Bio - Lecture 7b

Bio - Lecture 7b - Photons excite electrons in pigments and...

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Sheet1 Page 1 Lecture 7b Photosynthesis occurs in two main stages: -Light-dependent reactions ->Make ATP from sunlight -Light-independent reactions ->Make sure from ATP Chloroplasts: Organelles that can make food for cells by converting light and CO2 into sugar and O2 (photosynthesis) -Found mainly in plants, but also in protista -Similar to mitochondria: ->Have a double membrane ->Have their own DNA -Different than mitochondria ->Larger than them ->More complex Light-dependent Reactions These reactions occur in the thylakoid membranes These membranes contain pigments and two different photosystems (I and II) -Photosystems are reaction centers that have a unique pair of "chlorophyll a" at the center Once enough energy is transferred into a photosystem, an e- is "Knocked off" the chlorophyll compound and the e- enters an e -This powers the enzyme ATP Synthase to make ATP -The e- leaving the chlorophyll is replaced by photolysis (breaking of H2O) thus releasing O2
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Unformatted text preview: Photons excite electrons in pigments and the electron is transferred to photosystem II (P680) where it eventually removes the e-The electron is replaced by photolysis-The electron (from chlorophyll) enters electron transport chain which brings H+ from teh stroma into the thylakoid-The H+ gradient powers the rotation of ATP Synthase, which makes ATP As the electron continues down the electron transfer chain they enter photosystem I (P700)-This photosystem reduces NADP+ to NADPH NADPH now carries energy to the light-independent reactions Light-dependent reactions made energy Light-INdependent reactions use energy-They convert CO2 into glucose They occur in the chloroplast stroma It is a cyclic pathway called the Calvin-Benson cycle **Reactants are the CO2 and NADPH **Product is glucose...
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