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Ch. 10: Photosynthesis (Ps) • Ps is the process that converts solar energy into chemical energy – Directly or indirectly, Ps nourishes almost the entire living world – Ps occurs in plants, algae, certain other protists, and some prokaryotes • Autotrophs sustain themselves without eating anything derived from other organisms – Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules – Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules • Heterotrophs obtain their organic material from other organisms – Heterotrophs are the consumers of the biosphere – Almost all heterotrophs, including humans, depend on photoautotrophs for food…show more content…
A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes • Photosystem consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes – Light-harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction center There is electron flow in the photosystems & the production of ATP & NADPH using light energy © 2011 Pearson Education, Inc. • A primary electron acceptor in the reaction center accepts excited electrons & is reduced as a result • Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is 1st step of Light Reactions • There are 2 types of photosystems (PS) in the thylakoid membrane: • Photosystem II (PS II) functions 1st (the # reflects order of discovery) & is best at absorbing a wavelength of 680 nm • The reaction-center chlorophyll a of PS II is called P680 • Photosystem I (PS I) is best at absorbing a wavelength of 700 nm • The reaction-center chlorophyll a of PS I is called P700 © 2011 Pearson Education, Inc. Linear Electron Flow • A photon hits a pigment & its energy is passed among pigment molecules until it excites P680 • An excited electron from P680 is

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