[sourcery]

The mitochondrion system is not the only energy pathway available to eucaryotes, let alone other micro-organisms.

[gore3000]

The mitochondrion system is not the only energy pathway available to eucaryotes,

Yup, and I said that, chloroplasts are another, as I already said. However, the system is quite involved, in fact it has slight differeneces in species with different lifestyles, but in all cases that very involved system had to be there from day one of that living thing because life cannot exist without energy.