Week 8 Flashcards
How much O2 needs to be reduced to stimulate CO2 fixation?
21% to 1-2%
Where do C4 plants primarily live?
Tropical grasslands, inclusing maize and sugar cane
What is the difference C4 and C3?
C4 plants CO2 initially by an auxillary mechanism, not present in C3 plants
Can C4 plants do C3 fixation?
Yes but this process and its biochemical machinery occurs predominately in a distinct tissue location, seperate from the C4 cycle
What is the anatomy of C4 plants leaves?
1-2 concentric cylinders of cells
These are completely enclosed and radiate form bundle-sheath
The bundle-sheath encolses the vascular bundle
Where does the C3 process occur?
Predominately, though not exclusively, in the chloroplasts of the bundle-sheath cells
What is the name of the anatomy of C4 plants?
Kranz anatomy
What connects the the radiate mesophyll and cells of the bundle-sheath?
They are connected by numerous plasmodesmata, these cytoplasmic connections through which metabolites are exchanged
What is the structure of the cell-wall of the bundle-sheath?
They are heavily thickened and often suberinized, consequently they are highly impermeable to gas, carbon dioxide and oxygen
What are the metabolites that are exchanged in C4 cycle?
C4 organic acids from the mesophyll into the bundle-sheath
Pyruvate from the bundle-sheath to the mesophyll
Where and how does the C4 cycle occur?
The chloroplasts of the mesophyll operate a C4 cycle, as they possess the enzyme, PEP carboxylase, that produces a C4 organic acid, oxaloacetate from PEP, bicarbonate (HCO3-)
What is PEP?
Phosphoenolpyruvate
What is the equilibrium of Bicarbonate and dissolved CO2?
Bicarbonate and dissolved CO2 is in equlibrium
How does the plant keep CO2 levels low?
The reaction is catalysed by the enzyme carbonic anhydrase. The action of carbonic anhydrase and PEP carboxylase keeps CO2 at low levels in the mesophyll and provides the diffusion gradient for CO2 entry into the leaf air spaces
What is the difference between Rubisco and PEP carboxylase?
PEP carboxylase does not fix O2 so isnt inhibited by ambient O2