Regulation of Photosynthesis PLS360

Regulation of Photosynthesis Quiz question Light energy is...

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Regulation of Photosynthesis Quiz question- Light energy is transferred through light harvesting complex as: energy resonance Quiz question- Thylakoid membranes are important for: organizing the components of electron transport chain Quiz question- Carbon fixation requires the expenditure of ATP molecules, which are generated by: equalizing the proton gradient across the thylakoid membrane Photosynthesis in the real world Plants do not control their environment and so must adjust their physiology to prevailing conditions -Adaptation vs. acclimation (Genetic changes) (Physiological changes that occur in an individual) Photosynthesis is a complex process and is affected by: -Light level -Temperature -CO2 concentration Figure 9.6 Light compensation point (CO2 uptake = CO2 evolution) Adaptation vs. acclimation Figure 9.7 and 9.9 (Sun plant grown at 920 irradiance, Shade plant grown at 92 irradiance) Strategies to maximize light Direct sunlight is far above saturation of photosynthesis, but most chloroplasts are not in direct sunlight Chloroplasts are shaded by other plants, other leaves, or other chloroplasts Steal light: growth habits such as height and branching Follow the sun: diaheliotropism (aka phototropism)- bending/growing toward the light [perpendicular to sun] Collect light: Light focusing and light scattering through leaf structure Positioning of chloroplasts Change composition and size of light harvesting complex *CQ: All else being equal, plants always want more light: False Too much of a good thing? Figure 9.11
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Light reactions Routes for light energy -Photochemical quenching -Emit light (fluorescence) -Emit heat (non-photochemical quenching) -Generate reactive/radical oxygen species (ROS) Participate in photochemistry (photochemical quenching) Re-emit as fluorescence Dissipate as heat (NPQ) Transfer electron to oxygen generating ROS Photoinhibition High light induces two types of Photoinhibition- light-induced reduction in photosynthesis Dynamic- changes in the light harvesting complex to increase NPQ (heat generation) [good] Chronic- ROS-induced damage to PSII requiring disassembly and repair [bad] Reactive Oxygen Species ROS can change many biological molecules- lipids, proteins and nucleic acids Carotenoids combat ROS production in 2 ways: -Carotenoids are antioxidants and scavenge ROS
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