Chapter 14 Response to Stimuli Flashcards
What is a stimulus?
A detectable change in the environment.
What is Taxes?
A simple response in organisms in which an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus.
What taxis do earthworms show?
Negative phototaxis, so they move away from light. They move towards dark environments such as in the soil to help them avoid dehydration, predators and to locate food.
What is Kinesis?
When an organism changes the speed of movement and the rate it changes direction.
What is a tropism?
Term given to when plants respond via growth, to stimuli.
Name a plant growth factor
IAA (indoleacetic acid)
What is the nervous system made up of?
Peripheral and the central nervous system.
What is the peripheral nervous system made up of?
Receptors, sensory and motor neurones.
What is the CNS made up of?
Brain and the spine
What are types of receptor cells?
Pacinian corpuscle
Rods
Cones
What does the pacinian corpuscle do?
Responds to pressure changes.
Where can you find pacinian corpuscle receptors?
Deep in the skin, mainly in fingers and feet.
What is the pacinian corpuscle made up of?
A single sensory neurone wrapped with layers of tissues separated by gel.
The sensory neurone in the pacinian corpuscle has special channel proteins in its plasma membrane.
What are stretch mediated sodium channels and how do they work?
Plasma membranes contain channel proteins which allows ion transportation and the membranes surrounding the sensory neurones have stretch mediated sodium channels.
These channels open and allow Na+ ions to enter the sensory neurone only when they are stretched and deformed.
How do rod cells process images?
In black and white
Explain the process of rod cells creating a generator potential
Pigment of rhodopsin must be broken down by light energy
There is enough energy from low intensity light to cause the breakdown
Enough pigment has to be broken down for the threshold to be met in the bipolar cell
Why can rod cells function at low light intensities?
The threshold can be reached in low light as so many rod cells are connected to a single bipolar cell (summation).
What pigment do cone cells contain?
Iodopsin.
Why do cone cells have high visual acuity?
Since there is only one cone cell connected to a bipolar cell.
This allows the brain to distinguish between separate sources of light.
Why can’t we see colour in the dark?
Cone cells can only respond to high light intensity
Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process.
- Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall
in pH
OR
Baro / pressure receptors detect rise in blood pressure; - Send impulses to cardiac centre / medulla;
- More impulses to SAN;
- By sympathetic (nervous system for chemoreceptors / CO2)
OR
By parasympathetic (nervous system for baro / pressure
receptors / blood pressure);
When the heart beats, both ventricles contract at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat
by the SAN.
(2 marks)
- Electrical activity only through Bundle of His / AVN;
- Wave of electrical activity passes over / through both ventricles at the
same time;
The fovea of the eye of an eagle has a high density of cones. An eagle
focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer. (3 marks)
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
Accept no retinal convergence.
Accept ‘bipolar/nerve cell’ for neurone. - (Cones send) separate (sets of) impulses to brain;
