6.1 Stimuli and response Flashcards
What is meant by phototropism
A directional growth in response to light
What is meant by gravitropism
A directional growth in response to gravity
When there’s directional growth towards a stimuli, is the tropism positive or negative
Positive
When there’s directional growth away from a stimuli, is the tropism positive or negative
Negative
Describe where IAA is produced
In the tops of roots and shoots
When IAA is present in the shoots what does it promote
Growth
When IAA is present in the shoots, what does it cause to happen to the cells
Causes cell elongation
When IAA is present in the roots, what is inhibited
Growth
What causes the movement of IAA in shoots
Light
Since IAA is moved by light, what happens when the side of the plant is in the shade
IAA diffuses to the shady side of the shoot
If IAA diffuses to the shady side of the shoot, what does the lead too
The build up of IAA concentration on the shady side compared to the light side
Since the concentration of IAA is higher on the shadier side, what does this cause
It promotes cell elongation and growth, so more of these 2 processes occur on the shadier side compared to the light side
When there’s increased growth and cell elongation on the shadier side of the shoot, what does this lead too
The shoot bending towards the light
When the shoot bends towards the light, what is the name of this
Positive phototropism
Explain how IAA causes positive phototropism in shoots ( 6 points)
- IAA is produced in the tip of the shoot, initially it is evenly transported to all regions as it begins to move down the shoot
- Light causes the movement of IAA
- IAA diffuses to the shady side of the shoot. A greater concentration builds up on this side than the light side
- Here it promotes cell elongation and growth occurs more on this side
- The shoot bends towards the light
- Called positive phototropism
What influences the movement of IAA in the roots
Gravity
In the roots, what side of the root will gain a greater concentration of IAA
The lower side
When the IAA accumulates on the lower side of the root, what happens
The IAA inhibits the elongation of the root cells, so the cells on the lower side of the root elongate less than the upper side
When the cells on the upper side of the root elongate more, what does this lead to
Causes the root the bend downwards towards gravity
When the root bends downwards towards gravity, what is the name of the process
Gravitotropism
Explain how IAA causes positive gravitropism in roots (5 points)
- Cells in the top of the root produce IAA. It is initially transported to all sides of the root
- Gravity influences the movement of IAA from the upper side of the root to the lower side of the root
- A greater concentration of IAA builds up on the lower side
- In the roots IAA inhibits the elongation of root cells, the cells on the lower side elongate less than the upper side
- This causes the root to bend downwards towards gravity, and it positive gravitopism
What is a taxis
A directional response to a stimulus
If the whole organism moves away from the stiumuli, is the taxis positive or negative
Negative taxis
If the whole organism moves towards the stimuli, is the taxis positive or negative
Positive taxis
What is a kinesis
When an organism changes the speed and the rate in changes in direction to find a more favourable environment
What are reflexes
Rapid involuntary responses
What are the roles of reflexes
- Protect against damage to body tissues
- Enable homeostatic control
- Enable escape from predators
A simple reflex arc only involves how many neurones
3
What is the role of sensory neurones
To carry electrical nerve impulses from the receptor to the central nervous system
What do intermediate neurones synapse with
Sensory neurones and then with a motor neurone
What are the 7 stages of a reflex arc
- Stimulus
- Receptor
- Sensory neurone
- Coordinator (intermediate nerurone)
- Motor neurone
- Effector
- Response
Explain the features of a sensory neurone
- Respond to one type of stimulus
- Acts as a tranducter, creating a generator potential
Receptors in the nervous system convert the energy of the stimulus into a nervous impulse, what is this known as
A generator potential
Describe the structure of a Pacinian corpuscle
- Single sensory neurone is at the centre of layers of tissue called lamellae each seperated by a gel
- A capsule surrounds the layers
- The sensory neurone at the centre has stretch mediated sodium channels in its membrane
In a Pacinian corpuscle, what are the layers of tissue called
Lamellae
In the Pacinian corpuscle, what are the layers of tissue (lamellae) separated by
A gel
In the Pacinian corpuscle, what type of stretch mediated channel is in the membrane of the sensory neurone at the centre
Sodium channels
Explain the stimulus which Pacinian corpuscles respond to
