The outer membrane is permeable to small organic molecules, whereas the inner membrane is less permeable and studded with transport proteins. The innermost matrix of chloroplasts, called the stroma, contains metabolic enzymes and multiple copies of the chloroplast genome. read more
The outer membrane is permeable to most ions and metabolites, but the inner membrane of the chloroplast is highly specialised with transport proteins. For example, carbohydrates are transported across the inner envelope membrane by a triose phosphate translocator. read more
the fluid filled space between the inner and outer mitochondrial membranes, the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. The main function of the intermembrane space is nucleotide phosphorylation. read more
The outer two membranes are similar in structure and orientation to the nuclear membranes: there is an outer membrane, an inner membrane, and a very small space between them called the—you guessed it!—intermembrane space. read more