Page 268 - Biology_F5

Nutrition
CH CH CH
2 3 3
H C O
3
N N CO CH 3
2
Mg
N N H H
H C=CH
2 CH CH CO CH CH=C(CH CH CH CH CH) CH
CH H CH 2 2 2 2 2 2 2 2 3 3
3 3 CH CH
3 3
FOR ONLINE READING ONLY
Figure 5.1: The Chemical structure of chlorophyll
There are several types of chlorophyll The initial stage of photosynthesis
including chlorophyll a, b, c, and d. Some can be viewed in two major phases or
organisms contain more than one type of reactions. These are light reaction (light
chlorophyll pigment. However, chlorophyll a dependent reaction), which takes place in
the thylakoid (grana) of the chloroplasts,
and b are more abundant in most plants, while and dark reaction (light independent
the majority of protoctists and cyanobacteria reaction), which occurs in the stroma of
contain chlorophyll c and d. Chlorophyll the chloroplasts. The light reaction is vital
absorbs red, blue and violet light but reflects for the subsequent stage of photosynthesis
green light. This makes all plants to appear (dark reaction), because it is during this
green in color. Principally, the function of stage energy, electrons, and hydrogen are
chlorophyll is to convert light energy into produced.
chemical energy. Other photosynthetic
pigments are beta carotenes and phycobilins Light reaction (Light dependent
(found in organisms, such as red algae and reaction)
cyanobacteria), the red phycobilin is called Light reaction of photosynthesis occurs
in the thylakoids of the chloroplasts.
phycoerythrobilin and the blue phycobilin is Normally, chloroplasts are aligned in
known as phycocyanin. They transfer light such a way that their thylakoids are held
energy to the chlorophyll to be utilised in at right angle to the light source in order
the photosynthesis process. Photosynthetic to maximise light absorption. Within the
bacteria contain photosynthetic pigments thylakoids, chlorophyll pigments are
called bacteriochlorophyll, which are arranged in groups called photosystems,
not contained in the chloroplast. This is which are specialised form of chlorophyll
that commonly exists in two forms,
because bacteria are single celled organisms, namely Photosystem I and Photosystem
whereas the entire cell is an equivalent of II. Chlorophyll photosystems are named
a chloroplast. in chronological order of their discovery
and not in a way they are involved in
Mechanism of photosynthesis light reaction. Thus, photosystem I was

Task 5.3 discovered before photosysytem II.
From the internet sources, search Photosystem I has a specialised form
for simulations on the mechanism of of chlorophyll called pigment 700
photosynthesis and make short notes. abbreviated as (P700) while Photosystem
II has specialised form of chlorophyll
pigment, 680 abbreviated as (P680). The

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