Photosynthesis is the process by which plants
and other photosynthetic organisms take solar
energy and convert it into chemical energy.
They do this by taking water and carbon dioxide,
two stable molecules which have very little
stored energy, and converting those atoms
from those molecules into molecules of glucose
and oxygen gas, molecules which are not as
stable and have more stored energy.
Photosynthesis is a metabolic pathway, meaning
it takes a series of chemical reactions to
go from H2O and CO2 to C6H1206 and O2.
There are two main divisions of photosynthesis.
These are known as the light reactions, where
the solar energy is collected and converted
into chemical energy, and the Calvin cycle,
where CO2 is converted into glucose by using
the chemical energy from the light reactions.
We will
be looking into the light reactions in greater
depth in the next video.
It is also important to remember that during
chemical reactions, atoms are not created
or destroyed.
Instead, old covalent bonds are broken, and
new covalent bonds are formed.
There are just as many atoms before photosynthesis
occurs as there are after.
When we look at the equation for photosynthesis,
we see that the product, glucose, has six
carbon atoms in it.
That means that we need to have six carbon
atoms added in the reactants.
That is why we see six CO2 in the reactants
because there is one atom of carbon in each
of those molecules.
We also see that glucose has 12 hydrogen atoms.
The only source of hydrogen in our reactants
is from water so we need six water molecules
in the reactants as well because there are
two hydrogen atoms in each of the water molecules.
When we count up all of the oxygen atoms in
the reactants, there are 18.
Six of those oxygen atoms will become a part
of the glucose that is formed, leaving us
with 12 oxygen atoms to make oxygen gas.
So we have six molecules of O2 in the products
along with the glucose.
In order to understand the significance of
photosynthesis, we need to look at another
metabolic pathway which is used to release
the energy stored in sugar molecules.
This pathway is called cellular respiration.
Cellular respiration is the breakdown of glucose
in the presence of oxygen gas to release the
stored energy into a usable form for the cells.
In this process, glucose and oxygen gas are
converted into carbon dioxide and water.
Hopefully, you
are able to see that the products of photosynthesis
are the reactants of cellular respiration
and that the products of cellular respiration
are the reactants for photosynthesis.
It is important to note that even though the
same atoms are used over and over again, the
matter is cycled, the energy is only flowing
in one direction.
The energy that is stored during photosynthesis
and released during cellular respiration originated
from the sun and is eventually lost as heat.
The sun is what powers the vast majority of
life on this planet, both the producers and
the consumers.
In the words of They Might be Giants--
THEY MIGHT BE GIANTS:
[SINGING] The sun is hot.
The sun is not a place where we could live.
But here on Earth, there'd be no life without
the light it gives.
We need its light, we need its heat, the sunlight
that we see.
The sunlight comes from our own sun's atomic
energy.
Photosynthesis and cellular respiration have
the same reactants and products.
The only difference is that one occurs in
plants and the other in animals.
True or false?
The carbon used to make sugars in photosynthesis
comes from the organic matter in the soil,
CO2 in the atmosphere, water from rain, photons
of light?
All of photosynthesis occurs in a single step.
True or false?
