Why is the biochemical production of energy more efficient than that of a man-made machine?

Answer 1

For one the life has had around 4 billion years to tinker with its machinery, find out what works best and what doesn't. This gives biological processes a hugs advantage over their man-made counterparts. Living creatures have developed a complex web of cellular "machinery" that has a huge number of control points and interactions with every other line of production and destruction (for lack of any better metaphors). This was only possible after billions of years of evolution.

Second, it has been a life or death struggle for organisms to develop strategies to obtain as much usable energy as possible from the nutrients it takes in. Many a species have gone extinct because they could not obtain the maximum amount of energy from its substrates. For man, the stakes are not quite as high. Or, as is the case of developing efficient alternative energy, man is either blind to what is at stake or refuses to accept it.