Plastids are the organelle present in the plant cells which bear some specific pigments, thus imparting specific colours to the plants.
Based on the type of pigments plastids can be classified into chloroplasts, chromoplasts and leucoplasts.
The chloroplasts contain chlorophyll and carotenoid pigments which are responsible for trapping light energy essential for photosynthesis.
In the chromoplasts, fat soluble carotenoid pigments like carotene, xanthophylls and others are present.
The leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients like amyloplasts which store carbohydrates, elaioplasts store oils and fats, whereas the aleuroplasts store proteins.
Chloroplasts of the green plants are found in the mesophyll cells of the leaves.
The chloroplasts are double membrane bound.
The space limited by the inner membrane of the chloroplast is called the stroma.
A number of organised flattened membranous sacs called the thylakoids.
Thylakoids are arranged in stacks like the piles of coins called grana.
There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
The membrane of the thylakoids enclose a space called a lumen.
The stroma contains enzymes, double stranded DNA molecules, ribosomes.