The advantages of SLP are that it does not require an electron-transport chain, or mitochondria, and that it is 'expedient', meaning that it is advantageous particularly in the short term (i.e., allows rapid organismal reproduction).
The disadvantage is that SLP can be wasteful (nonecono-mical) over longer time spans. In short, when energy resources are abundant (i.e., food is plentiful), when success comes from replicating fast, and if neither peak nor chronic energy needs are high (especially over long periods), then SLP, in the absence of the cellular respiration provided by an ETS, can be advantageous.
Alternatively, when food is not plentiful it pays to be economical, capturing the most energy from a given amount of food. This is also true for organisms with high maintenance costs, which require efficient conversion of food into energy just to maintain, for example, their complex bodies, or which must periodically expend large amounts of energy over relatively short periods (e.g., such as when an animal is running away from a predator). The evolution of the economy of cellular respiration, and associated ETSs, did not occur within sophisticated animals, but instead it occurred within bacteria. We can infer, therefore, that the advantages of cellular respiration were accrued especially given relatively low food densities, and particularly under crowded conditions such as those seen in bacteria adhering to surfaces within so-called biofilms. ETSs are also crucial when energy is being extracted from chemicals that do not lend themselves to SLP, including many inorganic but energy-rich minerals (see section titled 'Chemolithotrophy').
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