IGCSE Biology | Practice Test — Answers | 25 Questions
Section A — Recall
Questions 1–10 | Definitions, facts, and naming
1.
Name the blood vessel that carries oxygenated blood from the left ventricle to the body.
Answer
Aorta
2.
Name the blood vessel that carries deoxygenated blood from the body back to the right atrium.
Answer
Vena cava
3.
Name the blood vessel that carries deoxygenated blood from the heart to the lungs.
Answer
Pulmonary artery
4.
Name the blood vessel that carries oxygenated blood from the lungs back to the heart.
Answer
Pulmonary vein
Exam tip: Remember — the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood. This is the opposite of what the names suggest, and it is a common exam trap.
5.
Name all three blood vessels connected to the liver.
Answer
Hepatic artery, hepatic vein, hepatic portal vein
6.
Name the two blood vessels connected to the kidneys.
Answer
Renal artery and renal vein
7.
State the two types of tissue found in the walls of arteries and veins (but not in capillaries).
Answer
Smooth muscle and elastic tissue
8.
Which type of blood vessel — artery, vein, or capillary — has valves along its length?
Answer
Vein
9.
State how thick the wall of a capillary is.
Answer
One cell thick
10.
State two structural differences between an artery and a vein.
Answer
Any two of the following:
- Arteries have thicker walls; veins have thinner walls
- Arteries have more muscle and elastic tissue in their walls; veins have less
- Arteries have a narrower lumen relative to their overall diameter; veins have a wider lumen
- Arteries have no valves; veins have valves along their length
Section B — Application
Questions 11–20 | Short explanations and scenarios
11.
Explain why the walls of arteries must be thick and contain large amounts of elastic tissue.
Answer
- Arteries carry blood at high pressure, pumped directly from the heart.
- The thick wall is needed to withstand this high pressure without bursting.
- The elastic tissue stretches when a surge of blood enters during a heartbeat, then recoils between beats — this maintains pressure and keeps blood moving smoothly.
12.
Explain why veins have a wider lumen than arteries.
Answer
- Blood in veins is at low pressure and is returning slowly to the heart.
- A wide lumen reduces resistance to blood flow, making it easier for low-pressure blood to move through the vessel.
- A narrow lumen would create too much resistance and could prevent the blood from reaching the heart.
13.
A student examines a cross-section of a blood vessel under a microscope. The wall is only one cell thick and the lumen is very narrow.
- (a) Identify the type of blood vessel.
- (b) Explain why this wall thickness is suitable for the blood pressure found in this vessel.
Answer
(a)
Capillary
(b)
- Blood pressure in capillaries is very low — the blood has lost most of its pressure by the time it reaches the capillary network.
- Because there is very little outward force from the blood, there is no risk of a thin wall bursting.
- Therefore a wall only one cell thick is sufficient to contain the blood.
14.
Explain why arteries do not need valves, but veins do.
Answer
- Arteries: carry blood at high pressure. This pressure is enough to keep blood moving forward in the correct direction on its own — valves are not needed.
- Veins: carry blood at very low pressure. There is not enough pressure to prevent blood from flowing backwards. Valves open when blood pushes forward and snap shut when blood tries to flow back, ensuring one-way flow.
Exam tip: If asked why valves are needed in veins, always link your answer to the low blood pressure in veins — not just “to prevent backflow” alone.
15.
Explain why the renal artery must have a thicker wall than the renal vein.
Answer
- Arteries carry blood at high pressure; veins carry blood at low pressure.
- The renal artery branches from the aorta and carries blood at high pressure to the kidneys — its thick wall is needed to withstand this pressure without bursting.
- The renal vein carries blood away from the kidneys at low pressure, after blood has passed through the capillary network. The pressure has dropped, so thinner walls are sufficient.
16.
Describe what would happen to blood flow in the legs if the valves in the veins stopped working. Explain your answer using your knowledge of blood pressure in veins.
Answer
- Blood would flow backwards (downward) in the leg veins instead of moving up toward the heart.
- This is because blood pressure in veins is very low — it is not strong enough on its own to prevent blood from falling back down under gravity.
- Without valves to stop backflow, blood would pool in the lower leg veins, causing swelling.
Note: This condition (where leg vein valves fail) causes varicose veins. You do not need to name this for the exam, but understanding why it happens is important.
17.
Name the blood vessel that:
- (a) carries oxygenated blood from the aorta to the liver
- (b) carries blood rich in digested nutrients from the small intestine to the liver
- (c) carries filtered blood from the kidneys back to the vena cava
Answer
(a)
Hepatic artery
(b)
Hepatic portal vein
(c)
Renal vein
18.
