Tropism, taxis and kinesis

• A pheromone is a chemical messenger
• The main function of pheromones is reproduction, but they can also be used as alarm signals or markers.
• Pheromones are used to locate mates, identify species and identify adult females able to get pregnant
• Before carrying out an experiment with animals at different temperatures, time should be allowed for them to get used to the temperature
• Animals should not be kept at high temperatures to reduce stress and suffering. High temperatures can result in denatured proteins
• Clean petri dishes should be used when experimenting with animal behaviour to prevent chemicals left by previous animals affecting subsequent animals
• Daylength is a reliable way to indicate the time of the year
• Behaviour refers to the observable, coordinated responses an animal makes to stimuli in its environment
• Innate behaviour describes instinctive behaviour which is genetically programmed; the organisms responds to environmental circumstances in a predictable way and the stimulus is likely to always produce the same response
• Two types of innate behaviour in invertebrates are commonly identified: taxis and kineses
• Taxis: a directional response towards or away from a stimulus
• Kinesis: a non-directional response to unfavourable environmental conditions
• An organism is phototactic is it responds to light
• Plant growth factors are made by cells and affect the tissues where they are produced
• Auxillary buds grow more with medium concentrations of plant growth hormones
• There is the same amount of auxin in the tip of a plant, regardless of light levels
• The shoot tip responds to light and is positively phototropic
• Removal of a stem tip prevents any response to stimulus
• Mica is a barrier to the movement of chemical messengers, but not electrical messages. Gelatin is a barrier to the movement of electrical messengers, but permeable to chemical messengers. The two can be used to prove that chemical messages are sent from the tip of a plant stem
• Response of shoot to light:

  • auxin is produced at tip
  • lateral movement of auxin causes it to accumulate on shaded side
  • more cell elongation on shaded side
  • shoot tip grows towards light - there is less cell elongation on illuminated side
• Response of shoots to gravity:

  • Auxin is produced in the tip of the shoot
  • Auxin accumulates on the underside of the shoot
  • Auxin stimulates cell elongation in shoots
  • Shoots grow up
• Response of roots to gravity:

  • Auxin is produced in the tip of the root
  • Auxin accumulates on the underside of the root
  • Auxin inhibits cell elongation in roots
  • Roots grow down
• To check all water has been removed from plant samples, the mass should be determined. The plant should then be allowed to dry for longer before it is then reweighed. Once the mass does not change, all the water has been removed
• Tropism is where part of a plant has a directional response to stimulus
• Tropism due to light is known as phototropism
• Tropism due to gravity is known as geotropism
• IAA stands for Indoleacetic acid
• A higher IAA concentration in shoots stimulates cell elongation and a higher IAA concentration in roots inhibits cell elongation
• IAA is known as a specific growth factor
• Taxis and kinesis are simple response that help a mobile organism to find and stay in a favourable environment
• In an unfavourable environment, kinesis means an increased speed of movement and decreased rate of turning
• In a favourable environment, kinesis means a decreased speed of movement and increased rate of turning
• Taxis and kinesis affect the movement of an entire organism. Tropism affects the growth of part of a plant
• Roots are positively geotropic, shoots are negatively geotropic
• IAA is a type of auxin