Chapter 14: Responses to stimuli Flashcards
stimuli
a change in the internal or external environment that leads to a response
taxes
a simple response seen in animals that involves movement away or towards a stimulus
kinesis
a simple response to a non-directional stimulus (humidity) in which the organism changes the speed at which it moves and the rate at which it changes direction
tropism
a plant growth response to a directional stimulus
receptor
detect stimuli
specific to one type of stimuli
e.g. light, pressure, glucose conc.
many different types
can be cells or proteins found on cell-membranes
effector
carries out a response
coordinator
formulates an appropriate response to a stimuli
negative taxes
a form of taxes that involves moving away from an unfavourable stimulus
positive taxes
a form of taxes that involves moving towards a favourable stimulus
positive tropism
…
negative tropism
…
phototropism
plant growth in response to light
gravitropism
growth in response to gravity
Why is it important that animals respond to stimuli?
The ability to respond to stimul
- increases chances of survival
- avoiding harmful environments
- maintain optimal internal enviornments for metabolism
reflexes
automatic, rapid responses to stimuli
Why are reflexes important?
automatic - don’t have to think/decide - rapid
reduce amount of harm/protect the body
relfex arc
the pathway of neurones linking receptors to effectors in a relfex
Briefly describe a simple reflex arc
stimulus
heat
receptor
thermoreceptors in skin detect heat
sensory neurone
send impulse from receptor to relay neurone
relay neurone
sends impulse from sensory to motor neurone
motor neurone
sends impulse to effector
effector
bicep muscle contracts to pull arm away
When can a reflex be overriden?
If there is a relay neurone in the reflex arc the reflex can be overriden
Characteristics of nervous communication.
localised
neurotransmiter are released directly onto target cells
short-lived
neurotransmitters are removed
rapid
electrical impulses travel fast
Why is it important for plants to be able to respond to stimuli?
increases their chances of survival
- allows them to grow towards light
- maximum absorption of light for photosynthesis
- roots can grow in the right direction
- climbing plants can find things to climb to reach sunlight
Are shoots negatively or positively phototropic?
Shoots are positively phototropic
They grow towards light.
Are roots negatively or positively phototropic?
Roots are negatively phototropic
They grow away from light
Are shoots negatively or positively gravitropic?
Shoot are negatively gravitropic.
They grow upwards
Are roots negatively or positively gravitropic?
Roots are positively gravitropic
They grow downwards
growth factors
hormone-like chemicals that speed up or slow down plant growth
produced in the growing parts of a plant (the tips of shoots and leaves)
transported to where they are neeeded
auxin
type of growth factor
in the shoots auxin stimulates growth in shoots by cell elongation where cell walls become stretched and loose making the cells longer
in the roots auxin inhibits cell elongation and growth
indoleacetic acid (IAA) is an auxin
Indoleacetic acid
an auxin produced in the shoot tips of flowering plants
moved around the plant to control tropism over short distances via diffusion and active transport and over long distance via the phloem
Briefly describe how phototropism works in the shoot tips of a plant.
- light comes in from one direction
- one side of the shoot receives more light than the other
- IAA builds up on the shaded side
- this uneven distribution menas uneven growth
- the higher concentration of IAA causes cell elongation on the shaded side
- the shoot bends towards the light
Briefly describe how phototropism works in the root tips of a plant.
- light comes in from one direction
- one side of the root receives more light than the other
- IAA builds up on the shaded side
- this uneven distribution means uneven growth
- the higher concentration of IAA inhibits growth
- the root bends away from the light
Briefly describe how gravitropism works in the shoots and roots of a plant.
- IAA builds up on the underside/lowerside of shoot and roots
- this uneven distribution means uneven growth
- the higher conc. of IAA on the underside of shoots causes cell elongation
- so that shoots grow upwards
- the higher conc. of IAA on the underside of roots inhibits cell growth
- so that roots grow downwards
How does kinesis keep simple organisms in a favourable environment?
kinesis
favourable: move slowly and don’t change direction as often so increases chance of staying in a favourable area
unfavourable: increase speed and turn more often so increases chance of moving into a favourable area -improving chances of survival
e.g. woodlice use kinesis to stay in areas of high humidity - reduces water loss and helps to conceal them
Pacinian corpuscle
receptors found deep in the skin
hands, soles of the feet, external genetalia, ligaments, etc
detect mechanical stimuli
changes in pressure/vibrations
a single sensory neurone or sensory nerve ending wrapped in layers of cell tissue/connective tissue called lamellae
photoreceptors
light receptors found in the eye
convert light into an electrical impulse
cones
a type of photoreceptor found packed in the fovea of the retina that give trichromatic vision
rods cells
a type of photoreceptor found in the peripheral parts of the retina that give us monochromatic vision
Briefly decribe what happens when a Pascinian corpuscle is in its resting state and when it is stimulated.
Resting:
- resting potential
- the stretch-mediated sodium channels are too narrow to let sodium ions to diffuse in
- the inside is more negative than the outside
Stimulated:
- Pressure is applied and the membrane is stretched/deformed
- causes stretch-mediated sodium channels to widen
- sodium ions able to diffuse in
- influx of sodium ions causes depolarisation of the membrane
- inside becomes more positive than the outside
- called the generator potential
- the generator potential could lead to an action potential
rod cells
low visual acuity
retinal convergeance
- more numerous than cone cells
sensitive
- monochromatic vision because different wavelengths cannot be distinguished
*
retinal convergeance
lots of rod cells are connected to 1 sensory neurone
this means that it is more likely that the threshold value will be reached to create a generator potential
becase lots of low level depolarisations in the rod cells can accumulate to reach the threshold value
What does it mean for rod cells to have low visual acuity?
What is the pigment found in rod cells?
Rhodopsin
control of heart rate
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