2.85 understand the role of auxin in the phototropic response of stems

This is commonly asked in exams! A few points need to be mentioned to get full marks:

What is the Role of Auxin in Phototropic response of Stems?

• Auxin is made in the tip of a root/shoot.
• When a shoot/stem is exposed to light, the shaded area accumulates more auxin and grows faster, causing it to bend towards the light.
• This is done via diffusion as the auxin diffuses from the tip down to the growing region. 
• Auxin stimulates mitosis and causes cellular elongation. 
• Auxin also changes the elasticity in cells. Increase in elasticity allows the cell to absorb more water, causing cell size to increase.

For more on Auxin and Tropisms click here.