Response to stimuli Flashcards
What is a tropism
a directional growth response in plants
How does phototropism work in shoots
Plant roots and shots grow in response to light
IAA diffuses to the shaded side of the plant shoot, promoting cell growth and elongation
this causing the plant shoot to bend towards the light source
POSITIVE phototropism
How does phototropism work in roots
IAA diffuses towards the shaded side of the root
this will inhibit growth and cell elongation so root will bend away from the light
this is a NEGATIVE phototropism
How does gravitropism response work in shoots
IAA diffuses towards the bottom of the shoots due to gravity
this promotes growth and cell elongation so shoots will bend and grow against gravity
NEGATIVE gravitropism
How does gravitropism responses work in roots
IAA diffuses towards the bottom of the roots due to gravity
this inhibits growth and cell elongation so roots will bend and grow towards gravity
POSITIVE gravitropism
What is a taxes response
directional response in movement due to stimuli
(positive = towards) (negative = against)
The 4 types of taxis
chemotaxis - chemical stimulus
phototaxis - light stimulus
geotaxis - gravity stimulus
Rheotaxis - movement stimulus
What is a kinesis response
A non directional response in movement due to stimuli
(positive = more movement) (negative = against)
What is a reflex response
rapid unconscious responses to have a protective effect
reflex arc structure
receptors pass a signal to the sensory neurone
sensory neurone to spinal cord
across a synapse to relay neurone
across a neuron to motor neurone to the effector
What are receptors and what do they do when simulated
Chemical structures that respond to specific stimuli
they will cause a generator potential which will lead to a response
Structure of a Pacinian corpuscle and where are they found
layers of connective tissue surrounding a sensory neurone ending
capsule surrounding these layers and a blood capillary
occur deep in skin on fingers and feet
How is the resting potential maintained in a Pacinian corpuscle
at resting state, the stretch mediated sodium ion channels are too narrow for Na+ to diffuse through
3 sodium ions outside and 2 potassium ions inside the sensory neuron
What is a resting potential
the difference in electrical charge inside and outside of the neuron when it is at rest
How is a generator potential established
pressure from a stimulus causes the stretch mediated sodium ion channel to open, so Na+ diffuses into the sensory neurone
2 types of receptors in the human retina
2 photoreceptors
rods
cones
How does a stimulus cause an image in the eye
rods and cones detect the stimulus to establish a generator potential
potential travels from rods and cones to bipolar cells
from bipolar cells to ganglion cells
from ganglion cells to optic nerve axons
to the brain, where it is relayed to the eye to produce an image
Properties of rods
x5
- cant distinguish between different wavelengths of light so images are processed in black and white
- rods can detect very low light intensities as may rod cells are connected to a single sensory neuron (HAVE A HIGH SPACIAL SUMMATION)
- action potential threshold is LOW as many rod cells are connected to a single bipolar cell
- Rhodopsin is the main pigment in rods
- rods have a low visual acuity so they cant distinguish between 2 separate sources of light
Properties of cones
x4
Three types that have different types of iodopsin pigment (red, green and blue)
absorb different wavelengths of light
can only respond to high light intensity as only one cone cell connects to a bipolar cell ( NO SPACIAL SUMMATION )
can distinguish clearly between separate sources of light ( HIGH VISUAL ACUITY)
Properties of cones
x4
Three types that have different types of iodopsin pigment (red, green and blue)
absorb different wavelengths of light
can only respond to high light intensity as only one cone cell connects to a bipolar cell so action potential threshold is high ( NO SPACIAL SUMMATION )
can distinguish clearly between separate sources of light ( HIGH VISUAL ACUITY)
Where are cone cells found in the eye
situated near the fovea as light is heavily focused around this area
The three survival responses in mobile organisms
TAXES
KINESIS
REFLEXES
