1. Photosynthesis Part 5
Page 118

2. Plants must prevent H2O loss
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

3. Adaptations to save H2O 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

4. Adaptations to save H2O 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

5. Adaptations to save H2O 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

6. (a) Spatial separation of steps (b) Temporal separation of steps
Fig
Sugarcane
Pineapple C4
CAM
CO2
CO2
Mesophyll
cell 1
CO2 incorporated
into four-carbon
organic acids
(carbon fixation)
Night
Organic acid
Organic acid
Figure C4 and CAM photosynthesis compared
Bundle-
sheath
cell
CO2
CO2
Day 2
Organic acids
release CO2 to
Calvin cycle
Calvin
Cycle
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps