14. RESPONSE TO STIMULI Flashcards
Define stimulus.
A change in the environment.
How are stimuli detected?
By receptors in sensory organs.
State the pathway of a response from a stimuli.
stimulus → receptor → coordinator → effector → response
Define a taxis.
A directional motile response
State what positive taxis is.
Movement of the organism towards a (favourable) stimulus.
State what negative taxis is.
Movement of the organism away from an (unfavourable) stimulus.
What stimuli are phototaxis in response to?
Light
What stimuli are chemotaxis in response to?
Chemicals
Define kinesis
A non-directional motile response
How does an organism’s movement change in response to a stimuli in kinesis?
The organism changes the speed at which it moves, and the rate at which is changes direction (turns)
Describe how an organism changes its speed and the rate at which it turns in kinesis when it experiences a favourable stimuli
It slows down and decreases the rate at which it turns
Describe how an organism changes its speed and the rate at which it turns in kinesis when it experiences an unfavourable stimuli
It speeds up and increases the rate at which it turns
What is a tropism?
A tropism is a directional plant growth response to a stimuli
Which stimuli is phototropism in response to?
Light
Which stimuli is gravitropism in response to?
Gravity
Which stimuli is hydrotropism in response to?
Water
Give an example of a plant growth factor.
Indoleactic acid (IAA).
What group of plant hormones does IAA belong to?
Auxins
Where is IAA produced?
Tips of shoots and roots (meristems)
How does IAA travel down the meristem?
Diffusion
Where will there be a higher concentration of IAA in shoots?
On the shaded side
Describe the effect of IAA on cells in shoots
Stimulates cell elongation
Describe the effect of IAA on the direction of growth of shoots
Causes shoots to grow towards the light (positive phototropism)
Where will there be a higher concentration of IAA in roots?
At the bottom / the side towards gravity
Describe the effect of IAA on the cells in roots
Inhibits cell elongation
Describe the effect of IAA on the direction of growth of roots
Causes shoots to grow towards the gravity (positive gravitropism)
Name the two structural divisions of the nervous system.
Central Nervous System (CNS) and Peripheral Nervous System (PNS).
Which two types of neurones exist within the peripheral nervous system?
Sensory neurones and motor neurones.
State the function of the sensory neurones.
Carries nerve impulses from receptors towards the CNS.
State the function of the motor neurones.
Carries nerve impulses away from the CNS to effectors.
Which two functional systems exist within the motor nervous system?
The voluntary and the autonomic nervous system.
What is the voluntary nervous system?
Carries nerve impulses to body muscles under voluntary (conscious) control.
What is the autonomic nervous system?
Carries nerve impulses to glands, smooth muscle and cardiac muscle under involuntary (subconcious) control.
Name the two divisions of the autonomic nervous system.
Sympathetic and parasympathetic nervous system.
The sympathetic nervous system is associated with which types of responses?
Fight or flight, preparing for action and energy release
The parasympathetic nervous system is associated with which types of responses?
Rest and recouperation, calm and self maintenance functions
Why are the sympathetic and parasympathetic nervous system antagonistic?
The responses they produce oppose one another and occur exclusively.
Name the two control centres in the nervous system
Brain and spinal cord
Name the three types of neurones within a reflex arc
Sensory neurone, relay neurone and motor neurone.
Why is it important that reflexes are innate, rapid and involuntary?
To minimise damage from dangerous stimuli.
As well as minimising harm from dangerous stimuli, describe two other functions of reflexes
Maintain posture and coordinating homeostasis
State the sequence of the main stages of a spinal reflex arc.
Stimulus → receptor → sensory neurone → intermediate neurone → motor neurone → effector → response
How many neurones are there in a simple reflex?
3
Receptors are examples of transducers. Define what a transducer is.
Converts energy from one form to another.
Give an example of a receptor found in the skin.
Pacinian corpuscle
State the function of the Pacinian corpuscle.
Detects changes in mechanical pressure.
Why would a generator potential not always cause an action potential?
The generator potential has to reach threshold for an action potential to be initiated.
