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biology a level year 2 > response to stimuli > Flashcards

response to stimuli Flashcards

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1
Q

what is a stimulus

A

a stimulus is a detectable change in the internal/external environment of organism that leads tp a response in the organism

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2
Q

why is responding to a stimuli important

A

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

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3
Q

what detects stimuli

A

receptors which are specific to one type of stimulus

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4
Q

what formulates a response to a stimuli

A

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

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5
Q

what carries out a response

A

responses are carried out by an effector

the response may be at a molecular level or involve the behaviour of a whole organism

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6
Q

what are hormonal responses

A

they are relatively slow process found in both plants and animals

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7
Q

what is another means of communication that animals have

A

they also have the more rapid means of communication which is the nervous system

which usually have many different receptors and control effectors

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8
Q

what links the receptors and effectors

A

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

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9
Q

what are the sequence of events involved in either chemical control/ nerve cells

A

stimulus - receptors - coordinator - effector - response

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10
Q

what is a taxes

A

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

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11
Q

how are taxes classified

A

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

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12
Q

what is phototaxis

A

when an organism moves away/ moves towards the light

this increases their chances of survival of organisms

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13
Q

what is chemotaxis

A

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

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14
Q

what is kinesis

A

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

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15
Q

what happens when n organism moves a considerable distance into an unfavourable environment

A

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

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16
Q

what is an example of kinesis

A

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

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17
Q

what is tropism

A

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)

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18
Q

what is phototropism

A

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

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19
Q

what factors do plants grow in response to

A

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
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20
Q

what are plant growth factors

A

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

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21
Q

explain the control of tropism by IAA

A

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

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22
Q

explain phototropism in flowery plants

A
  1. Cells in the top of the shoot produce IAA, which is then transported down the shoot
  2. the IAA is initially transported evenly throughout all regions as it begins to move down at the shoot
  3. Light causes the movement of IAA from the light side to the shaded side of the shoot
  4. a greater concentration of IAA builds up on the shaded side of the shoot than on the light side
  5. As IAA causes elongation of the IAA on the shaded side of the shoot, the cells on the side alongside more
  6. The shaded od the shoot elongates faster than the light side, causing the shoot tip to bend towards thelight
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23
Q

what does IAA do

A

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

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24
Q

describe gravitropism in flowering plants

A
  1. 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
  2. a greater concentration of IAA builds up on the lower side of the root than in the upper side
  3. 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
  4. 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
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25
Q

in shoots the greater elongation(…)

A

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

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26
Q

how is IAA transported

A

transport if IAA is one direction, namely away from the tip of shoots and roots where it is produced

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27
Q

what are the effects of IAA on plants

A

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

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28
Q

what happens as the cell matures

A

as the cells mature they develop rigity - therefore older parts of the shot / root will not be able to respond to the IAA

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29
Q

what is the acid growth hypothesis

A

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

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30
Q

what can the elongation of cells on one sire of a stem or root lead to

A

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

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31
Q

what is a reflex arc

A

it is the simplest type of nervous response to a stimulus is a reflex arc

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32
Q

what are the two major divisions of the nervous system

A

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

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33
Q

what is the peripheral nervous system divided into

A

it is divided into:
-sensory neurones

-motor neurones which

34
Q

what are sensory neurones

A

carry nerve impulses (electrical signals) from receptors towards the central neurones

35
Q

what are motor neurones

A

which carry nerve impulses away from the central nervous system to effectors

36
Q

what are the subdivisions of the motor neurones

A
  1. the voluntary nervous system

2. the automatic nervous system

37
Q

what is the voluntary nervous system

A

it carries nerve impulses to body muscles and is under voluntary (conscious control)

38
Q

what is the autonomic nervous system

A

it carries nerve impulses to glands, smooth muscle and it s not under voluntary control, that is involuntary

39
Q

what is the spinal cord

A

the spinal cord is a column of nervous tissue that runs along the back and less inside the vertebral column for protection

40
Q

what are the features of a reflex arc

A

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
41
Q

how many neurones are involved in a reflex arc

A

3 neurones

42
Q

describe the reflex arc

A

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:

