14.0 Response to stimuli Flashcards
What is a taxes?
Simple reponse where the direction of movement is determined by the direction of the stimulus
What is a kinesis?
Not movement towards or away from a stimulus.
Instead it is the change in speed or rate at which
it changes direction
What is a tropism?
Growth of a part of a plant in reponse to a
directional stimulus
How do woodlice use kinesics to stay moist?
When in a dry area they start to move rapidly
and change direction a lot. Increases their
chances of moving back into a damp area.
What growth factor controls phototropism?
Indoleacetic acid
How does IAA control phototropism in flowering shoots?
- Cell in shoot tip produce IAA.
- Originally IAA is transported evenly down the shoot.
- IAA moves away from light to shaded area. 4. Greater concentration of IAA means elongation of shoot cells.
- Shaded side elongates faster so tip bends
towards light
How does IAA control gravitropism in flowering roots?
- Cells in the root tip produce IAA.
- Originally IAA is distributed evenly down the root. 3. IAA moves towards the pull of gravity.
- More IAA on lower side of root.
- In root IAA inhibits the elongation of root cells.
- Cells on upper side therefore grow faster and root bends downwards
Compare the response to IAA in the root and the shoot
In shoot increases enlongation, mediated by
light. In roots inhibits elongation and is mediated
by gravity.
How does IAA cause cells to elongate?
Increases the plasticity of their cell walls using
the acid growth hypothesis
What is the acid growth hypothesis?
Active transport of hydrogen ions from the
cytoplasm into spaces in the cell wallcausing the
cell wall to become more plastic.
What are receptors?
Cells that detect a specific stimuli
What does the pacinian corpuscle detect?
Changes in mechanical pressure
What is the special type of sodium channel pacinian corpuscles have?
Stretch-mediated sodium channels
How does the pacinian corpuscle function?
At rest the stretch mediated sodium channels are
too narrow to allow sodium ions to diffuse
across. When pressure is applied the membrane
becomes deformed and stretched. This causes the
stretch mediated sodium channels to widen and
allows the sodium ions to diffuse through. This
causes the membrane to become depolarised and
creates a generator potential
What evidence do we have for tropisms in plants?
removing or covering shoot tip prevents tropism
[tip causes tropism]. placing micin (prevents
movement of chemicals e.g. IAA) across shoot
inhibits tropism [tropism caused by movement of
chemicals] . placing gelatine (prevents
movement of electrical signals) across shoot
does not affect tropism [tropism not caused by
movement of electrical signals] . if shoot tip is
moved to one side, that side grows faster and the
shoot bends the other way [IAA promotes
growth in shoot] . when in light or darkness the
overall levels of IAA remain the same [light does
not inhibit or breakdown IAA but rather
redistributes it]
What don’t rod cells do?
They can’t distinguish between different
wavelengths of light and therefore lead to black
and white images.
What do cone cells do?
Detect high light intensity only, produces colour
images, three different types each one
responding to a different wavelength of light
What pigment do cone cells contain?
Iodopsin
What pigment do rod cells contain?
Rhodopsin
How many neurones is each cone cell connected to?
Each cone cell connects to one bipolar neurone
which connects to one sensory neurone
Why can we see at low light intensities?
Several rod cells connect to one bipolar neurone
allowing spatial summation to occur.
What charge is resting potential?
-65mV
What region of the brain controls heart rate?
medulla oblongata
How is heart rate controlled?
- A wave of excitation is spreads out from the
SAN across both atria causing them to contract. - Wave of excitation cannot cross atrioventricular
septum. - Wave of excitation then enters AVN.
- After a short delay this conveys a wave of
excitation across the purkyne tissue which
together makes up the bundle of His. - Wave of excitation is released from purkyne tissue and causes both ventricles to contract from the bottom up.
What is the function of the sympathetic nervous system?
Stimulates effectors and speeds up activity
What is the function of the parasympathetic nervous system?
Inhibits effectors and so slows down any
activity.
What autonomic nervous system causes an increase in heart rate?
Sympathetic nervous system
What happens when carbon dioxide levels in the blood are too high?
- This causes pH to lower.
- Chemoreceptors detect this and increase the frequency of impulses to the medulla oblongata which increases the frequency of impulses to the SAN via the sympathetic nervous system.
- This means more wave of excitations are produced by the SAN which increases blood flow.
- Increased carbon dioxide removal
What happens when blood pressure is too high?
Pressure receptors detect this and transmit more
impulses to the medulla oblongata. The
parasympathetic nervous system then sends an
impulse to the SAN which decreases heart rate
What happens when blood pressure is too low?
Pressure receptors detect this and increase the
frequency of impulses to the medulla oblongata.
The sympathetic nervous system then sends an
impulse to the SAN increasing heart rate
