How does energy transformation happen in photosynthesis?
During photosynthesis solar energy is converted into chemical energy in the form of energy rich bond of ATP molecule.
ATP (Adenosine triphosphate) and ADP (Adenosine diphosphate) molecules are termed currency of energy. ADP molecule is converted into ATP molecules, whenever energy is available in certain exothermic reactions of metabolism.
ATP molecules are store- house of energy. ATP molecule is broken down into ADP molecule in presence of enzyme ATPase, releasing energy whenever energy is required.
The synthesis of ATP molecules, utilizing solar energy during photosynthesis, is termed photo-phosphorylation.
These ATP molecules produced during light reaction of photosynthesis are utilized in dark reaction of photosynthesis (Calvin cycle).
ATP molecules synthesized during photo-phosphorylation may also be used in other metabolic reactions.
Photo-phosphorylation is of 2 types, i.e. Cyclic and Non-cyclic photo-phosphorylation.
Chlorophyll molecules entrap solar energy . There are 2 types of photo-systems in chlorophyll. These are photo-system -I and photo-system-II .
The electrons of chlorophyll molecule of photo-system I get excited which pass through series of electron carriers in electron transport system arranged in the order of decreasing energy level.
During the passage of electrons from carriers of higher energy level to the carriers of lower energy level, the energy is lost which is utilized for converting ADP molecule into ATP molecule.
Photo-system I is concerned with light reaction of photosynthesis only, constituting cyclic photo-phosphorylation.
The electron transport during Photo-system II results in the synthesis of NADPH2 in presence of enzyme NADP reductase. NADPH2 is used in reduction reaction of Calvin cycle.
Both Photo-systems participate in non-cyclic photo-phosphorylation that results in the synthesis of NADPH2 in addition to the synthesis of ATP molecules.