After floating around for a while and enjoying the fresh air, I became restless and started to search for a new adventure. Since I heard that green plants enjoy having carbon dioxide molecules over for company, I thought I'd give it a try. Sure enough, I was in luck! As I was floating over a beautiful green pasture in a small farm, I spotted a particularly green spot of grass. It seemed like a perfect place to stop for a rest so I settled near a long blade of grass. I guess I was in the wrong place at the wrong time because the grass just captured me! I proceeded slightly hesitantly (you just can never tell about strangers), but soon I saw that I had no reason to worry. The stroma was very nice in that I was able to enter the chloroplast but refrain from proceeding into the thylakoid sac. I began to relax as I saw that the grass was very friendly, just lacking a little in manners. However, once I was safely inside the stroma, I was grabbed by an enzyme! He quickly passed me to one of his friends, who was also an enzyme. It's certainly the truth that enzymes help processes move along quickly because before I knew it, I was in a glucose molecule. In most ways, a glucose molecule is the same in both people and plants. The difference was that this time I was in the leaf of a plant instead of a person's bloodstream. Fairly soon, I was converted from being part of a gas, CO2, into part of a molecule, glucose. Pretty neat, isn't it?
6CO2 + 12H2O + energy -----> C6H12O6 + 6O2 + 6H2O
The general idea of photosynthesis is to make food (sugar)
from the energy of sunlight. When looking at the overall
equation summarizing the reactants and products of photosynthesis,
it appears to be a simple process. While there is much known
about photosynthesis, it is by no means an easy process. Instead,
the process must be considered slowly due to its many steps that
often consist of various molecules. However, it is definitely
worth the time to understand photosynthesis for two major reasons.
First of all, it is amazing to consider how resourceful plants
are to use carbon dioxide already present in the air in order
to fuel their own life-sustaining processes. More importantly
(at least to us), photosynthesis releases oxygen into the air.
Without oxygen, humans as well as animals would have absolutely
no chance for survival. Interestingly enough, oxygen is produced
as a mere by-product of photosynthesis; that is, when a plant
splits a water molecule, it only needs the hydrogen from the water
and releases the oxygen because it is useless. The fortunate
output of oxygen from plants during photosynthesis certainly
stresses the coincidental nature of life.
Chlorophyll molecules cluster on the surface of the chloroplast of a leaf. The chloroplasts on an average maple tree have an average surface area of 140 square miles when spread out. This means that there is an uncountable number of chlorophyll molecules on just one tree.
Photons, or rays of sunlight, hit the chlorophyll molecules causing them to absorb light energy. In response to this addition of energy, their electrons jump to a higher energy orbit.
These high-energy electrons are picked up by carrier molecules in the thylakoid membrane with the help of a chlorophyll-enzyme combination. As these electrons are removed, they are replaced by electrons from water with the aid of a water-splitting enzyme.
When the carrier molecules reach the inner side of the membrane, an enzyme removes the hydrogen ions and places them in the thylakoid sac while leaving the original electrons on the carrier molecules.
The hydrogen ions must leave the sac through a channel of the ATP-producing enzyme. As these ions move, the enzyme gains energy from the movement and reattaches phosphate groups to partial ATP molecules. Think of this as a machine where the moving ions cause a gear to shift that puts the enzyme's gear into motion ultimately producing ATP molecules.
The old electrons on the carrier molecules are re-energized by sunlight.
(The Calvin Cycle) Inside the stroma, five enzymes get to work to produce the much-needed sugar. The stroma is located inside the chloroplast but outside of the thylakoid sac. For simplicity, these enzymes will be named one through five.
Enzyme 1 takes 3 CO2 molecules from the surrounding air and attaches them to three five-carbon sugars.
Enzyme 2 takes the three six-carbon sugars from the first enzyme and rearranges them to six three-carbon sugars. (To make the process simpler, the oxygen will be left out).
Enzyme 3 adds hydrogen to the six sugars and discards one of the sugars.
Enzyme 4 takes the remaining five three-carbon sugars and changes them into three five-carbon sugars.
Enzyme 5 energizes these sugars with ATP.
Therefore, photosynthesis is a fairly complex process that
incorporates ATP, CO2 from the surrounding air, water, and light
energy in order to produce glucose molecules and oxygen. This seems
to be an inefficient manner in which to produce glucose since for
one trip through photosynthesis, only one glucose molecule is
produced for the plant's immediate use. The other five glucose
molecules are needed to fuel the next attempt at photosynthesis. As
a result, the plant can really only use 1/6 of its efforts for use,
the others must remain in transit. However, photosynthesis remains
paradoxically efficient as it reduces more than ten percent of
CO2 in the air into carbohydrates by itself. Unfortunately,
there has been a growing concern that the drastic increase of
CO2 levels in the atmosphere due to global warming will
not be able to continue to be reduced by photosynthesis. This could
result in altering the entirety of the carbon cycle by disrupting its
equilibrium between production and destruction of carbon.
