response to stimuli Flashcards
what is a stimulus
a stimulus is a detectable change in the internal/external environment of organism that leads tp a response in the organism
why is responding to a stimuli important
it increases the chance of survival for an organism
e.g. can detect and move away from harmful stimuli e.. predators and extremes of temp, or to detect and move towards a source of food
The organisms that survive have a better chance of raising offspring and of passing their alleles to the next generation - therefore there is a selection pressure favouring organisms with appropriate responses
what detects stimuli
receptors which are specific to one type of stimulus
what formulates a response to a stimuli
a coordinator formulates a suitable recognise to a stimulus
coordination may be at the molecular level or involve a large organ such as the brain
what carries out a response
responses are carried out by an effector
the response may be at a molecular level or involve the behaviour of a whole organism
what are hormonal responses
they are relatively slow process found in both plants and animals
what is another means of communication that animals have
they also have the more rapid means of communication which is the nervous system
which usually have many different receptors and control effectors
what links the receptors and effectors
each receptor and effectors are linked to a central coordinator of some type
the central coordinator connects information from each receptor with the appropriate effector
what are the sequence of events involved in either chemical control/ nerve cells
stimulus - receptors - coordinator - effector - response
what is a taxes
it is a simple response whose direction is determined by the direction of the stimulus
as a result, a motile organism respond to environmental changes moving its whole body either towards a favourable stimulus or away from an unfavourable one
how are taxes classified
taxes are classified according to whether the movement is towards the stimulus - positive taxis
or away from the stimulus - a negative stimulus
and also by the nature of the stimulus
what is phototaxis
when an organism moves away/ moves towards the light
this increases their chances of survival of organisms
what is chemotaxis
when a species will move towards/away from an area with glucose (a nutrient)
again this will increase their chances of survival because they use glucose as a source of food
what is kinesis
it is a form of response in which the organism does not move towards or away from a stimulus
Instead, it changes the speed at which it moves and the rate at which it changes direction
If an organism crosses a sharp dividing line between a favourable and an unfavourable environment, its rate or turning increases
This increases the chances of a quick return to a favourable environment
what happens when n organism moves a considerable distance into an unfavourable environment
its rate or turning may slowly decreases ao that it moves in long straight lines before it turns, often very sharply
this type of response tends to bring the organic, into a new region with favourable conditions
what is an example of kinesis
woodlice lose water from their bodies in dry conditions
When they move from a damp area into a dry one, they move more rapidly and change direction more often
This increases their chances of moving back into the damp area. Once back in the damp areas, they slow down and change direction less often.
This means they are more likely to stay within the damp area
However. if alter some time spent changing direction rapidly they are still in the dry area, their behaviour changes. Instead, they move rapidly in straight lines, which increases their chances of moving through the dry area and into a new damp one
In this way, they spend more time in favourable damp conditions than in less favourable drier ones
This prevents them from drying out and so increases their chances of survival
what is tropism
it is the growth of a plant in response to a directional stimulus
it can be a positive response or a negative response depending on whether it is growing towards (positive) a stimulus or away from a stimulus (negative)
what is phototropism
this is when the plants’ shoot grow towards or away from light
The response in both cases increases the probability that the roots will gro into the soil, where they are better able to absorb water and mineral ions
what factors do plants grow in response to
plants do not have a nervous system
plants respond to
-light because light is needed for photosynthesis
- gravity- plants need to be firmly anchored in the soil. Roots are sensitive to gravity and grow in the direction of its pull (positive gravitropism)
- water- almost all plant roots grow towards water (positive hydrotropism) in order for it to be used in phototropism and other metabolic processes as well as for support
what are plant growth factors
plant growth factors involve hormone-like substances or, more correctly, plant growth factors
plant growth factors are produced in small quantities e.g.plant factor indoleacetic acid IAA, which belongs to a group of substances called auxin. IAA controls plant cell elongation
explain the control of tropism by IAA
tropism is the directional growth of a plant in response to a directional stimulus
In the case of light, we can observe that a young shoot will grow towards light that is directed as it from one side (unilated light). This is known as positive photropism
