Science — CBSE Class 10 board question

(a) The respiratory pigment in human beings is haemoglobin, found in red blood cells. Its function is to transport oxygen from the lungs to all body tissues.

(b) Lungs always retain a residual volume of air so that there is sufficient time for oxygen to be absorbed into the blood and carbon dioxide to be released, ensuring a continuous exchange of gases even between breaths.

(c) ATP (Adenosine Triphosphate) is called the energy currency of living beings because energy released during the breakdown of glucose is stored in ATP molecules. This stored energy is then used to power various cellular reactions whenever required — just like currency is used for different transactions.

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• For (a), name haemoglobin explicitly and state it carries O₂ — examiners expect both.
• For (b), the key idea is continuity of gas exchange; without residual air, the alveoli would collapse between breaths, stopping diffusion entirely.
• For (c), link ATP to both storage of energy (from respiration) and utilisation (for cellular reactions) — the "currency" analogy must be explained, not just stated.