A blood vessel has the following features: very thick wall with large amounts of muscle and elastic tissue; narrow lumen; no valves. Identify the type of blood vessel and explain why each of these features is present.
Answer
This is an artery.
- Thick wall: arteries carry blood at high pressure; the thick wall withstands this pressure without bursting.
- Muscle and elastic tissue: the elastic tissue stretches to absorb the surge of blood from each heartbeat, then recoils to maintain pressure and smooth out blood flow. The muscle gives the wall the strength it needs.
- Narrow lumen: the large amount of wall tissue results in a relatively narrow central channel — this is a natural consequence of the thick walls.
- No valves: the high blood pressure keeps blood moving forward in the correct direction, so valves are not needed.
19.
Describe how blood pressure changes as blood travels from the aorta, through the capillaries, and into the veins. Explain why the pressure changes at each stage.
Answer
- Aorta → highest pressure. Blood has just been pumped out of the left ventricle at full force. Pressure is at its maximum here.
- Capillaries → lower pressure. As blood passes through the vast capillary network, it loses pressure. The blood has been pushed through many narrow vessels over a long distance, and much of the force has been used up.
- Veins → lowest pressure. By the time blood enters the veins, most of the pressure from the heartbeat has been lost. Blood flows slowly back to the heart at very low pressure.
20.
State two structural differences between a capillary and a vein.
Answer
Any two of the following:
- Capillaries have walls one cell thick; veins have thicker walls (with some muscle and elastic tissue)
- Capillaries have a very narrow lumen; veins have a wide lumen
- Capillaries have no valves; veins have valves along their length
- Capillaries have no muscle or elastic tissue in their walls; veins have some of both
Section C — Challenge
Questions 21–25 | Multi-part and extended answers
21.
Compare the structure of arteries, veins, and capillaries. In your answer, refer to each of the following:
- (a) the relative thickness of the wall
- (b) the composition of the wall (types of tissue present)
- (c) the diameter of the lumen
- (d) the presence or absence of valves
Answer
(a) Wall thickness
- Arteries: very thick wall
- Veins: thinner wall than arteries
- Capillaries: wall is only one cell thick (extremely thin)
(b) Wall composition
- Arteries: large amounts of smooth muscle and elastic tissue
- Veins: some smooth muscle and elastic tissue (less than arteries)
- Capillaries: no muscle or elastic tissue
(c) Lumen diameter
- Arteries: narrow lumen relative to wall thickness
- Veins: wide lumen relative to wall thickness
- Capillaries: extremely narrow — just wide enough for a single red blood cell to pass through
(d) Valves
- Arteries: no valves
- Veins: valves present at intervals along the length of the vessel
- Capillaries: no valves
22.
This question is about how the structure of blood vessels is related to blood pressure.
- (a) Explain how the elastic tissue in artery walls helps to maintain blood flow between heartbeats.
- (b) Explain why veins need valves but arteries do not. Refer to blood pressure in your answer.
- (c) Explain why capillary walls do not contain muscle or elastic tissue. Refer to blood pressure in your answer.
Answer
(a) Elastic tissue in arteries
- Each heartbeat forces a surge of high-pressure blood into the artery.
- The elastic tissue in the wall stretches to accommodate this surge.
- Between heartbeats, when no blood is being pumped, the elastic tissue recoils (springs back), pushing on the blood and maintaining pressure.
- This keeps blood moving smoothly and continuously, rather than in separate pulses.
(b) Valves in veins but not arteries
- Arteries carry blood at high pressure. This pressure is sufficient to keep blood moving forward — there is no tendency for blood to flow backwards, so valves are not needed.
- Veins carry blood at very low pressure. The pressure alone cannot prevent blood from flowing backwards (especially in vessels below the heart, where gravity acts against the flow). Valves open when blood pushes forward and close when blood tries to go back, ensuring one-way flow.
(c) No muscle or elastic tissue in capillaries
- By the time blood reaches the capillaries, it has lost most of its pressure — the pressure is very low.
- There is very little outward force pressing on the capillary walls, so there is no risk of the walls bursting.
- Muscle and elastic tissue are only needed to withstand high pressure. Since capillary pressure is very low, a wall of just one cell is sufficient — no muscle or elastic tissue is required.
23.
A student examines two blood vessel cross-sections under a microscope and records these observations:
- Vessel X: thick wall, narrow lumen, no valves visible
- Vessel Y: thin wall, wide lumen, valves present
- (a) Identify vessel X and vessel Y.
