Living organisms increase the entropy of their surroundings over the course of their lives by generating heat (largely through the controlled burning - or oxidation - of glucose, which produces carbon dioxide and heat). The localized decrease in entropy that occurs during biosynthesis is compensated for by the greater increase in entropy of the universe that results from the production of heat through catabolic metabolism. This raises the following question. How much heat must an organism produce in order to live and grow and how does this compare to the minimum that would be required to obey the Second Law of Thermodynamics?
Jeremy L. England addresses this question in a paper in the Journal of Chemical Physics. It turns out that bacterium Escherichia coli produces only about six times the amount of heat than the minimum required to live and divide in accordance with with the Second Law of Thermodynamics. This implies a high though not maximal degree of efficiency, since the experimental value (previously determined by others and not the author of this particular article) is within an order of magnitude of the minimum value calculated by the author of this paper. So E. coli are substantially but not perfectly optimized for efficient growth.
It is possible that, even though E. coli evolved to grow rapidly when the conditions were good, all life requires at least some amount of "waste" for the sake of robustness. Having some excess energetic capacity allows for mobilization of resources needed for appropriate responses when environmental conditions change, even if that capacity is not needed under ideal conditions.
J. Chem. Phys. 139, 121923 (2013); http://dx.doi.org/10.1063/1.4818538 (8 pages)
(Received 28 April 2013; accepted 1 August 2013; published online 21 August 2013)