1. Variations of Photosynthesis
Chapter 10

2. What you need to know!
The metabolic adaptations of C4 and CAM plants to arid, dry regions.

3. Types of Photosynthesis
C3 Plants: most dicots, average flowering plants
C4 Plants: Most monocots, grasses, grains, lilies
CAM: cacti and succulents

4. Photorespiration
RuBisco has a strong affinity towards O2 which leads to the formation of undesired products that are degraded in peroxisomes
This lowers efficiency of the carbon fixation
It occurs in C3 plants where light Rx and Calvin Cycle take place in the same chloroplast
Competitive enzyme inhibition

5. C3 Photosynthesis
“Regular” photosynthesis: open stomata during the day  running all Rxs side by side (including photorespiration)
Side note:
ATP are used for carbon fixation and all other cellular demands
Respiration in mitochondria are used to cover ATP demands
Occurs day and night

6. C4 Photosynthesis
More efficient variation of PS that prevents photorespiration
It includes 2 types of photosynthetic cells
Mesophyll cells
Bundle sheath cells
Chloroplasts in mesophyll cells only do Light Rxs
Bundle sheath cells do the Calvin Cycle.

7. C4 Photosynthesis
CO2 is bound by enzymes called PEP carboxylase to another acceptor producing OAA (Oxaloacetate) which is converted into malate (both are C4 molecules)
Malate is transported to bundle sheath cells where they do the Calvin Cycle
CO2 is released to the regular RuBP.
No light Rx take place in the bundle sheath cells
No O2  no photorespiration

8. CAM Photosynthesis Crassulacean Acid Metabolism
Stomata only open at night (colder, less transpiration)
Binding CO2 to an intermediate molecule
OAA then malate (PEP – Carboxylase)
Malate releases CO2 during the day with stomata closed (reduced water loss)
Limited storage of CO2 in malate makes this less efficient (succulents and cacti grow very slowly)