What is the purpose of the outer mitochondrial membrane?
The purpose of mitochondria is to generate ATP, utilising a chemiosmotic gradient across the inner mitochondrial membrane. Protons are pumped out of the mitochondria into the intermembrane space, but because the outer mitochondrial membrane is highly permeable to ions, the pH of the intermembrane space quickly equilibrates with the rest of the cell. As the outer membrane apparently does not contribute to maintaining this chemiosmotic gradient, what is its purpose? It seems to be doubly redundant in chloroplasts as H+ transport doesn't even occur across the inner membrane.