Section 6 - 14 Response to stimuli Flashcards
Define - Stimulus
Detectable change in the internal or external environment of an organism that leads to a response in the organism.
Define - Selection pressure
External agents which affect an organism’s ability to survive in a given environment.
Define - receptors
Specific to one type of stimulus. A stimulus is detected by a receptor.
What does an effector do?
Produce a response.
What are the bodies two ways of communication?
The nervous system
the hormonal system.
What is the central coordinator?
Acts as a switchboard connecting information from reach receptor with the appropriate effector,
Summarise the sequence of events of communication
Stimulus -> receptor -> coordinator -> effector -> response
Define - Taxis
A simple response whose direction is determined by the direction of the stimulus.
What are the two types of taxis?
Positive - movement towards the stimulus
Negative - Away from the stimulus
Define - Kineses
Form of response in which the organism does not move towards or away from a stimulus. Instead, it changes speed and rate of change in direction to stay in optimum conditions more.
Define - Tropism
The growth of part of a plant in response to a directional stimulus.
What are the two types of tropism?
Positive - towards the stimulus
Negative - away from stimulus
How do shoots grow?
Towards the light - positive phototropism and Away from gravity - negative gravitropism
How do roots grow?
Away from light - negative phototropism. and towards gravity - positive gravitropism
Give examples of stimuli plants respond to
Light, gravity and water.
What is a plant growth factor?
External stimuli a plant response to: Exert influence by affecting growth made by cells throughout the plant rather than in particular organs affect the tissues that release them rather than acting on a distant target organ
Give an example of a plant growth factor
Indoleacetric acid (IAA) - a type of auxin controlling plant cell elongation.
Define - positive phototropism
young shoots growing towards the light that is directed at it from one side - unilateral light
Describe phototropism in flowering plants
- cells at tip of shoot produce IAA - transported down the shoot
- IAA initially transported evenly throughout all regions as it begins to move down the shoot
- light causes movement of IAA from the light side to the shaded side of the shoot
- greater conc. of IAA builds up on the shaded side of the shoot than on the light side.
- IAA causes elongation of shoot cells and there is a greater concentration on the shaded side the cells on this side elongate more
- shades side of shoot elongates faster than the light side causing the shoot tip to bend towards the light.
Explain the gravitropism in flowering plants
- cells in tip of root produce IAA transported along root
- IAA initially transported to all sides of the root
- gravity influences the movement of IAA from the upper side to the lower side of the root
- greater conc. of IAA builds upon the lower side of root than upper
- IAA inhibits elongation of root cells there is a greater conc of IAA on the lower side the cells on this side elongate less than those on the upper side
- relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity.
How does phototropism effect shoots?
High IAA conc. stimulates cell elongation causing positive phototropic response.
What effect does phototropism have on roots?
high IAA conc. inhibits cell elongation causing a negative phototropic response
What effect does gravitropism have on shoots?
high IAA conc. stimulates cell elongation causing a negative gravitropic response
What effect does gravitropism have on roots?
high IAA conc. inhibits cell elongation causing positive gravitropic response.
What effects does IAA have on plant cells?
- increase plasticity - ability to stretch cell walls
- elongate young cell walls.
- As older the cell walls become more rigid for older parts are unable to respond.
What is the acid growth hypothesis?
The proposed explanation of how IAA increases plasticity of cells.
- Active transport of hydrogen ions from cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion.
explain the acid growth hypothesis
Active transport of hydrogen ions from cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion.
What are the two major divisions of the nervous system?
- Central nervous system - brain and spinal cord
- peripheral nervous system - pairs of nerves that originate from the brain or spinal cord
What is a sensory neurone?
Carrying nerve impulses from receptors to central nervous system
What is a motor neurone?
Carry nerve impulses away from central nervous system to effectors.
Explain the human nervous system
State the aspect of a reflex arc
- rapid
- short-lived
- localised
- involuntary
State the stages of reflex arc (AKA spinal reflex arc)
- stimulus
- receptor
- sensory neurone
- coordinator/relay neurone
- motor neurone
- effector
- response
What are reflex actions important?
- involuntary and require no decision making
- protect the body from harm - not learnt so effective from birth
- fast as neurone pathway is short
- rapid action as no decision making
- Does not coordinate with the brain if the action is powerful enough - speeds up
What are dendrons?
Parts of the reflex arc that sends impulses to the CNS
What is an axon?
Part of the reflex arc that sents impulses away from the central nervous system
What is the sympathetic system?
- Stimulates effectors and speeds up activity
- control response to stress
- heightened awareness
- flight or fight
- part of autonomic system
What is the parasympathetic system?
- Inhibits effects and slows activities
- controls in relaxed environments
- awareness dulled
- rest and digest
- part of autonomic system
Why can the heart be called mycogenic?
It has the capsity to beat itself with no external help.
