alternative carbon fixation bio 201 exam1

types of plants

• C3

• C4

• CAM

what happens in C3 plants when there is no CO2 available?

• rubisco fixes O2 to RuBP instead, initiating photorespiration

• RuBP + O2 → 3PGA + phosphoglycolate

• phosphoglycolate is discarded bc it is a useless 2 c sugar

carbon fixation in C4 plants

• carbon is fixed by PEPcase (high affinity for CO2, none for O2) in the mesophyll cells

• PEPcase adds CO2 to PEP, making malate

• malate moves to BSC through plasmodesmata and broken into CO2 and pyruvate

• CO2 is fixed by rubisco and calvin cycle begins

carbon fixation in CAM plants

• stomata closed during the day and opened at night

• CO2 is fixed by pepcase in cytosol of mesophyll cells and then stored in the vacuole as malate for the night

• malate comes out of vacuole during the day, CO2 is chopped off and fed to calvin cycle which can proceed because the light reactions are happening

Enzyme fixing CO2

C3 - rubisco

C4 and CAM - pepcase

timing of carbon fixation and calvin cycle

C3 and C4 - both during the day

CAM - carbon fixation at night, calvin cycle during day

anatomy of carbon fixation and calvin cycle

C3 and CAM - both in mesophyll cells

C4- carbon fixation in mesophyll, calvin cycle in BSC

mesophyll cell location

under dermal tissue

bundle sheath cell location

between mesophyll cells and vascular tissue