Describe structure and function of Chloroplasts with diagram.

$\Rightarrow$ Majority of the chloroplasts of the green plants are found in the mesophyll cells of the leaves.
$\Rightarrow$ These are lens-shaped, oval, spherical, discoid or even ribbon-like organelles.
$\Rightarrow$ They are having variable length $(5-10 \mu \mathrm{m})$ and width $(2-4 \mu \mathrm{m})$.
$\Rightarrow$ Their number varies from $ 1$ per cell of the Chlamydomonas, a green alga to $20-40$ per cell in the mesophyll.
$\Rightarrow$ The chloroplasts are also double membrane bound. Of the two, the inner chloroplast membrane is relatively less permeable.
$\Rightarrow$ 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.
 $\Rightarrow$ Thylakoids are arranged in stacks like the piles of coins called grana (singular: granum) or the intergranal thylakoids.
$\Rightarrow$ There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
$\Rightarrow$The membrane of the thylakoids enclose a space called a lumen.
$\Rightarrow$ The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
$\Rightarrow$ It also contains small, double-stranded circular $DNA$ molecules and ribosomes.
$\Rightarrow$ The ribosomes of the chloroplasts are smaller $(70 \mathrm{~S})$ than the cytoplasmic ribosomes $(80S)$.