6.1 Nervous Communication Flashcards
What two things can organisms detect change in?
- Internal environment
- External environment
What detects a change in the environment?
Receptors
What initiates a response to the change in the environment?
Effectors
What is the change in the environment called?
Stimulus
Tropism definition
The growth of a plant in response to a directional stimulus
What is phototropism?
Growth in response to the direction of light
Are shoots positively or negatively phototropic?
Positively - they grow towards light
Are roots positively or negatively phototropic?
Negatively - they grow away from light
What is gravitropism?
Growth in response to the direction of gravity.
Are shoots positively or negatively gravitropic?
Negatively - they grow upwards, away from gravitational pull
Are roots positively or negatively gravitropic?
Positively - they grow downwards, towards gravitational pull.
What is hydrotropism?
Growth in response to water
What type of auxin controls cell elongation?
IAA (indoleacetic acid)
How does a directional stimulus distribute IAA?
Unevenly
How does IAA create positive phototropism in shoots?
If a shoot is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts cause cells in the shaded area to elongate.
Cell elongation causes the shoot to bend towards the light.
How does IAA create negative phototropism in roots?
If a root is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts inhibits cell elongation on the shaded part.
The root bends away from the light.
How does IAA cause negative gravitropism in shoots?
If a shoot is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside cause cells in the underside to elongate.
Cell elongation causes the shoot to bend away from the gravitational pull.
How does IAA cause positive gravitropism in roots?
If a root is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside inhibits cell elongation on the lower side.
The root bends towards the gravitational pull.
What are taxes?
A taxis is a simple response whose direction is determined by the direction of the stimulus. (Whole body is moved towards a favourable stimulus or away from an unfavourable one.)
What are kineses?
A kinesis is a form of response in which the organism does not move away from or towards a stimulus. It is a non-directional response. The organism changes the speed it moves at and the rate at which it changes direction.
What is the order of neurones in a reflex arc?
- (Receptors)
- Sensory neurone
- Relay neurone
- Motor neurone
- (Effectors)
What do pacinian corpuscle respond to changes in?
Mechanical pressure
Structure of pacinian corpuscle?
Rings of connective tissue which surround a single sensory neurone.
How are generator potentials produced in pacinian corpuscles?
- At resting potential, the stretch-mediated sodium channels in the sensory neurone surrounding membrane are too narrow for sodium to enter.
- When pressure is applied, the membrane is deformed and stretched.
- Stretch-mediated sodium channels are widened allowing sodium ions to diffuse into the neurone.
- The membrane becomes depolarised and a generator potential has been produced.
- This generator potential in turn produces an action potential if the threshold value is reached.
