14. Response to stimuli Flashcards
(35 cards)
Stimulus
Detectable change in internal or external environment of an organism, leading to response.
Tropism
Move entire body in response to stimulus,
Positive = towards
Negative = away
Describe a named growth factors role in Tropism
IAA is a type of auxin that stimulate cell elongation in shoots and inhibit cell growth in roots.
Describe phototropism in shoots(4)
Light is needed for LDR, plant must grow towards light.
- Shoot tip produces IAA,
- IAA diffuses to other cells,
- IAA diffuses to shaded side of shoot, causing uneven cell elongation.
- This leads to plant bending towards light source.
positive phototropism
Describe phototropism in roots (4)
Roots do not require light.
IAA inhibits cell elongation, root cells elongate more on lighter side.
root bends away from light.
Negative phototropism
Describe gravitropism in both shoots AND roots
Shoots,
- IAA diffuse to lower side, more cell elongation on bottom of shoot.
- curve upwards
- Negative gravitropism
Roots
- IAA on bottom of root, inhibiting cell elongation
- root curves downwards
- Positive gravitropism
What is a reflex
Rapid, automatic response to protect organism from danger.
what three neurons are involved in the reflex arc?
Sensory neuron, Relay neurone, Motor neurone.
Kinesis
An organism changes the speed of movement and rate it changes direction.
How would an organism respond with kinesis when it has moved to an area of harmful stimuli?
Increase rate that it changes directions to return to favourable conditions.
After being moved from positive stimuli to negative stimuli.
Why would an organism reduce changes in direction?
straighter line = more likely to move to favourable stimuli.
when surrounded by negative stimuli
Give the 7 steps of a reflex arc
- Stimulus
- Receptor neuron
- Sensory neuron
- intermediate neuron
- motor neuron
- effector
- response
Why are reflex arcs important? (3)
Involary - don’t overload brain.
protect - not learnt, from birth
fast - shorter neuron pathway, few synapses, no decision making
What is meant when cardiac tissue is described as myogenic?
Initiates its own rhythm of contractions, without nervous stimulation.
Where is the sinoatrial node (SAN) located?
right atrium
where is the atrioventricular node located?
right atrium, near the border of right and left ventricle.
Where is the bundle of his located?
Runs through the septum.
Where are the purkyne fibres located?
in the walls of ventricles?
What is the role of the SAN?
Wave of depolarisation across the atria causing it to contract.
What pigment is found in rod cells?
Rhodipsis
What is the role of rhodopsin/ iodopsin in rod/ cone cells
Broken down by light energy, creating generator potential
Give three differences between rod and cone cells
- rods produce a B/W image, cones in colour
- rhodopsin found in rods, iodopsin found in cones
- rods have low visual activity, cones have high
Why do rod cells have a low visual activity?
Why is this important?
Many rod cells to one sensory neurone (retinal convergence), less able to separate light sources.
Generator potential more likely at low light intensity.
How do iodopsin and rhodopsin differ?
Three types of Iodopsin (RGB) absorbing light at different wavelengths
Iodopsin is broken down at high light intensity
ONE cone cell attaches to ONE bipolar cell
