- Photosynthesis
Below are some notes on Photosynthesis, read them carefully. Focus on understanding the flow of  electrons through the Photosynthetic apparatus. Learn and understand the components of the apparatus and what each does, Be sure you understand how the 6 Carbon Sugar, Glucose is synthesized from CO2 and a 5 Carbon sugar.

But at all times remember; these are reactions in a Biological system, they happen Zillions of times a day inside a leaf cell.

To examine Photosynthesis, it is convenient to divide the process into reactions that occur in the Thylakoid membranes ( the "Z-scheme" or light reactions) and reactions that occur in the stroma of Chloroplasts (the Calvin Cycle or Dark reactions).

These two sets of reactions not only occur in different places within the Chloroplast, but are also biochemically different.

  • The Z-scheme uses pigments to capture light and transfer that Energy to electrons.
  • The Calvin Cycle captures Carbon from the air and reduces it to form the sugar, Glucose.

Photosynthesis

The Z - Scheme - The Z - scheme, as shown below, represents the movement of an electron during photosynthesis, both in space and with respect to the free Energy of the electron. Electrons are removed from water (Water is oxidized) raised in energy (twice), passed from molecule to molecule until the electron (and its Energy) are used to reduce NADP+ to from NADPH. The image below is of the Thylakoid membrane, the Z - scheme is in red (it actually looks more like an N to me).

The components of the Photosynthetic apparatus: (Mouse over the terms to highlite).
Antenna complexes -The two antenna complexes (one for each Photosystem) contain Chlorophyll, accessory pigments, and proteins. They collect radiant Energy to excite rxn center chlorophylls.
Photosystem I (PS I) - PS I is very much like PS II with its own proteins, ions, a molecule called phylloquinone, a reaction center chlorophyll, P700 , and Ferredoxin. Ferredoxin is the iron-containing molecule that passes the excited electron to NADP+.
Photosystem I I (PSII) - PS II contains proteins, pigments, metal and other ions, Plastoquinones, Pheophytin, and a special reaction center chlorophyll molecule, P680 .
The Cytochrome B6/F Complex - The cyt b6-f complex contains proteins, metal ions and a special iron-sulfur protein. It also translocates protons across the Thylakoid membrane, much like the etc.
The Oxygen Evolving Complex (OEC) - The OEC is part of PS II. It contains several Mn and Fe containing proteins which oxidize water (a tough thing to do) and generate O2.
ATPase - ATPase is an Enzyme that generates ATP from ADP + Pi using chemiosmotic energy from the Proton gradient created by spitting water and the translocation of Protons.
The path of electrons: Electrons move from Water to PS II to the Cytochrome B6/F complex to
PS I and finally to NADP to make the reduced Energy carrier, NADPH.

To see an animation of the the process, click here

Summary - At Photosystem System II, radiant Energy from the sun is transfered to a reaction center electron, raising its Energy level. As the electron moves down an Energy gradient from PS II to the Cytochrome cytb6-f complex (a series of re/dox reactions, like the electron transport chain), a Proton (H+) is transfered across the Thylakoid membrane by the complex. These protons will be used to generate ATP, as they move thru an ATPase back out into the stroma of the Chloroplast. ATP is generated by the Photosynthetic apparatus in this way is called Photophosphorylation. The electron then travels to PS I, where it is again "excited" by Sunlight. The High Energy electron is transferred to NADP+, froming NADPH (a reduction reaction, a net gain of chemical Energy).

Photophosphorylation