Write an introduction to the biosynthetic process of photosynthesis.

(N/A) The products of the light reaction are $ATP$,$NADPH$,and $O_{2}$. Of these,$O_{2}$ diffuses out of the chloroplast,while $ATP$ and $NADPH$ are used to drive the processes leading to the synthesis of food.
This is the biosynthetic phase of photosynthesis. This process does not directly depend on the presence of light,but is dependent on the products of the light reaction,i.e.,$ATP$ and $NADPH$,besides $CO_{2}$ and $H_{2}O$.
Testing: Immediately after light becomes unavailable,the biosynthetic process continues for some time and then stops. If light is made available again,the synthesis restarts. Thus,the biosynthetic phase is dependent on the products of the light reaction,which is why it is also called the dark reaction.
Research of $C_{3}$ reaction: $CO_{2}$ is combined with $H_{2}O$ to produce $(CH_{2}O)n$ or sugars,for which $ATP$ and $NADPH$ are utilized.
Scientists were interested in determining how this reaction proceeds and what the first product formed is when $CO_{2}$ is fixed.
After World War $II$,radioisotopes were put to beneficial use in research.
The discoverer: The use of radioactive $^{14}C$ by Melvin Calvin in algal photosynthesis studies led to the discovery that the first $CO_{2}$ fixation product was a $3$-carbon organic acid. He also contributed to working out the complete biosynthetic pathway,which is why it is called the Calvin cycle.
The first product identified was $3$-phosphoglyceric acid,or in short,$PGA$.
Scientists conducted experiments on a wide range of plants,leading to the discovery of another group of plants where the first stable product was an organic acid with $4$ carbon atoms. This acid was identified as oxaloacetic acid,or $OAA$.
Since then,$CO_{2}$ assimilation during photosynthesis is classified into two main types:
$(1)$ Plants in which the first product of $CO_{2}$ fixation is a $C_{3}$ acid,i.e.,the $C_{3}$ pathway.
$(2)$ Plants in which the first product is a $C_{4}$ acid $(OAA)$,i.e.,the $C_{4}$ pathway.