explain phototropism in flowery plants
- Cells in the top of the shoot produce IAA, which is then transported down the shoot
- the IAA is initially transported evenly throughout all regions as it begins to move down at the shoot
- Light causes the movement of IAA from the light side to the shaded side of the shoot
- a greater concentration of IAA builds up on the shaded side of the shoot than on the light side
- As IAA causes elongation of the IAA on the shaded side of the shoot, the cells on the side alongside more
- The shaded od the shoot elongates faster than the light side, causing the shoot tip to bend towards thelight
what does IAA do
IAA causes bending of roots in response to light
However whereas a high concentration of IAA increases cell elongation in shoots, it inhibits elongation in roots
e.g. an IAA concentration of 10 parts per million increases shoot elongation by 200% but decreases toot elongation by 100%
As a result, in roots, the elongation of cells is greater on the light side than on the shaded and so roots bend away from light, that is they are negatively phototropic
describe gravitropism in flowering plants
- cells in the tip of the root produce IAA, which is then transported along the root
2) the IAA is intially transported to all sides of the root
3) gravity influences the movement of IAA form the upper side to the lower side of the root than in the upper side - a greater concentration of IAA builds up on the lower side of the root than in the upper side
- As IAA inhibits the elongation of root cells and there is a greater concentration of IAA on the lower side, the cells on this side elongates less than those in the upper side
- The relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity
in shoots the greater elongation(…)
the greater the concentration of IAA on the lower side cell elongation increases causing the side to elongate more than the upper side
As a result, the shoot grows upwards away from the force of gravity
how is IAA transported
transport if IAA is one direction, namely away from the tip of shoots and roots where it is produced
what are the effects of IAA on plants
IAA has a number of effects on plant cells including increasing the plasticity (ability to stretch) of their cell walls
The response only occurs on young cell walls where cells are able to elongate
what happens as the cell matures
as the cells mature they develop rigity - therefore older parts of the shot / root will not be able to respond to the IAA
what is the acid growth hypothesis
the proposed explanation of how IAA increases the plasticity of cells is called the acid growth hypothesis
it involves the active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate
what can the elongation of cells on one sire of a stem or root lead to
it leads to the root/ stem to bend
This is the means by which plants respond relatively quickly to environmental stimuli like light and gravity.
These response can be explained in terms of the stimuli causing uneven distribution of IAA, as described earlier, as it moves away from the tip of the stem or root
what is a reflex arc
it is the simplest type of nervous response to a stimulus is a reflex arc
what are the two major divisions of the nervous system
the central nervous system (CNS), which is made up of the brain and spinal cord
the peripheral nervous system (PNS), which is made up of pairs of nerves that originate from either the brain or the spinal cord
what is the peripheral nervous system divided into
it is divided into:
-sensory neurones
-motor neurones which
what are sensory neurones
carry nerve impulses (electrical signals) from receptors towards the central neurones
what are motor neurones
which carry nerve impulses away from the central nervous system to effectors
what are the subdivisions of the motor neurones
- the voluntary nervous system
2. the automatic nervous system
what is the voluntary nervous system
it carries nerve impulses to body muscles and is under voluntary (conscious control)
what is the autonomic nervous system
it carries nerve impulses to glands, smooth muscle and it s not under voluntary control, that is involuntary
what is the spinal cord
the spinal cord is a column of nervous tissue that runs along the back and less inside the vertebral column for protection
what are the features of a reflex arc
it is:
- rapid
- short - lived
- localised
- totally involuntary
- involving response to sensory stimulus is called a reflex. The pathway of neurones involved in a reflex is known as a reflex arc
how many neurones are involved in a reflex arc
3 neurones
describe the reflex arc
one of the neurones is in the spinal cord and so this type of reflex is also called a spinal reflex the main stages of a spinal reflex arc is:
- the stimulus is detected by a receptor
- a sensory neurone passes nerve impulse to the spinal cord
- a coordinator (intermediate neurones) -links the sensory neurone to the motor neurone in the spinal cord
- the nerve impulse passes along a motor neurone from the spinal cord to the effector (e.g. a muscle in the upper arm)
- the effector is stimulated to contract if it is a muscle or secrete if it is a hormone
- the response is carried out
why are reflex arcs important
any action made for survival is clearly of value
-they are voluntary and therefore do not require the decision making powers of the brain, this leaving it free to carry more complex responses.
