The photosynthetic pigments in purple bacteria are located on extensive
infoldings of the outer membrane that sometimes look like little
hollow bags or vesicles, sometimes are interconnected in hollow
tubules, and more often appear as dense, stacked layers of unit
These photosynthetic membrane structures have their counterparts
in blue-green algae and in the chloroplasts of eucaryotes. Green
bacteria carry their photosynthetic pigments in quite different
cigarshaped vesicles, which are just under the outer membrane but
are not connected with it.
The light reactions of photosynthesis occur in these membrane folds
or vesicles, and the dark reactions take place in the cytoplasm.
The outer membrane frequently has larger infoldings called mesosomes,
which seem to be involved in cell division. These and the photosynthetic
apparatus are the nearest things that bacteria have to organs.