6.1.1 Survival and response Flashcards
(13 cards)
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
- Cells in tip of shoot / root produce IAA
- IAA diffuses down shoot / root (evenly initially)
- IAA moves to lower side of shoot / root (so concentration increases)
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend away from gravity whereas roots bend towards gravity
Diagram for gravitropism in flowering plants
Explain phototropism in flowering plants
- Cells in tip of shoot / root produce IAA
- IAA diffuses down shoot / root (evenly initially)
- IAA moves to shaded side of shoot / root (so conc. ↑)
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend towards light whereas roots bend away from light
Diagram for phototropism in flowering plants
Describe the simple responses that can maintain a mobile organism in a
favourable environment
- Taxes (tactic response)
○ Directional response
○ Movement towards or away from a directional stimulus - Kinesis (kinetic responses)
○ 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 of taxis and kinesis
taxis - woodlice moving away from light to avoid predators
kinesis - 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
Diagram for the protective effect of a simple (eg. 3 neurone) reflex
