Response to stimuli Flashcards
what is a stimulus?
A detectable change in the internal or external environment of an organism
what is the sequence of stimulus and response?
stimulus –> receptor –> coordinator –> effector –> response
what is taxis?
taxis is a simple response whose direction is determined by the direction of the stimulus
what is kenisis?
a forms of response in which the organism does not move towards or away from a stimulus but it changes the speed at which it moves an the rate it changes direction
what is a tropism?
the growth of part of a plant in response to a directional stimulus
what are three factors that plants respond to?
– light
– gravity
– water
what are the events if phototropism in flowering plants?
– cells in tip of shoot produce IAA which is then transported down the shoot
– the IAA is initially transported evenly throughout all regions as it begins to move down the shoot
– light causes the movement of IAA from the light side to the dark side of the shoot
– a greater concentration of IAA builds up on the shaded side rather than the light side
– as IAA causes elongation of shoot cells
– the shaded side of the shoot elongates faster than the light side so bends towards light
what are the events of gravitropism in flowering plants?
– cells in the tip of the root produce IAA, which is transported along the root
– the IAA is initially transported to all sides of the root
– gravity influences the movement of IAA from the upper side to the lower side
– a greater concentration of IAA builds up on the lower side of the root than on the upper side
– as IAA inhibits the elongation of root cells their is a greater concentration of IAA on lower side
– greater elongation of cells on upper side than lower side
what are the two major divisions of the nervous sytem?
– the central nervous system
– the peripheral nervous system
what are the two parts the PNS is divided into?
– sensory neurones
– motor neurones
what two parts is the motor nervous system divided into?
– voluntary nervous system
– autonomic nervous system
what are the main stages of a spinal reflex arc?
– the stimulus
– receptor
– sensory neurone
– coordinator
– motor neurone
– effector
– response
what is the importance of the reflex arc?
– they are involuntary and therefore do not require decision-making powers of the brain
– protect the body from harm
– they are fast
– action is rapid
what does the Pacinian corpuscle do?
respond to mechanical stimuli such as pressure
How does the Pacinian corpuscle function?
– at it’s resting state stretch-mediated sodium channel are too narrow to allow sodium ions to pass along them
– when pressure is applied it is deformed and membrane is stretched
– sodium channel are widened
– influx of sodium ions causes depolarisation
– the generator potential in turn creates an action potential
what are rod cells?
cells in the eye which cannot distinguish different wavelengths of light and therefore lead to images being seen only in black and white
what are cone cells?
cells in the eye which can respond to different wavelengths of light
what are the two sections of the autonomic nervous system?
– sympathetic nervous system
– parasympathetic nervous system
what does the sympathetic nervous system do?
stimulates effectors and speeds up activity
what does the parasympathetic nervous system do?
inhibits effectors and so slows down any activity
what are the sequence of events that controls heart rate?
– wave of electrical excitation spreads out from the sinoatrial node across both atria so they contract
– a layer of non-conductive tissue prevents the wave crossing to the ventricles
– the wave of excitation enters a second group of cells called the atrioventricular node
– after a short delay wave spreads through the ventricles and down the bundle of His
– the bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles
– the wave of excitation is released causing ventricles to contract quickly
how is heart rate controlled by chemorecptors?
– when CO2 is high Ph is low
– the chemoreceptor in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to medulla oblongata
– centre increases the frequency of impulses by sympathetic nervous system to sinoatrial node
– increased blood flow causes more CO2 to be removed
– PH of blood rises to normal and the chemoreceptors in wall reduce frequency of nerve impulses
– medulla oblongata reduces frequency of impulses to the sinoatrial node
how is heart rate controlled by pressure receptors when blood pressure is high?
– pressure receptors transmit more nervous impulses to the centre of the medulla oblongata that decrease heart rate
– sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart
how is heart rate controlled by pressure receptors when blood pressure is low?
–pressure receptors transmit more nervous impulses to the medulla oblongata hr increases
– the centre sends more impulses via the sympathetic nervous system to the sinoatrial node
what is tropism?
when plants respond, via growth, to stimuli
