Like mitochondria, the chloroplast is also bound by a double membrane. The outer membrane is smooth while the inner one gives rise to membranous sacs called thylakoids (the stack of thylakoids is known as a granum (plural = grana]) floating in a fluid termed the stroma.

The function of chloroplast:

Chloroplasts are the sites of photosynthesis in eukaryotes. They contain chlorophyll, the green pigment necessary for photosynthesis, and associated accessory pigments. These pigments are present in thylakoids of the grana of chloroplasts.