- (b) Explain the structural differences between X and Y in terms of the blood pressure each vessel carries.
- (c) Predict what would happen to blood flow if the valves in vessel Y stopped working. Use your knowledge of blood pressure to explain your answer.
Answer
(a) Identification
Vessel X = Artery | Vessel Y = Vein
(b) Structural differences linked to pressure
Vessel X (artery):
- Carries blood at high pressure from the heart.
- Thick wall: needed to withstand the high pressure without bursting.
- Narrow lumen: a consequence of the thick muscular walls surrounding the channel.
- No valves: high pressure keeps blood moving forward on its own.
Vessel Y (vein):
- Carries blood at low pressure back to the heart.
- Thin wall: sufficient because the low pressure poses no risk of bursting.
- Wide lumen: reduces resistance to flow, helping low-pressure blood move easily.
- Valves: prevent backflow because low pressure alone cannot keep blood moving in one direction.
(c) Valves fail in vessel Y
- Blood would flow backwards in vessel Y instead of moving toward the heart.
- This is because blood pressure in veins is very low — without valves, there is nothing to stop blood from flowing back the wrong way.
- Blood would pool in the vessel, causing swelling in the surrounding tissue.
24.
This question is about the named blood vessels in the human body.
- (a) Name the blood vessel that: (i) carries oxygenated blood from the aorta to the liver; (ii) carries blood away from the liver to the vena cava; (iii) carries blood from the small intestine to the liver.
- (b) The hepatic portal vein is described as unusual. Give two reasons why it is unusual compared to a typical vein.
- (c) Describe the complete route blood takes from the left ventricle to the kidneys and back to the right atrium. Name every blood vessel along the route.
Answer
(a) Named vessels
- (i) Hepatic artery
- (ii) Hepatic vein
- (iii) Hepatic portal vein
(b) What is unusual about the pulmonary vessels
- The pulmonary artery carries deoxygenated blood (from the heart to the lungs) — unusual because arteries normally carry oxygenated blood.
- The pulmonary vein carries oxygenated blood (from the lungs back to the heart) — unusual because veins normally carry deoxygenated blood.
(c) Route: left ventricle to kidneys and back
Left ventricle → aorta → renal artery → kidney (capillaries) → renal vein → vena cava → right atrium
Exam tip: When tracing a blood route, always start with the vessel leaving the heart (aorta from left ventricle) and end with the vessel returning to the heart (vena cava to right atrium). The organ’s capillaries go between the named artery and vein.
25.
This question asks you to apply your knowledge of blood vessel structure.
- (a) The aorta is the largest artery in the body. It receives blood directly from the left ventricle with each heartbeat. Explain why the aorta needs especially large amounts of elastic tissue in its wall.
- (b) Blood in the veins of the legs must travel upward, against gravity, back to the heart. Explain two structural features of leg veins that help make this possible.
- (c) Explain why capillary walls do not need to be as thick as artery walls. Refer to blood pressure in your answer.
Answer
(a) Elastic tissue in the aorta
- The aorta receives blood directly from the left ventricle at the highest pressure in the entire circulatory system.
- Each heartbeat sends a powerful surge of blood into the aorta, causing a large rise in pressure.
- The large amount of elastic tissue allows the aorta wall to stretch considerably to absorb this surge without damage.
- Between heartbeats, the elastic tissue recoils strongly, maintaining pressure and keeping blood moving smoothly through the rest of the arterial system.
- Because the aorta experiences the greatest pressure of any vessel, it needs more elastic tissue than smaller, downstream arteries where pressure has already dropped slightly.
(b) Two features that help blood travel upward in leg veins
- Valves: valves in the leg veins prevent blood from flowing back down under gravity. Each time blood is pushed upward, the valve opens; when blood tries to fall back, the valve snaps shut, holding the blood in place.
- Wide lumen: the wide lumen reduces resistance to flow, making it easier for low-pressure blood to move upward through the vessel toward the heart.
(c) Why capillary walls can be thin
- Blood pressure in capillaries is very low — the blood has passed through arteries and spread across a vast capillary network, losing most of its pressure along the way.
- Because the outward force pressing on the capillary wall is minimal, there is no risk of a thin wall bursting.
- Artery walls must be thick because they face high pressure. Capillary walls face very low pressure, so a wall of just one cell thickness is entirely sufficient — no additional layers of muscle or elastic tissue are needed.
Exam tip: For any question asking why a blood vessel has a particular structure, always link the structure to the blood pressure. Thick wall = high pressure. Thin wall = low pressure. This is the core principle of the whole topic.
