Respiration

The term 'respiration' was coined by Pepys (1966, as recorded in the textbook) to describe the biological oxidation of food substances -- carbohydrates, proteins and fats -- inside living cells, a process in which oxygen is consumed, carbon dioxide is released, and chemical energy is set free. The organic molecules that get oxidised to yield this energy are called respiratory substrates, and glucose is by far the most commonly used one, though any organic compound with oxidisable carbon-carbon bonds can serve the role. Respiration proceeds by systematically breaking the C-C bonds of these complex organic molecules through oxidation, and the liberated energy is captured partly as ATP and partly lost as heat. Because respiration is essentially the biochemical reverse of photosynthesis, its net equation is written as glucose plus oxygen yielding carbon dioxide, water and roughly 686 kilocalories (2868 kJ) of energy per mole of glucose oxidised: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}$. The plant physiologist Blackman further classified respiration by the nature of the substrate used: 'floating respiration' uses carbohydrates, fats or organic acids and is the common, non-toxic mode seen in most cells, whereas 'protopl …