Describe an activity to illustrate the phenomenon of phototropism and explain why this occurs.

(N/A) Activity:
$(i)$ Take a potted plant and place it in a cardboard box that is open from one side. Position the box such that the open side faces a window,allowing the plant to receive light from one direction.
$(ii)$ Observe the plant for a few days. You will notice that the shoot bends towards the light source.
$(iii)$ Now,rotate the plant so that the shoot is facing away from the light. Leave it undisturbed for a few days.
$(iv)$ Observe the plant again; the shoot will gradually bend back towards the light source.
Explanation:
When growing plants detect light,a hormone called auxin,which is synthesized at the shoot tip,plays a crucial role. Auxin always diffuses towards the shady side of the shoot. This higher concentration of auxin on the shady side stimulates the cells to grow longer than those on the side facing the light. Consequently,the unequal growth causes the plant shoot to bend towards the light,a phenomenon known as phototropism.