L8 - Tropisms

• Tropism


  A plant growth response to a one-sided stimulus
• When plants grow towards a one sided stimulus, this is known as a positive tropism
• When plants grow away from a one sided stimulus, this is a negative tropism
• Tips of shoots grow towards light. This is a positive phototropism.
• Tips of roots grow away from light. This is a negative phototropism.
• Auxins


  Plant hormones that cause a phototropic response. Auxins accumulate on the side where there is no light. This side grows and the plant ends up growing towards the light.
• Roots show a positive gravitropism, where they grow down towards gravity to ensure they get enough water.
• Shoots show a negative gravitropism, where they grow away from gravity.