Page 73 - Medicinal Plants_PharmD general

Calvin cycle) use ATP & NADPH produced by Light reactions to fix
carbon dioxide and produce sugars.

Chlorophyll Pigments

The chlorophyll are the most important photosynthetic plant
pigments. They are responsible for conversion of light energy to chemical
one. Today, at least seven types can be distinguished; chlorophyll (a) and
(b) are the most common and most active. The green pigment chlorophyll
is located within the thylakoid membrane.

The chlorophyll molecule possesses four pyrrole rings arranged
round a central magnesium atom and are linked to each other by the way
of -CH =CH- groups (forming the porphyrin ring). The double bonds of
which are responsible for absorption spectrum of chlorophyll (Figure 19).
Over 99% of the chlorophyll (a) molecules, all chlorophyll (b) and
carotenoids act as light harvesting pigments. Chlorophyll (a) maximally
absorbs light with wavelengths of 430 nm (blue) and 662 nm (red).
Chlorophyll (b) maximally absorbs light of 453 nm (blue) and 642 nm
(red). It is not as abundant as chlorophyll a. Plants are green because
chlorophyll reflects green light (not absorb it).

Pigments absorb light energy and the energy is passed inward from
pigment to pigment until it reaches the reaction center (a special form of
chlorophyll a). Then the energy is transferred to an electron boosting it to
a higher energy level (Figure 20).

The electromagnetic spectrum is the entire range of wave lengths of
light emitted by the sun (Figure 21). Photosynthetic organisms use only a
small portion of the spectrum called visible light (400 – 700 nm).

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