Efficiency Of Cellular Respiration
One can easily determine the energy efficiency of cellular respiration by calculating the standard free energy change, a thermodynamic quantity, between the reactants and products. On this basis, biochemists often quote the overall efficiency of cellular respiration as about 40%, with the additional 60% of the energy given off as heat.
However, many cells regulate the different enzymes of respiration so that they are in nonequilibrium states, leading to a higher overall efficiency. Calculations of the free energy change, a different thermodynamic quantity, account for these regulatory effects and show that cellular respiration often has an efficiency of 60% or more.
Interestingly, some plants have two separate electron transfer chains in their mitochondria. The alternate electron transfer chain only operates occasionally, but when it does, it gives off most of its energy as heat, rather than ATP. This seemingly wasteful generation of heat is so great in some species that it volatilizes chemicals in their flowers which attract insect pollinators.
See also Respiratory system.
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Peter A. Ensminger