paper 2: Stimuli and Receptors Flashcards
define tropism
a directional growth response to a stimulus
what is positive phototrophism
plant grows towards the light
what is negative phototrophism
plant grows away from the light
what is positive gravitropism
plant grows with gravity
what is negative gravitropism
plant grows against gravity
where is IAA produced
cells in the tip of a root/shoot
what does a high concentration of IAA do in a shoot.
IAA stimulates cell elongation in the shoot
at does high concentrations of IAA do in a root
IAA inhibits cell elongation in the root
describe steps by which IAA cases positive phototropism in shoots
- cells in tje tip of the shoot produce IAA
- IAA diffuses to the shaded side of the shoot, increases its concentration
- IAA stiumulation cell elongation on shaded side
- cells elongate more on the shaded side than the light side, bending the shoot towards the light
describe the steps by which IAA causes positive gravitropism in roots
- cells in the tip of the eoot produce IAA
- IAA diffuses to th lower side of the root
- IAA inhibits cell elongation
- cells elongate less on the lower side than the upper side
what is a taxis
a directional movement to a stimulus
what is kinesis
a non-directional movement to a stimulus
explain how a woodlice uses kinesis if it was an unfavourable environment suhc a slow humidity
negative taxis, allows woodlice to move away from area of low humidity towards a more favourab;e environment
what is a reflex
reflex = rapid, involuntary response ti a stimulus
xplain why organisms have reflexes
the prtoect against damage to body tissues and can help them escapre from predators
state 3 neurons in a reflex arc in the correct order
sensory neurone, intermediate neurone, motor neurone
describe the sequence of events in a reflex arc
- stimuli is detected by receptor
- sends information to the sensory neurone
- information sent to intermediate neurone in spinal cord
- information sent to motor neurone
- impulse sent to effector where response occurs
define a receptor
detect stimuli and forms a generator potential
what type of stimulus does the pacinin corpuscle detect
pressure
draw and label a diagram of a pacinian corpuscle
describe the steps by how pacinian corpuscle causes a generator potential
- the lamellae deform
- stretch mediated sodium ion channels in the neurone membrane open
- sodium ions diffuse into the neurone- depolarising it
- this produces a generator potential, which, if reaches threshold, causes an action potential
- the greater the pressure, the more Na+ channels open and the greater the generator potential
list the difference between rods and cones in terms of position in retina, pigment, detecting colour, sensitivity, visual acuity and retinal convergence
explain why cones have a higher visual acuity than rods
- each cone connects to a single neurone so a separate set of nerve impulses is sent to the brain from each cone cell
whereas
- several rod cells connect to a single neurone (retinal convergence) so one set of nerve impulses ar sent to the brain from multiple rods
explain why cones see more colour and rods only see black and white
cones see colour as there are 3 different types of cone with different iodopsin so each one identifies a different wavelength of light.
rods contain rhodopsin which cannot distinguish between the different wavelengths of light
explain why rods are more sensitive than cones to low light intensities
multiple rod cells connect to a single neurone (retinal convergence) so the generator potentials combine (spatial summation) to reach threshold in the neurone
only one cone cell connects to a single neurone so a high light intensity is required for a generator potential to reach threshold in the neurone
starting with the sinoatrial node, describe the steps of how heart rate is initiated and coordinated
- heart is myogenic
- sino atrial node initiates the heartbeat by geerating electrical impulses
- these electrical impulses are sent across the atria causing them to contact
- a layer of non-conducting tissue prevents the impulses spreading to the ventricles so the ventricles dont contract
- the atrioventricular node delays the impulses to give time for blood to leave the atria and fill the ventricles before the ventricles contract
- the impulses then travel down the bundle of His and up the purkinje fibres
- the ventricals contract from the bottom up
where are the chemoreceptors found and what do they detect
found in the aorta and carotid arteries and they detect changes in concentration of CO2 and pH
where are the pressure recpetors found and what do they detect
found in walls of aorta and carotid arteries and detect chnages in blood pressure
what does the sypathetic nerve do in terms of heart rate
increases heart rate
what does the parasympathtic nerve do in terms of heart rate
decreases heart rate
during exercise, explain how an increase in heart rate occurs
- during exercise, muscles aerobically respire more to produce more ATP for muscle contraction. This prouces more carbon dioxide
- since carbon diocide is an acidic gas, blood pH becomes lower
- this is detected by chemoreceptors in the aorta and carotid arteries. the chemorecptors send more nerve impulses to the medulla in the brain
- the medulla sends more nerve impulses down the sympathetic nerve and less impulses down the parasympathetic nerve to the sionatria node.
- the sinoatrial node produces more frequent electrical impulses resulting in an increased heart rate
after exrcise, explain how a decrease in heart rate occurs
- chemoreceptors detcect a decrease in blood carbon dioxide and an increase in blood pH
- less nerve impulses sent to the medulla
- more nerve implses sent down the parasympathetic nerve and less impulses are sent down the sympathetic nerve to the sinoatrial node
- less frequent electricla impulses sent from the sinoatrial node
explain how a decrease in heart rate occurs when blood pressure is too high
- pressure receptors (baroreceptors) in the walls of the aorta and carotid arteries detect a rise in blood pressure
- less nerve impulses are sent to the medulla from the pressure receptors
- more nerve impulses are sent down the parasympathetic nerve and less impulses are sent down the sympathetic nerve to the sioatrial node
- less frequent electrical impulses from the sinoatrial node, which decreases heart rate
explain how an increase in heart rate occurs when blood pressure is too low
- pressure receptors detect a fall in blood pressure
- more nerve impulses are sent from the pressure receptor to the medulla
- more nerve umpulses are sent down the sympathetic nerve and less impulses are sent down the parasympathetic nerve to the sinoatrial node
- more frequent electrical impulses are sent from the sioatrial node, increasing heart rate
