Photosynthesis
California Standard 1.f.
There are three stages in photosynthesis:
Stage 1- Energy is captured from sunlight
Stage 2 - Light energy is converted to
chemical energy, which is temporarily stored
in ATP and the energy carrier molecule
NADPH
Stage 3 - The chemical energy stored in ATP
and NADPH powers the formation of organic
compounds, using carbon dioxide, CO2
The chemical reactions that
occur in the first and second
stages of photosynthesis are
called the “light reactions”
while the third stage is called
the “dark reaction”.
Stage 1: Energy is captured from sunlight.
We have talked about the chlorophyll
molecule so far. However, there are two
types of chlorophyll molecule; chlorophyll a
and b.
There are also a second type of pigment
molecules. They are called carotenoids.
These pigments are responsible for the
yellow and orange colors we see in the
fall and for the yellow and red fruits and
vegetables we see at the grocery.
Carotinoids absorb wavelengths of
light that are different from those
of chlorophyll. Therefore, the
plants can absorb more light energy
during photosynthesis.
and carotinoid pigments
Molecular make up of
Chlorophyll a and b
The electrons that leave the
thylakoid membrane are replaced
by the electrons from the splitting of
the water molecule into H and O
ions.
The oxygen molecule from the
water is then released into the
environment for us to breathe.
Remember:
1) Chlorophyll is the molecule which
is the pigment that captures the
energy from sunlight. This energy
causes the water molecule to ‘split’
releasing an electron. It is the
chlorophyll molecule which causes
the leaf to look green.
2) The transfer of electrons from
water takes place in the thylakoid
membrane and this is where
oxygen is released.
3) The granna are stacks of
thylakoids in the chloroplast
organelle.
4) The chloroplast is the organelle
which you can see under the
microscope and which is
responsible for photosynthesis.
Chloroplast with stroma, thylakoid
and granum.
Chloroplast is the organelle
which captures sunlight and turns
it into carbohydrates and energy.
Chloroplast organelle
Stacks of granna
Oh… thank you Lord… now I
understand!!!
But I still think Mr. Post is wacked.!
Stage 2: Light energy is converted to
chemical energy
There are two types of electron transport
chains both occur in the thylakoid
membrane.
1. The first type is one that produces
ATP from ADP.
2. The second is the one that produces
NADPH from NADP+.
The first gains or loses a P
molecule while the second gains or
loses a H ion.
Both of these energy molecules are
used in the third stage of
photosynthesis.
We have covered the first two stages of
photosynthesis. They are both called the
light-dependent stages.
The light-dependent stages can be
summarized as follows:
1. Pigments in thylakoids absorb light
2. The electrons that are excited by light
move through the electron transport
chains in thylakoid membranes
3. These electrons are replaced by
electrons from the water molecule, which
is split by an enzyme.
4. Oxygen atoms from water form to
create oxygen we breathe.
5. H ions accumulate inside thylakoids
that supply the energy to make ATP and
NADPH
Stage 3: Energy is stored in organic compounds
The transfer of carbon dioxide from the atmosphere to
organic compounds is called carbon dioxide
fixation.
This process is independent of light, therefore it is
know as the “dark reactions” or light-independent
reactions of photosynthesis.
The general process of photosynthesis involves 3
molecules of carbon dioxide with 3 molecules of
water to form a 3-carbon sugar and oxygen
gas.
The reactants are carbon dioxide and water to form
the products: carbohydrates (starch) and oxygen gas.
3H2O + 3CO2 ----------> C3H6O3+
3O2
The oxygen we breath comes from the
molecule water.
The most common means by which CO2 is
fixed is through the Calvin Cycle. However,
there are other means to fix Carbon but this is
the one we will study.
If you did not know, the Calvin Cycle was
named after Melvin Calvin who discovered
this means of CO2 fixation while a professor
of chemistry at University of California at
Berkeley in 1947 using Carbon 14. He
received a Noble Prize for his discovery in
1961 and died in 1997.
Dr. Melvin Calvin is shown below in his
“mad” scientist lab at UC Berkeley, circa
1952.
Just remember ‘C’ stands for carbon dioxide
fixation and ‘C’ is the first letter in Calvin
Cycle that is the process that fixes Carbon and
produces Carbohydrates.
Get it? C for Carbon, C for Calvin and C
for carbohydrates.
Or put another way… C-C-C. Get it?
FORGET IT!
The Calvin Cycle: end result is a 3 carbon sugar (3
Ribulose 1,5 bisphosphate)
Points to remember about the Calvin Cycle:
1. It is one means to fix CO2
2. Energy from ATP and NADPH are
used which came originally from
photosynthesis.
3. It is one means of making organic
compounds by plants which are later
used by animals; that is you and me.
Factors that affect photosynthesis:
1) Light intensity until all pigments
are saturated,
2) level of CO2 concentration
until saturation occurs,
3) temperature ranges due to enzyme
activity.
The beginning and the end of
photosynthesis
The End
Mr. Post having a
bad hair day.