How does the circulatory system transport materials around the body?
The four-chambered heart and the pathway of blood, the structure and function of arteries, veins and capillaries, and the components of blood including red and white cells, platelets and plasma.
An SQA National 5 Biology answer on transport systems in animals, covering the four-chambered heart and the pathway of blood, the structure and function of arteries, veins and capillaries, and the components of blood including red and white cells, platelets and plasma.
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What this dot point is asking
The SQA wants you to describe the four-chambered heart and the pathway of blood, explain how arteries, veins and capillaries are each suited to their job, and describe the components of blood: red blood cells, white blood cells, platelets and plasma.
The heart
The pathway of blood links two circuits: blood is pumped from the heart to the lungs to be oxygenated, returns to the heart, and is then pumped out to the rest of the body, returning once more to the heart.
Blood vessels
The three types of vessel each have a structure that suits the job:
So the thick artery copes with the surge of high pressure from the heart, while the thin capillary is built for exchange.
The components of blood
The red blood cell is a good example of specialisation: its biconcave shape gives a large surface area, and losing its nucleus leaves more room for haemoglobin.
Examples in context
Example 1. A cut and clotting. When you cut yourself, platelets gather at the wound and trigger a clot that plugs the gap, stopping blood loss and keeping pathogens out. This shows the role of platelets in clotting, one of the blood's components.
Example 2. Exchange at a muscle. During exercise, blood flows through capillaries in a working muscle. The thin, one-cell-thick capillary wall lets oxygen and glucose diffuse out to the muscle cells and lets carbon dioxide diffuse in, exactly the exchange the capillary structure is built for.
Try this
Q1. Name the two lower chambers of the heart. [1 mark]
- Cue. The right and left ventricles.
Q2. State the function of platelets in the blood. [1 mark]
- Cue. Blood clotting.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style4 marksDescribe how the structure of an artery, a vein and a capillary each suits its function.Show worked answer →
A 4-mark answer should match structure to function for the three vessels.
An artery carries blood away from the heart at high pressure, so it has a thick, muscular wall and a narrow lumen to withstand the pressure.
A vein carries blood back to the heart at low pressure, so it has a thinner wall, a wider lumen, and valves to stop blood flowing backwards.
A capillary has a wall only one cell thick, which allows efficient exchange of oxygen, nutrients and waste between the blood and the body cells.
Markers reward (1) thick muscular artery for high pressure, (2) vein with valves for low-pressure return, and (3) thin-walled capillary for exchange, with a further mark for a clear function.
SQA N5 style3 marksDescribe the structure of a red blood cell and explain how it is adapted to carry oxygen.Show worked answer →
A 3-mark answer should link three structural features to oxygen transport.
A red blood cell is biconcave (a disc thinner in the middle), which gives a large surface area for absorbing oxygen.
It has no nucleus, leaving more room to be packed with the protein haemoglobin.
Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin, then releases it where oxygen is needed in the tissues.
Markers reward (1) the biconcave shape and large surface area, (2) no nucleus to hold more haemoglobin, and (3) haemoglobin carrying the oxygen.
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Sources & how we know this
- SQA National 5 Biology Course Specification — SQA (2019)