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
enhances 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
“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.
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.