Introduction to plant responses

• what is tropism?

  a directional growth response in which the direction of the response is determined by the direction of the external stimulus
• what is a nastic response?

  a non-directional response to a stimulus
• what are the different types of tropism?

  • phototropism - light, benefit is photosynthesis
  • geotropism - gravity, plants grow away from gravitational pull
  • chemotropism - chemical changes, fertilisation, pollen tube elongation, flowering
  • thigmotropism - contact, movement, change in growth orientation
• what is the difference between tropism and trophism?

  • tropism - directional growth
  • trophism - feeding method e.g. heterotrophic
• what is the function of a hormone?

  • chemical messenger which transport information from one part of an organism to another and bring about a change
  • alter activity of one or more specific target organs
  • control functions that don't need instant responses
• how are hormones transported in plants?

  • specialised tissues xylem and phloem - mass flow
  • diffusion from cell to cell
  • active transport
• what are some effects of hormones?

  • cell growth
  • cell division stimulation
  • differentiation of vascular tissue
  • cell elongation
• what is positive tropism?

  • growth response towards a stimulus e.g. positive phototropism (auxin)
• what is negative tropism?

  • growth response away from a stimulus e.g. negative geotropism (auxin)
• what is synergy?

  • when two hormones amplify each other's effect e.g. auxin/cytokinin
• what is antagonism?

  • when two hormones cancel out to some degree each other's effect e.g. seed germination/dormancy (giberellin/ABA)
• what are the effects of auxins?

  • control cell elongation
  • prevent leaf fall
  • maintain apical dominance
  • stimulate ethene release - fruit ripening
• what are the effects of gibberellins?

  • stem elongation
  • trigger mobilisation of food stores in a seed at germination
  • stimulate pollen tube growth in fertilisation
• what are the effects of Abscisic Acid (ABA)?

  • maintain dormancy of seeds and buds
  • stimulates cold protective responses e.g. antifreeze production
  • stimulate stomatal closing
• what are the effects of Ethene?

  • fruit ripening
  • promotes abscission in deciduous trees
• what are the effects of cytokinins?

  • cell division
  • morphogenesis and bud formation
  • growth of lateral buds
  • leaf expansion
  • stomatal opening