Describe structure and function of Chloroplasts.

Explanation

Majority of the chloroplasts of the green plants are found in the mesophyll cells of the leaves.
These are lens-shaped, oval, spherical, discoid or even ribbon-like organelles .
They are having variable length (5-10 urn) and width (2-4 `mu`m).
Their number varies from 1 per cell of the Chlamydomonas, a green alga to 20-40 per cell in the mesophyll.

The chloroplasts are also double membrane bound. Of the two, the inner chloroplast membrane is relatively less permeable.
The space limited by the inner membrane of the chloroplast is called the stroma.
A number of organised flattened membranous sacs are called the thylakoids, are present in the stroma.
Thylakoids are arranged in stacks like the piles of coins called grana (singular: granum) or the intergranal thylakoids.
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 of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
It also contains small, double-stranded circular DNA molecules and ribosomes.
The ribosomes of the chloroplasts are smaller (705) than the cytoplasmic ribosomes (80S).