How does phototropism occur?

Auxin is a growth hormone in that is found in plants. When it is released, it causes the affected cells to elongate. Auxin is released along the shaded side of the plant, at the shoot tip. This causes the cells at the shaded side of the plant to elongate so the shoot top leans to one side, towards the sun. This increase the surface area of the plant that is exposed to sunlight so more photosynthesis can occur.