Photosynthesis Photosynthesis in Nature The pathways of Photosynthesis 6CO H 2 O  C 6 H 12 O 6 + 6H 2 O + 6O 2

Photosynthesis in nature Producers are plants and other autotrophs Key organelle- chloroplast Location hierarchy plant leaf mesophyll cell chloroplast thylakoid memb. stroma

Chloroplast Ultrastructure 4-7 μm 3 functional compartments 1) intermembrane space 2) thylakoid lumen 3) stroma

The Nature of Sunlight Electromagnetic energy- wave & particle Photosynthesis uses visible light Red and violet most efficient Green reflected?

Role of Pigment Molecules Substances that absorb visible light Chlorophyll a-most important Accessory pigments chlorophyll b and carotenoids Organized into photosystems yy

Photosystems: light-harvesting complexes of the thylakiod membrane Antenna complex- contains ch. a, ch. b and carotenoids Reaction center chlorophyll-a single specialized ch. a Primary electron acceptor-traps e- released from the reaction center

Photosynthetic Unit Photosystem I- ch. a-known as P700 Photosystem II- ch. a-known as P680 P700 and P680 identical, but associated with a different protein Thousands of photosynthetic units/chloroplast

The Pathway of Photosynthesis The light reactions (thylakoid) 1) noncylic electron flow 2) cyclic electron flow The Calvin cycle (stroma)

The Light Reactions Incorporates photolysis and chemiosmosis Occurs in the thylakoid membrane and lumen Produces ATP and NADPH

Photolysis 2H 2 O  4H + + 4e- + O 2 Occurs in the lumen Source of e- for the ETC Oxygen is a byproduct

Linear Electron Flow (Noncyclic electron Flow) Produces NADPH Produces O 2 Occurs in the thylakoid membrane Moves e- from water to NADP

Cyclic Electron Flow Simplest pathway Uses photosystem I Generates ATP only Electron starts and ends in chlorophyll a Function: to continue to produce ATP when NADP is in excess

Photosynthesis vs. Cellular Respiration (chemiosmosis) Photosynthesis Source of H + and e- is water Light provides the energy ATP synthase ETC present Proton motive force Cellular Respiration Source of H + and e- is food Chemical bonds from food provide the energy ATP synthase ETC present Proton motive force

Calvin Cycle Three phases 1) Carbon Fixation 2) Reduction 3) Regeneration of RuBP

Photorespiration, C 4 Plants, and CAM Plants Photorespiration-evolutionary relic Role of Rubisco CAM plants-specially adapted for arid environments, stomates open at night C 4 plants-anatomical and chemical adaptations for dry climates

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