In this way, this brain is not overlooked with situations in which the response is always the same
- they protect the body from harm
- they are fast, because the neurone pathway is short with very few typically one or two synapses
- the absences of any decision - making process also means the action is rapid
what are receptors
the central nervous system receives sensory information from its internal and external environment through a variety of receptors each type responding of stimulus
(this is primary the function of the brain)
what is sensory perception
sensory perception involves making sense of the info from the receptors
what is the pacinian corpsucle
the pacinian corpuscle responds to changes in mechanical pressure
As with all sensory receptors, a Pacinian corpsucle is specific to a single type of stimulus - in this case it is mechanical pressure e.g. heat, light or sound
what is a transducer
receptors produces a generator potential by acting as a transducer
All stimuli involves a change in some form of energy.
It is the role of the tranducer to convert the change in form of energy by the stimulus into a form - namely a nerve impulses
what are the nerve impulse in the form of
the nerve impulse is also a form of energy
Receptors in the nervous system convert the energy of the stimulus into a nervous impulse known as a generator potential
how do receptors function
i1. in its normal (resting) state, the stretch- mediated sodium channels of the membrane around the neurone of the receptor are too narrow to allow sodium ions to pass along them. In this state, the neurone of the receptor has a resting potential
2. when the stimulus is detected by the receptor, it is deformed and the membrane around its neurone becomes stretched
3. This stretching widens the sodium channels in the membrane and the sodium ions diffuse into the neurone
4. The influx of sodium ions changes the potential of the membrane (i.e. it becomes depolarised, thereby producing a generator potential
5. The generator potential in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurones, to the central nervous system
where are the receptor cells in the mammalian eye
the light receptor cells of the mammalian eye are found on its innermost layer, the retina
what are the two main types of receptors in the retina
rod cells
cone cells
both rod and cone cells act as tranducers by conserving light energy into the electrical energy of a nerve impulse
how are images seen in rods
rod cells can’t distinguish different wavelengths of light and therefore lead to images being seen only in black and white
how many rod cells are there
20 million in each eye
what are rod cells connected to
many rod cells are connected to a single sensory neurone in the op[tic nerve
what are rod cells used for
rod cells are very sensitive to light (they work well in dim light)
This is because many rod cells join one single bipolar neurone
and so many weak generator potentilas combine to reach the threshold and trigger and action potential
what are cone cells
cone cells are three different types, each responding to a different range of wavelengths of light
Depending upon the proportion of each type that is stimulated can perceive images
how many cone cells are there in each eye
around 6 million cone cells often with their separate bipolar cell connected to a sensory neurone in the optic nerve
why do cone cells respond only to high intensity
cone cells often have their own separate bipolar cell connected to a sensory neurone in the optic nerve
This means that the stimulation of a number of cone cells cannot be combined to help exceed the threshold value and create a generator potential
As a result, cone cells only respond to high light intensity and not to low light intensity
why do rods have low visual acuity
visual acuity is the abiltity to tell apart points that are close together
Rods give low visual acuity because many rods join the sam bipolar neurone which means light from two points close together can’t be told apart
what are the different pigment that cone cells contain
cone cells contain different types of pigment from that found in rod cells
The pigment in cone cells (iodopsin) requires a higher light intensity for its breakdown. Only light at high intensity will involve provide enough energy to break it down and create a generator potential
how many different types of cone cells are there
3 different types of cone each containing a specific type of iodopin
As a result, each cone cell is sensitive to a different specific range of wavelengths
these pigments are:
red sensitive
green sensitive
blue sensitive
when they are simulated in different proportions you see different colours
how is the distribution of rod and cone cells on the retina
the distribution of rod and cone cells on the retina is uneven
Light is focused by the lens on the part of the retina opposite the pupil. This point is known as the fovea. This fovea, therefore, receives the highest intensity of light - reason why there are cone cells, not rod cells at the fovea
how is the concentration of cone cells distributed in the fovea
the concentration of cone cells diminishes further away from the fovea. At the peripheries of the retina where light intensity is at its lowest, only rod cells are found all this shows how the distribution of rod and cone cells, and the connections they make in the optic nerve, can explain the differences in sensitivity and visual activity in mammals
what is the autonomic nervous system
the autonomic nervous system controls the involuntary (subconscious) activities of internal muscles and glands
it has two divisions
what are the two subdivisions of the nervous system
the sympathetic nervous system
the parasympathetic nervous system
what is the sympathetic nervous system
in general, this stimulates effectors and so speedup any activity
It acts rather like an emergency controller, it controls effectors when exercising extraneously/ or experiencing powerful emotions
In other words, it helps us to deal with stressful situations
