Photorespiration (Exam 2) Flashcards
Why does photorespiration occur?
O2 (instead of CO2) is fixed by Rubisco to RUBP
how often does photorespirtion occur?
20-25% of the time
when the calvin cycle evolved,
O2 concentrations were low
3.2 bya =
no free O2 in the atmosphere
increase temp =
increase oxygenase rxn (rubisco)
(in photoresp) plant recovers 3PGA from
phosphoglycolate thats made in the process (photoresp) & uses 1 net ATP
photoresp requires
3 organelles:
- ) chloroplast
- ) peroxisome
- ) mitochondria
photoresp slows down
photosynthesis & uses ATP
photoresp becomes more common @
high temperatures (>30* C)
C4 plants virtually eliminate
photorespiration by concentrating CO2 in the bundle sheath cells
budle sheath cell =
where calvin cycle occurs
C4 chloroplasts have fewer
numbers of thylakoids
draw the photorespiration cycle
plzzzzz
in C4 plants, light reactions occur in
mesophyll cells
(C4) the first product of fixation =
oxaloacetate (OAA) (4 carbons)
(C4) how is OAA made?
bicarbonate (HCO3-) is fixed to PEP in the cytoplasm of mesophyll cells to make OAA
C4 rxns require
the use of ATP
C4 rxns lose
2 phosphates
C4 plant examples
corn, sugarcane, euphorbia, portuluca
C4 plants are active
in hot weather (temperate or tropical)
C4 plants evolved
30 mya
when C4 plants evolved
CO2 was so low
C4 plant %
1% of land plants
C4 plants separate
initial carbon fixation & light-dep rxns from calvin cycke
anatomy of C4 leaves
Kranz “wreath” anatomy
(In C4) bundle sheath cells carry out
calvin cycle (light indep rxns)
(In C4) mesophyll cells carry out
light dep rxns + C4 rxns (first fixation event in cytoplasm)
draw C4 reaction scheme
plzzzzz
CAM aka
Crassulacean Acid Metabolism
CAM first noted in
Kalanchoe
CAM utilizes __ ________, but…
C4 fixation, but occurs at night
CAM converts
OAA to malate (or other C4 acids) & is stored in the vacuole of the mesophyll cell overnight
why do CAM plants store malate overnight?
to reduce transpiration
(CAM) during the day…
stomata are closed & the C4 acids are moved from the vacuole to the cytoplasm where they are decarboxylated (CO2 in released)
(CAM) in the morning
CO2 concentrations are high
(CAM) in the afternoon
photorespiration can occur
(CAM) during the day
(CAM) calvin cycle & light-dep rxns occur
do CAM plants have Kranz anatomy?
NO
(CAM) C4 rxns in
photosynthetic chlorenchyma
(CAM) rxns all occur
in the same cell!
(CAM) plants live in
arid environments or microsites
(CAM) plant examples
mostly tropical epiphytes (grow on other plants but are not parasites)
agave, orchids, cactus, tillandsia, bromeliads
