Final answer:
PABA and 2-amino-4-hydroxy-6-methyl pterin are essential precursors or coenzymes for the biosynthesis of folic acid in the body.
Step-by-step explanation:
The substances that are precursors or coenzymes essential for the biosynthesis of folic acid in the body are p-amino benzoic acid and 2-amino-4-hydroxy-6-methyl pterin. These components contribute to the synthesis of folic acid along with glutamic acid. Folic acid is a vitamin for human beings, while microorganisms synthesize their own folic acid from PABA.