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Q.
During photosynthesis when PGA is changed into phosphoglyceraldehyde, which of the following reactions occur?
NTA AbhyasNTA Abhyas 2020Photosynthesis in Higher Plants
Solution:
Photosynthesis is the process of converting light to chemical energy and using that to produce glucose.
The general word formula for photosynthesis is -
$6C O_{2}+12H_{2}O \rightarrow \, C_{6}H_{12}O_{6}+6H_{2}O+6O_{2}$ in presence of light and chlorophyll. The whole photosynthesis process is divided into two broad parts -
Light reaction where the light energy is used to generate ATP and $N A D P H_{2}$ which is later used in the Dark reaction to reduce carbon dioxide into glucose (carbohydrate) molecule. The free oxygen released as a byproduct in the photosynthesis occurs by splitting water. The oxygen of the carbon dioxide is used in making the glucose molecule through the Calvin cycle.
The second phase of the photosynthesis process is the light independent reaction where glucose is produced by fixing $C O_{2}$ . This process occurs in the stroma of the chloroplast and utilizes the products of the light reaction. $C O_{2}$ fixation is brought about by Calvin cycle or $C_{3}$ pathway. This cycle involves three mains steps of carboxylation, reduction and regeneration. The important enzyme RuBisCO catalyzes the reaction of $C O_{2}$ (1C) with 1,5-RUBP (5C) to form an unstable 6C compound which then forms 2 3C compounds - Phosphoglyceric acid (PGA) by hydrolysis. In the next step, PGA is reduced to the phosphoglyceraldehyde using ATP and NADPH. This step is reduction because NADPH donates electrons to reduce PGA.