A chloroplast is of the type of plant organelle known as plastids. They contain the green pigment chlorophyll and sites for photosynthesis in plant cells only. The organelle has two membranes separated by a thin intermembrane space. Inside the chloroplast is a fluid called stroma (DNA, ribosomes, and enzymes are within it) which surrounds a membranous system of flattened sacs called thylakoids. Photosynthetic enzymes are embedded in these thylakoids and the stacks of thylakoids are named grana.