Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
Comparison of Chlorophyll Content in Shade and Sun Leaves of the Lemonade
Berry Plant (Rhus integrifolia).
Ryan C. Clark and Josue J. Mandujano
Department of Biological Sciences
Saddleback College
Mission Viejo, CA 92692
Chlorophyll is a green, photosynthetic pigment that absorbs sunlight, and
uses this energy to produce ATP and NADPH. It is, therefore, the foundation for
the life functions of all plants. Chlorophyll content varies with different plants but
can vary in different leaf types of a certain plant. The amount of chlorophyll in a
leaf depends on the quantity of sunlight the leaf in question receives. Given that
photosynthesis occurs with more efficiency if it has more sunlight, it was predicted
that the sun leaves, which receive more direct sunlight than the shade leaves would
contain higher chlorophyll content than shade leaves. A spectrophotometer and
chlorophyll extraction were used to determine whether sun or shade leaves, would
contain more chlorophyll. Five mL of 80% concentrated acetone were mixed with
two 6 mm leaf chads in scintillation vials. A 1 mL solution was inserted via styrene
cuvette into the spectrophotometer for analysis. It was discovered that in the
samples taken, half of the shade leaves of the lemonade berry contained more
chlorophyll than the sun leaves and half of the sun leaves contained more
chlorophyll than the shade leaves. However, the total combined average of the
samples taken show that the sun leaves have a higher chlorophyll content than
shade leaves. The results of the experiments therefore, supported the hypothesis
that the sun leaves would contain a higher concentration of chlorophyll than the
shade leaves.
Introduction
Pigments are chemical compounds which
reflect only certain wavelengths of visible light (Speer,
1995). Chlorophyll is a green pigment that contains a
porphyrin ring and it is located in the thylakoids. It is
the utilization of this porphyrin ring with its freemoving
electrons that is the basic pathway by which
chlorophyll captures sunlight’s energy. Of the several
different kinds of chlorophyll, chlorophyll “a”, which
is found in all plants and algae that photosynthesize, is
the most important type of chlorophyll (Speer, 1995).
Chlorophyll a is the type of chlorophyll that
makes photosynthesis possible. It does this by passing
on its energized electrons to molecules which will
manufacture sugars (Speer, 1995). A second type of
chlorophyll, chlorophyll b only occurs in plants and
green algae that transfers energy to chlorophyll a.
Photosynthesis is divided into two different and distinct
stages – the Light Reaction, and the Calvin Cycle
(Farabee, 2001). In the Light Reaction, which occurs
continuously during the process, in the grana of the
thylakoid membrane contained in the chloroplast in
Photosystem II, photophosphorylation occurs. This is
due to light energy causing the removal of an electron
from P680 in Photosystem II (Campbell and Reece,
2005). The P680 replaces the electron by taking it
from a water molecule, which is split into its H + ions
and O 2− ions. The O 2− ions then combine to form
diatomic oxygen, which is released. The electron is
captured by the primary electron acceptor and passed
from Photosystem II to Photosystem I via an electron
transport chain. While the electron moves through the
electron transport chain to Photosystem I, it moves to a
lower energy level, and it, along with other electrons
moving along the chain, provides energy for the
synthesis of ATP. Light energy excites an electron in
P700 reaction center of Photosystem I, the electron is
boosted to higher energy potential, and the electron is
captured by Photosystem I’s primary electron acceptor.
The electron that moved down the transport chain from
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Saddleback Journal of Biology
Spring 2008