Question

A young green plant receives sunlight from one dirction only. what will happen to its shoot and roots why?

Answer 1

the direction from which the light is coming will be followed by the shoot . that is the shoot will move upward in the direction of sunlight and the shoot will go below the ground.

Answer 2

The shoot of the plant will ultimately grow in the direction of sunlight whereas the root will grow inside the ground away from it. 
This movement is known as the Phototropic movement.
When light falls on a plant, a hormone called auxin which is synthesised at the tip of the plant helps the cells to grow longer.