Response to stimuli Flashcards
tropism
the response of a plant to a directional stimulus
2 x Growth factor examples
auxin (IAA) - cell elongation
giberellins - germination and flowering
Describe growth factors
made in the growing regions
move short distances by diffusion and AT
long distances via the phloem
IAA and phototropism in shoots
moves to the shaded side and promotes cell elongation
so the shoot grows towards the light
IAA and phototropism in roots
shaded side and inhibits growth
so shoots grow away from light
What is the purpose of Kinesis and Taxis?
keeps mobile organisms in favourable conditions
Taxes
moves towards or away from a directional stimulus
Kinesis
no directional stimulus - turns moves more to find more favourable area
Reflex
rapid response to a stimulus without conscious control
What effector controls blinking?
orbiculosis oculi muscle
What are the advantages of reflex action?
get away from danger
fast
prevent harm
do not have to be learned
Describe the process of the pacinian corpuscle response?
detects stimulus
pressure causes lamellae to deform
stretch mediated sodium ion channels ope
Na + diffuses into the neurone
greater the pressure the more ions open
depolarisation
if threshold is reached an action potential is initiated
How is an action potential created in The Human Eye?
light is focused onto the retina by the lens
light is absorbed by pigments on the photo receptor
causes some sodium ion channels to open
if threshold is met then an action potential is generated
Describe Rods
monochromatic
more sensitive to low light
low visual acuity
mostly in the peripheral of the retina
Describe Cones
trichromatic
less sensitive to low light
higher visual acuity
each cone has it’s own bipolar neuron
Describe the control of heart rate
SAN initiates the heartbeat
sends impulses across the atria, causing them to contract
non conductive tissue prevents the impulse from reaching the ventricles
AVN delays the impulse
AVN then sends the impulse down the Bundle of His to the Purkinje fibres
this causes ventricles to contract from the base up
Describe the left ventricle
highest blood pressure
most cardiac muscle = greatest force
pumps blood to whole body
What nervous system is responsible for changing the Heart Rate?
autonomic
slow down heart rate
chemo/bororeceptors detect
send impulses medulla oblongata in the brain
parasympathetic neurones secrete acetylcholine
heart rate slows
speed up heart rate
chemo/bororeceptors detect change impulses to the medulla oblongata impulses along sympathetic sympathetic neurones secrete noradrenaline heart rate speeds up
