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Back to Part One

The second part of the photosynthesis processes are the thermochemical reactions also known as: light independent reactions, dark reactions, carbon fixation, and the Calvin cycle. *what a mouth full* The previous part, photochemical reactions can be found on another page. click here to go there now.

It takes 6 turns of the Calvin cycle for the final product to be made. Another thing to note...The term dark reactions can be misleading, in that they don't always happen in the dark. Soon after it turns dark all the energy from the photochemical reactions is used up and the "dark" reactions must stop.

Step 1- six-6-carbon molecules produced A. CO diffuses into the stroma.
B. An enzyme fuses CO to a 5 carbon molecule (RuBP) forming a 6 carbon molecule.
C. In six turns of the cycle, 6-CO bind to 6 RuBP molecules producing 6- carbon molecules.

Step 2-The six-6 carbon molecules are made into 12-3 carbon molecules
A. The 6- carobon molecules from step 1 splits and form two 3-carbon molecules. (The three carbon molecules are called phosphoglyceric acid or PGA)
B. In six turns of the cycle, 12 molecules of PGA are formed

Step 3- PGA is turned into phosphoglyceraldehyde (PGAL)
A. Each PGA receives a phosphate from ATP. (ADP left)
B. Each PGA receives a hydrogen from NADPH. (NADP left)
C. In six turns of the cycle
* 12 ATP used
* NADPH used
* 12 phosphates left
* 12 molecules PGA, NADP and ADP made

Step 4- Energy need of the cell determines what is made
A. Most of the PGAL regenerates RuBP
B. After 6 turns, some PGAL is turned into glucose