Ch3 Adaptations to the Physical Environment3.pdf

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Spencer Barrett

 to assimilate eff., plants pack mesophylls w/ large amounts of Rubisco (makes up 30% of dry weight of some species)  binds O a2d CO (pa2t. under high O and lo2 CO conc., and2esp. at high leaf temp.)  reverses light rxns when Rubisco binds O instead of CO 2 2  2 G3P  CO + R2BP  resembles respiration (uses O and2produces CO ; requir2s ARP and NADPH from light rxns) o photorespiration  the tendency of Rubisco to undergo this rxn (which partially undoes what it accomplishes when it assimilates C) makes photosynthesis inefficient and self- limiting  photorespiration is a wasteful and counterproductive process, and C assimilation therefore tends to inhibit itself as levels of CO dec2ine in the leaf tissue Modification of Photosynthesis in Environments with High Water Stress  plants must maintain high CO conc2 in leaf cells  some keep stomates open to allow free gas exchange b/w atm.  but transpiration leads to water loss  detrimental in hot/dry envmts  CO 2nters plants through diffusion (even though CO conc. is2only 0.038% in atm; but atm-to-plant difference is much less than plant-to-atm)  the atm. diff drives water out of plants too C 4hotosynthesis  has additional step to the initial assimilation of CO in 2 phot3synthesis  CO 2s first joined w/ a three-carbon phosphoenol pyruvate (PEP
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