Auxin is a Plant Hormone
1. Auxin controls growth in the tips of roots and shoots
2. It responds to moisture, light and gravity.
Shoots Grow Towards Light
1. When a shoot tip is exposed to light, more auxin is on the shadey side.
2. Therefore, there is more growth on the shaded side causing the shoot to bend and grow towards the light.
Shoots Grow Away from Gravity
1. If a shoot is growing on its side, gravity creates an unequal spread of auxin, with more growing on the lower side.
2. This causes the shoot to grow away from gravity as the lower side is growing faster.
Roots Grow Towards Moisture
1. The more moisture, the more auxin. So if either side of a root have different levels of moisture, the side with the more moisture will have more auxin.
2. This means that side will grow faster and the root will grow towards the moisture.