Describe the plant secretion found in human urine.

(N/A) The plant hormone found in human urine is $Indole-3-acetic \text{ acid } (IAA)$, which is the most common naturally occurring auxin in plants. $IAA$ was first isolated from human urine. It is a phytohormone that promotes cell elongation, root initiation, and apical dominance in plants. Its presence in human urine is attributed to the consumption of plant-based foods, as the human body does not synthesize $IAA$ endogenously.