AIIMS 2018 Botany Auxins MCQ Question

Auxin, a class of plant hormones that regulate growth, was first isolated from human urine, specifically from the compound indole-3-acetic acid (IAA), which is a naturally occurring auxin. Option B, callus, refers to a mass of undifferentiated plant cells that can produce auxins but was not the source of the initial isolation. Coconut milk (option C) contains cytokinins, another type of plant hormone, but is not related to the discovery of auxin. Thus, option A is the correct choice as it directly relates to the historical context of auxin's isolation.