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Biology Mock AS 2 > Co ordination of response > Flashcards

Co ordination of response Flashcards

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1
Q

what do receptor cells do

A

send signals via either the nervous system or the hormonal system to the brain or spinal cord

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2
Q

what is CNS

A

the brain and spinal cord

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3
Q

what is PNS

A

all of the nerves in the body

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4
Q

how is information sent through nervous system

A

in the form of electrical impulses known as neurones

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5
Q

what are hormone/chemical messengers produced by and carried by

A

chemical substances produced by endocrine glands and carried by the blood

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6
Q

what do hormones do

A

transmit information from one part of an organism to another and bring about change by altering the activity of one or more specific target organs

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7
Q

why are hormones used to control functions that don’t need instant responses

A

Hormones are slower in action than nerve impulses

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8
Q

what do endocrine glands do

A

secrete hormones directly into the blood

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9
Q

how can endocrine glands be stimulated

A

by the action of another hormone or by the arrival of a nerve impulse

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10
Q

what is found in all types of neurones

A

axon
axon terminal containing nerve endings
cell body

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11
Q

what is the structure of an axon

A

long fibre

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12
Q

what does cell body contain

A

nucleus and other cellular structures

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13
Q

what does nerve ending at the axon terminal allow

A

neurones to connect to and receive impulses from other neurones, forming a network for easy communication

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14
Q

what does myelinated mean

A

axon is insulated by a fatty layer known as the myelin sheath

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15
Q

what is a myelin sheath made up of

A

specialised cells known as Schwann cells which wrap themselves around the axon

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16
Q

what are nodes of ranvier

A

uninsulated gaps between the Schwann cells

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17
Q

how do electrical impulses moved in myelinated cells

A

jump from one node to the next, speeding up impulse transmission

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18
Q

in non myelinated neurones is the axon insulated by Schwann cells

A

no, the impulse travels more slowly as it moves through the entire length of the axon

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19
Q

what does sensory neurone do

A

carry impulses from receptors to the brain and spinal cord in the CNS

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20
Q

where are relay neurones found

A

found entirely within the CNS and connect sensory and motor neurones

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21
Q

what do motor neurones do

A

carry impulses from the CNS to effector muscles or glands

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22
Q

describe structure of motor neurone

A

A large cell body at one end that lies within the spinal cord or brain

highly-branched dendrites extending from the cell body, providing many connections with the axon terminals of other neurones

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23
Q

structure of relay neurone

A

Short neurones with axons and highly branched dendrites

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24
Q

structure of sensory neurones

A

A cell body that branches off in the middle of the axon

The dendrites are attached to a receptor cell

The section of neurone that links the axon terminal with the cell body is known as a dendron

The section of neurone that connects the cell body with the CNS is the axon

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25
Q

what does CNS do

A

acts as a coordinating centre for the impulses that arrive from the receptors, determining which part of the body needs to respond and sending out a new set of impulses along motor neurones

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26
Q

what does motor neurone do

A

send impulses to the effectors to bring about a response

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27
Q

what do circular muscles contract to do

A

constrict the pupil, limits the amount of light entering the eye and prevents damage to the retina

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28
Q

what do radial muscles do

A

contract to dilate the pupil, maximises the amount of light entering the eye, improving vision

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29
Q

charge inside a resting (transmitting no impulses) axon and why?

A

always has a negative electrical potential compared to outside the axon
The difference in charge between the inside and outside of the neurone is due to different numbers of ions on each side of the neurone cell surface membrane

  • membrane is polarised

-70mv

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30
Q

what two factors contribute to establishing and maintaining resting potential

A

The active transport of sodium ions and potassium ions

A difference in membrane permeability to sodium and potassium ions

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31
Q

what do sodium potassium pumps in cell surface membrane and what does this do

A

use ATP to actively transport sodium ions (Na⁺) out of the axon and potassium ions (K⁺) into the axon

The two types of ions are pumped at an unequal rate; for every 3 sodium ions that are pumped out of the axon, only 2 potassium ions are pumped in

This creates a concentration gradient across the membrane for both sodium ions and potassium ions

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32
Q

why can potassium ions inside neurone diffuse out at a faster rate

A

The neurone membrane is less permeable to sodium ions than potassium ions

This results in more positive ions on the outside of the neurone than on the inside, generating a negative charge inside the neurone in relation to the outside

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33
Q

at what point is neurone membrane polarised

A

Once resting potential is reached

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34
Q

what needs to happen to membrane for a nerve impulse in neurone to be initiated and how does that occur.

