stimuli internal and external lead to a response Flashcards
(30 cards)
Taxes definition
Directional movement in response to stimuli
Kineses definition
Kinesis: A response to a stimulus that is non-directional, changing the speed at which an
organism moves and the rate at which its direction changes
Tropism definition
growth of part of a plant in response to directional stimulus
Do plant shoots grow towards or away from: light, gravity, water and why?
Light- move towards light- positive phototropism- so leaves are in a favourable position to capture light for photosynthesis
Gravity:- move away from the source of gravity- negative gravitropism- taller- more likely to be in light for photosynthesis.
Water: negatively hydrotropic- no need for shoot to be in water
Do plant roots grow towards or away from: light, gravity, water and why?
light: negative phototropism- more likely roots will grow in soil where they can absorb water and mineral ions
gravity- positively gravitropic- want to increase probability roots are in soil to absorb water and mineral ions, and act as an anchor
water: positively hydrotropic- water needed for metabolic reactions
What is IAA
how does it effect shoot cells v root cells
how does it work?
a plant growth factor that controls cell elongation
shoot- stimulates elongation and growth
root- inhibits elongation and growth
acid growth hypothesis
increases plasticity of cell walls
active transport of H+
only works in young cells- older cells have developed regidity
Phototropism in plants: process
- cells in shoot tip detect light
- cells in tip of shoot produce IAA
- IAA initially transported to all regions as it moves down the shoot
- light causes IAA to move to shaded side
- higher concentration of IAA in shaded side than light side, cells elongate more on shaded side- plant grows more on shaded side
- shoot tip bends towards the light
Gravitropism process
- cells in root tip produce IAA and transported to root
- IAA initially transported to all regions of root
- Gravity influences IAA to move to lower side
- greater concentration of IAA in lower side than upper side of root-cells elongate less on lower than upper as growth is inhibited
- greater elongation on upper- root bends down towards gravity
What is a reflex?
rapid and involuntary response to a stimulus working in a protective nature.
what are the two major divisions of the nervous system?
central nervous system- brain and spinal cord
peripheral nervous system- pairs of nerves that originate from the brain or spinal cord
What do sensory neurons do?
carry nerve impulses from receptors to motor neuron
what does motor neuron do?
carries nerve impulse away from CNS to effector
what is the motor nervous system split up into?
voluntary nervous system- nerve impulses under voluntary control
automatic nervous system- carries nerve impulses to glands, smooth muscle, cardiac muscle- involuntary
reflex arc
- stimulus
- receptor
- sensory neurone- passes NI to spinal cord
- coordinator-links sensory and motor neurone in spinal cord
- motor neurone
- effector-muscle or gland
- response
Pacinian corpuscles:
what does it act as?
what do they respond to changes in?
acts as a transducer
respond only to changes in mechanical pressure
Structure of a Pacinian corpuscle:
-neurone at the centre of connective tissue with viscous gel in between
What channel does it have?
Stretch mediated sodium channels- permeability to sodium changes when they are deformed
How do Pacinian corpuscles produce a _______
Generator potential
- normal channels of membrane too narrow to allow Na to pass through
- this is the resting potential
- pressure applied- membrane/ receptors deformed- opens up- Na+ diffuse in
- influx of Na + changes potential of the membrane-causes more na+ CHANNELS TO OPEN becomes depolarised- produces generator potential
What is the resting potential? how is it maintained
the difference in electrical charge inside and outside of a neurone when its at rest- polarised
active transport of Na+ out and K+ into the neurone- 3:2 ratio- inside negative, outside positive
Rod cells:
can they distinguish between wavelengths of light?
cannot distinguish between wavelengths of light- black and white
Rod cells: threshold
what needs to happen before a generator potential is created?
how do rods challenge this?
what’s a consequence of this?
- Threshold value has to be exceeded before a generator potential is created in the bipolar cells
- many rod cells for each sensory neuron- greater chance that the threshold value will be exceeded- summation
- brain cannot distinguish between separate sources of light- two dots appear as a single blob- low visual acuity
Cones:
how many different types and why? what does this allow for?
why is visual acuity high?
why in high light intensity?
3 types respond to different wavelengths of light- allow to see in colour
- single cone cell for each sensory neurone/bipolar neurone- brain can distinguish between separate sources of light as the impulse comes from multiple different sensory neurones.- high visual acuity
- single cone cell single sensory neurone/bipolar neurone- no summation- threshold value can only be exceeded using one cone cell to create a generator potential- high light intensity
- iodopsin- requires higher light intensity than rhodopsin to be broken down to start a generator potential- higher light intensity
Rods V Cones shape? which one is there more of? distribution? summation and visual acuity can it distinguish between different wavelengths of light? what light intensity is it sensitive to? What pigment?
Rods: rod shaped More than cone cells more in periphery of retina, absent in fovea has summation low visual acuity cannot distinguish between wavelengths of light- black and white sensitive to low light intensity rhodopsin
Cones: Cone shaped less than rods many cone cells in fovea, few in periphery no summation- high visual acuity can distinguish between wavelengths of light- different colours sensitive to high light intensity iodopsin
what does sympathetic nervous system do?
- stimulates effectors so speeds up activity
- controls effectors when exercising or stressed.
