Page 4 - LN-PHOTOSYNTHESIS IN PLANTS

evolves O 2 as its oxidation product.
Thus, he inferred that O 2, which is evolved by the green plants comes from the water
(H 2O) not from the CO 2 N (later proved by the use of radioisotopic techniques).
Thus, the overall reaction of the photosynthesis is represented as

It is also to be noted that it is not a single step reaction that determines the process
of photosynthesis instead it is a multi step process.
Conclusion
He concluded that the light is necessary to oxidize the photosynthetic substrate (H 2S
– Photosynthetic bacteria) and (H 2O-Green plants) and release byproduct sulphur
and 02 in Bacteria and Green plants respectively.
In absence of sunlight, this process does not occur.
Chloroplasts: The Site of Photosynthesis
These are the green plastids that function as the site of photosynthesis, i.e., helps in
the synthesis of organic food.
The process of photosynthesis takes place in the green leaves of the plants because
chloroplasts are abundantly present in the mesophyll cell of the leaves.
Chloroplast aligned themselves with their flat surfaces parallel to the walls of the
mesophyll cells under optimum light intensities and they would be perpendicular to
the walls of the mesophyll cells when the intensity goes very high.
Chloroplast is double membranous, DNA containing cell organalle.
Internally, a chloroplast contains a proteinaceous matrix or fluid called stroma, the
membrane system called lamellae or thylakoids. At some places, the thylakoid gets
aggregated to form stacks of discs, called
grana.

The clear division of labour occurs within the chloroplasts, i.e., the membrane
system is responsible for the synthesis of ATP and NADPH (photochemical phase),
whereas the stroma has enzymes, which are responsible for the reduction of carbon
dioxide into carbohydrates and formation of sugars.
As the former sets of reactions are dependent on light so are called light reactions
while, the latter is dependent on the products of light reactions, i.e., ATP and NADPH
(and independent from direct sunlight), thus are called dark reactions.
It is to be noted that dark reactions does not rely that they occur in darkness or that
they are not light dependent.
Pigments Involved in Photosynthesis