what is the parasympathetic nervous system
this inhibits effectors and so slows down any activity, it controls activities under normal resting conditions
It is concerned with conserving energy and replenishing the body’s reserves
what do we mean when we say that the action of the sympathetic and parasympathetic systems are antagonist
they oppose each other
what are the muscles of the heart called
the cardiac muscle
what do we mean when we say that the cardiac muscles are myogenic
it is myogenic which means that its contractions are initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic)
what are the sinoatrial node (SAN)
within the walls of the right atrium of the heart is a group of cells known as the sinoatrial (SAN) form here, the initial stimulus for contractions originates
The sinoatrial node has a basic rhythm of stimulus that determines the beat of the heart hence reformed to as the pacemaker
what is the sequence of events that controls the basic heart rate is:
- a value of electrical spreads out from the sinoatrial across both atria, causing them (the atrium) to contract
- a layer of non-conductive tissue (atrioventricular septum) prevents the wave from crossing the ventricles
- the wave of excitation enters the second group of cells called the atrioventricular node (AVN), which lies between the atria
- the atrioventricular node, after a short delay, conveys a wave of electrical excitation between the ventricular along with a series of specialised muscle fibres called Purkyne tissue which collectively made up a structure called the bundle of His
- the bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles where the bundle branches into smaller fibres of Purkyne tissue
- the wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards
what controls changes to the heart rate
changes to the heart rate are controlled by a region of the brain called the medulla oblongata
this has two centres concerned with heart rate:
-a centre that increases heart rate, which is linked to the sinoatrial node by the sympathetic nervous system
-a centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic nervous system
what are chemoreceptors
chemoreceptors are found in the wall of the carotid arteries, the aorta and in the medulla the arteries that serve the brain)
these are sensitive to changes in the pH of the blood that results from changes in carbon dioxide concentration
what is the process of chemoreceptors control
- when the blood has a higher than normal concentration its pH is lowered
- the chemoreceptors in the wall of the carotid arteries and the aorta detects this and increase the frequency of nervous impulses to the centre in the medulla oblongata increasing heart rate
- the centre increases the frequency of impulses vai the sympathetic nervous system to the sinoatrial node. This, in turn, increases the rate of production of electrical waves by the sinoatrial node and therefore increases the heart rate
- the increased blood flow that this causes leads to more CO2 concentration of the blood returns to normal
- as a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata
- the medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore leads to a reduction in the heart rate
what happens when the blood pressure is higher than normal
the pressure receptors transmit more nerve impulses to the centre in the medulla oblongata decreasing heart rate
This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heartbeats
what happens when the blood pressure is lower than normal
when blood pressure is lower than normal, pressure receptors transmit more nerve impulses to the centre in the medulla oblongata that increasing heart rate
This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heartbeat
how do receptors work
when a nervous system receptor is in its resting state ( not stimulated) there is a difference of charge inside and outside of the cell
the inside is negatively charged relative to the outside
This means there is voltage across the membrane. The voltage is also known as the potential difference. The potential difference when a cell is resting is called the resting potential
The resting potential is generated by ions pumps and ion channels
what is a generator potential
When a stimulus is detected, the cell membrane is excited and becomes more permeabele
This allows more ions to move in and outof the cell altering the potential difference
This change in dofference is due to a stimulus called the generator potential
A bigger stimulus excited the membrane more, causing a bigger movement of ions ad a bigger change in potential difference - so a bigger generator potential is produces
what is the action potenital
if the generator potential is big enough it will trigger an action potential which is an electrical implies that runs along a neurone
Sn action potential is only triggered if the generator potential reached a certain level called the threshold level
Action potentials are all one size, so the strengthofg the stimulus is measured by the frequency of action potentials ( the number of action potentials triggered during a certain period of time).
If the stimulus is too weak the generator potential won’s reach the threshold so there is no action potential
what are the pacinian corpuscles
these are pacinian corpuscles are mechorecptors - they detect mechanical stimuli e.g. pressure and vibrations.
They’re found in your skin. Pacinian corpuscles contain the end of a sensory nerve ending is wrapped in loads of layers of connective tissue called lamellae
what happens when the pacinian corpuscle is stimulated
When a Pacinian corpuscle is stimulated e.g. by a tap on the arm, the lamellae are deforemd and press on the sensory nerve ending. This causes the sensory neurone’s cell membrane to stretch, deforming the stretch - mediated sodium ion channels
The channel open and sodium ions diffuse into the cell, creating a generator potential
If the generator potential reaches the threshold, it triggers an action potential
