Describe how plants react to the environmental factor of Light

One environmental factor which has an effect on a plant is light.

The stems of a plant grow towards the light, and roots grow away from the light. 

We call this phototropism

(Photo = Light       and      Tropism = movement)

As the stems want to grow towards the light, they like the light and so we call this positive phototropism.

The roots grow away from the light, therefore they do not like it and we call this negative phototropism.

The plant hormone auxin helps the plant stem grow towards the light.

Auxin makes the plant cells elongate - they grow longer. The hormone auxin acts on the side of the stem which is in the shade.

So the auxin makes the shaded side of the stem longer.

This means that one side of the stem is longer than the other and so the stem bends towards the light. 

This is because the side of the stem in the sun is shorter.