Chloroplast

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Chloroplasts are only present in plant cells because they process photosnythesis. They are specialized member of the family that is closely related to the plastid (an organelle). Chloroplast contain pigment chlorophyll, enzymes, and molecules that function during photosynthesis. Contents of chloroplast are partitioned from the cytosol by an envelope consisting of at least two membranes separated by a very narrow intermembrnae space. Inside the chloroplast is another membranous system in  the form of flattened ,interconnected sac called thylakoids.
When they are stacked together they are called ganum. The fluid outside of the thylakoid are called stroma that contain the chloroplast DNA and ribosomes.