Responds to mechanical stimuli such as pressure
What does increased pressure do to the lamellae of the Pacinian corpuscle
Deforms the lamellae
When pressure has deformed the lamellae, what does this in turn deform
The stretch-mediated sodium ion channels in the membrane of the sensory neurone
When the stretch-mediated sodium ion channels in the membrane of the sensory neurone of the Pacinian corpuscle deforms, what happens to the sodium ion channel, and what does this lead to
The sodium ion channels open and sodium ions diffuse in
Once the sodium ions have diffused into the sensory neurone, what happens to the inside of the neurone
It becomes more positive
When the inside of the neurone becomes more positive, what is the name of this
Depolarisation
What is produced when the inside of the neurone becomes more positive/ depolarisation
A generator potential
What is the pigment in rod cones
Rhodopsin
What is Rhodopsin in rod cones sensitive to
Low light intensity
What is the pigment inside cone cells
Iodopsin
Is iodopsin in cone cells sensitive to low light intensity
No
Why do rod cells have low visual acuity
Because a number of rod cells are connected to a single bipolar neurone. Meaning it will generate a single impulse to the brain regardless of how many neurones are stimulated
A number of rod cells are connected to a single ______ neurone
Bipolar
Why are rod cell images only black and white
Rhodopsin cannot distinguish between different wavelengths, it is broken down by all wavelengths
In what light intensity can Rhodopsin be broken down in
Low light intensity
Why do cone cells have high visual acuity
Each cone cell is connected to a single bipolar neurone, meaning that the brain receives separate impulses from each cone cell
In what light can iodopsin be broken down in
Broken down in bright light
Why are cone cells sensitive to colour
- There are 3 types of cone cells each with a different type of iodopsin
- Each type of iodopsin is sensitive to different wavelengths of light
Can stimulation of each cone cell be combined to help reach threshold, and why
No as each cone cell has their own bipolar cell
What is a stimulus
Any detectable change in environment of organisms that leads to a response
What are the 2 communication systems that result in a response
- Electrical
- Chemical
What is the name of the system where the communication system is electrical
Nervous system
What is the name of the system where the communication system is chemical
Endocrine
What are the 5 generic steps from stimuli to a response in both endocrine and nervous system
- Stimuli
- Receptor
- Coordinator
- Effector
- Response
Receptors are specific to how many different types of stimuli
Specific to 1 stimuli
What is the name of IAA
Indoleactic acid
What is the role of IAA
Control the plant cell elongation
What is the name of the node in the cardiac cycle that sends out regular waves of electrical activity across the atria
The sino atrial node
What does the sino atrial node sending out regular waves of electrical activity result in
The atria contracts
In the heart what prevents impulses passing from walls of atria to the ventricles
Non-conducting tissue
What is the name of the node that detects electrical activity in the atria and then sends out electrical activity to the ventricles
Atrioventricular node
What is the name of the part of the ventricle where the atrioventricular node sends the electrical activity to
The apex of the ventricle
What are the name of the smaller fibres in the ventricles, where the impulses travel up
The smaller Purkyne fibres
When the ventricles contract from which part of the ventricle does the contraction occur from
From the apex upwards
Explain the events which take place during the cardiac cycle to produce and transmit a wave of electrical activity to make the heartbeat
- The sino atrial node send out regular waves of electrical activity across the atria
- This causes the atria to contract
- Non conducting tissue between the atria and ventricles prevents the impulses passing from walls of atria to ventricles
- This delay ensures the atria is empty of blood before ventricles contract
- Instead the atrioventricular node is able to detect the electrical activity in the atria and after the delay sends out electrical activity down the bundle of HIS to the apex of the ventricle
- Impulses travel up the smaller Purkyne fibres and ventricles contract from the apex upwards
What is the name of the bundle where the electrical activity get sent down from the atrioventricular node to the apex of the ventricles
Bundle of His
What does SAN stand for
Sino atrial node
What does AVN stand for
Atrioventricular node
The heart can contract without any nervous stimulation, what is the term as to why
The heart is myogenic
What initiates the sequence of muscle contractions in the heart
The sinoatrial node (SAN)
