LIFE 102 Lecture Notes - Carbon Fixation, Cell Membrane, Signal Transduction
Document Summary
Concept 10. 4: alternative mechanisms of carbon fixation have evolved in hot, arid climates. Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis. On hot, dry days, plants close stomata, which conserves h2o but also limits photosynthesis. The closing of stomata reduces access to co2 and causes o2 to build up. These conditions favor a seemingly wasteful process called photorespiration. In most plants (c3 plants), initial fixation of co2, via rubisco, forms a three-carbon compound. In photorespiration, rubisco adds o2 instead of co2 in the calvin cycle. Photorespiration consumes o2 and organic fuel and releases co2 without producing atp or sugar. Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less o2 and more co2. Photorespiration limits damaging products of light reactions that build up in the absence of the calvin cycle.
