In this video we'll talk about the Calvin
cycle and carbon fixation.
So let's talk about the second step of photosynthesis.
The Calvin cycle functions like a sugar-producing
factory within the chloroplast.
It uses carbon dioxide and the chemical energy
generated by the light reactions to form glucose.
This process is known as carbon fixation.
Carbon fixation is specifically taking carbon
in an inorganic form like carbon dioxide and
converting it into an organic molecule, like
glucose.
Going from inorganic to organic is what makes
it carbon fixation.
Now in order to make an organic molecule,
one thing that is required is a bunch of high-energy
electrons.
The NADPH molecules which were produced during
the light reactions contain these high-energy
electrons.
You may remember, we had described NADPH as
a shuttle bus for electrons.
Well, these electrons are going to be dropped
off, they're going to be added to carbon dioxide
along with some hydrogen protons to form sugar.
Much of the energy of the sugar molecule will
be found in these high-energy electrons.
In fact, we'll look at the role these high-energy
electrons play when we discuss cellular respiration.
So here we have our entire equation for photosynthesis.
We have our reactants at the top of this diagram,
being water and carbon dioxide, and we see
the water is going into the light reactions
the CO2 is going into the Calvin cycle.
We also have light, which is supplying the
energy for this chemical reaction.
Well, coming out of the light reactions we
have oxygen gas, which is one of our chemical
products and we also have ATP and NADPH.
These are two forms of chemical energy.
That chemical energy from the light reactions
is going to combine with the carbon dioxide
in the Calvin cycle to form glucose.
So, water and carbon dioxide go into photosynthesis,
oxygen gas and sugar come out.
Water specifically goes into the light reaction
and out comes oxygen gas and the chemical
energy.
CO2 and the chemical energy go into the Calvin
cycle and out comes glucose, an organic molecule
that also is very energy-rich.
This sugar molecule can now be stored and
used later by the plant or also by animals
which consume that plant.
The last aspect of photosynthesis to discuss
is the impact that photosynthesis has on the
atmosphere.
And the answer is, a lot!
There's a big impact on the atmosphere because
of photosynthesis.
It's what adds oxygen gas to the atmosphere
while using up carbon dioxide.
In fact, oxygen gas is a highly reactive molecule
and so all of the oxygen gas currently in
our atmosphere was generated by photosynthesis.
In fact, if there were not a constant supply
of plants and protists performing photosynthesis,
the oxygen gas in our atmosphere would be
depleted as it reacts with other molecules
on the surface of the Earth.
So with that, that finishes our discussion
of photosynthesis.
In the next video we are going to talk about
cellular respiration or how it is we go about
getting the energy out of the sugar molecules
produced by photosynthesis.
Thanks for your attention, see you in the
next video.
