6.1 STIMULI & RESPONSE Flashcards
What are taxes?
- A simple response whose direction is determined by a stimulus.
- Taxes is when the whole body moves away from the unfavorable region.
What is kinesis?
- A simple response whose direction is determined by a stimulus.
- Kinesis is when the organism changes its speed and rate of direction based on what environment is favourable or not.
Why do organisms display taxes/kinesis?
To increase their chance of survival as they respond to the changes in their environment.
What is a tropism?
A plant growth response to a directional stimulus.
What is a gravitropism?
A response to gravity.
What is a phototropism?
A response to light.
What is IAA?
A growth factor that is part of the auxin group.
What is the effect of IAA in roots?
Inhibits cell elongation.
What is the effect of IAA in shoots?
Stimulates cell elongation.
Explain the phototropism in a shoot?
- Tip cells make IAA, and it diffuses down the shoot.
- In the presence of light, the IAA moves to the shaded side, and diffuses down there.
- There is a greater concentration of IAA on the shaded side than the light side.
- The shaded side grows faster, as IAA stimulates cell elongation, so cause the plant to bend and grow towards the light.
Explain the phototropism in a root?
- Tip cells make IAA, and it diffuses down the root.
- In the presence of light, the IAA moves to the shaded side, and diffuses down there.
- There is a greater concentration of IAA on the shaded side than the light side.
- The lowerside grows slower, as IAA inhibits cell elongation, so cause the plant to bend and grow away from the light.
What type of phototropism do shoots show?
Positive phototropism
What type of phototropism do roots show?
Negative phototropisms
Explain the gravitropism in a root? (opposite for shoots)
- Tip cells make IAA, and it diffuses down the root.
- Under gravity, the IAA moves to the lower side and diffuses down there.
- There is a greater concentration of IAA on the lower side than the upper side of the root.
- The lower side grows slower, as IAA inhibits cell elongation, so cause the plant to bend and grow down towards gravity.
Outline the reflex arc.
- Stimulus
- Receptor: generates nerve impulse to the sensory neurone.
- Sensory neurone passes impulse to the spine.
- Relay neurone links the sensory neurone to the motor neurone in the spinal cord.
- Motor neurone carries impulses from the spine to the muscles.
- Reaches the effector in the muscle which controls the response.
Why is the reflex arc so important?
- Involuntary so doesn’t overload the brain with decision-making in important scenarios.
- Fast as it is a very short pathway.
Which nervous system is the reflex arc a part of?
The peripheral nervous system where nerves come from the spinal cord and the brain.
What is the Pacinian corpuscle?
A receptor that responds to specific mechanical stimuli. This stimulation then leads to a generator potential and action potential.
Outline the way the Pacinian corpuscle works.
- At rest, the stretch-mediated sodium channels on the membrane of the PC are closed to achieve resting potential.
- Upon pressure the PC deforms to open the stretch mediated sodium channels.
- This allows sodium ions to diffuse into the PC neurone.
- Causes a change in membrane potential, depolarising it and producing a generator potential.
- This turns into an action potential and sends an impulse.
What are the photoreceptors in the eye?
- Cone cells
- Rod cells
What are the features of cone cells?
- Found in the fovea
- Trichromatic
- Good visual acuity
- Low light sensitivity
Why do cone cells have good visual acuity?
Each cone cell is connected to an individual bipolar cell, so each cone cell sends individual impulses.
Why do cone cells have low light sensitivity?
No retinal convergence, therefore no spatial summation so need a bigger stimulus to reach the action potential.
What are the features of rod cells?
- Found on the periphery of the retina but NOT the fovea.
- Only see black & white
- Low visual acuity
- High light sensitivity
