Metabolic energy consumption has long been thought to play a major role in the aging process ({it 1}). Across species, a gram of tissue on average expends about the same amount of energy during life-span ({it 2}). Energy restriction has also been shown that increases maximum life-span ({it 3}) and retards age-associated changes ({it 4}). However, there are significant exceptions to a universal energy consumption during life-span, mainly coming from the inter-class comparison ({it 5, 6}). Here we present a unique relation for life-span energy consumption, valid for $sim$300 species representing all classes of living organisms, from unicellular ones to the largest mammals. The relation has an average scatter of only 0.3 dex, with 95% ($rm 2-sigma$) of the organisms having departures less than a factor of $pi$ from the relation, despite the $sim$20 orders of magnitude difference in body mass, reducing any possible inter-class variation in the relation to only a geometrical factor. This result can be interpreted as supporting evidence for the existence of an approximately constant total number $rm N_r sim 10^8$ of respiration cycles per lifetime for all organisms, effectively predetermining the extension of life by the basic energetics of respiration, being an incentive for future studies that investigate the relation of such constant $rm N_r$ cycles per lifetime with the production rates of free radicals and oxidants, which may give definite constraints on the origin of ageing.
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