Plant Hormones (Tropisims and Auxins)

• Plants rely entirely on hormones
• Plant hormones act locally and don't flow around the entire organism
• Auxin controls the growth at the ends of the shoots and roots
• 1. When auxins are produced, they dissolve and diffuse backward along the roots/shoots. In a shoot, the auxin stimulates growth but in a root it inhibits growth.
• Auxins always accumulate on the shaded side and lower side.
• Shoots are positively phototropic as they grow towards the light but negatively geotropic as they grow away from gravity.
• In shoots, the auxin will accumulate in the shaded side. As auxins stimulate growth, the plant will grow faster on the shaded side. This means the shoot will curve towards the light.
• In shoots the auxins stimulate growth more on the lower side, so that side will grow faster and the shoot will grow upwards away from gravity.
• Roots are negatively phototropic and positively gravitopic.
• In a root auxins inhibit growth so if a root is exposed to light, the upperside will grow faster and curve away from the light. This curve downwards also means the root will curve towards gravity and grow downwards.