Photosynthesis
When you and me eat, we find our food. When plants eat, they make their own food and
energy. They make their food and energy through a process called photosynthesis.
Through photosynthesis oxygen is also produced. Photosynthesis is "a process in which
green plants synthesize carbohydrates from carbon dioxide and water....The reverse of
this reaction provides energy for plants, for animals that eat plants, for animals that
eat animals that eat plants" for animals that eat animals that eat animals that eat
plants, etc. (Levine 726) All humans rely on these plants to produce oxygen from
photosynthesis. The presence of light and of the green pigment chlorophyll makes the
change of carbon dioxide and water to glucose and oxygen possible. It was Jan Ingenhouz
with Jean Senebier in Geneva that founded the basic gist of the theory of photosynthesis
in plants.
My experiment involves testing different brands of plant food on plants to see what
brand of plant food makes the plant grow the tallest. I will test three types of plant
food on three sets of plants and one set with no food. I will water the plants all the
same amount and let all the plants get the same amount of sun, then measure the height of
all the plants at the end of six weeks and record the data.
The first step of photosynthesis is the absorption of light by a chlorophyll molecule.
"The energy of the absorbed photon is transferred from one chlorophyll molecule to
another until it reaches a site called a reaction center....One oxygen molecule is
produced per eight photons absorbed." (Alberty 708) James Huheey, professor at the
University of Maryland, talks about chlorophyll in his book Inorganic Chemistry:
"Chlorophyll absorbs low-energy light in the far red region....Such absorption serves a
twofold function: (1)The energy may be passed along to the chlorophyll system and used in
photosynthesis; (2)It protects the biological system from photochemical damage." (629)
"Chlorophyll a and chlorophyll b contain networks of alternating single and double bands,
and have strong absorption bands in the visible part of the spectrum....," says Robert
Alberty, who is a professor of chemistry at the Massachusetts Institute of Technology.
(708)
Photosynthesis, "...which occurs entirely in the chloroplasts of green cells, involves a
number of steps catalyzed by enzymes. The chloroplasts contain chlorophyll a,
chlorophyll b, carotenes, electron carriers, and enzymes, and have internal membranes
that keep reactants separated," says Alberty. (708)
James Huheey talks about some "features of the chlorophyll system which enhance[s] its
usefulness as a pigment in photosynthesis:
"First, there is an extensive conjugation of the porphyrin ring. This lowers the energy
of the electronic transitions and shifts the absorption maximum into the region of
visible light. Conjugation also helps make the ring rigid and thus less energy is wasted
in internal thermal degration." (631)
"In order for phosphorescence to occur there must be an excited state with a finite
lifetime. If such an excited state is available then there is time for a chemical
reaction to take place to take advantage of the energy prior to phosphorescence....The
presence of a metal atom is necessary in order that phosphorescence takes place." (Huheey
631)
"Chlorophyll contains a conjugated ring system that allows it to absorb visible
radiation...." (Levine 726) In Inorganic Chemistry, James Huheey reports about ring
system:
"The chlorophyll ring system is a porphyrin in which a double bond in one of the pyrrole
rings has been reduced. A fused cyclopentanone is also present....In addition, other
pigments such as carotenoids are present which absorb higher energy light." (629)
The exact frequency of the light that is absorbed by the chlorophyll depends upon the
nature of the substituents on the chlorophyll.
Photosynthesis is a crucial process that is necessary for the human race and other races
that breath the oxygen that the plants produce to live. Photosynthesis is a complex
process that we know only broad details about. Chlorophyll and light are what is needed
for plant to photosynthesize. I think that my experiment will prove the best brand of
plant food out of the three. The best brand would be the one that makes the plant grow
highest. So consider just how important that green plants really are to the human race
and their survival on the earth.
Works Cited
Alberty, Robert A. Physical Chemistry. New York: Wiley, 1983.
Asimov, Isaac. Photosynthesis. New York: Basic, 1968.
Brock, William H. The Norton History of Chemistry. New York: 1993.
Huheey, James E. Inorganic Chemistry. New York: Harper, 1972.
Levine, Ira N. Physical Chemistry. New York: McGraw, 1978.
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