Photosynthesis is a complex and lengthy process. In 1905 A.D. Blackman divides the process into two phases namely: I. Light Phase and 2. Dark Phase. Both the phases are described here:
(a) Light Phage: Light is essential for this phage. In this process, water breaks down to O2, e- (electron) and Hydrogen (proton = H+) with the help of energy obtained from sunlight. Such break down is called as Photolysis or Photolysis of water. A large amount of light energy is assimilated into chemical compound named ATP (Adenocine Tri Phosphate) and NADPH2 (Nicotinamide Adenocine Dinucleotide Hydrogen Phosphate) as chemical energy.
ATP and NADPH2 are called assimilatory Power. This process of formation of ATP by using light energy is called Photophosphortlation. Photophosphorilation may be of two types – Cyclic and Non-cyclic. Two pigment systems (Pigment system-1 and Pigment system-2) control the light phase of photosynthesis.
Fig: A short representation of the process of photosynthesis
(B) Dark Phase: Light is not required in this process. ATP a NADPH2, produced in light phase, are utilised in this process to manufacture carbohydrates. The process of manufacture of carbohydrate is as follows: – CO2, from the atmosphere, enters inside the leaf thus in the cell, through stomata. CO2 combined with Ribulose 1,5 Diphosphate, present in the cell produces an unstable compound named Keto acid. This Keto acid, later on, breaks down into two molecules named a 3 -Carbon compound named 3-Phosphoglyceric acid (first stable compound). This Phosphoglyceric acid then converted to 3- Phosphoglyceraldehyde and Dihydroxy Acetone Phosphate utilising ATP and NADPH2, produced earlier in the light phase. By several successive reactions, these 3-Phosphoglyceric acid and Dihydroxi Aceton Phosphate ultimately produce Carbohydrate (Sucrose-Sugar) in one side and Ribulose 1,5, Diphosphate on the other side.