Purkyne tissue is initially grouped together in a structure called what
Bundle of His
What happens to the Purkyne tissue beyond the Bundle of His
Branches into smaller fibres
What do chemoreceptors detect
Changes in carbon dioxide
What do pressure receptors detect
Changes in pressure
Where are chemoreceptors and pressure receptors found
In the aorta close to the heart andv in the carotid arteries
Where do the carotid arteries pass through
The neck to the brain
What does the parasympathetic nervous system help the body to do
Relax
Where is the inhibitory centre and the acceletory centre
In the medulla oblongata
What does activating the inhibitory centre in the medulla do
Sends impulses along the parasympathetic nervous system
What type of response does the sympathetic nervous system initiate
Fight or flight response
What does activiating the acceletory centre in the medulla do
Sends impulses along the sympathetic nervous system
What happens to the pH when the concentration of carbon dioxide increases
The pH falls
What are the receptors that detect the change in carbon dioxide levels
Chemoreceptors
After the chemoreceptors have detected a change in carbon dioxide, what happens
The chemoreceptors send impulses to the cardiac centre in the medulla
What nervous system is activated when there’s high carbon dioxide concentrations
Sympathetic nervous system
When there’s high concentrations of carbon dioxide, what does this do to the frequency of impulses sent out by the SAN
Increases the frequency
When there’s a decrease in the carbon dioxide concentration, what happens to the number of impulses that are sent to the cardiac muscle in the medulla
Fewer impulses are sent
When there’s a decrease in carbon dioxide what nervous system is activated
Parasympathetic nervous system
At lower levels are carbon dioxide, what happens to the frequency of impulses sent out by SAN
A decrease
What is releases at the synapse with the SAN
A neurotransmitter
What is the name of the centre that the medulla contains
Cardio regulatory centre
What are the 2 parts of the cardio regulatory centre
- Acceleratory centre
- Inhibitory centre
What is the acceleratory centre responsible for
Speeding up the heart rate
What is the inhibitory centre response for
Slowing down the heart beat
What is the coordinator in the nervous system
The central nervous system
What are the 2 types of nervous systems
- Central
- Peripheral
What are the 2 types of pathways in the peripheral nervous system
- Sensory pathway
- Motor pathway
In the sensory pathway of the peripheral nervous system, do the electrical impulses travel towards or away from the central nervous system
Towards the central nervous system
In the motor pathway of the peripheral nervous system, do the electrical impulses travel towards or away from the central nervous system
Away from the central nervous system
What are the 2 types of nervous systems within the motor pathway of the peripheral nervous system
- Somatic (voluntary)
- Autonomic (Involuntary)
What is an example when the somatic nervous system is used
- Walking
- Skeletal muscles
-etc
What is an example of when the autonomic nervous system is used
- Cardiac muscle
- Glands
What are the names of the 2 divisions from the autonomic nervous system
- Sympathetic division
- Parasympathetic division
What are the 3 mains reasons about the benefit of having simple reflex arcs
- Involuntary response
- Protects body from harm
- Fast
- Don’t have to be taught/ from birth
What is the maximum number of neurones in a reflex arc
3
Why does having a maximum of 3 neurone in the reflex arc make it fast
As there’s only 2 synapses, synapses slow the speed
Give 2 reasons why reflex arcs are fast
- No decision making
- Few synapses
What is the order from stimuli to response in the nervous system
- Stimuli
- Receptor in skin
- Sensory neurone passes nerve impulses to spinal cord
- Relay neurone pass nerve impulses across spinal cord
- Motor neurone passes nerve impulses to muscle
- Effector
- Response
What root does the sensory neurone always go down
Down the dorsal (back) root
What root does the motor neurone always go down
The ventral root
What is grey matter, in terms of neurone body
Areas where neurones don’t have myelin
What is white matter, in terms of neurone body
Area where neurones are covering in myelin
What are 2 features of receptors
- Specific to single type of stimuli
- Acts as a transducer to produce a generator potential
What do transducers do
Changes 1 form of energy into another form
What does the Pacinian corpuscle respond to
Changes in mechanical pressure
In terms of being a transducer, what does the Pacinian corpuscle do
Convert mechanical energy into electrical energy which creates a generator potential
When pressure is applied to the end of a sensory neurone, what happens
