6 Response To Changes In Environment Flashcards
Stimulus
A detectable change in the internal or external environment of an organism that leads to a response in the organism
Coordinator
Acts like a switchboard, connecting information from each receptor with the appropriate effector
Stimulus and response sequence of events
Stimulus -> receptor ->coordinator -> effector -> response
Taxes
A simple response whose direction is determined by the direction of stimulus. As a result, mobile organisms respond directly to environmental changes by moving its whole body either towards a favourable stimulus (positive taxis)or away from an unfavourable one(negative taxis)
Kineses
A form of response in which the organism doesn’t move towards or away from a stimulus
Instead it changes the speed at which it moves and the rate at which it changes direction
Why is response to stimuli advantageous?
Organisms increase their chance of survival by responding to changes in their environment
Tropisms
A tropism is the growth of part of a plant in response to a directional stimulus
In most cases the plant part grows towards (positive response) or away from (neg response) the stimulus
-Plant shoots grow towards light (pos phototropism) and away from gravity (neg gravitropism) so that their leaves are in the most favourable position to capture light for PS
-plant roots grow away from light (neg phototropism) and towards gravity (pos gravitropism) to increase probability that roots will grow into the soil, where they are better able to absorb water and mineral ions
Indoleacetic acid (IAA)
Plant growth factor
Belongs to a group of substances called auxins
Controls plant elongation
Phototropism in flowering plants
- Cells in the tip 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 the shoot
- Light causes the movement of IAA from the light side to the shaded side of the shoot
- A greater conc of IAA builds up on the shaded side of the shoot than on the light side
- As IAA causes elongation of shoot cells and there is a greater conc of IAA on the shaded side of the shoot, the cells on this side elongate more
- The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light
In roots a high conc of IAA inhibits cell elongation. As a result in roots the elongation of cells is greater on the light side and so the root bends away from light - negatively phototropic
Gravitropism in flowering plants
- Cells in the tip of the root produce IAA, which is transported along the root
- The IAA is initially transported to all sides of the root
- Gravity influences the movement of IAA from the upper side to the lower side of the root
- A greater conc of IAA builds up on the lower side of the root than the upper side
- As IAA inhibits the elongation of root cells and there is a larger conc of IAA on the lower side, the cells on this side elongate less than those in the upper side
- The 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 conc of IAA on the lower side increases cell elongation and causes this side to elongate more than the upper side
So shoots grow upwards away from force of gravity
Shoot tip removed
No response
Tip must either detect the stimulus or provide the messenger or both as its removal prevents any response
Light proof cover placed on over shoot tip
No response
Light stimulus must be detected by the tip
Thin, impermeable barrier of mica inserted on light side
Movement of chemical down shaded side
Shoot bends towards light
Mica on light side allows hormone to pass only down the shaded side where it increases growth and causes bending
Mica inserted on shaded side
Movement of chemical down shaded side is prevented by mica
No response
Tip removed, gelatin Block inserted and tip replaced
Movement of chemical down shaded side
Shoot bends towards light
Gelatin allows chemicals to pass through it, but not electrical signals, the bending which occurs must be due to chemical passing from tip
Tips removed and replaced but displaced to one side
Shoots bend towards side where no tip is present
Central nervous system
Made up of brain and spinal cord
Peripheral nervous system
Made up of pairs of nerves that originate from either the brain or spinal cord
Divides into sensory nervous system and motor nervous system
Two major divisions of nervous system
Central nervous system
Peripheral nervous system
Sensory neurones
Carry nerve impulses (electrical signals) from receptors towards the CNS
Motor neurones
Carry nerve impulses away from the CNS to effectors
Motor nervous system divides into
Voluntary nervous system
Autonomic nervous system
Voluntary nervous system
Carries nerve impulses to body muscles and is under voluntary (conscious) control
Autonomic nervous system
Carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control , that is involuntary (subconscious)
spinal cord
column of nervous tissue that runs along the back and lies inside the vertebral column for protection. emerging at intervals along the spinal cord are pairs of nerves
reflex arc
involuntary response to sensory stimulus
involve three neurones
e.g. 1. the stimulus- heat from hot object
2. a receptor- temp receptors in skin on back of hard, which generates nerve impulses in the sensory neurone
3. a sensory neurone- passes nerve impulses to spinal cord
4. a coordinator (intermediate neurone)- links the sensory neurone to the motor neurone in the spinal cord
5. a motor neurone- carries nerve impulses from the spinal cord to a muscle in the upper arm
6. an effector- the muscle in the upper arm, which is stimulated to contract
7. the response- pulling the hand away from hot object
importance of reflex arcs
- involuntary and therefore do not require the decision-making powers of the brain, thus leaving it free to carry out more complex responses
- they protect the body from harm. effective from birth and dont have to be learnt
- they are fast, because the neurone pathway is short with very few synapses where neurones communicate with each other
- absence of any decision-making process also means the action is rapid
pacinian corpuscle
responds to changes in mechanical pressure
- specific to a single type of stimulus
- produces a generator potential by acting as a transducer
pacinian corpuscle- specific to single type of stimulus
only responds to mechanical pressure
pacinian corpuscle- produces a generator potential by acting as a transducer
PC transduces the mechanical energy of the stimulus into a generator potential
pacinian corpuscle structure and function
Pacinian Corpuscles are located deep in the skin, and are mostly found on fingers, soles of the feet as well as external genitalia.
