None of us would be here were it not for the
amazing process that takes place in plants
called Photosynthesis.
This process allows all of life to exist;
things would not be able to carry out any
process involving energy without obtaining
the chemical energy stored by photosynthetic
organisms in sugars.
However, the actual process of photosynthesis
is complicated.
We’re here to make this awesome process
simple.
Photosynthesis takes place in the chloroplasts
of plants.
Just a square millimeter of a leaf contains
about 500,000 chloroplasts!
The chloroplasts are responsible for a plant’s
color, and contain green chlorophyll pigments
as well as red, orange, or yellow carotenoid
pigments.
Since these pigments can only absorb light
energy that is a specific color, green chlorophyll
pigments absorb the more powerful blue to
violet sun rays and reflect green, while carotenoid
pigments absorb the less powerful green sun
rays and reflect yellow or red.
Did you know this is actually why plants change
colors during the different seasons?
When the sun is not as strong in a region
that is in the fall or spring season, the
green chlorophylls can’t use the less powerful
light, so the plant reverts to using carotenoid
pigments to extend the process of photosynthesis
until winter.
The differently colored carotenoid pigments
take over and cause the brilliant red, orange,
and yellow colored plants.
A bunch of chlorophyll and carotenoid pigments
work together and form an “antenna complex”.
The first of these complexes is photosystem
2, which has many pigments connected to a
reaction center.
These pigments become unbalanced when photons
from sunlight strikes them.
They then transfer the imbalance to a reaction
center.
In the reaction center, a molecule known as
pheophytin receives the imbalance and has
to give up some electrons, which pass to a
series of reactions known as the Electron
Transport Chain.
During the time of transfer, electrons from
H2O molecules replace the lost electrons of
pheophytin and are taken by separating the
Oxygen atom from its Hydrogen atoms.
The Oxygen is released into the atmosphere
and the Hydrogens are placed in a temporary
spot.
The Hydrogens in this temporary spot are a
very important part of Photosynthesis that
we’ll get to in a little while.
The electron transport chain eventually dumps
extra electrons taken from pheophytin into
a second “antenna complex” called Photosystem
1 that acts similar to the last photosystem
but energizes these dumped electrons in the
reaction center instead.
The electrons are used to make NADPH, which
has an important role in making sugar.
First let’s get back to the Hydrogens put
into a temporary spot.
The temporary spot houses many of these Hydrogen
atoms, which really want to go to an area
where they are less concentrated.
Therefore, the chloroplasts only let the Hydrogens
move through a small hole to the outside that
has a pump connected to it.
The motion of the Hydrogens crossing over
generate energy in the form of ATP, similar
to how hydroelectric dams use water flowing
through them to spin energy generators.
ATP molecules have large atoms that really
don’t like being next to each other and
are constantly pushing each other away, so
cells could use the energy of the atoms flying
away from each other when ATP molecules are
broken for energy.
But ATP is not very stable, so plants take
in CO2 and use the NADPH from Photosystem
1 to convert the energy into sugars, which
also have atoms that are pushing each other
away.
This sugar manufacturing stores the energy
of the sun and allows all biological life
to occur.
So next time you burn a piece of wood or eat
some spaghetti, remember that you are using
energy stored from the sun.
