Biology A2 · Energy and respiration. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Every living cell needs a constant supply of energy for active transport, for movement and for anabolic reactions such as DNA replication and protein synthesis. This energy is supplied by ATP, the universal energy currency of all cells.
ATP is small and soluble, so it moves easily inside a cell. It is hydrolysed in one step to ADP and phosphate, releasing a small, useful amount of energy, and it is remade quickly.
Different respiratory substrates release different amounts of energy per gram. The respiratory quotient (RQ) compares the carbon dioxide given out with the oxygen taken in, and so shows which substrate is being respired.
Students often write RQ upside down. Carbon dioxide always goes on top and oxygen on the bottom, so a lipid gives a value below 1, not above it.
Answer: RQ = 0.69 (no unit)
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