Topic 14 - Response to Stimuli Flashcards
Stimulus
A detectable change in the internal or external environment of an organism
Receptors
Specific to one type of stimulus, with the coordinator finding an appropriate response
Taxis
A specific movement, with directed motion
Kinesis
A random movement, with undirected motion
Positive Taxis
A specific movement towards a stimulus
Negative taxis
A specific movement away from a stimulus
Tropism
The growth of a plant in relation to a directional stimulus
Growth factors
The hormone-like substances which allow plants to respond to light, water and gravity
IAA
The growth factor in plants
Gravitropism in flowering plants
1) Cells in the tip of the root produce IAA, which is then transported to all sides of the root
2) Gravity influences the movement of IAA from the upper side to the lower side of the root
3) A greater concentration of IAA builds up on the lower side of the root than on the upper side.
4) As IAA inhibits the elongation of root cells and there is a greater concentration of IAA on the lower side, the cells on this side elongate less than those on the upper side.
5) The relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity.
Phototropism in flowering plants
1) Cells in the tip of the shoot produce IAA, which is then transported down the shoot
2) The IAA is initially transported evenly throughout all the regions as it begins to move down the shoot
3) Light causes the movement of IAA from the light side to the shaded side of the shoot
4) A greater concentration of IAA builds up on the shaded side of the shoot than on the light side.
5) As IAA causes elongation of shoot cells there is a greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more.
6) The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light.
CNS
Consists of the brain and the spinal cord in nervous organisation
Peripheral nervous system
Consists of pairs of nerves that originate from the brain or spinal chord
Sensory neurons
One division of the PNS which carry nervous impulses from receptors towards the CNS
Motor neurons
One division of the PNS which carry nervous impulses from the CNS towards effectors
Voluntary nervous system
One division of the motor nervous system which carries out nervous impulses to muscle under conscious control
Autonomic nervous system
One division of the motor nervous system which carries out nervous impulses to glands, smooth muscle and cardiac muscle under subconscious control
Process of the reflex arc in order:
1) stimulus
2) receptor
3) Sensory neurone
4) intermediate neurone
5) motor neurone
6) effector
7) Response
Importance of reflex arcs
- They are involuntary so they do not require thinking power
- They are fast due to short pathway
- Protect the body from harm
Features of sensory reception as illustrated by the pacinian corpuscle
The Pacinian corpuscle is:
- Specific to one type of stimulus
- The producer of a generator potential though acting as a transducer (converts the stimuli into energy)
Stretch mediated
The same of the sodium channel that is part of the pacinian corpuscle, which is deformed to allow for the movement of sodium ions
Describe how a Pacinian corpuscle produces a generator potential when stimulated.
1) When pressure is applied to the Pacinian corpuscle it becomes stretched
2) The stretched mediated sodium ion channels open and there is an influx of sodium ions that diffuse across the membrane
3) The influx of sodium ions causes a depolarisation causing the membrane potential to rise.
4) If it rises above the threshold then the generator potential is reached
5) The generator potential in turn creates an action potential.
Fovea
The location of cones in the eye
Periphery
The location of rods in the eye
How many cones are connected to one bipolar cell
1
How many rod cells are connected to one bipolar cell
3
Visual acuity of cones
Good
Visual acuity of rods
Poor
Sensitivity of rods in low light
Sensitive
Sensitivity of cones in low light
Not sensitive
Summation
The reason for the visual acuity of cones and the sensitivity of rods
Rhodopsin
The chemical broken down when rods absorb light
Iodopsin
The chemical broken down when cones absorb light
Sympathetic nervous system
One division of the autonomic nervous system which speeds up activity and makes someone more aware
Parasympathetic nervous system
One division of the autonomic nervous system which slows down activity in normal circumstances
Sinoatrial node
The group of cells that stimulate atrial systole
Atrioventricular Node
The group of cells send electrical signals down the bundle of His and across the Purkinje fibres to stimulate ventricular systole
Medulla Oblongata
The periphery of the brain with two centres to help increase and decrease heart rate
Chemoreceptors
The receptors found in walls of the carotid artery which detect changes in pH
Steps that control heart rate with variations of pH:
1) pH is lowered from high concentration of CO2 in the blood
2) Chemoreceptors detect the change in pH, increasing the frequency of impulses to the centre in the medulla oblongata that increases heart rate
3) The centre increases the number of frequencies via the sympathetic nervous system to the SA node, increasing the HR
4) pH rises to normal levels, which is detected by chemoreceptors
5) Blood flow increases so more CO2 is removed by the lungs
6) The medulla oblongata reduces the frequency of nervous impulses to the SA node, returning the HR to normal
Steps that control the heart rate with pressure receptors:
1) Blood pressure is higher than usual
2) Pressure receptors detect the change and increases the number of impulses sent to the centre of the medulla oblongata to reduce HR
3) The centre sends impulses via the parasympathetic nervous system to the SA node
4) The heart rate decreases
