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BIO120H1 (305)
Chapter 3

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James Thomson

Chapter 3 Adaptations to the Physical Environment Light Energy and Heat 3845 A 4647 C 4858 AGreen plants will primarily absorb light of wavelengths of 400 nm violet and 700 nm red belonging to the photosynthetically active region of the spectrum Irradiance intensity of light of all wavelengths hitting a surface Albedo proportion of light reflected by a surface albedo of waterplantsground soil Chlorophyll is a plants primary pigment it absorbs red and violet light and reflects blue and green thus most plants are primarily green in colour Plants also have accessory pigments namely xanthophylls and carotene which absorb and reflect different wavelengths Most deepsea algae can absorb green light and reflect red and violet this is because water is more likely to absorb longer wavelengths like red especially with increasing depth The first stage of photosynthesis is the collection of light This is accomplished by a plants photosystem consisting of chlorophyll and accessory pigments The light reactions are a series of chain reactions which eventually end with the creation of ATP and NADPH H2O is required for these reactions to proceed and O2 is released as a byproduct The Calvin Cycle produces PGAL or G3P multipurposed energy source Carbon fixation is the first step in the Calvin cycle CO2 is added to RuBP and undergoes a series of reactions catalyzed by rubisco The cycle must occurs three times with three CO2 molecules reacting with three RuBP molecules to make one G3P this is because one of the produced G3P can be used for energy needs while the rest are recycled back into RuBP Photorespiration may occur when oxygen levels are particularly high in the plants cells The oxygen competes for rubiscos active site impeding carbon fixation Considerably less G3P is produced during photorespiration compared to photosynthesis making it inefficient C3 plants can keep their levels of CO2 high by simply keeping their stomatas open as they often live in moist environments where water levels arent an issue C4 plants often found in dry environments overcome photorespiration by storing CO2 in the form of malate CO2 is taken in and reactions with PEP in the mesophyll layer to produce oxaloacetate which is then converted to malate and moved to the bundle sheath cells by plasmodesmata for storage When CO2 is required malate is carboxylated relasing CO2 and a pyruvate the pyruvate travels back to the mesophyll where it is converted back to PEP T
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