Using sinoatrial node as pacemaker
what is the hearts pacemaker?
sinoatrial node
What features of sensory recpetion are illustrated by the Pacinian corpuscle?
- specific to a single type of stimulus
- Response to changes in mechanical pressure
- produces a generator potential by acting as a transducer
- This means energy is converted or transduced into a different type of energy
- the mechanical energy of stimulus into the generator potential energy.
Where is the Pacinian corpuscles found?
- deep in the skin
- finger, soles of feet and external genitalia
- Also in joints, ligaments and tendons (able body to know which joint is moving direction)
What is the structure of a Pacinian Corpuscle?
- Single sensory neurone in centre of layers of tissue separated by gel.
- The neurone has a sodium channel in its plasma membrane - called stretch-mediated sodium channel
- As permeability to sodium changes when they are deformed eg. stretching
Why is the sodium channel within a Pacinian Corpuscle called a stretch-mediated sodium channel?
As permeability to sodium changes when they are deformed eg. stretching
What are the functions of a Pacinian Corpuscle?
- At rest the Stretch-mediated sodium channels are too narrow to allow sodium ions to pass through - Called resting potential
- when pressure applied it is deformed and the membrane is stretched
- This widens sodium channel and sodium diffuses into the neurone
- the influx of sodium depolarises producing a generator potential
- this creates an action potential that can pass along the neurone and to the CNS.
Where are light receptor cells found?
the innermost layer of the eye
retina
What are the two types of light receptor cells and what do they do?
- rod cells
- Cone cells
Act as transducers by conserving light energy into electrical energy of a nerve impulse.
why are rod cells black and white?
Can not distinguish different wavelengths of light.
- As there is only one type of rhodopsin
Explain how Rod Cells work
- light strikes cell
- rhodopsin breaks down forming retinal and opsin
- causes the rod cells to depolarise (less negative)
- generator potential occurs
- lead to action potential in bipolar neuron
What is the stimuli for rod cells?
- low intensity light on the retina
- rhodopsin and summation is sensative
- multiple cells to one neurone so more easy to be broken down
State the characteristics of rod cells
- summation
- low visual acuity (can’t distinguish between wavelengths)
- sensitive to low light intensity (rhodopsin and summation is sensitive)
- Black and white vision only
What is the stimuli of cone cells?
- bright light
- retina fovea
What pigment is found in rod cells?
rhodopsin
break down to opsin and retinal
Black and white vision only
What pigment is found in cone cells?
- 3 types of iodopsin
- red, green and blue
Explain how cone cells produce an action potential
- light strikes cone cell in retina fovea
- iodopsin break down
- causing depolarisation
- generator potential occurs
- action potential in bipolar neuron
What are the characteristics of cone cells?
- no summation
- high visual acuity (one cone to one neuron so know which wavelength has been sent)
- responds to high light intensity (as not sensitive to light so a lot more is needed)
- different cone cells activated by different wavelengths
- colourvision
Explain the control of heart rate
- wave of electrical excitation spreads from sinoatrial node causing both atria to contract
- wave reaches the atrioventricular node
- short delay so ventricle can fill
- This is because the atrioventricular septum (layer of tissue between atria and venticle) is no conducting
- the signal passes down the bundle of his to the purkyne fibres
- wave released from purkyne tissues causing ventricles to contract from the base up (from apex)
What is the region of the brain that controls heart rate?
Medulla Oblongata
What are the two divisions of the medulla oblongata and what do they do?
- cardioexcitatory centre - increases HR - link to SA node by the sympathetic nervous system
- cardioinhibitory centre - decrease HR - link to SA node by parasympathetic nervous system
How do chemoreceptors respond to an increased rate of respiration?
- Increased CO2 production
- Decreased pH of the blood
- Chemoreceptors detect in carotid arteries in the brain
- increase impulses in cardioexitatory centre
- increase impulses to SA node via the sympathetic nervous system
- SA node increases heart rate
- increase removal of CO2
- Blood pH returns to normal
How do chemoreceptors respond to a decreased rate of respiration?
- Decreased CO2 production
- increased pH of the blood
- chemoreceptors detect in carotid arteries of the brain
- increased impulses in cardioinhibitory centre
- increased signal to SA node via the parasympathetic nervous system
- SA node decreases heart rate
- decreased removal of CO2
- blood pH return to normal
EQUATION
Blood pressure
Blood pressure = cardiac output x total peripheral resistance
During exercise, the blood pressure decreases as TPR decreases so that pressure overall is the same as CO = HR x SV
where are pressure receptors found?
in walls of carotid arteries and aorta.
Called Baroreptors
What happens if the blood pressure is too high?
- barorecpetors increase impulses to cardioinhibitory centre
- more impulses sent to SA node via the parasympathetic nervous system
- SA node decreases HR
What happens if blood pressure is too low?
- HR needs to be increased
- Baroreceptors increase impulses to cadioexcitatory centre
- more impulses sent to SA node via the sympathetic nervous system
- SA node increases HR
