In chloroplast, where does the process take place



Like mitochondria, chloroplasts, which occur exclusively in plants, have a basic structure that consists of two biomembranes. The outer membrane is very permeable, the inner one is not.


The grana, which are already noticeable in the light microscope, are characteristic. Grana are dictyosome-like, interconnected stacks of cisterns made of so-called Thylakoids (gr. = baggy). If the grana are very long, one also speaks of Slats.

Cross section through a chloroplast

Thylokoid stacks in a chloroplast

One can distinguish three reaction spaces of the chloroplast (mitochondria only two!):

  1. the space between the two membranes (yellow)
  2. the stroma (gray)
  3. the thylakoids (green)

Spatial scheme of a chloroplast

This old drawing from my study days (1978) shows a spatial scheme of a chloroplast. The chloroplast DNA is shown in red.


Chloroplasts are derived from blue-green algae (endosymbiont theory) and can divide in a similar way to prokaryotes. In the English Wikipedia article there is a detailed section on the division of chloroplasts: "Chloroplast division".


The important process of photosynthesis takes place in the chloroplasts, both the light reaction and the dark reaction. The light reaction takes place in the thylakoids, the dark reaction in the stroma.