Introduction:
Photosynthesis is perhaps the most important of the many interesting
photochemical processes known in biology; not only was the evolution
of the Earth´s atmosphere dependent on it, but also animal life
derives energy from the Sun, via photosynthesis, by eating plants. It
is estimated that the total mass of organic material produced by green
plants during the biological history of the Earth represents 1% of the
planet´s mass, and that photosynthesis fixes annually the equivalent
of ten times Mankind´s energy consumption.
From the point of view of organic synthesis, the overall process
consists of the formation of carbohydrates by the reduction of carbon
dioxide:
The essence of the process is the use of photochemical energy to split
water and hence to reduce CO2. Molecular oxygen is
liberated in the reaction, although it appears at an earlier stage in
the sequence of steps than the reduction of CO2. True
photochemical processes appear to produce compounds of high chemical
potential, which can drive the synthetic sequence from CO2
to carbohydrate in a cyclic fashion.