Photosynthesis Page 4

Light Reactions of Photosynthesis

• V. The "Z" Scheme
• B. Electron transport system
• 1. Coupled with PS I & II
• 2. Releases energy in steps
• 
• C. Cyclic ATP formation (PS I)
• 
• 1. Oldest means of ATP formation
• D. Noncyclic ATP formation (PS I & II)
• 
• 1. Photolysis = Water molecule is split to release 2 H+ + O- + e-
• 2. e- => PSII + light energy => higher energy state
• 3. electron transport => lower energy state + H+ pumped
• 4. e- => PSI + light energy => higher energy state
• 5. electron transport energy reduces NADP- to NADPH
• 6. ATP synthesized via ATPsynthetase as H+ diffuses down gradient
• VI. Evolution of Photosynthesis transformed Earth's atmosphere from one that had 0% to current 20% Oxygen by volume between 2 & 1.5 billion years ago.
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