Mader Biology 8th Ed Photosynthesis Two Reactions Light Reaction Energy Harvest Dark Reaction Calvin Cycle Carbon Fixation Mader Biology 8th Ed Photosynthesis Light Reaction Chlorophyll absorbs solar energy and energizes electrons Electrons move down electron transport chain Solar energy ATP NADPH Calvin Cycle Reaction CO2 is taken up and reduced to a carbohydrate Reduction requires ATP and NADPH ATP NADPH Carbohydrate Mader Biology 8th Ed Photosynthesis Overview Mader Biology 8th Ed Photosynthesis Overview Mader Biology 8th Ed Light Reactions Light reactions consist of two electron pathways Noncyclic electron pathway Cyclic electron pathway Both pathways produce ATP but only the noncyclic pathway also produces NADPH Mader Biology 8th Ed Noncyclic Electron Pathway Electron flow can be traced from water to a molecule of NADPH Uses two photosystems PS I and PS II Photosystem consists of pigment complex and electron acceptor molecules in the thylakoid membrane Pigment complex helps gather solar energy Mader Biology 8th Ed 250 400 Mader Biology 8th Ed Mader Biology 8th Ed Mader Biology 8th Ed Mader Biology 8th Ed Cyclic Electron Pathway Cyclic pathway in PS I Pathway only results in ATP production and not in NADP reduction or O2 release Thought to be the older mechanism Provides additional ATP Mader Biology 8th Ed Noncyclic Electron Pathway Mader Biology 8th Ed Cyclic Electron Pathway X Mader Biology 8th Ed Mechanical Analogy for the Light Reactions Mader Biology 8th Ed How does the ATP mill work Stroma pH 8 2 photons 2 photons pH 5 in light Mader Biology 8th Ed ATP synthase Thylakoid space Thylakoid membrane Stroma Mader Biology 8th Ed Stroma Mader Biology 8th Ed