the chloroplast
The chloroplast is the site of photosynthesis. Part of the photosynthesis reactions occur in an internal membrane within the organelle. Many of the pigments and other molecules necessary for photosynthesis are embedded within these internal membranes, The chloroplast contains many of these internal membranes, allowing numerous photosynthetic reactions to occur simultaneously, and making photosynthesis very efficient. These internal membranes stack on top of each other, just like a stack of pancakes.