Download Photosynthesis Part 5

To prevent water loss C3 plants close
stomata which results in photorespiration
 Photorespiration – plants fix O2 instead of
CO2 – producing a 2C compound
instead of G3P
 Photorespiration = use of ATP from light
reactions but with no sugar production


C4 Plants
› Corn, Sugar Cane
› Plant prefaces the
Calvin Cycle w/
reactions that
incorporate CO2
into 4C compounds
› 4C transported from
mesophyll to bundle
sheath cells to
supplies CO2 to
Calvin Cycle

C4 Plants
› PEP carboxylase is
highly efficient at
fixing CO2
› Fix CO2 rapidly to
keep high
concentration
gradient that favors
movement into stoma
› Fix large amount of
CO2 rapidly so stoma
can be closed most
of the time

CAM Plants
› Crassulacean Acid Metabolism
› Plants in arid conditions (eg. pineapples)
› Close stomata during the day – open
stomata at night
› Fix carbon in a 4C compound (like C4
plants) at night
› 4C releases CO2 for Calvin Cycle during the
day
Fig. 10-20
Sugarcane
C4
Pineapple
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
Calvin
Cycle
CAM
CO2
2 Organic acids
release CO2 to
Calvin cycle
Night
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps