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Supramolecular Chemistry, UAF, 2005
Photosynthesis
Where does the energy come from that
sustains all life?
The Sun!!
Well most of it anyway……
Supramolecular Chemistry, UAF, 2005
What is photosynthesis?
In the process of photosynthesis, plants
convert the energy of sunlight into the
energy in the chemical bonds of
carbohydrates-sugars and starches.
Supramolecular Chemistry, UAF, 2005
Discovery of the process:
For many years, people wondered how a few
seedlings could develop into a large tree.
The mass of seedlings are only a few grams,
where as the mass of a tree is several tons.
Dutch physician Jan Van Helmont devised an
experiment.
He concluded that the mass grew from the
water, because that was the only thing he had
added to the pot.
This was just one of the things needed for
photosynthesis to occur.
Supramolecular Chemistry, UAF, 2005
What makes photosynthesis complete?
Helmont did not realize that carbon dioxide
in the air also plays a major role in the
contribution of mass growth.
The carbon in carbon dioxide is what is
used to make carbohydrates in
photosynthesis.
Supramolecular Chemistry, UAF, 2005
Later on, scientist Joseph Priestly
performed an experiment that would give
rise to why oxygen is released in
photosynthesis, and why sunlight is
needed for it to photosynthesize.
Priestly placed a candle in a jar along with
a mint plant.
He then realized that the candle could only
stay lit when the mint plan was present.
This would mean that the plant was
releasing oxygen.
Supramolecular Chemistry, UAF, 2005
Why is Photosynthesis important?
Through experiments, it was realized that
in the presence of light, plants transform
carbon dioxide and water into
carbohydrates and release oxygen.
Plants that are able to use a source of
energy, such as sunlight, to provide food
directly from simple inorganic molecules
are known as autotrophs.
This is made possible through
photosynthesis.
Supramolecular Chemistry, UAF, 2005
WHAT IS THE
DIFFERENCE BETWEEN A
HETEROTROPH & AN
AUTOTROPH?
Supramolecular Chemistry, UAF, 2005
the equation for photosynthesis is:
Supramolecular Chemistry, UAF, 2005
The sugars that result from photosynthesis are
produced by adding the hydrogen ions and electrons
from water to carbon dioxide, NOT by splitting CO2 and
adding water!
oxidized
H+ and e-
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
reduced
Supramolecular Chemistry, UAF, 2005
Bromothymol Blue
Used to test for the presence of carbon
dioxide (CO2)
If CO2 is present it is a yellow color
If CO2 is NOT present it is a blue color
Supramolecular Chemistry, UAF, 2005
Supramolecular Chemistry, UAF, 2005
Light Absorption & Light Energy
The actual process of photosynthesis
begins when light is absorbed by pigments
in the plant cell.
The principal pigment in plants is
chlorophyll which gives the plant its green
color.
Supramolecular Chemistry, UAF, 2005
Plant Photosynthesis
internal leaf structure
outer membrane
chloroplasts
inner membrane
thylakoid
Supramolecular Chemistry, UAF, 2005
Photosystems use some wavelengths of light but reflect
others…
Supramolecular Chemistry, UAF, 2005
Another way in which light energy is
trapped in chemical form involves
adenosine triphosphate or ATP.
During photosynthesis, green plants
produce ATP, which is the energy storing
compound used by every living cell.
The energy is released by means of
breaking the phosphate bonds which
make up the ATP cycle.
The energy is used in almost all cellular
activities.
Supramolecular Chemistry, UAF, 2005
Respiration vs. Photosynthesis
Supramolecular Chemistry, UAF, 2005
Photosynthesis and respiration are complementary
processes in the living world.
Photosynthesis uses the energy of sunlight to produce
sugars and other organic molecules.
These molecules in turn serve as food.
Respiration is a process that uses O2 and forms CO2 from
the same carbon atoms that had been taken up as CO2 and
converted into sugars by photosynthesis.
In respiration, organisms obtain the energy that they need to
survive.
Photosynthesis preceded respiration on the earth for
probably billions of years before enough O2 was released to
create an atmosphere rich in oxygen.
(The earth's atmosphere presently contains 20% O2.)
Supramolecular Chemistry, UAF, 2005
Self-Evaluation Questions
1. In the process of photosynthesis, plants convert
the energy of sunlight into what?
2. When Helmont devised an experiment, he
concluded that the mass grew from the_____,
which was the only thing he had added to the soil.
3. What scientist gave rise to the explanation of
plants giving off oxygen, and the reason sunlight is
needed in order for plants to photosynthesize?
4. Fill in the missing part of the equation for
photosynthesis--Carbon dioxide + water yields
what? (two things)
5. What do you call plants that obtain their nutrients
in organic molecules through photosynthesis?
Supramolecular Chemistry, UAF, 2005