✅14 - Response To Stimuli Flashcards
What is a stimulus?
A detectable change in the internal or external environment of an organism that leads to a response.
What is are receptors?
Specific to one type of stimulus.
What forms a suitable response to a stimulus?
A coordinator
What producers a response?
An effector
What is a taxis?
A simple response whose direction is determined by the direction of the stimulus.
How are taxes classified?
According to whether the movement is towards (positive) or away from (negative) the stimulus.
How does a mobile organism respond to environmental change directly?
By moving its whole body either towards or away from a favourable/unfavourable stimulus.
What is a kinesis?
A form of response in which the organism does not move towards or away from a stimulus, but instead changes the speed at which it moves and the rate at which it changes direction.
How does a kinesis increase the chance of a quick return to a favourable environment?
The rate of turning increases when the stimulus is less directional
What is tropism?
The growth of part of a plant in response to a directional stimulus.
What type of phototropism do plant shoots show?
Positive, they grow towards light.
What type of gravitropism do plant tools show?
Positive
How do plants respond to gravity?
They need to be firmly anchored in the soil, so roots grown in the direction of its pull.
How do plants respond to water?
Almost all plant roots grow towards water, so are positively hydrotrophic, in order to absorb it and use it for photosynthesis and other metabolic processes.
What is the main plant growth factor?
IAA (Indoleacetic Acid)
What does IAA control?
Cell elongation
Describe the process of phototropism in flowering plants:
- Cells in the tip of shoot produce IAA, transported down the shoot.
- The IAA is transported evenly throughout all regions as it begins to move down shoot
- Light casques movement of IAA from light side to shaded side of shoot
- A greater concentration of IAA builds up on shaded side
- Cells on shaded side elongate more, casing the tip to bend upwards.
How does IAA affect roots?
A high concentration inhibits cell elongation in roots, so in roots cell elongation is greater on the light side than the shaded side.
Describe the process of Gravitropism in plants:
- Cells in root tip produce IAA, transported along the root
- Gravity influences the movement of IAA from paper side to lower side of the root
- A greater concentration of IAA builds up on the lower side of root
- As IAA inhibits elongation of root cells, cells on the lower side elongate less than the upper side
- this causes the root to bend downwards towards the centre of gravity
How does IAA cause cell elongation?
It increases the plasticity and stretch of the cell walls, as plant cell walls develop rigidity as the mature
Describe the acid growth hypothesis:
The active transport of hydrogen ions from the cytoplasm into spaces in the cell walls causes the cell wall to become more plastic allowing it to elongate by expansion.
What makes up the CNS?
The brain and spinal cord
What makes up the PNS?
Pairs of nerves that originate from either the brain or spinal cord.
What is the peripheral nervous system divided into?
Sensory neurones and motor neurones
What can the motor nervous system be divided into?
The voluntary nervous system and the autonomic nervous system
What does the voluntary nervous system do?
Carries nerves impulses to body muscles and is under voluntary control
What does the autonomic nervous system do?
Carries nerve impulses to lands, smooth muscle and cardiac muscle and is not under voluntary control
What are the stages of the reflex arc?
Stimulus Receptor Sensory neurone Relay neurone Motor neurone Effector Response
What are the features of sensory receptors?
They are specific to a single type of stimulus
They produce a generator potential by acting as a transducer
What is a transducer?
It converts energy from one form to another
Describe the function of the Pacinian Corpuscle:
- In its normal resting state, stretch mediated sodium ion channels are closed, it has resting potential
- When pressure is applied, the lamellae are deformed and the neurone is stretched
- This stretching widens the sodium channels in the membrane and ions can diffuse into the neurone
- The influx of ions changes the potential of the membrane, producing a generator potential as it becomes depolarised
- The generator potential in turn creates an action potential that passes along the neurone and into the CNS
How do receptors in the eye work?
They detect the light and convert it into the electrical energy of a nerve impulse
How many rod cells are connected to a sensory neurone?
Many
What intensity of light do rod cells detect?
Low
Why are multiple rod cells connected to one sensory neurone?
It is easier to reach the threshold or a generator potential
Are rod cells monochromatic or trichromatic?
Monochromatic
What pigment do rod cells contain?
Rhodopsin
Do rod cells give low or high visual acuity?
Low
Are there more rod cells or cone cells in the eye?
Rods
Where are the rod cells located?
More to the periphery of the retina, absent from the fovea
Where are the cone cells located?
Fewer at the periphery of the retina more concentrated at the fovea
How many types of cone cells are there?
Three - each responding to different wavelengths of light
How is a generator potential created in the rod cells?
Rhodopsin must be broken down. There is enough energy from low low intensity light to cause this.
What is a consequence of rod cells only being linked to one bipolar cell?
Only a single impulse will travel to the brain regardless of how many of the rods are stimulated, giving low visual acuity
How many cone cells re connected to each bipolar nerve?
1
Why do cone cells only respond to high intensity light?
It takes a much greater amount of energy to reach the threshold to create a generator potential.
What is the pigment in cone cells?
Iodopsin
Why is each cone cell specific to different wavelengths?
There are different types of cone cell, each with a different type of iodopsin.
Why are cone cells located on the fovea?
It receives the highest light intensities
What does the sympathetic nervous system do?
It stimulates effectors and so speeds up any activity.
What does the parasympathetic nervous system do?
It inhibits effectors and so slows down any activity. Controls activities under normal resting conditions, and is concerned with conserving energy.
What does myogenic mean?
The heart muscle’s contraction is initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic)
Where is the Sinoatrial node located?
In the wall of the right atrium
Where does the initial stimulus for contraction initiate?
The Sinoatrial Node
Describe the sequence of events that controls the heart rate:
- A wave of electrical excitation spreads out from the SAN, across both atria, causing them to contract.
- A layer of non conductive tissue (atrioventricular septum) prevents the wave crossing the ventricles
- The wave of excitation enters a second group of cells called the AV node, between the atria
- The AV node conveys a wave of electrical impulse between the ventricles down the Purkyne fibres which make up the bundle of His
- The bundle of His conducts the wav through the AV septum to the base of the ventricle, where they branch off into smaller fibres
- The ventricles contract from the bottom upwards.
Why is i essential that heart rate can be altered?
To meet demands for oxygen
What is the region of the brain called which controls heart rate?
The medulla oblongata
What are the two centres of the medulla oblongata?
- A centre that increases heart rate - linked to the SAN by the sympathetic nervous system
- A centre that decreases heart rate, linked to the SAN by the parasympathetic nervous system
Where are chemoreceptors found in the heart?
In the wall of the carotid arteries
What are chemoreceptors sensitive to?
Changes in the pH of blood resulting from changes to CO2 concentration
How is heart rate controlled by chemoreceptors?
- Chemoreceptors detect changes and increases frequency of nervous impulses to the medulla oblongata
- The centre increases the frequency of impulses via the sympathetic nervous system to the SAN, increasing the rate of production of electrical waves by the SAN and therefore the heart rate
- Increased blood flow then leads to more CO2 being removed by the lungs so concentration returns to normal
Where are pressure receptors located in the heart?
In the walls of the carotid arteries
What do the pressure receptors do when blood pressure is higher than normal?
More nerve impulses transmitted to the medulla oblongata that decrease heart rate. The centre sends impulses via the parasympathetic nervous system to the SAN, which then decreases heart rate.
What do the pressure receptors do when blood pressure is lower than normal?
They transmit more nervous impulses to the medulla oblongata that increases heart rate. The centre sends impulses via the sympathetic nervous system to the SAN and heart rate increases.
