Question

State how concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light.

Answer 1

when sunlight is fallen on the plant the hot side is increased in pressure because of heat! therefore because of pressure difference auxin from hot side moves to shady side.

this make the behind the sun side to grow long .but in our reference frame it is appears to be bending.

hope it helps.!

Answer 2

Auxin is a hormone. Auxin synthesized at the top of the shoot of a plant. When sunlight falls on the shoot side auxin diffuses towards the dark(shady) shoot side.  This auxin concentration stimulates the cell to grow longer on the dark shoot side so that the plant appears to bend to the light