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Photosynthesis160-page10 - electron transport system are...

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Photosynthesis - 10 How it works: Light energy splits water molecules (photolysis) in photosystem II producing hydrogen protons, electrons and oxygen. Light energy hitting photosystem II excites electrons in its p680 reaction center causing the chlorophyll molecule to lose electrons. They are picked up by electron carriers and passed slowly “down” the chain releasing energy as they go. Some of this energy is used to pump H + into the inner thylakoid compartment forming a H + gradient. This gradient ultimately drives the mechanism that produces ATP by chemiosmosis. (See a bit later). Light energy hitting photosystem I excites its reaction center chlorophyll electrons as well. They are picked up by other electron carriers and transferred to NADP + , which will also pick up a H + forming NADPH. The electrons released from photosystem II, once they have passed through the
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Unformatted text preview: electron transport system, are used to replace the electrons lost by photosystem I that were used to form NADPH. • Water’s electrons are passed to photosystem II. The water's H + is used in the H + gradient (and can be passed to NADP + ) and its oxygen is released as oxygen gas molecules. To summarize, the low energy electrons from water are elevated in energy by passing through both photosystem II and photosystem I on the path to being trapped by NADP + where their potential energy will be used for the high energy reduction of carbon in the Calvin cycle. Along the way, ATP, needed for the endergonic Calvin cycle, is also produced. Organization of the Light Reaction Components in the Thylakoid...
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