Describe the structure of chloroplast.

Explanation

Chloroplasts are the main site of photosynthesis and both energy yielding process (Light reaction ) and fixation of carbon dioxide (Dark reaction ) that takes place in chloroplast . It is a double wall membrance bounded organelle, discoid or lens shaped, 4 -10 `mu m` is diamter and ` 1 -33 mu m` is thickness . The membrance is a unit membrance and space beween them is 100 to `200 Å` A colloidal and proteinaceous matrix called stroma is present inside.
A sac liked membranous system called thylakoid or lamellase is present in stroma and they are arranged one above the other forming a stack of coin like structure called grnum ( plural grana). Each chloroplast contans 40 t0 80 grana and each graana consists of 5 to 30 thyaliods .
Thylakoids found in granum are called grana lamellae and in stroma are called stroma lamellae. Thylakoid disc size is 0.25 to 0.8 micro in diameter. A thinnre lamella called Fret membrance connects grana. Pigment system I is located on outer thykoid membrance facing stroma and Pigment system I is located on inner membrance facing lumen of thylakoid . Grana lamellae have both PS I and PS II whereas stroma lamellae have only PS I . Chloroplast contains 30-35 % Proteins , 20-30% phospholipids , 5 - 10% chlorophyll , 4 - 5 % , Carotenoids , 70 S ribosomes , circular DNA and strach grains. Inner surface of lamellar membracne consists of small spherical structure called as Quantasomes . Presence of 70 S rbosome and DNA gives them status of semi-autonomy and proves endosymbiotic hypothesis which says chloroplast evolved from bacteria . Thylakoid contains pigment systems which produces ATP and NADPH ` + H^(+)` using solar energy . Stroma contains enzymes which reduces carbondioxide into carbohydrates .