  1. the stimulus is detected by a receptor
  2. a sensory neurone passes nerve impulse to the spinal cord
  3. a coordinator (intermediate neurones) -links the sensory neurone to the motor neurone in the spinal cord
  4. the nerve impulse passes along a motor neurone from the spinal cord to the effector (e.g. a muscle in the upper arm)
  5. the effector is stimulated to contract if it is a muscle or secrete if it is a hormone
  6. the response is carried out
43
Q

why are reflex arcs important

A

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
44
Q

what are receptors

A

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)

45
Q

what is sensory perception

A

sensory perception involves making sense of the info from the receptors

46
Q

what is the pacinian corpsucle

A

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

47
Q

what is a transducer

A

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

48
Q

what are the nerve impulse in the form of

A

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

49
Q

how do receptors function

A

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

50
Q

where are the receptor cells in the mammalian eye

A

the light receptor cells of the mammalian eye are found on its innermost layer, the retina

51
Q

what are the two main types of receptors in the retina

A

rod cells

cone cells

both rod and cone cells act as tranducers by conserving light energy into the electrical energy of a nerve impulse

52
Q

how are images seen in rods

A

rod cells can’t distinguish different wavelengths of light and therefore lead to images being seen only in black and white

53
Q

how many rod cells are there

A

20 million in each eye

54
Q

what are rod cells connected to

A

many rod cells are connected to a single sensory neurone in the op[tic nerve

55
Q

what are rod cells used for

A

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

56
Q

what are cone cells

A

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

57
Q

how many cone cells are there in each eye

A

around 6 million cone cells often with their separate bipolar cell connected to a sensory neurone in the optic nerve

58
Q

why do cone cells respond only to high intensity

A

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

59
Q

why do rods have low visual acuity

A

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

60
Q

what are the different pigment that cone cells contain

A

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

61
Q

how many different types of cone cells are there

A

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

62
Q

how is the distribution of rod and cone cells on the retina

A

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

63
Q

how is the concentration of cone cells distributed in the fovea

A

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

64
Q

what is the autonomic nervous system

A

the autonomic nervous system controls the involuntary (subconscious) activities of internal muscles and glands

it has two divisions

65
Q

what are the two subdivisions of the nervous system

A

the sympathetic nervous system

the parasympathetic nervous system

66
Q

what is the sympathetic nervous system

A

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

67
Q

what is the parasympathetic nervous system

A

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

68
Q

what do we mean when we say that the action of the sympathetic and parasympathetic systems are antagonist

A

they oppose each other

69
Q

what are the muscles of the heart called

A

the cardiac muscle

70
Q

what do we mean when we say that the cardiac muscles are myogenic

A

it is myogenic which means that its contractions are initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic)

71
Q

what are the sinoatrial node (SAN)

A

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

72
Q

what is the sequence of events that controls the basic heart rate is:

A
  1. a value of electrical spreads out from the sinoatrial across both atria, causing them (the atrium) to contract
  2. a layer of non-conductive tissue (atrioventricular septum) prevents the wave from crossing the ventricles
  3. the wave of excitation enters the second group of cells called the atrioventricular node (AVN), which lies between the atria
  4. 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
  5. 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
  6. 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
73
Q

what controls changes to the heart rate

A

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

74
Q

what are chemoreceptors

A

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

75
Q

what is the process of chemoreceptors control

A
  1. when the blood has a higher than normal concentration its pH is lowered
  2. 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
  3. 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
  4. the increased blood flow that this causes leads to more CO2 concentration of the blood returns to normal
  5. 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
  6. the medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore leads to a reduction in the heart rate
76
Q

what happens when the blood pressure is higher than normal

A

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

77
Q

what happens when the blood pressure is lower than normal

A

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

78
Q

how do receptors work

A

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

79
Q

what is a generator potential

A

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

80
Q

what is the action potenital

A

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

81
Q

what are the pacinian corpuscles

A

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

82
Q

what happens when the pacinian corpuscle is stimulated

A

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

biology a level year 2 (14 decks)

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