IGCSE · Practice questions · Circulatory systems

Once round, or twice through.

Six original Cambridge-style questions on the parts of a circulatory system and on comparing the single circulation of a fish with the double circulation of a mammal.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Count the trips through the heart.

Circulatory system: blood vessels + a pump + valves for one-way flow.
Single (fish): heart → gills → body → heart; once through the heart.
Double (mammal): pulmonary circuit to the lungs, systemic circuit to the body; twice through the heart.
Advantage: say high pressure to the body, so faster delivery of oxygen and glucose.

Recall

[3 marks]

Describe what is meant by a circulatory system.

A system of blood vessels (arteries, capillaries and veins)... ✓
...with a pump, the heart, which pushes the blood round... ✓
...and valves, which ensure the blood flows in one direction only. ✓

Recall

[3 marks]

Extended. Describe the route taken by blood in the single circulation of a fish, starting at the heart.

The heart pumps deoxygenated blood to the gills. ✓
In the gills the blood takes up oxygen and becomes oxygenated. ✓
The blood flows from the gills to the body organs, then returns to the heart: it passes through the heart once per circuit. ✓

Recall

[4 marks]

Extended. Describe the double circulation of a mammal.

The right side of the heart pumps deoxygenated blood to the lungs (the pulmonary circulation). ✓
Oxygenated blood returns from the lungs to the left side of the heart. ✓
The left side pumps the oxygenated blood to the rest of the body (the systemic circulation), and deoxygenated blood returns to the right side. ✓
So the blood passes through the heart twice in each complete circuit. ✓

Explain

[3 marks]

Extended. Explain the advantages of a double circulation for an active mammal.

Blood returning from the lungs is pumped again, so it reaches the body at high pressure and flows quickly. ✓
Oxygen and glucose are delivered rapidly to respiring cells, supporting a high metabolic rate (activity and keeping warm). ✓
Blood goes to the lungs at lower pressure, so the delicate lung capillaries are not damaged; and oxygenated and deoxygenated blood are kept separate. ✓

Analysis

[3 marks]

Extended. The table shows the blood pressure in two vessels of a fish.

Vessel	Blood pressure / kPa
artery leaving the heart, before the gills	4.0
artery leaving the gills, going to the body	2.4

(a) Calculate the percentage fall in pressure across the gills. (b) Explain how a double circulation avoids this problem in a mammal.

(a) Fall = 4.0 − 2.4 = 1.6 kPa; (1.6 ÷ 4.0) × 100 = 40%. ✓
(b) In a mammal, blood from the lungs returns to the heart (left side) instead of going straight to the body. ✓
It is pumped a second time, so its pressure is raised again before it goes to the body organs. ✓

Explain

[2 marks]

Explain why valves are needed in a circulatory system.

Valves close when blood starts to flow backwards. ✓
This keeps the blood flowing in one direction, so it is pushed on round the circuit rather than back towards the heart or into the chamber it came from. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.