Light Reactions of Photosynthesis

I.  Survival of nearly all organisms ultimately depends on        
    photosynthesis = main pathway by which carbon and energy enter 
    the biosphere.

     A. Autotrophs
          1. Photoautotrophs
          2. Chemoautotrophs

     B. Heterotrophs

II.  Location of Light Reactions

     A. Leaves and Stems
     B. Cells with Chloroplasts
     C. Chlorplast membranes
          1. Thylakoids
          2. Granna

III. Nature of Light

     A. Photon = E = hc/W

          1. E = quantum energy (Einsteins = joules/mole quantum)

          2. h = Planck's constant (6.626 X 10-34 joule sec)

          3. c = speed of light (2.998 X 108 m/sec)

          4. W = wave length of light (350 - 720 X 10-9 m)

IV. Light Trapping Pigments

     A. Absorb specific wave lengths & transmit the remaining wave 
        lengths of light.

     B. Chlorophyll (Plants)

          1. Chlorophyll a
          2. Chlorophyll b

     C. Carotenoids (Plants)

     D. Phycobilins (Red Algae & Cyanobacteria)

V. The "Z" Scheme

     A. Photosystem I & II = harvest light energy

          1. Thousands of pigment molecules in thylakoid membranes

          2. Absorption of photons raises energy level of pigment 
             molecules

          3. Pigment molecule returns to ground state when energy 
             is released in the form of heat and electrons.

     B. Electron transport system

          1. Coupled with PS I & II

          2. Releases energy in steps

          3. Forms ATP from ADP and some of the released energy

     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 + ATP

          4. e- => PSI + light energy => higher energy state

          5. electron transport energy reduces NADP- to NADPH

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.