Where are Pacinian corpuscle most abundant?
On the fingers, soles of the feet and external genitalia.
Pacinian corpuscle contains a specific type of sodium ion channel in its CSM. What are they called?
Stretch-mediated sodium ion channel
Why are these sodium ion channels referred to as ‘stretch-mediated’?
Their permeability to sodium changes when they are deformed.
What happens to the lamellae in the pacinian corpuscle when pressure is applied?
It deforms
What happens to the stretch mediated sodium ion channels in the pacinian corpuscle membrane when pressure is applied?
They widen, open, and sodium ions diffuse into the neurone.
The ending of the sensory neurone at the centre of the Pacinian corpuscle becomes depolarised. What does this mean?
The influx of sodium ions changes the potential difference across the membrane, producing a generator potential.
If the generator potential in the pacinican corpuscle reaches threshold, what will happen?
An action potential will be propogated down the sensory neurone
Where are photoreceptors found in the eyes?
The retina
Name the two main types of photoreceptors
Rod cells and cone cells.
What does the break down of the photosensitive pigments inside photoreceptors cause?
A depolarisation called a generator potential
When will the generator potential produced from a photoreceptor initiate an action potential?
When the generator potential reaches threshold
Name the photosensitive pigment inside rod cells
Rhodopsin
Why is Rhodopsin sensitive to light?
Because it’s broken down in low light intensities
When are rod cells mostly utilised to produce images
In low light intensities / at night
Is the image produced from rod cells colour or black and white?
Black and white
Name the photosensitive pigment inside cone cells
Iodopsin
Name the three different types of cone cells
Blue light cones, green light cones and red light cones
Why can we see more than three colors, even though there are only three types of cone cell?
Because the wavelengths absorbed by the cones overlap
When are cone cells mostly utilised to produce images
In high light intensities / in the day
Define visual acuity
Visual acuity is the clearness and sharpness of your vision
Which type of photorecetor produce a high visual acuity but a low visual sensitivity?
Cone cells
Why do cone cells produce a high visual acuity but a low visual sensitivity
Each cone cell synapses with a separate neurone so there is no retinal convergence, and no summation of impulses
Which type of photorecetor produce a low visual acuity but a high visual sensitivity?
Rod cells
Why do rod cells produce a low visual acuity but a high visual sensitivity
Multiple rod cells synapse with one neurone so there is retinal convergence, and spatial summation of impulses to overcome the threshold potential.
Where in your field of vision is your visual acuity the highest?
In the centre (the fovea)
Why is your visual acuity the highest in the centre?
Because cone cells are concentrated in the fovea
Where are rods found in your retina?
Around the edges of the fovea
What is the blind spot?
Where the optic nerve connects to your retina, so there are no photoreceptors here
Which part of the brain controls heart rate?
Medulla
How would the medulla increase the heart rate?
It would increase the impulses sent through the parasympathetic nerves
How would increased impulses sent through the parasympathetic nerves decrease heart rate?
It would decrease impulses sent from the SAN
How would the medulla decrease the heart rate?
It would increase the impulses sent through the sympathetic nerves
How would increased impulses sent through the sympathetic nerves decrease heart rate?
It would increase impulses sent from the SAN
Name the two stimuli that can cause a change in heart rate
Changing blood pressure and changing carbon dioxide concentration
Name the receptors that detect a change in blood pressure
Baroreceptors
Name the receptors that detect a change in carbon dioxide concentration
Chemoreceptors
Where in the body are baroreceptors and chemoreceptors found?
Aorta
When baroreceptors and chemoreceptors detect a change, what do they send impulses to?
The medulla
If the blood pressure increased, how would the heart rate change as a response to this?
It would decrease (to decrease the blood pressure)
If the blood pressure decreased, how would the heart rate change as a response to this?
It would increase (to increase the blood pressure)
If the carbon dioxide concentration of the blood increased, how would the heart rate change as a response to this?
It would increase (to increase carbon dioxide excreted)
If the carbon dioxide concentration of the blood decreased, how would the heart rate change as a response to this?
It would decrease
