Plant Hormones - Auxins

• Which stimuli can plants detect?

  • Touch
  • light
  • gravity
• Do plants have a nervous system?

  no they rely on hormones
• True or false? Plant hormones only act locally.


  true
• Auxins are a family of plant hormones produced in the tips of shoots and roots. Once produced, they diffuse backwards along the shoot or root.
• Which two of the terms mean the same thing?

  Both geotropism and gravitropism refer to growth of parts of plants in response to the force of gravity.
• Auxins always accumulate on the:

  Lower side

  shaded side
• Shoots are considered:

  • Positively phototropic 
  • Negatively geotropic 
• A statement about plant roots?

  They are negatively phototropic but positively gravitropic
• The shoot will grow towards the left. This is because the light is on the left, and so auxins will accumulate on the right side (which will be in the shade). Auxins stimulate growth in shoots, so the right side of the shoot will grow faster, causing the shoot to lean over to the left.

  
• What is a phototropism?

  Plant growth response to light.
• Where are auxins made in the plant?

  In the growing tip of a stem or root
• What happens to make a root grow in the direction of the force of gravity?

  The top side grows more than the bottom side
• What is positive phototropism?


  Plants grow towards the light source
• What effects do auxins have on plants?

  Shoot cell growth and root cell inhibition
• Tip for remembering which side of the shoot or root auxins accumulate on:

  1. Light breaks down auxin, so there will be more auxin on the shaded side.
  2. Gravity pulls auxins downwards, so there will be more auxin on the lower side.