Describe the Structure of Chloroplast - QS Study
QS Study

Position:

The chloroplast is present in the green pans of the plant, especially in leaves.

Number:

One too many per cell. Each higher plant cell: 20 to 40. Example- Spirogyra. Each lower plant cell: Less than that of a higher plant chloroplast. Chlamydomonas contains only a single chloroplast.

Structure:

It may be of the following structures:

(a) Spiral chloroplast. Example- Spirogyra.

(b) Belt-shaped chloroplast. Example- Ulothrix.

(c) Cup-shaped chloroplast. Example- Chlamydomonas.

(d) Star-shaped chloroplast. Example- Zygnema.

a1

Fig: Different parts of chloroplast (a simplified figure seen through the electron microscope)

 Structure of chloroplast:

The structure of chloroplast is very complicated. In a chloroplast, three parts are seen clearly when it is observed through the electron microscope

  • Membrane
  • Stroma
  • Grana

Membrane: A chloroplast is covered with a two-layered membrane. It is composed of lipid and protein. Structurally it is similar to the plasma membrane.

Stroma: the hydrophilic matrix is covered with the membrane. This matrix is called Stroma Ribosome, osmophilic granules etc. are present in the stroma.

Grans: Grana, which are sacs of coin-shaped double membranes called thylakoids are suspended in the stroma. The thylakoids contain chlorophyll and other pigments In each chloroplast there are usually about 40 to 60 grand and each granum may contain from 2 or 3 to more than 100 stacked thylakoids.

Two grans remaining side by side are linked together by some minute tubules, called stroma lamellae (sing lamella).

In the inner wall of each granum coin, there are some crystalline substances, called choantosome. Each choantosome contains chlorophyll-a, chlorophyll-b, carotin, zanthophyll, phospholipids, quinon, sulpholipid and different enzymes.