The mitochondrion, like the nucleus, has two or more membrane layers. How is the innermost of these layers different from that of the nucleus?

The double membrane of the mitochondria is highly folded,and therefore wider when unfolded than that of the nucleus.This is an adaptive feature  to increase the surface area for reactions (electrochemical  gradient) by accommodating protons pumped into it by the proton motive force(PMF)  from the matrix to set up the electrochemical gradients needed to generate the energy needed by ATPase synthase enzymes for ATPs synthesis.

Required number of protons needed to be accommodated by the double membrane to generate enough energy for ATPase synthesis,therefore larger surface area is needed.

Explanation:

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.