The pressure distorts the layers of cells around the neurone. This stretches the membrane of the sensory neurone so the sodium ion channels open. Sodium ions diffuse in. This results in a dipolar membrane which creates a generator potential
What are the 2 receptors in the eye
- Rods
- Cones
How many types of rods are there
Only 1
Are the more rods or cones
More rods
Are rods found at the periphery of the retina or at the fovea
At the periphery of the retina
How many types of cones are there
3 types each corresponding to different wavelengths of light
How are cones distributed in the eye
Few at the periphery of retina, concentrated at fovea
What does the SAN being myogenic mean
Acts independently of nervous system
Why is the SAN know as the pacemaker of the heart
The SAN starts the heart beat
What is the SAN located
In the wall of the right atrium
Where is the AVN located
In the wall of the right atrium
With increased respiration, what increases, and what is the effect in the pH of the blood
Partial pressure of carbon dioxide increases, so the pH of the blood decreases
When there is an increase in partial pressure of carbon dioxide, where do the impulses get sent to
The cardioacceleratory centre in the medulla oblongata
When there is a decrease in partial pressure of carbon dioxide, where do the impulses get sent to
The cardioinhibitory centre in the medulla oblongata
What is the role of the SAN
To initiate the rhythm of the heart
What does the SAN sent out
A broad wave of dipolarisation
Where does the wave of dipolarisation from the SAN get sent
Across both atria
What does the wave of dipolarisation sent from the SAN result in
The contraction of bot atria, atrial systole
After a delay after the SAN sends out a wave of dipolarisation, what does the AVN do
Picks up the wave of dipolarisation
Once the AVN has picked up the wave of dipolarisation, what happens
The AVN transmits electrical activity as an impulse to the apex of the heart, through the Bundle of His
What does the Bundle of His do
Transmits electrical activity from the AVN to the apex of the heart
When the impulse reaches the apex of the heart, what happens
The impulse spreads out through a series of fibres (Purkinje fibres)
Why is it important that the ventricular contract bottom up
To push the blood up and out of the heart through the arteries
Why is the delay between the SAN wave and the AVN picking up the wave important
To allow the ventricles to fill before ventricular systole
What does autonomic mean
Self governing
What is the word used to describe the relationship between parasympathetic and sympathetic nervous system
Antagonistic
What is the name of the receptors that detect changes in pressure
Baroreceptors
When there’s a high blood pressure, what detects that and what is the effect
Baroreceptors detects the change in pressure, in high blood pressure the medulla oblongata sends impulses along the parasympathetic pathway which inhibits SAN activity so slows down the heart rate
Where there’s low blood pressure, what detects this, and what is the result
Barorecpetors detect change in pressure, in low blood pressure the medulla oblongata sends impulses along the sympathetic pathway which increases the frequency of SAN dipolarisation waves which increases the heart rate
Exercise causes an increase in heart rate, Describe the role of receptors and of the nervous system in this process (4 marks)
- Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall
in pH
OR
Baro / pressure receptors detect rise in blood pressure; - Send impulses to cardiac centre / medulla;
- More impulses to SAN;
- By sympathetic (nervous system for chemoreceptors / CO2)
OR
By parasympathetic (nervous system for baro/ pressure receptors/ blood pressure)
When the heart beats both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of heartbeat by the SAN (2 marks)
- Electrical activity only through Bundle of His / AVN;
- Wave of electrical activity passes over / through both ventricles at the
same time;
For ‘electrical activity’ accept impulses /
depolarisation / action potential
The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea. Explain how the fovea enables an eagle to see its prey in detail. (3 marks)
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
Accept no retinal convergence.
Accept ‘bipolar/nerve cell’ for neurone. - (Cones send) separate (sets of) impulses to brain;
The, retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night (3 marks)
- High (visual) sensitivity;
Accept retinal convergence. - Several rods connected to a single neurone;
Accept ‘bipolar/nerve cell’ for neurone - Enough (neuro)transmitter to reach/overcome threshold
OR
Spatial summation to reach/overcome threshold; more for ‘several’
Explain how resting potential is maintained (2 marks)
- Membrane more permeable to potassium ions and less permeable to
sodium ions; - Sodium ions actively transported / pumped out and potassium
ions in.
