Science — CBSE Class 10 board question

Double circulation means blood passes through the heart twice in one complete cycle.

1. Pulmonary circulation: De-oxygenated blood from the body → right atrium → right ventricle → lungs (for oxygenation).
2. Systemic circulation: Oxygenated blood from lungs → left atrium → left ventricle → pumped to the rest of the body.

This separation prevents mixing of oxygenated and de-oxygenated blood, ensuring efficient oxygen supply.

Source: Chapter 5, Section 5.4.1

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• Examiners expect both circuits named (pulmonary + systemic) and the correct sequence of chambers involved in each.
• The key phrase "blood passes through the heart twice" defines double circulation and should appear.
• Mentioning that this prevents mixing of oxygenated/de-oxygenated blood shows conceptual understanding — worth the extra half-mark.
• Do not confuse left and right sides: oxygenated blood returns to the left side; de-oxygenated blood enters the right side.