Double circulation
- CBSE · NCERT Class 10, Ch 5 Life Processes
- ICSE Class 10, Unit 3 Human Anatomy and Physiology
Double circulation means blood passes through the heart twice in one trip round the body: once going to the lungs, once going to the body.
The heart's right side and left side do not mix. The upper chambers are the atria, which ICSE books call auricles. Each side pumps blood round its own loop:
- Lung loop: right ventricle, pulmonary artery, lungs, pulmonary veins, left atrium. The blood picks up oxygen in the lungs.
- Body loop: left ventricle, aorta, body, vena cava, right atrium. The blood gives oxygen to the body.
Keeping the loops apart means oxygen-rich blood never mixes with used blood. Birds and mammals need this steady supply, because they use energy all the time to keep warm.
A small example
Count the passes through the heart. A fish heart has 2 chambers, and blood goes through it once per round. In humans, a drop of blood from your toe passes through the right side on its way to the lungs. It passes through the left side on its way back out. That is 2 passes.
Where marks go
In CBSE, Question 16 of the 2026-27 Science sample paper, option A, shows three hearts. The board's Science marking scheme for 2026-27 gives 1 mark for picking the four-chambered heart. The reason carries 2 marks: separate sides, no mixing, and enough oxygen for a high need for energy. Naming the heart is only part of the marks.
In ICSE, the 2024 Biology paper asked for the odd one out among four arteries. The answer was the pulmonary artery, which carries blood low in oxygen. CISCE's 2024 Biology report says marks were lost for choosing the coronary or renal artery. The 2027 specimen paper asks for the path of the lung loop in order.
Sources
Facts last checked against these sources on 30 September 2026.
- Science, Class X (2026-27), Chapter 5: Life Processes · NCERT
- Science (086) Marking Scheme, Class X 2026-27 - Question 16 · CBSE Academic Unit
- Science (086) Sample Question Paper, Class X 2026-27 - Question 16 · CBSE Academic Unit
- ICSE Biology syllabus, Examination Year 2028 (January 2026) - Class X, Unit 3 · CISCE
- ICSE 2024 Analysis of Pupil Performance: Biology - Question 2(iv)(e) · CISCE
- ICSE 2027 Specimen Question Paper: Biology - Question 1(x) · CISCE
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