2 (j) Co-ordination and Response Flashcards
Positive Geotropism
Grow in the direction of gravity
e.g. Plant Roots
Negative Geotropism
Grow against the direction of gravity
Positive Phototropism
Grow towards light
Word Tropism meaning
A directional growth response in response to a stimulus
Auxin
Plant hormone
Controls growth of cells in the tips of roots + shoots in response to light + gravity
How does auxin move
Diffuses downwards
What do auxin in shoot cells cause?
Cell Elongation
Even distribution of auxin = shoot growing evenly
What happens when a shoot is exposed to light?
More auxin accumulates on the shaded side of the shoot -> causes more cell division/more growth/more elongation
Animals vs Plant Responses
Animals:
* detect stimulus by neurones -> more rapid and short duration using electrical impulses
- Plants detect stimulus for a long duration, with slower response. Involves auxin (growth regulation) using phloem cells
Hydrotropism
Responses to water
Geotropism
Responses to gravity
Phototropism
Resposes to light
Homeostasis
The maintenance of a constant internal environment
Examples of Homeostasis
- Body water content
- Body water temperature
What does a co-ordinated response require?
- Stimulus
- Receptor
- Effector
Order of a Response
- Stimulus
- Receptor
- Sensory Neurone
- Relay Neurone
- Motor Neurone
- Effector
- Response
What happens in a co-ordinated response/reflex arc
- Stimulus detected by receptors
- Electrical impulse generated and passes from receptor-> sensory neurone -> relay neurone (in spinal cord) -> motor neurone
- Between each neurone there is a synapse
- Motor neurone is connected to a muscle or gland that brings about a response
What happens at a synapse
- Electrical impulse arrives at pre-synaptic neurone
- This releases the neurotransmitters stored in vesicles
- The neurotransmitters diffuses across the synaptic cleft
- They bind to the membranes of the receptors on the post - synaptic neurone
- Stimulates another electric impulse
What makes up the central nervous system?
Brain and spinal cord
Linked to sense organs by nerves
Is the eye a receptor?
Yes
