Use of product of light reaction of Photosynthesis - ATP & NADPH

 

The use of products of light reaction

ATP, NADPH and oxygen  are the ultimate product of light reaction of photosynthesis. Out of these oxygen is  diffused out of the chloroplast while ATP and NADPH are used  to synthesize food in the form of carbohydrates or sugars . The phase of synthesis of food  is called the biosynthetic phase of photosynthesis. 

In the biosynthetic phase of photosynthesis, ATP and NADPH, are used for synthesizing the food. CO2 is fixed to form a CO2 fixation product. This stage is also called the dark phase as it is independent of light but deals with the products of the light reaction. 

👌👌Remember- Dark reaction or biosynthesis phase of photosynthesis takes place in the stroma of the chlorophyll. 

During this phase, glucose is formed by using ATP and NADPH. This process does not directly depend on the presence of light but  depends on the products of the light reaction ATP and NADPH.

The biosynthesis phase is immediately started after the light reaction  but the biosynthetic process continues for some time  and then stops. If light is available again then it starts again. Therefore the biosynthetic phase is called the dark reaction . 

Earlier it was regarded that  ATP and NADPH are used in the biosynthetic phase when carbon dioxide is combined with water to produce carbohydrates  or sugars. But scientists were trying  to find out how this reaction proceeded and what was the first product when carbon dioxide  is  combined with water by using the product of light reaction. 

Several efforts were made on how carbon dioxide is fixed to form carbohydrates or sugar during the biosynthesis phase.  Melvin Calvin worked by using radioactive 14C in the process of  photosynthesis in algae.  Malvin Calvin  demonstrated  that when carbon dioxide is  fixed in a plant then the product of  3-carbon organic acid is formed. Hence it was called the Calvin cycle. after him. This 3 carbon organic acid was 3-phosphoglyceric acid.

Now scientists started to work that in every plant the first product  was  3-phosphoglyceric acid to be formed after the fixation of carbon dioxide.

With the reference of various experiments that were conducted by the scientist, Another group of plants was discovered . In this group of plants, the first product was four carbons that were obtained  after the fixation of CO2. This product  was  oxaloacetic acid (OAA). 

Two main types of plants on the basis of carbon di oxide fixation. 

Those plants in which the first product of CO2 fixation is a three carbon containing compound called 3 phospho glyceric acid are   C3 plants  and those plants  in which the first product is a four carbon containing compound called oxaloacetic acid are  C4 plants.