active cell-to-cell movement of auxin

diffusion, which is facilitated by auxin influx carriers, allow auxin entry into cell

when auxin is in cell, it disassociates

the negatively charged ions cannot exit the cell

auxin efflux carriers use ATP to pump out these ions

the carriers are localized on a certain side of the cell, which directs flow of ions in required direction. this ensures directionality

position of the carriers can be changed depending on different factors

creates a higher concentration of auxin in the intercellular space of cell & lower concentration in adjacent cell

auxin flows down concentration gradient, entering adjacent cell & causing an auxin influx

coordination between cells can lead to localization of carriers on the same side

as auxin transport continues, auxin accumulates on the shaded side

this results in greater elongation of cells on shaded side of stem, resulting in greater curvature towards the light source