Red blood cells: carry oxygen. They are packed with haemoglobin, which joins to oxygen in the lungs and releases it in the tissues. They have no nucleus and a biconcave shape to carry the most oxygen.
- White blood cells: part of the immune system; they engulf pathogens and make antibodies.
- Platelets: small cell fragments that help the blood clot at a wound, forming a scab to stop bleeding and keep out microbes.
- Plasma: the straw-coloured liquid that carries the blood cells, dissolved glucose and amino acids, carbon dioxide, urea and hormones.
How red blood cells are adapted
Red blood cells are a good example of a specialised cell. They have no nucleus, leaving more room for haemoglobin; they are biconcave discs, giving a large surface area for oxygen to diffuse across; and they are small and flexible so they can squeeze through narrow capillaries. All these features help them carry as much oxygen as possible.
How haemoglobin carries oxygen
In the lungs, where the oxygen concentration is high, haemoglobin joins with oxygen to form oxyhaemoglobin. As the blood reaches the body's tissues, where the oxygen concentration is low because cells are respiring, the oxyhaemoglobin releases its oxygen, which diffuses into the cells. The red blood cells then return to the lungs to collect more. This reversible loading and unloading is why a steep oxygen gradient at both the lungs and the tissues keeps oxygen moving in the right direction.
What the plasma transports
The plasma is more than just liquid: it transports many dissolved substances at once. It carries the soluble products of digestion (glucose and amino acids) from the gut to the cells, carbon dioxide from the cells to the lungs, urea (a waste from the liver) to the kidneys, hormones from glands to their target organs, and heat around the body. Exam questions often ask what the plasma carries, so learn this list rather than just saying it carries the blood cells.
Coronary heart disease
Risk is increased by a diet high in saturated fat, smoking, lack of exercise and high blood pressure.
Treating coronary heart disease
- Stents: a small mesh tube is inserted to hold a narrowed artery open, restoring blood flow. The benefit is quick, but there are surgical risks.
- Statins: drugs taken regularly to lower blood cholesterol, slowing the build-up of fatty deposits. They work over the long term but can have side effects.
- Lifestyle: a healthy diet, regular exercise and not smoking reduce the risk in the first place.
Try this
Q1. Name the protein in red blood cells that carries oxygen. [1 mark]
- Cue. Haemoglobin.
Q2. State one lifestyle change that reduces the risk of coronary heart disease. [1 mark]
- Cue. Any one of: eat less saturated fat, exercise regularly, do not smoke.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksName the four components of blood and give the function of each.Show worked answer →
A Unit 1 recall question worth 4 marks (1 each). Reward: red blood cells carry oxygen (using haemoglobin); white blood cells defend the body against pathogens; platelets help the blood to clot at wounds; and plasma is the liquid that carries blood cells, dissolved food, carbon dioxide, urea and hormones. Markers credit each component with a correct function. A common error is to give a structure but no function, or to confuse platelets with white blood cells.
WJEC style4 marksExplain how a build-up of fatty material in the coronary arteries can lead to a heart attack.Show worked answer →
A Unit 1 explain question. Reward: fatty material builds up inside the coronary arteries, which supply the heart muscle with blood (1); this narrows the arteries, reducing blood flow and so the oxygen reaching the heart muscle (1); the heart muscle cannot respire enough, so it is starved of oxygen (1); if the artery becomes blocked the muscle cells die, causing a heart attack (1). Markers credit narrowing, reduced oxygen supply and the effect on the heart muscle. A common error is not mentioning that the coronary arteries supply the heart itself.
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