Pound for Pound, All Life Uses Same Amount of Energy

If energy is the currency of life, biologists are closing in on the cost of living.
No matter whether you're talking elephants or bacteria, a new study proposes that, pound for pound, all living things' at-rest metabolisms use similar amounts of energy. Though living things vary greatly in complexity and size, their energy usage falls between 3 and 90 watts per kilogram of biomass. For comparison, a MacBook Pro is supposed to draw about 12 watts when operating from its battery.
"Our interpretation is that there aren't very many accidents in nature, so it's not just a coincidence that all these different organisms fall within this narrow window," said Peter Reich, an ecologist at the University of Minnesota, and a co-author of the work. "That suggests that natural selection selects for this range."
Using energy to stave off entropy is one of the basic functions of life. Different forms of life use different energy sources. Plants use photosynthesis to turn sunlight into chemical energy. Other organisms feed on plants or other organisms to obtain the energy needed to sustain themselves. The new paper suggests that no matter how an organism gets its energy, the basic biochemistry of life requires that all organisms' cells use energy at fairly similar rates.
The new work means that if you had an elephant-sized mound of bacteria, it would use, within about an order of magnitude of variation, the same amount of energy as an actual elephant. This information from here