UNIT 6 - Stimuli, Response and Homeostasis Flashcards
what is a tropism
Tropisms is the growth part of a plant in response to a stimulus
what substance controls plant elongation
IAA
how does IAA work in meristem cells
meristem cells produce IAA which moves to the shaded side of the plant causing the concentration of IAA to build up causing elongation of the shaded side causing the shoot to bend towards the light
how does IAA work in root cells
IAA inhibits the cell elongation in roots so the roots that are exposed to sunlight will grow more
what is a taxis
a directional response to a =n external stimulus where a direction is determined by the direction of the stimulus
what is kineses
kineses is a non directional response from an organism to the presence and intensity of an external stimulus in order to move to the more favourable conditions
compare and contrast taxis and kineses
- taxis are more energy efficient than kinesis
- both provide survival sdvantages
- taxis is quicker at finding favourable conditions to kinesis
- taxis makes them less exposed to predators than kinesis which makes them more susceptible
what is the peripheral nervous system divided into
sensory neurones and motor neurones
what do sensory neurones do
carry nerve impulses from receptors towards the CNS
what do motor neurones do
carry nerve impulses away from the CNS to the effectors
what can the motor nervous system be divided into
- voluntary nervous system
- autonomic nervous system
what is the spinal corf
a column of nervous tissue that runs along the back and lied inside the vertebral column for protection
outline the reflex arc
- The stimulus: heat from hot object
- The receptor: temperature receptors in the skin generate nerve impulses in the sensory neuron
- The sensory neuron: passes nerve impulses to the spinal cord
- A coordinator / relay neuron: links sensory to motor in spinal cord
- The motor neuron: nerve impulses from the spinal cord to a muscle in the upper arm
- The effector: muscle in upper arm contracts after stimulation
- The response: pulling hand away
what are the reasons why reflex actions are important
- protect body from harm
- short and fast which is important in withdrawal reflexes
- doesn’t require a decision making process
what do receptors do
detect stimuli
what is the Pacinian corpuscle
a transducer that produces a generator potential
what is the structure of the pacinian corpuscle
the single sensory neurone is at the centra of the layers of tissue each seperated by a gel
how do the pacinian corpuscle transduce to produce a generator potential
at resting the stretch mediated sodium channel proteins are too narrow to allow Na+ through so there is a resting potential
when there is pressure applied the stretch mediated channel proteins widen and this allows Na+ ions to diffuse into the neurone producing a generator potential which turns into an action potential in a neurone and passes along the sensory neuron
what are the two types of receptor in the eye
rods and cones
what do rod and cone cells do
act as transducers by conserving light into the electrical energy of a nerve impulse
outline the features of Rod cells
cannot distinguish between different wavelengths of light and therefore lead to black and white images
there are more rod cells than cone cells
multiple rod cells are connected to a single sensory neurone in the optic nerve via bipolar cells for the threshold value to be exceeded
rods are very sensitive to changed in light intensity
low visual acuity
vital in spotting danger like predators
how do rod cells work as transducers
to create the generator potential the pigment called rhodopsin in broken down to depolarise rod cells and this energy comes from light and then the depolarised rod cell can produce an action potential
why do rod cells have bad visual acuity
multiple rod cells being connected to a single bipolar cell will generate a single impulse travelling to the brain and this means the brain cannot distinguish between the separate sources of light
outline the features of cone cells
there are three different types all responding to a different wavelength of light
each cone cell has their own bipolar cell which means in order to exceed the threshold value there must be high light intensity
cone cells contain a different type of pigment from that in rod cells and this required higher energy for breakdown
cone cells have very accurate vision and therefore a good visual acuity
compare and contrast rod and cone cells
cones cells detect colour whereas rod cells detect black and white
cone cells see in high light intensity whereas rods work in low level intensity
each cone cell has their own bipolar cell whereas rod cells share a bipolar cell
cones have good visual acuity and rod cells don’t
