2.15 - Alternative Paths for Photosynthesis Flashcards
Compare the cyclic and non-cyclic electron flow.
alt. paths for photosynthesis
Cyclic-> when the light rxns occur in a continuous cycle, ie: after photosystem 2, the electron goes to the primary electron acceptor but instead of Fd taking the e- to NADP+ reductase, it brings it back to the cytochrome complex. This produces more ATP and no NADPH.
Non-Cyclic-> the light rxns occur as normal in a linear fashion.
Why do plants switch between cyclic and non-cyclic electron flows?
It depends on what is needed.
If more NADPH is required then, the light rxns occur as normal, in a linar chain.
If more ATP is required, then the light rxn brings the energized electron back into the cycle to repeat the process which creates only more ATP
What climate are C3, C4, and CAM plants located in?
C3-> moderate temperature environments, ie. southern ontario
C4-> tropical like, hot, humid and dry environments
CAM-> desert like conditions
What is a C3 plant?
- a plant that contains a 3 carbon starting molecule (3PG) in the calvin cycle
- it closes it’s stomata if the temp gets too hot or dry which causes less intake of CO2.
- This causes a slow calvin cycle
What is a C4 plant?
What are it’s qualities?
- Rubisco begins to react with O2 which is no good (photorespiration)
- an extra step is added: a catalyst called PEP carboxylase is added take PEP and turn it into oxaloacetate, maltate, then CO2. Then that is added to the calvin cycle
- the calvin cycle is also pushed further into the leaf to protect it. It becomes surronded by the bundle sheeth cells
What are CAM plants?
- these are plants that only open their stomata at night b/c it is impossible to open them during the day due to extremely warm climates
- they only take in CO2 at night where there is no sunlight so light rxns cannot be used
- when the CO2 is taken in, it is converted into organic acids, which are then convered back into CO2 during the day so the light rxns can still occur. And the stomata remains closed
