6.1.1 Survival and response

• What is a stimulus?

  A change in an organism's internal or external environment
• Why is it important that organisms can respond to stimuli?

  Organisms increase their chance of survival by responding to stimuli
• What is a tropism?

  • ● Growth of a plant in response to a directional stimulus
  • ● Positive tropism = towards a stimulus; negative tropism = away from stimulus
• Summarise the role of growth factors in flowering plants

  • ● Specific growth factors (hormone-like growth substances) eg. Auxins (such as IAA) move (via phloem or diffusion) from growing regions eg. shoot / root tips where they’re produced
  • ● To other tissues where they regulate growth in response to directional stimuli (tropisms)
• Describe how indoleacetic acid (IAA) affects cells in roots and shoots

  • ● In shoots, high concentrations of IAA stimulates cell elongation
  • ● In roots, high concentrations of IAA inhibits cell elongation
• Explain gravitropism in flowering plants

  1. Cells in tip of shoot / root produce IAA
  2. IAA diffuses down shoot / root (evenly initially)
  3. IAA moves to lower side of shoot / root (so concentration increases)
  4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
  5. So shoots bend away from gravity whereas roots bend towards gravity
• Explain phototropism in flowering plants

  1. Cells in tip of shoot / root produce IAA
  2. IAA diffuses down shoot / root (evenly initially)
  3. IAA moves to shaded side of shoot / root (so conc. ↑)
  4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
  5. So shoots bend towards light whereas roots bend away from light
• Describe the taxes responses that can maintain a mobile organism in a favourable environment

  • ○ Directional response
  • ○ Movement towards or away from a directional stimulus
  • Example: woodlice moving away from light to avoid predators
• Describe the kinesis responses that can maintain a mobile organism in a favourable environment

  • ○ Non-directional response
  • ○ Speed of movement or rate of direction change changes in response to a non-directional stimulus
  • ○ Depending on intensity of stimulus
  • Example: woodlice moving faster in drier environments to increase their chance of moving to an area with higher humidity to prevent drying out)
• Explain the protective effect of a simple (eg. 3 neurone) reflex

  • ● Rapid as only 3 neurones and few synapses (synaptic transmission is slow)
  • ● Autonomic (doesn’t involve conscious regions of brain) so doesn’t have to be learnt
  • ● Protects from harmful stimuli eg. escape predators / prevents damage to body tissues
• RP10: Describe how the effect of an environmental variable on the movement of an animal (eg. woodlice) can be investigated using a choice chamber

  1. Set up choice chamber (different compartments) to create different environmental conditions
  2. ○ Eg. humidity → add a drying agent to one side and damp filter paper to other
  3. ○ Eg. light → shine a light but cover one half with black card
  4. Control other environmental conditions
  5. ○ Eg. if investigating humidity control light intensity with a dim even light above
  6. Use a teaspoon to place a set number of animals eg. 12 woodlice on centre of mesh platform and cover with lid
  7. After a set amount of time eg. 10 minutes record the number of animals in each section
  8. Repeat after gently moving woodlice back to centre
• RP10: The woodlice were left for 15 minutes before their movement was recorded when investigating the effect of humidity. Explain why. (2)

  • ● Time to establish humidity / for substance to absorb water /water from paper to evaporate
  • ● Woodlice no longer affected by handling
  • ● So that behaviour is typical of that humidity
• RP10: Explain how you would ensure the safe and ethical handling of animals. (2)

  • ● Safely - cover open wounds / wash hands with soap after - to minimise risk of infection
  • ● Ethical - handle carefully/return to habitat ASAP
• RP10: Explain why a mesh platform is used when investigating the effect of humidity. (1)

  To keep woodlice a safe distance from drying agent
• Describe how the effect of an environmental variable on the movement of an animal (eg. maggots) can be investigated using a maze

  Mazes are used to investigate turning behaviour in response to different environmental conditions:

  1. Change environment at one end of T shape eg. add food source
  2. Place animal eg. maggot in stem of T
  3. Record whether animal turns towards or away from food source
  4. Repeat with a large number of maggots
  5. ○ Wipe / clean maze between trials
  6. Repeat with food on other side of T
• RP10: Explain why the same organism is not used more than once. (2)

  ● Reduces stress on maggots

  ● Prevents chance of learned behaviours
• RP10: Explain why a clean petri dish / maze is used each time. (2)

  ● Animals may leave chemicals / scents

  ● Which influence behaviour of other animals
• Explain which statistical test should be used to analyse results

  • ● Chi-squared
  • ● As data are categorical and comparing frequencies
  • ● To see if there is a significant difference between observed and expected frequencies
  • ○ Expected = equal numbers each side