B14 - Response to stimuli Flashcards
Define a taxis.
A response in which the direction of the stimulus determines the direction.
Give an example of a taxis.
Algae which moves towards light. This increases their chance of survival as they require light to photosynthesize.
Earthworms: move away from light, which leads them to soil to find better nutrients and safety.
Define a kinesis.
Change of speed in turning direction. The faster an organism turns, the more likely it is to find a favourable environment.
Give an example of a kinesis.
Woodlice - they will more rapidly change direction when in a dry area in order to try and find a damp one.
Define a tropism
Growth of a plant in response to a directional stimulus.
Give an example of a plant growth factor.
IAA (Indoleacetic Acid)
Phototropism: Which part of the plant produces IAA?
Cells in the tip
Which area does light cause IAA to move?
Towards the shaded side.
Phototropism: Which direction does the shoot bend towards?
Towards the light, as the plant has elongated on the shady side due to a higher IAA concentration.
Gravitropism: Which side does gravity influence IAA?
Forces the IAA to the lower side of the root
What is the Central Nervous System [CNS]?
Brain and Spinal Chord
What is the reflex sequence?
Stimulus, receptor, sensory, intermediate, motor, effector, response
What is the importance of reflex arcs?
Involuntary, protect the body from harm, they are fast, rapid.
Where are Pacinian Corpuscles found?
Deep in the skin
Describe the structure of a Pacinian Corpuscle.
A single sensory neuron at the centre of layers of tissue.
What is located in the membrane of the Corpuscle?
Stretch-mediated sodium channels. These allow Na+ ions to enter only when they are stretched and deformed [as a result of external pressure]
What is produced by the sudden influx of sodium ions [Pacinian Corpuscle]?
A generator potential as the potential of the membrane is changed.
What colours do Rod cells pick up?
Black and white, as they are unable to detect other wavelengths.
What light intensity are rod cells to pick up?
Low intensity
How do rod cells create a generator potential?
Rhodopsin must be broken down, and the energy from low light intensity causes this.
Why do rod cells give low visual acuity?
The brain cannot distinguish between the separate sources of light as many rod cells can share the same neuron.
Are there more cone or rod cells?
Rod cells.
What pigment do cone cells contain?
Iodopsin, which requires a higher light intensity to break down.
Where on the eye are cone cells most concentrated?
Fovea (the centre)
What is the sympathetic nervous system?
The fight or flight response
What word describes the behaviour of the sympathetic and parasympathetic nervous systems?
Antagonistic - normally oppose one another
What is the parasympathetic nervous system?
‘Rest and digest’
Where is the Sinoatrial Node located?
The right atrium
What does the SAN do?
Releases a wave of depolarisation across the atria, which therefore contracts.
What does the Atrioventricular Node (AVN) do?
Releases another wave
Why doesn’t the wave travel through the atria to the ventricle?
There is a non-conductive layer between the atrium and ventrcile.
What is Purkyne tissue?
Specialised muscle fibres which conveys a wave of electrical excitation.
What is the Bundle of His?
All of the collective Purkyne tissue.
What is the function of the Bundle of His?
Conducts the wave through the atrioventricular septum to the base of the ventricles.
Where are chemoreceptors found?
In the wall of carotid arteries and aorta
What is the medulla oblongata?
Controls change in heart rate, which has two centres.
What do chemoreceptors do?
Increases the frequency of impulses to the medulla oblongata.
What do pressure receptors do?
Sensitive to blood pressure:
High = decrease the heart rate via parasympathetic
Low = increase HR via sympathetic.