cone cells are pointed shaped and rod cells are round shaped
there are three different types of cone cells and only one of rod cells
fewer cone cells to rod cells
more cone cells are the centre and more rod cells at the periphery
what is the blind spot
the point at which neurones and blood vessels plunge down through the restina
are there more rod or cone cells on the fovea and why
more cone cells as the fovea is where the lens focuses the light on which means to receives the highest light intensity
what is trichromatic theory
there are 3 different types of cone cells that receive red blue and green and all other colours are perceived and created by light waves stimulating combinations of the cone cells
what is dark adaptation
when you are in a dark room for a prolonged period the photosensitive pigments are being formed faster than they are being broken down increasing sensitivity to light
what is light adaptation
when you are in a light room for a prolonged period of time the photosensitive pigments are broken down quicker than they are being made and this decreases sensitivity to light
what are plant growth factors and where are they produced
they are chemicals that regulate plant growth response to stimuli and they are produced in growing regions like meristem
how do plant growth factors travel around a plant
diffusion between cells and the phloem mass transport
explain why roots show gravitropism
- gravity causes IAA to accumaltae on lower side of the root
- IAA inbibits elongation of roots
- cells elongate on the upper side of the root so the root bends downwards
many organisms respond to temperature via kinesis rather than taxis why?
less directional stimuli and there is no clear gradient from one extreme to the other
how could a stident recognise Kinesis in an organisms movement
- organism crosses sharpy division between favourable and unfavourable and turning increases
- if organisms moves considerable distance into unfavourable conditions and turning decreases and starts to move in long straight lines
give an example of a simple reflex
- rapid response to potentially dangerous stimuli
- instinctive
what features are common to all sensory receptors
- act as energy transducers which establish a generator potential
- respond to specific stimuli
outline the pathway of light from a photoreceptor to the brain
photoreceptor —-> bipolar neuron —-> ganglion cell of optic nerve —-> brain
define what myogenic means
contraction of heart is intiated within the muscle itself rather than by nerve impulses
state the name and location of the 2 nodes involved in heart contraction
- sinoatrial node within the wall of the right atrium
- atrioventricular node near the lower end of the right atrium in the wall that seperates the 2 atria
describe how heartbeats are initiated and coordinated
- SAN initiates wave of depolarisation
- this spreads across both atria causing them to contract
- layer of fibrous non conducting tissue called the atrioventricular septum delays impulse while ventricles fill and valves close
- AVN conveys the wave of depolarisation down the septum via the bundle of his which branches into the Purkinje fibres along the ventricles
- the bundle of His conducts a wave through the AVS to the left and right into the base of the ventricles
- wave of depolarisation is released from the Purkinje tissues causing ventricles to contract from bottom up at the same time
state the formula for cardiac output
CO = stroke volume x heart rate
what is the autonomic nervous system
system that controls the involuntary actions of glands and muscles
there are 2 sub divisions called the sympathetic and parasympathetic
name the receptos involved in changing heart rate and where they are located
Baroreceptors detect changes in pressure in the blood in the carotid body
Chemoreceptors detect changes in pH due to increase in CO2 conc and this is located in the carotid body and aortic body
how does the body responf to an increase in blood pressure
- Baroreceptors send impulses to the medulla oblongata
- more impulses oto the SAN via the parasympathetic nervous system
- simulates the release of acetylcholine which decreases heart rate
how does the body responf to a decrease in blood pressure
- Baroreceptors send impulses to the medulla oblongata
- more inpulses to the SAN via the sympathetic nervous system
- estimulates the release or noradrenaline which increases heart rate and strenght of muscle contraction
how does the body respond to an increase in CO2 concentration
- chemoreceptors detect decrease in pH and send more impulses to the medulla oblongata
- more impulses to the SAN via the sympathetic nervous system
- heart rate increase so rate of blood flow increases and therefore gas exchange increases and ventilation rate increases
