Download Calvin Cycle, C4 and CAM Plants

Chapter 8
Calvin Cycle, C4 and CAM Plants
You Must Know
• How the Calvin cycle uses the energy
molecules of the light reactions (ATP and
NADPH) to produce carbohydrates (G3P) from
CO2.
• The difference between C3, C4, and CAM
plants.
Figure 8.UN03
H2O
CO2
Light
NADP
ADP
Calvin
Cycle
Light
Reactions
ATP
NADPH
O2
[CH2O] (sugar)
anabolic
For net synthesis of
one G3P, the cycle
must take place
three times, fixing
three molecules of
CO2
3 CO2
Carbon fixation
3  5C
6  3C
Calvin
Cycle
Regeneration of
CO2 acceptor
5  3C
Reduction
1 G3P (3C)
(Note: for the next three slides, you only need to
remember the names of molecules that are
marked with a red arrow.)
Figure 8.17-1
Input 3
as 3 CO2
Phase 1: Carbon fixation
Rubisco
3 P
3 P
P
P
6
P
3-Phosphoglycerate
RuBP
Calvin
Cycle
Ru
BP?
Figure 8.17-2
Input 3
as 3 CO2
Phase 1: Carbon fixation
Rubisco
3 P
3 P
P
P
6
phosphorylation
P
3-Phosphoglycerate
RuBP
6
ATP
6 ADP
reduction
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP
6 Pi
6
P
G3P
1
P
G3P
Output
Phase 2:
Reduction
Glucose and
other organic
compounds
Figure 8.17-3
Input 3
as 3 CO2
Phase 1: Carbon fixation
Rubisco
3 P
3 P
P
P
6
P
3-Phosphoglycerate
RuBP
6
ATP
6 ADP
Calvin
Cycle
3 ADP
3
ATP
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration
of RuBP
6 NADP
6 Pi
P
5
G3P
6
P
G3P
1
P
G3P
Output
Phase 2:
Reduction
Glucose and
other organic
compounds
The following two sides contain
background Information on why C4 and
CAM photosynthesis is adaptive in
some environments.
Photosynthetic organisms evolved for roughly
800,000,000 years in a low O2 environment.
Leaf cross section
Chloroplasts
Vein
Figure 8.3a
Mesophyll
Stomata
What happens when a plant closes its
stomata?
• Water loss decreases
• CO2 concentrations decreases
• O2 concentrations increase
CO2 O2
H2O
In photorespiration, rubisco
adds O2 instead of
CO2 in the Calvin cycle,
producing a two-carbon
compound. It uses up ATP
without producing any sugar.
Rubisco
Evolutionary Relic
of low
atmosphere
competitive
inhibition
C4
1
CO2
C4
Mesophyll Organic
cell
acid
CO2 2
Bundlesheath
cell
Calvin
Cycle
Sugar
(a) Spatial separation of steps
An enzyme in the mesophyll
cells has a high affinity for
CO2 and can fix carbon into
a four-carbon compound
even when CO2
concentrations are low.
C4 Plants
Sugarcane
Corn
Switchgrass
CAM Plants
• CAM plants open
their stomata at
night, incorporating
CO2 into organic
acids.
• Stomata close during
the day, and CO2 is
released from
organic acids and
used in the Calvin
cycle.
CO2
Organic
acid
1
CAM
Night
CO2 2
Calvin
Cycle
Day
Sugar
(b) Temporal separation of steps
CAM Plants
CAM
C3
C4
Advantages?
Disadvantages?