Photosynthesis
Reactants
Products
carbon + water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Review: Light reactions
• Convert solar energy to chemical energy
– ATP  energy ATP
– NADPH  electron donator
• What can we do now?
  build stuff !!
photosynthesis
The second phase of photosynthesis is called the
Calvin Cycle (Light-Independent phase)
LIGHT-DEPENDENT PHASE
(Requires Sunlight)
LIGHT-INDEPENDENT PHASE
(Does Not Require Sunlight)
REMEMBER: This is when the chemical energy produced in the
first phase is combine with Carbon Dioxide to create sugar.
LIGHT-INDEPENDENT
REACTIONS/ Calvin Cycle
SUGAR ASSEMBLY- SECOND PHASE
The light-INDEPENDENT reactions (or Calvin cycle) use
the chemical energy produced in the light-dependent
reactions (ATP and NADPH) and carbon dioxide to
create sugar.
The Calvin Cycle
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The Calvin Cycle takes place in the stroma of
the chloroplast.
STROMA
(Fluid interior)
Carbon Dioxide enters the plant leaf through
openings called stomata.
THE CALVIN CYCLE
At the beginning of the Calvin Cycle, six CO2 molecules
bond with six 5-carbon sugar called RuBP (Ribulose
Biphosphate) to form an six unstable 6-carbon sugar.
(An enzyme called Rubisco is responsible for joining these molecules.)
O
C
C
C
C
O
RuBP
CARBON DIOXIDE
C
C
C
C
C
C
UNSTABLE 6-CARBON SUGAR
C
C
THE CALVIN CYCLE
This step is called Carbon Fixation, because a carbon is
“fixed” onto the RuBP.
O
C
C
C
C
O
RuBP
CARBON DIOXIDE
C
C
C
C
C
C
UNSTABLE 6-CARBON SUGAR
C
C
THE CALVIN CYCLE
(CO2)
(RuPB)
6 carbon sugar
THE CALVIN CYCLE
C
C
C
C
C
C
C
C
C
C
C
C
UNSTABLE 6-CARBON SUGAR
PGAs
The unstable 6-carbon sugars immediately split to
form twelve stable 3-carbon molecules.
These molecules are called PGA’s
(phosphoglycerate)
THE CALVIN CYCLE
(CO2)
6 Carbon sugar
(RuPB)
(PGA)
3 Carbon
molecules
THE CALVIN CYCLE
12 NADPH and 12 ATP (from the light dependent
reactions) then give their energy to turn the 3carbon PGA molecules into PGALs (3-carbon
sugars called glyceride tri-phosphate with
higher energy bonds).
ADP, P, and NADP+ are released and
then return to the thylakoid membrane
to be re-energized.
C
C
C
ADP +
ATP
C
C
C
NADPH
NADP+
C
C
C
C
C
C
2 PGAL
molecules
THE CALVIN CYCLE
(CO2)
6 carbon sugar
(RuPB)
3 carbon
molecules
(PGA)
ATP
ADP +
NADPH
NADP+
(PGAL)
2 PGALs are transferred out of the chloroplast to the
cytoplasm of the cell where they are combined to make a
six-carbon glucose.
(CO2)
(RuPB)
6 carbon sugar
3 carbon
molecules
(PGA)
ATP
ADP +
NADPH
NADP+
(PGAL)
(2 PGAL)
(Sugar)
(CO2)
(RuPB)
6 carbon sugar
3 carbon
molecules
ADP +
ATP
ATP
ADP +
NADPH
NADP+
(PGAL)
(PGAL)
(Sugar)
The ten remaining PGAL molecules each with 3-carbon atoms, reorganize using 6
ATP molecules to make 6 molecules of RuBP (the 5-carbon sugar) to start the
cycle all over again.
Question 3
A molecule of adenosine that has two
phosphate groups bonded to it is ______.
A. AMP
B. ADP
C. ATP
D. ACP
The answer is B. ADP is adenosine diphosphate.
Adenosine
P
P
P
Adenosine triphosphate (ATP)
P
P
Adenosine diphosphate (ADP)
Adenosine
P
P
Question 4
What is the function of the protein molecule
shown in this diagram?
ATP
Protein
P
ADP
ADP
Energy
This protein molecule has a specific binding site for
ATP. In order to access the energy stored ATP, the
protein molecule binds the ATP and uncouples one
phosphate group. This action releases energy that
is then available to the cell.
ATP
Protein
P
ADP
ADP
Energy
Question 6
The function accomplished by the light-dependent
reactions is ________.
A. energy production
B. sugar production
C. carbon fixation
D. conversion of sugar to PGAL
The answer is A. The
light-dependent
reactions transfer
energy from the sun to
chlorophyll, and pass
energized electrons to
proteins embedded in
the thylakoid
membrane for storage
in ATP and NADPH
molecules.
Sun
Light energy transfers to chlorophyll.
Chlorophyll passes energy down through the
electron transport chain.
Energized electrons provide energy that
splits
H2 O
H+
NADP+
bonds P to ADP
forming
oxygen
ATP
released
NADPH
for the use in
light-independent reactions
Question 7
The first step in the Calvin cycle is the ________.
A. replenishing of RuBP
B. production of PGAL
C. Splitting of six-carbon sugar into two
three-carbon molecules
D. Bonding of carbon dioxide to RuBP
The answer is D. The carbon atom from CO2
bonds with a five-carbon sugar to form an
unstable six-carbon sugar. This molecule then
splits to form two three-carbon molecules.
Photosynthesis Overview
copyright cmassengale
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