6. responding to changes in environment P2 Flashcards
SURVIVAL AND RESPONSE
explain why plants show positive phototropism
- IAA diffuses to shaded side of shoot tip.
- as IAA diffuses down shaded side, it causes active transport of H+ ions into the cell wall
- disruption to H-bonds between cellulose molecules and action of expansions make cell more permeable to water
- cells on shaded side elongate faster due to higher turgor pressure
- shoot bends toward light
SURVIVAL AND RESPONSE
explain why roots show positive gravitropism
- gravity causes IAA to accumulate on lower side of root
- IAA inhibits elongation of root cells
- cells on upper side of root elongate faster, so the root top bends downwards
SURVIVAL AND RESPONSE
define taxis and kinesis
taxis: directional movement in response to external stimulus
kinesis: non- directional response to presence and intensity of external stimulus
SURVIVAL AND RESPONSE
state the advantage of taxis and kinesis
maintain mobile organism in optimum order environment e.g. to prevent dessication.
SURVIVAL AND RESPONSE
many organisms respond to temperature and humidity via kinesis rather than taxis. why?
less directional stimuli; often no clear gradient from one extreme to the other
SYNAPTIC TRANSMISSION
outline what happens in a simple reflex arc
receptor detects stimulus —> sensory neuron —> relay neurone in CNS coordinates response —> motor neurone —> response by effector
SURVIVAL AND RESPONSE
give the advantages of a simple reflex
rapid response to potentially dangerous stimuli since only 3 neurones involved
doesn’t have to be learnt
SURVIVAL AND RESPONSE
what features are common to all sensory receptors?
act as energy transducers which establish a generator potential
respond to specific stimuli
SURVIVAL AND RESPONSE
what features are common to all sensory receptors?
act as energy transducers which establish a generator potential
respond to specific stimuli
RECEPTORS
describe the basic structure of a Pacinian corpuscle
- single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
- stretch-mediated Na+ channels on plasma membrane
- capillary runs along base layer of tissue
RECEPTORS
what stimulus does a Pacinian corpuscle respond to and how
pressure deforms membrane, causing stretch-mediated Na+ ion channels to open.
if the influx of Na+ raises membrane to threshold potential, a generator potential is produced.
action potential moves along sensory neuron.
RECEPTORS
name the two types of receptor cell found in the retina
cone cells
rod cells
RECEPTORS
where are rod and cone cells located in the retina?
Rod: evenly distributed around periphery but not central fovea
cone: mainly central fovea no photoreceptors at blind spot
RECEPTORS
compare and contrast rod and cone cells
pigment
ROD - rhodopsin
CONE- iodopsin
visual acuity
ROD - many rod cells synapse with one bipolar neuron (low resolution)
CONE - one cone cell synapses with one bipolar neuron (high resolution)
colour sensitivity
ROD- monochromatic: all wavelengths of light detected
CONE - tricolour: red, blue, green wavelengths absorbed by different types of iodopsin
light sensitivity
ROD- very senstitive: spacial summation of subthreashold impulses
CONE- less sensitive: not involved in night vision
RECEPTORS
outline the pathway of light from a photoreceptor to the brain
photoreceptor —> bipolar neurone —> ganglion cell of optic nerve —> brain
RECEPTORS
The fovea of the eye of an eagle had a high density of cones. Explain how the fovea enables an eagle to see its pray in detail
high visual acuity as each cone is connected to a single neurone.
comes send separate sets of impulses to brain.
RECEPTORS
The retina of an owl has a high density of rod cells, explain how this enables an owl to hunt its prey at night.
high visual sensitivity.
several rods connected to a single neurone.
enough neurotransmitter to reach threshold (spacial summation)
RECEPTORS
explain how the resting potential of -70mV is maintained in the sensory neurone when no pressure is applied
membrane more permeable to potassium ions and less permeable to sodium ions.
sodium ions actively transported/pumped out and potassium ions in.
RECEPTORS
explain how applying pressure to the Pacinian corpuscle produces changes in membrane potential
pressure causes membrane to become stretched/deformed
sodium ion channels in membrane open and sodium ions move in
greater the pressure, more channels open, more sodium ions enter.
RECEPTORS
How would destruction of parts of the myelin sheath result in slower responses to stimuli?
Less/no saltatory conduction/ impulse unable to ‘jump’ from node to node.
more depolarisation over length.
RECEPTORS
the membrane potential was the same whether medium or heavy pressure was applied. explain why
Threshold has been re wedged which causes maximum response (all or nothing principle)
CONTROL OF HEART RATE
define myogenic
contraction of the heart is initiated within the muscle itself rather than by nerve impulses
CONTROL OF HEART RATE
state the name and location of the two nodes involved in heart contraction
Sinoatrial node (SAN): within the wall of the right atrium
Atrioventricular node (AVN): near lower end of right atrium in the wall that separates the two atria.
CONTROL OF HEART RATE
describe how heartbeats are initiated and coordinated
- SAN initiates a wave of depolarisation across both atria
- layer of fibrous, non-conducting tissue delays impulse (prevents it directly going to ventricles) while ventricles fill and valves close.
- impulses travel to AVN, down septum via bundle of His, which carries impulses to the Purkinje fibres.
- Purkinje fibres carry impulse from bottom of heart up both ventricles simultaneously, ventricles contract.