Hormonal Coordination in Plants and Animals

Core concept

Auxin, produced at a plant's shoot tip, moves to the shaded side of the stem when light hits from one direction, causing greater cell elongation there and bending the shoot towards the light source. In humans, the pancreas releases insulin to regulate blood sugar, the adrenal glands release adrenaline during stress or danger (triggering the 'fight or flight' response, increasing heart rate and alertness), and the thyroid gland releases thyroxine to regulate metabolism — each hormone acting on specific target organs even though it travels throughout the entire bloodstream.