(a)(i) The first step in the breakdown of glucose — in both aerobic and anaerobic respiration — is the splitting of glucose (a six-carbon molecule) into pyruvate (a three-carbon molecule). This process is called glycolysis and it takes place in the cytoplasm of the cell.
(a)(ii) ATP is called the energy currency of the cell because energy released during respiration is stored in ATP molecules. Whenever the cell needs energy for activities like muscle contraction, protein synthesis, or nerve impulse conduction, ATP is broken down to release a fixed, usable amount of energy (~30.5 kJ/mol).
(a)(iii) Residual volume is the volume of air that always remains in the lungs even after breathing out. It ensures sufficient time for oxygen to be absorbed into the blood and for carbon dioxide to be released from the blood into the alveoli.
Source: Chapter 5, Section 5.3 — Respiration
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