mini test on response Flashcards
define phototropism
directional response to light
what is auxin
a phytohormone (growth factor produced in response to light)
on what side of the plant does auxin accumulate
shady side
effect of auxin on plant shoots
causes cell elongation by breaking down the cell walls using H+ ions to increase acidity, weakens hydrogen bonds between molecules- water enters
the effect of a plant growth factor depends on
- conc. of growth factor
- stem or roots
- developmental stage of the plant
- species of plant
- other growth factors present (synergism or antagonism)
define photoreceptors
structures or pigments that are sensitive to light, often of a specific wavelength
define phototropins
a group of photoreceptors primarily responsible for triggering phototropisms
where is auxin made?
meristems and young leaves
effect of IAA on root growth (phototropism)
negative- redistributes to the shaded side of the root and inhibits root growth so the side with a lower concentration will grow faster and the root will bend away from the light
effect of IAA on root growth (geotropism)
positive- redistributes to the underside of the root and inhibits growth so the root will bend towards gravity
define stimulus
a detectable change in the internal/external environment
define receptor
a cell or organ that detects change in internal/external environment
- detects a specific stimulus and converts energy into a generator potential which can cause an action potential in the sensory neurone
define coordinator
connects information between the receptor and appropriate effector
define effector
a cell, tissue, organ, or system that carries out a response
define taxes and kineses (vague)
simple responses that can maintain a mobile organism in a favourable environment
what’s the difference between taxes and kineses
taxes is directional but kineses is moving more or less
what do you use to keep a section of a choice chamber dry
calcium chloride
purpose of the cell body of a neurone
contains the nucleus and organelles
purpose of the dendrites in a neurone
conducts impulses towards the cell body
purpose of the axon in a neurone
transmits impulses away from the cell body
define nerve
complex tissue containing a bundle of axons of many neurons with a protective covering
purpose of schwaan cells
produce multiple plasma membrane layers which wrap around the axon and dendron, causing it to become myelinated
importance of myelination
action potential can be generated at nodes of ranvier, allowing saltatory conduction to occur instead of generating an action potential along the whole length of the neurone
define transducer
something that converts energy from one form to another
define ligand
molecule that binds to a receptor, causing a change within a cell (e.g. nt)
how is a resting potential generated
1) sodium potassium pump (3 Na+ out, 2 K+ in) - axon becomes overall negative
2) potassium leak channel (K+ leave via facilitated diffusion)
what is the negative charge for resting potential
-70mV
action potential - stimulus
- excites membrane
- L-gated Na+ ion channels open
- Na+ in down electrochemical gradient
- neurone becomes less negative
action potential - depolarisation
- of threshold of -55mV is met, V-gated Na+ channels open
- more Na+ in
- positive feedback, overall charge becomes +ve
action potential - repolarisation
- Na+ channels close at threshold of +30mV
- V-gated K+ channels open and K+ diffuse out of neurone down conc. gradient
- membrane begins to return to resting potential
action potential - hyperpolarisation
- K+ channels slow to close so ‘overshoot’ occurs
- becomes more negative than resting potential
action potential - final step
- Na+ K+ pump returns membrane to resting potential
why is the refractory period important
ensures unidirectional flow as the neurone is too negative for V-gated Na+ channels to open
(recently depolarised area of neurone can’t be restimulated by the depolarisation it just initiated in the nearby node)
define mechanoreceptor
detects mechanical deformation (e.g. pacinian corpuscle, baroreceptors-blood pressure)
generator potential in pacinian corpuscle
- deformation of fluid filled capsule of membranes
- Na+ influx into axon by stretch-mediated Na+ channels
- causes generator potential
what is retinal convergence
spatial summation of rods to bipolar neuron
+ve and -ve of spatial summation in rods
- high sensitivity as can summate signals to meet thresholds so can see in lower light intensities
- low visual acuity
what pigment do rod cells contain
rhodopsin
what pigment do cone cells contain
iodopsin
what is glutamate
an inhibitory nt, rod cells stop releasing it when hyperpolarised (in light) so potential generated in bipolar neurone
how is unidirectional flow created in synaptic transmission
- refractory period
- L-gated Na+ channels are only on post synaptic membrane
what is acetyl choline
the primary nt in the parasympathetic division of the autonomic nervous system
- involved in rest and digest
what ions are involved at an inhibitory synapatic transmission
K+ out of membrane and Cl- into membrane to create hyperpolarisation
what does myogenic mean
a characteristic of cardiac muscle where it can initiate its own contractions without the need for nervous stimulation
sinoatrial node
generates electrical impulse in the heart
