Page 57 - Medicinal Plants_PharmD general

Chloroplasts

These auto-reproductive green plastids (Figure 9) are restricted to
the green plant cell. The plastids are the complete photosynthetic unit and
utilized the light energy of the sun to reduce carbon dioxide to carbohydrate
in the presence of water.

The complex process of photosynthesis implies the necessity for a
high degree of organization within the chloroplast. This is demonstrated
by electron micrograph sections.

Like mitochondria, chloroplasts (Figure 9) have a double-
membrane envelope, called the chloroplast envelope, but unlike
mitochondria, chloroplasts also have internal membrane structures called
thylakoids.

A series of membrane called lamella are extending throughout the length
of the chloroplast. At intervals, the lamella are densely packed forming
granules known as grana which are composed of stack of thylakoids. The
grana are distributed in a matrix called stroma. Each chloroplast, has
several grana where between the protein layers of the granum, the
chlorophylls are present. The chlorophyll molecules are localized in bodies
known as quantasomes. During photosynthesiss, the grana & thylakoids
deal with the electron-transfer in light reaction and the stroma with CO2
fixation in dark reaction.

Other coloured plastids (chromoplasts) which are found in ripening fruits
are often derived from chloroplasts.

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