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chapter 10 (photosynthesis (thylakoids (light reactions in thylakoid…
chapter 10
photosynthesis
chloroplasts - organelle where sunlight is converted into chemical energy and is stored in sugar and other organic molecules
autotrophs( most plants)- self feeders produce organic molecules from CO2 and other raw inorganic materials
heterotrophs (decomposers)- obtain organic material by second mode of nutrition
in eukaryotes that are autotrophs photosyntheis occurs in chloroplasts organelles containing thylakoids. stacks of thylakoids form grana
thylakoids
light reactions in thylakoid membranes split water releasing O2, producing ATP and forming NADPH
chloroplasts split water into hydrogen and oxygen. incorporating the electrons of hydrogen into sugar molecules
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light
light is a form of electromagnetic energy the colors we see are visible light including those wavelengths that drive photosynthesis.
pigments absorb light of specific wavelengths; chlorophyll a is the main photosynthetic pigment in plants. other accessory pigments absorb different wavelengths of light and pass energy onto chlorophyll
pigments go from a ground state to an excited state when a photon of light boosts one of the pigments electrons to a higher energy orbital. ecited state is unstable
a photosystem is composed of a reaction center complex surrounded by a light harvesting complex that funnel the energy of photons to the reaction center complex. special pair of chlorophyll a molecules absorb energy one of its electrons is boosted to a higher energy level and transfered to the primary electron acceptor.
photosystem II contains p680 chlorophyll a molecules in the reaction center complex, photosynthesis I contains p700 molecules
linear electron flow during the light reactions uses both photosystems and produces NADPH, ATP, and oxygen cyclic electron flow employs only one photosystem,producing ATP but no NADPH or O2
calvin cycle
occurs in the stroma , using electrons from NADPH and energy form ATP. one molecule of G3P exits the cycle per three CO2 molecules fixed and is converted to glucose and other organic molecules
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carbon fixation
C3 plants close their stroma on hot days conserving water but keeping CO2 out and O2 in. photorespiration can occur under these conditions: rubs=isco binds O2 instead of CO2 consuming ATP releasing CO2 without producing ATP or carbohydrate.
C4 plants minimize the cost of photorespiration by incorporating CO2 into four carbon compounds in mesophyll cells. compounds are exported to bundle sheath cells where they release carbon dioxide for use in the calvin cycle
CAM plants open their stomata at night incorporating CO2 into organic acids which are stored in mesophyll cells. during the day the stomata is closed and the CO2 is released from the organic acids for use during the calvin cycle