Plant Responses

• What is different about coordination in plants?

  The response is longer in plants due to being rooted, limiting mobility, and their ability to have a rapidly responding nervous system; instead using complex chemical production and reactions.
• What is an example of these chemicals?

  Plant hormones, that are produced in one region of the plant and are transported through transport tissues and from cell to cell.
• What are some of the key plant hormones?

  Auxin, gibberellin, ethene, abscisic acid (ABA).
• What are auxins?


  Growth and development stimulates produced in the meristems, the tips of roots and shoots, travelling up the roots or down the shoots in transport tissue and from cell to cell.
• What are its 4 key roles?

  Controlling of cell elongation; maintenance of apical dominance; involved in ethene release, stimulating or preventing abscission and ripening; involved in tropisms.
• What is an example of auxin?


  Indole acetic acid.
• How does auxin affect cell walls?


  Auxin presence allows cell walls to stretch more easily, increasing their plasticity, through binding to specific receptor sites in the plant cell membrane, causing a fall in pH (about 5) to the optimum pH for enzymes needed to keep walls flexible.
• What happens to auxin levels as cells mature?


  Auxin is destroyed, and the fall in hormone causes a rise in pH so maintaining plasticity become inactive, resulting in the walls becoming rigid and cells no longer being able to expand and grow.
• What's auxins role in cell elongation of the stem?

  Auxin accumulates in the stem from being produced in the stem tip, and causes cell elongation through increasing the plasticity of the cell wall.
• What's auxins role in cell elongation of the roots?

  Auxin accumulates in the roots from both being produced in the root tip but also through receiving auxin from the shoot tip, and promotes root growth; however high auxin concentration above the threshold inhibits root growth, as roots will display negative phototropism and grow away from the sun.
• What will happen if the shoot tip is severed?

  Stems will grow directly upwards, while roots growth will slow due to decreased auxin, and due to apical dominance being lost, lateral shoots will grow more prominently.
• What's auxins role in apical dominance?


  High concentrations of auxin supress the growth of lateral shoots, and promote growth of the main apical shoot, due to auxin moving back down the stem inhibiting lateral growth; however due to lower concentrations further down the stem, lateral growth will be stronger.
• How does auxin prevent or stimulate abscission?


  When auxin levels fall due to a fall in light levels, the leaves respond by releases the gaseous plant hormone ethene, which triggers the abscission process.
• How does auxin prevent or stimulate ripening?


  Auxin delays the ripening process, and it is when these levels drop that gaseous hormone ethene rise, causing ripening.
• What are gibberellins?


  These are plant hormones produced in the plastids of a plant.