Multiple choice ______ is involved in the biosynthesis of IAA Boron Copper Manganese Zinc Reveal answer Fill a bubble to check yourself D Correct answer Explanation Zinc is required for the biosynthesis of IAA (Indole-3-Acetic Acid), the primary auxin in plants. Zinc acts as a cofactor for enzymes involved in tryptophan synthesis, which is a precursor for IAA production.