Responses in Plants and Animals

• What is a taxis response?

  A taxis response is a direction response towards or away from a stimulus.
• In taxis responses moving towards a stimulus is positive taxis while moving away from a stimulus is negative taxis.
• What is a kinesis response?

  A kinesis response is a non-directional movement in response to a stimulus
• Woodlice move more slowly and made less turns in high humidity and move more and make more turns in dry air, this is an example of a kinesis response.
• What is a choice chamber?

  Choice chambers have areas with different conditions and organisms can move freely to their favoured area. This allows scientists to investigate taxis/kinesis responses by recording the movement of the organisms.
• When investigating kinesis/taxis responses using choice chambers we must demonstrate good practice, how can this be done?

  1. We can place the woodlice in the centre of the petri dish.
  2. Give them an appropriate amount of time to move around.
  3. Repeat the experiment and control for all variables.
  4. Use mesh to protect the woodlice from any drying agents.
  5. Release them safely back into their habitat.
• What is tropism?

  Tropism is the growth response of a plant towards or away from a directional stimulus, involving coordination by plant growth factors.
• In tropism moving towards a stimulus is positive tropism while moving away from a stimulus is negative tropism .
• What are the two types of tropism that you need to know?

  1. Phototropism (P)
  2. Gravitropism (G)
• What is phototropism?

  Phototropism is the growth of a plant in response to light.
• What is gravitropism?

  Gravitropism is the growth of a plant in response to gravity.
• How do plants respond to directional stimuli?

  Plants respond to directional stimuli using specific growth factors - these are hormone-like chemicals that speed up or slow down plant growth.
• Growth factors are produced in the growing regions of the plant and move to where they are needed in other parts of the plant. Growth factors called auxins stimulate the growth of shoots by cell elongation.
• What is cell elongation?

  This is where the cell walls become loose and stretchy causing the cell to become longer.
• What impact does high concentrations of auxins have on roots?

  high concentrations of auxins inhibits growth in roots.
• Phototropism in shoots:

  Cells in the tip of the shoots produce IAA, which is transported down the shoot. Initially it is transported to all sides but light causes IAA to move from the light side to the shaded side, due to this a greater concentration of IAA builds up on the shaded side. IAA causes cell elongation so cells on the shaded side are elongated more, meaning that shaded sides will grow faster and the shoot will bend towards the light.
• Gravitropism in roots:

  IAA will gather on the lower sides of the roots due to gravity, inhibiting cell elongation. Due to this the bottom side of the root grows slower than the top side so the roots will grow downwards.