• Photosynthesis can be summarized as the
following equation:
6 CO2 + 6H2O + Light energy  C6H12O6 + 6 O2
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
use
Energy from
sunlight
Calvin cycle
Thylakoid
membranes
to produce
ATP
Go to
Section:
NADPH
takes place in
take place in
O2
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars
Fig. 10-5-1
H2O
Light
NADP+
ADP
+ P
Light
Reactions
Chloroplast
i
Fig. 10-5-2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Fig. 10-5-3
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Calvin
Cycle
Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Fig. 10-21
H2O
CO2
Light
NADP+
ADP
+ P
i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin
Cycle
G3P
Starch
(storage)
Chloroplast
O2
Sucrose (export)
The ‘Light Reactions’
STROMA
(low H+ concentration)
Cytochrome
Photosystem I
complex
Light
Photosystem II
4 H+
Light
Fd
NADP+
reductase
NADP+ + H+
NADPH
Pq
H2O
THYLAKOID SPACE
(high H+ concentration)
e–
1
e–
1/
Pc
2
2
3
O2
+2 H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
STROMA
(low H+ concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
Calvin Cycle of Photosynthesis!
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
• The Calvin cycle has three phases:
– Carbon fixation (catalyzed by rubisco)
– Reduction
– Regeneration of the CO2 acceptor (RuBP)
• Carbon enters the cycle as CO2 and leaves as
a sugar named glyceraldehyde-3-phospate
(G3P)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Shortest Summary Possible
• Photosynthesis consists of the light reactions (the
photo part) and Calvin cycle (the synthesis part)
• The light reactions (in the thylakoid membranes):
– Split H2O – Releasing electrons, H+, and O2
– Electrons travel through ETC pumping H+ into thylakoid
space
– Electrons combine with NADP+ to make NADPH
– The O2 leaves the plant via stomata
– ATP is generated as H+ diffuses through ATP synthase
– Both ATP and NADPH are used to power the Calvin Cycle
in the stroma.
Summary Continued
• The Calvin Cycle (in the stroma)
– Uses ATP and NADPH as energy sources to extract
carbon from CO2
– CO2 combines with RuBP (Ribulose Bisphosphate)
with the help of an enzyme called Rubisco. This is
called carbon fixation.
– The second phase is reduction. A sugar called G3P
(Glyceraldehyde 3 Phosphate) which will later become
many types of carbohydrates including glucose.
– Stage three is Regeneration. RuBP is remade so it
can accept more CO2 and go through the cycle again.
Additional Photosynthesis Information
• Photosynthesis occurs in the thylakoid
membrane and in the stroma.
• The terms light reactions and dark reactions
were once used.
• The terms ‘light dependent’ and ‘light
independent’ or ‘Calvin Cycle’ are better.
Fig. 10-4
The oxygen produced by photosynthesis comes from the
splitting of water.
Reactants:
Products:
6 CO2
C6H12O6
12 H2O
6 H2 O
6 O2
• Plants store excess sugar as starch in structures
such as roots, tubers, seeds, and fruits.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Factors Effecting Photosynthesis
1. Temperature
2. Carbon Dioxide Concentrations
3. Light Intensity
4. Adequate Water
5. Quality of the Light
6. Duration of the Light
7. Mineral Elements
8. Air Pollutants
See p. 240 - 241
Factors Affecting Photosynthesis