Explain structure of granum.

$\Rightarrow$ 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 $(70S)$ than the cytoplasmic ribosomes $(80S).$