14 - Response to Stimuli Flashcards
What is the basic sequence of events beginning with a stimulus?
Stimulus, Receptor, Coordinator, Effector, Response
Name a plant growth factor.
Indoleacetic acid (IAA)
Where is IAA produced?
Tips of roots and shoots
How does IAA cause positive phototropism in shoots?
IAA moves from illuminated side to shaded side
Higher concentration on shaded side cause faster rate of cell elongation
Shoot bends towards light
How does IAA cause positive gravitropism in roots?
Gravity influences IAA to move from upper side to lower side of root.
Cells on upper side elongate more as IAA inhibits cell elongation in roots
Root bends downwards.
How does IAA cause positive gravitropism in roots?
Gravity influences IAA to move from upper side to lower side of root.
Cells on upper side elongate more as IAA inhibits cell elongation in roots
Root bends downwards.
What kinds of organisms display taxes and kineses? Give an example.
Organisms without complex nervous systems. For example, flatworms.§
What is the purpose of taxes and kineses?
Enable organisms to stay in a favourable environment.
What is a kineses?
A non-directional response to a stimulus, affected by the intensity of the stimulus.
What is a taxis?
A directional response to a stimulus.
Give three types of neurone.
Sensory, relay (intermediate), motor
How many neurones does a reflex arc involve?
3
Describe the reflex arc pathway.
Stimulus, Receptor, Sensory, Relay, Motor, effector, Response
What stimulus does the Pacinian corpuscle respond to?
Mechanical pressure
How does the Pacinian corpuscle function?
- When pressure is applied, stretch mediated sodium ion channels open
- Sodium ions diffuse in
- This establishses an electrical potential difference (depolarisation)
- Which causes a generator potential
- Causing an action potential
Name two receptors in human eyes.
Rods
Cones
What pigment is broken down in rod cells?
Rhodopsin
What pigment is broken down in cone cells?
Iodopsin
What is visual acuity?
The ability to distinguish separate points.
How do eye receptors work?
When hit by light, pigment breaks down
Describe the connection pathway between rods and the optic nerve.
Multiple rods connect to one bipolar cell
Multiple bipolar cells synapse to a sensory neurone on the optic nerve
How are cones connected to the optic nerve?
One cone connects to one bipolar cell
Connecting to a single sensory neurone
How is summation used in rod cells? What kind of summation is this?
Multiple stimulated rods generate a sufficient generator potential to react the threshold
So a less sharp image is formed, but can be seen in lower light Spatial.
What does myogenic mean?
Occurs without external stimulation
Describe the process of heart contraction. (6)
SAN sends out wave of excitation
Atria contract
(delay) AVN sends out wave of excitation
Bundle of His/Purkinje fibre conducts wave of excitation to apex
Ventricles contract
What controls changes to the heart rate?
Two centres in the medulla; the accelerator centre and inhibitory centre
How is the accelerator centre connected to the SAN?
Sympathetic nervous system
How is the inhibitory centre connected to the SAN?
Parasympathetic nervous system
Where are blood pressure receptors found?
Cartoid arteries and aorta
How do blood pressure receptors work?
When blood pressure is higher than usual, more impulses are sent to the inhibitory centre, which reduces heart rate. And vice versa
what do chemoreceptors detect (nervous system)?
Changes in pH of blood due to CO2 concentration
When more carbon dioxide is in the blood, what occurs?
pH decreases
chemoreceptors send more impulses to accelerator centre
heart rate increases
carbon dioxide removed
pH returns to normal
Suggest one precaution that would ensure the response really was due to light. (1)
Use heat filter in front of lamp.