They are also found in joints, tendons and ligaments. Pacinian Corpuscles have a single sensory neurone, located in the centre of connective tissue called lamellae which forms layers separated by a gel.
The Pacinian Corpuscle contains stretch mediated sodium channels in the cell surface membrane. When not under pressure these channels are closed, however under pressure these become deformed. As a result they open and allow the rapid influx of sodium ions to occur. The positive charge on the sodiums changes the membrane potential, causing the membrane to become depolarised. This results in an generator potential being created which goes on to
create an action potential in the axon.
pacinian corpuscle function
- in its normal state, the stretch-mediated sodium channels of the membrane around the neurone of a pacinian corpuscle are too narrow to allow sodium ions to pass along them. in this state, the neurone of the pacinian corpuscle has a resting potential
- when pressure is applied to the PC, it is deformed and the membrane around its neurone becomes stretched
- this stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone
- the influx of sodium ions changes the potential of the membrane (it becomes polarised), thereby producing a generator potential
- the GP in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurones, to the CNS
receptors in the eye
light receptor cells of the mammalian eye are found on its innermost layer, the retina.
the millions og light receptor cells found in the retina are of two main types: rod cells and cone cells
both act as transducers by conserving light energy into the electrical energy of a nerve impulse
rod cells
cannot distinguish different wavelengths of light and so lead to images being seen only in black and white
more numerous than cone cells
many are connected to a single sensory neurone in the optic nerve
rod cells are used to detect light of very low intensity
a certain threshold has to be exceeded before a generator potential is created in the bipolar cells to which they are connected
as a number of are connected to a single bipolar cell, there is a much greater chance that the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell
so rod cells allow us to see in low light intensities (ie night) but only in black and white
rod cells- generator potential
in order to create a GP the pigment in the rod cells must be broken down. there is enough energy from low light intensity to cause this breakdown.
rod cells- cons
having many rod cells linking to a single bipolar cell is that light received by rod cells sharing the same neurone will only generate a single impulse travelling to the brain regardless of how many neurones are stimulated
so in perception, the brain cannot distinguish between the separate sources of light that stimulated them
two dots close together cannot be resolved and so will appear as a single blob
rod cells therefore give low visual activity
cone cells
of three diff types, each responding to a diff wavelength of light
depending on the proportion of each type that is stimulated, we can perceive images in full colour
often cone cells have their own separate bipolar cell connected to a sensory neurone in the optic nerve
so the stimulation of a number of cones cannot be combined to help exceed the threshold value and so create a generator potential
cone cells only respond to high LI
they contain diff types of pigment from that found in rod cells
pigment requires higher LI for its breakdown
if 2 adjacent cone cells are stimulated, the brain receives 2 separate impulses
where are cone and rod cells found
distribution of RC and CC in 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. the fovea therefore receives the highest intensity of light. therefore cone cells, but not rod cells, are found at the fovea
the conc of CC diminishes further away from the fovea
at the peripheries of the retina, where light intensity is at its lowest, only rod cells are found
what are the divisions of the autonomic nervous system?
- sympathetic NS
- parasympathetic NS
sympathetic NS
stimulates effectors and so speeds up any activity
acts like an emergency controller
it controls effectors when we exercise strenuously or experience powerful emotions
ie it helps us to cope with stressful situations by heightening our awareness and preparing us for activity(the fight or flight response)
parasympathetic NS
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
antagonostic
oppose each other
e.g. sympathetic and parasympathetic NS
if one system contracts a muscle, the other relaxes it
what makes the heart myogenic?
its contraction is initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic), as is the case with other muscles
what controls heart rate
within the wall of the right atrium of the heart is a distinct group of cells known as the sinoatrial node
it is from here that the initial stimulus for contraction originates
the SAN has a basic rhythm of stimulation that determines the beat of the heart
sequence of events that controls the basic heart rate is
- a wave of electrical excitation spreads out from the sinoatrial node 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 atrioventricular node, which lies between the atria
- the AVN, after a short delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively make 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
modifying the resting heart rate
the rate can be altered to meet varying demands for oxygen
during exercise the resting heart rate may need to more than double
changes to the rate are controlled by a region of the brain called the medulla oblongata
what are the two centres within the medulla oblongata concerned with heart rate?
- a centre that increases heart rate, which is linked to the sinoatrial node by the sympathetic NS
- a centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic NS
chemoreceptors
found in the wall of the carotid arteries (arteries that serve the brain)
sensitive to changes in the pH of the blood that result from changes in carbon dioxide conc
in solution, CO2 forms an acid and therefore lowers the pH
control by chemoreceptors
- when the blood has a higher than normal conc of CO2, its pH is lowered
- the chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the freq of nervous impulses to the centre of the medulla oblongata that increases heart rate
- this centre increases the freq of impulses via the sympathetic NS to the SAN. this, in turn, increases the rate of production of electrical waves by the SAN and therefore increases the heart rate
- the increased blood flow that this causes leads ot more CO2 being removed by the lungs and so the CO2 conc 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 freq of nerve impulses to the medulla oblongata
- the medulla oblongata reduces the freq of impulses to the SAN, which therefore leads to a reduction in the heart rate
control by pressure receptors
- when blood pressure is higher than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. this centre sends impulses via the parasympathetic NS to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heart beats
- when blood pressure is lower than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate. this centre sends impulses via the sympathetic NS to the SAN, which increases the rate at which the heart beats
pressure receptors
occur within the walls of the carotid arteries and the aorta
