The Dark Reactions, named
after Melvin Calvin who discovered it, are among the most difficult to
explain. The Dark Reactions do not necessarily need light to complete the
process, unlike in the Light Reactions. The leaf takes in CO2 from
the atmosphere. Then a chemical called RDP (which is a 5-carbon sugar and
also a CO2 acceptor) combine to make an unstable 6-carbon sugar
called RDPCO2. Since this compound is unstable, it splits into two PGA
compounds, or two 3-carbon sugars. The two PGA compounds go two separate
ways. One PGA molecule joins together with the ATP energy and the NADPH2
(the hydrogen stored from the light reactions) to form PGAL. PGAL is a
nutrient that further breaks down and releases the RDP to be recycled and
used again in the Dark Reaction. The PGAL also forms C6H12O6,
which is glucose, or food that the plant uses. Also, some water molecules
are released from the other PGA molecule as a bi-product and released as
oxygen into the air during transpiration.
Some links to places like this
are:
http://khanda.unl.edu/~nikku/psynthesis.html
