13.10 a Survival and response Flashcards
Simple reaction pathway
Stimulus
Receptor
Coordinator
Effector
Response
Why do organisms need to respond to changes in their environment?
_ Avoid harm
- Keep in favourable conditions
- Grow towards/away from stimuli
Kineses
Random movement in response to a stimuli
Taxes
Directional movement of an organism either towards or away from a stimulus
Positive taxis
Towards the stimulus
Negative taxis
Away from the stimulus
Why do we need reflex actions?
- To protect us against damage to body tissue
- help escape from predators
- Enable homeostatic control
- Find food, mates or suitable living conditions
Receptor example
Sensory neurone
Connects nerve impulse to relay neurone
Relay neurone
Goes between senspory neurone and motor neurone
Effector
What are the advantages of simple reflex arcs
- Rapid
- Protects against damage to the body tissue
- Dont have to be learnt
- Helps escape predators
- Enables homeostatic control
Positive tropism
Grows towards the stimulus
Negative tropism
Grows away from the stimulus
Gravity tropism term
Geo
Salt tropism term
Halo
Light tropism term
Photo
Water tropism term
Hydro
Explain IAA as a plant growth factor
- IAA is produced in the tips of the roots and shoots
- Diffuses to the growing region
- Causes cell elongation in shoots
Inhibits cell elongation in roots - IAA transported to the more shaded part of the roots or shoots in phototropism
- IAA moves to the underside of the roots and shoots in geotropism
Explain IAA in shoots
- IAA is synthesised in the shoot tips
- IAA diffuses into the growing region
- Light causes the movement of IAA from the light side to the shaded side
- Higher concentration of IAA on the shaded side
- Causes directional growth as there is a greater cell elongation on shaded side
- Shaded side grows faster and causes shoot to bend towards light
Explain IAA in the roots
- IAA synthesised in the root tips
- IAA diffuses into the growing region
- Light causes the movement of IAA from the light side to the shaded side, towards gravity
- Higher concentration of IAA on the shaded side
- Cell elongation inhibited on the shaded side
- Results in directional growth away from light and towards gravity
