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O-Level Transport in Humans
What the O-Level syllabus expects for Transport in Humans, and how to practise it.
What the syllabus expects
- Recognise the principal blood vessels leading to and away from the heart, lungs, liver and kidney.
- Connect how arteries, veins and capillaries are each built to the roles they carry out.
Scope: Naming the specific muscle layers within arteries and veins is not required. - Set out how materials pass between capillaries and tissue fluid.
- Name the components of blood and their transport and defence roles: red blood cells carrying oxygen via haemoglobin; plasma carrying blood cells, ions, dissolved food, hormones, carbon dioxide, urea, vitamins and plasma proteins; white blood cells performing phagocytosis, antibody formation and tissue rejection; and platelets converting fibrinogen to fibrin to bring about clotting.
- Name the different ABO blood groups and set out every possible donor-recipient pairing for blood transfusions.
- Set out how the heart is built and how it works, in terms of muscular contraction and the action of the valves.
- Outline the cardiac cycle by describing what occurs during systole and diastole.
Scope: Candidates need not cover heart-muscle histology, nor name any nerves or their transmitter chemicals. - Set out coronary heart disease as the blocking of the coronary arteries, name likely causes such as poor diet, a sedentary lifestyle and smoking, and give measures that can help prevent it.
How it's examined
Questions on this topic most often ask you to explain, describe. About 9% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (5 marks)
Describe how a diet high in fat, together with smoking, can lead to coronary heart disease.
Show the worked answer
A diet high in fat/cholesterol leads to fatty deposits (atheroma/plaques) building up in the walls of the coronary arteries. This narrows the lumen and makes the arteries less elastic, reducing the flow of blood and therefore oxygen to the heart muscle. Smoking makes this worse: carbon monoxide binds to haemoglobin so the blood carries less oxygen, while nicotine raises heart rate and blood pressure and makes the blood clot more easily. A blood clot (thrombosis) can then block a narrowed coronary artery, cutting off oxygen to part of the heart muscle so those cells die, causing coronary heart disease / a heart attack.
Example 2 (3 marks)
People with aplastic anaemia often feel light-headed, especially when they are active or when standing up. Explain why this happens.
Show the worked answer
In aplastic anaemia the bone marrow makes too few red blood cells, so there is less haemoglobin and the blood carries less oxygen to the body. When Daniel is active, or when he stands up, the brain's oxygen demand increases (and gravity makes it harder for blood to reach the brain). The reduced oxygen supply cannot meet this demand, so brain cells respire less and receive too little oxygen, which makes the person feel light-headed/dizzy.
Example 3 (2 marks)
Propose one way in which aplastic anaemia could affect the heart, and explain your reasoning.
Show the worked answer
In aplastic anaemia the bone marrow fails to make enough red blood cells, so the blood carries less haemoglobin and therefore less oxygen. To compensate and still deliver enough oxygen to the body's tissues, the heart has to beat faster and harder (increased heart rate), which over time can strain/enlarge the heart.
More worked questions on this topic
- A patient can undergo an operation known as a coronary bypass, in which a blood vessel is remov (2 marks)
More O-Level Pure Biology topics
Cell Structure and Organisation · Movement of Substances · Biological Molecules · Nutrition in Humans · Respiration in Humans · Excretion in Humans · all of O-Level Pure Biology