Question

Give the detailed structure of chloroplast.

Accepted Answer

Chloroplasts are chlorophyll-containing, disc-shaped, cytoplasmic organelles that are present only in plant cells. Chloroplast is meant for photosynthesis in the plant cell. They also help in the storage of starch, pigments etc. A chloroplast is a double-membrane structure and the inner membrane forms flattened disc-like sacs called thylakoids. Thylakoid is found in the aqueous matrix of a chloroplast. Stacks of thylakoids form the grana, which act as the functional units of chloroplasts. Chloroplast is meant for photosynthesis in the plant cell. The detailed structure of a chloroplast is as follows:

Unit membrane- Each chloroplast is enclosed by two unit membranes, an outer membrane and an inner membrane. Each membrane is trilaminar and made up of lipoprotein and 50A thick. The space between the two membranes is known as periplastidial space.
Stroma or Matrix—It is a transparent, clear and homogeneous colloidal gel-fluid present within the inner membrane. The matrix contains about 50 per cent of the chloroplast proteins, ribosomes, DNA, RNA, vitamins E and K, and different types of ions, etc.

Thylakoids—The inner membranous structure is organised into flattened sacs called thylakoids (thylakoids). These are embedded in the aqueous matrix. In higher plants, the thylakoids are arranged in stacks, like a pile of coins. These stacked thylakoids constitute the grana. The number of thylakoids in a granum may vary from a few to more than 50. The grana are Interconnected by a network of anastomosing tubules called frets or straw lamellae. The size of the grana may range from 0.3 µm to 2-7 µm. The chloroplasts may contain 40 to 60 grana in their matrix. Granum is the functional unit of a chloroplast.

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