Question: why auxin is present in human urine?
Answer: Human urine shows common presence of indole-3-acetic acid (IAA), compound having similar properties to plant hormone, auxin. ... It is formed by breakdown of serotonin, mainly in liver and then is excreted in the urine. Serotonin is a neurotransmitter synthesised from tryptophan, similar to how auxin is made in plants.