Topic 6: response to stimuli Flashcards
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Define stimulus
A stimulus is a detectable chnage in the environment.
These chnages can be detected by receptors
Organisms increase their chnace of survival by responding tot stimuli via different response mechanisms
What is a tropism?
Term given to when plants respond via growth to stimuli
Can be negative or positive- grow towards or away from stimulus
What are tropisms controlled by?
Give an example
growth factors
e.g. IAA
Outline what IAA is
IAA (indoleacetic acid) is a type of auxin and can control cell elongation in shoots and inhibit growth of cells in the roots. It is made in the tip or the roots and shoots but can diffuse to other cells
What is a phototropism?
Light is needed for the LDR in photosynthesis so plants grow towards light
This is a positive phototropism
- shoot tip cells produced IAA, causing cell elongation
- The IAA diffuses to other cells
- if there is unilateral light, the IAA will towards the shaded side of the shoot resulting in higher conc of IAA there
- cells on shaded side elongate more and hence plants bend towards light
roots do not photosynthesise, they must anchor the pplant deep in the soil
In roots, high IAA conc inhibits cell elongation, so roots elongate more on lighter side away from light
this is negative phototropism
outline gravitropism
IAA will diffuse from upper side to lower side of a shoot
if a plant is vertical, this causes the cell to elongate and plant grows upwards
if a plant is on its side, it will cause shoot to bend upwards- negative gravitropism
IAA moves to lower sides of roots so that the upper side elongates and the roots bend down towards gravity and anchors the plant in- positive gravitropism
what is a reflex
rapid, automatic response to protect from danger
Define Taxes
an organism will move its entire body a favourable stimulus or away from an unfavourable stimulus
positive taxes= towards stimulus
Define kinesis
an organism changes the speed of movement and rate it changes direction
Define receptor
- detect stimuli
only respond to specific stimuliand this leads to establishment of a generator potential
Name 3 types of receptor
-pacinian corpuscle
-rods
-cones
draw a pacinian corpuscle
How does stretch-mediated sodium channels link to pacinian corpuscle function?
membranes of pacinian corpuscle have stretch-mediated sodium channels
these open and allow sodium ions to enter sensory neurone only when they are stretched and deformed
when pressure is applied it deforms and na+ floods in leading to generator potential
Describe rod cells
process images in black and white
detect light of very low intensity- many rod cells connect to one sensory neurone- retinal convergence
brain cannot distinguish between separate sources of light- LOW VISUAL ACUITY
Describe cone cells
process images in colour
three types with different pigments, red green and blue
need HIGH light intensity
one cone cell to one biolpolar and one ganglion cell and one sensory neurone
high visual acuity
where are most cones located?
fovea
what is meant by myogenic?
heart contracts on its own accord but the rate of contraction is controlled by wave of electrical activity
Describe how SAN controls Hr
- SAN releases a wave of depolarisation across the atria causing it to contract
- AVN releases another wave of depolarisation when the first reaches it. A non-conductive layer between the atria and the ventricles prevents the wave travelling down the ventricles
- instead the bundle of his conducts the wave down the septum and the purkyne fibres
- therfore there is a short delay between second pump so the atria have time to pump blood into ventricles
- finally the cells repolarise
2 parts of autonomic NS
1- sympathetic NS
2- parasympathetic NS
more impulese sent by sympathetic NS…
increase hr
changes in ph are detected by…
chemoreceptors
change in pressure….
baroreceptors
when ph decreases..
impulses via sympathtic NS to increase Hr to increase heart rate to remove CO2