A

the membrane needs to be depolarised
when an action potential is generated; lead to the reversal of resting potential from around -70 mV to around +30 mV

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35
Q

what exactly is action potential

A

rapid movement of sodium ions and potassium ions across the membrane of the axon

An action potential is the potential electrical difference produced across the axon membrane when a neurone is stimulated

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36
Q

when do voltage gated ion channels close

A

when the membrane is at rest, but they are involved in the generation and transmission of action potentials

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37
Q

what occurs when neurone is stimulated

A

A small number of sodium ion channels in the axon membrane open

Sodium ions begin to move into the axon down their concentration gradient

This reduces the potential difference across the axon membrane as the inside of the axon becomes less negative

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38
Q

what happens when threshold potential is met (-55)

A

more sodium ion channels open, leading to a further influx of sodium ions

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39
Q

when is action potential only initiated

A

if the threshold potential is reached

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40
Q

when is the membrane said to be depolarised and action potential has been generated

A

Once the charge has been reversed from -70 mV to around +30 mV

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41
Q

what happens as soon as action potential is generated

A

all the voltage gated sodium channels in this section of membrane close

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42
Q

what is opened after voltage gated sodium channels are closed

A

Voltage gated potassium channels in this section of axon membrane now open

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43
Q

what does opening of voltage gated potassium channel allow (repolarisation)

A

diffusion of potassium ions out of the axon down their concentration gradient causing inside of the axon to become negatively charged again, a process known as repolarisation

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44
Q

in resting potential where is it more negative

A

the inside of the axon always has a negative electrical potential compared to outside the axon

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45
Q

during the refractory period what happens

A

The membrane is unresponsive to stimulation so a new action potential cannot be generated at this time
This makes the action potentials discrete events and means the impulse can only travel in one direction

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46
Q

what happens when repolarisation ends

A

The voltage gated potassium channels then close, and the sodium-potassium pumps work to restore resting potential

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47
Q

when can membrane be stimulated again

A

Only once resting potential is restored

48
Q

what does depolarisation of membrane at the site of the first action potential cause

hint - The action potential is said to move along the axon in a wave of depolarisation

A

sodium ions to diffuse along the cytoplasm into the next section of the axon, depolarising the membrane in this new section, and causing voltage gated sodium channels to open

triggers another action potential in this section of the axon membrane
This process then repeats along the length of the axon

49
Q

why cant sodium ions that diffuse backwards along the membrane initiate a new action potential

A

due to the hyperpolarised nature of the membrane

50
Q

when will a impulse be transmitted

A

if the initial stimulus is sufficient to increase the membrane potential above a threshold potential

51
Q

how can stimulus size be detected by the brain

A

as the intensity of a stimulus increases, the frequency of action potentials transmitted along the neurone increases

52
Q

why is speed of conduction slow in unmyelinated neurones

A

depolarisation must occur along the whole membrane of the axon

By insulating the axon membrane myelin increases the speed at which action potentials can travel along the neurone

53
Q

can depolarisation occur in sections of the axon that are surrounded by myelin sheath membrane

A

depolarisation cannot occur, as the myelin sheath stops the diffusion of sodium and potassium ions

54
Q

where can action potential occur

A

at the nodes of Ranvier - the gaps between the Schwann cells that make up the myelin sheath

55
Q

what is saltatory conduction

Saltatory conduction allows the impulse to travel much faster than in an unmyelinated axon of the same diameter

A

The action potential therefore appears to ‘jump’ from one node to the next

56
Q

where do sodium ions diffuse along the axon

A

within the Schwann cells and the membrane at the nodes of Ranvier depolarises when the sodium ions arrive

57
Q

how can it be possible to design medication that prevent impulse transmission

A

drugs may bind to sodium ion channels, preventing them from opening and therefore preventing an influx of
sodium ions when an axon is stimulated

Preventing sodium ion influx prevents membrane depolarisation and an action potential cannot be generated

58
Q

where are synapses found in sense organs

A

between sensory receptor cells and sensory neurones

59
Q

where are synapses found in muscles

A

between motor neurones and muscle fibres

60
Q

what is the gap between neurones called

A

synaptic cleft

61
Q

what is the neurone before the synapse known as and its structure

A

presynaptic neurone and has a rounded end known as the synaptic knob

62
Q

where are neurotransmitters contained

A

within vesicles in the synaptic knob

63
Q

explain synaptic transmission
when an action potential arrives at the end of the axon of the presynaptic neurone….

A

the presynaptic membrane becomes depolarised, causing voltage gated calcium ion channels to open

Calcium ions diffuse into the synaptic knob via calcium ion channels in the membrane

The calcium ions cause vesicles in the synaptic knob to move towards the presynaptic membrane where they fuse with it and release chemical messengers called neurotransmitters into the synaptic cleft by exocytosis

64
Q

what happens when neurotransmitters diffuse across synaptic cleft

A

bind with receptor molecules on the postsynaptic membrane; this causes associated sodium ion channels on the postsynaptic membrane to open, allowing sodium ions to diffuse into the postsynaptic cell

65
Q

what happens if enough neurotransmitter molecules bind with receptors on postsynaptic membrane

A

an action potential is generated, which then travels down the axon of the postsynaptic neurone

66
Q

what does generation of action potential depend on

A

whether or not threshold potential is reached, which in turn depends on the number of action potentials arriving at the presynaptic knob

67
Q

what does a large amount of neurotransmitters allow at presynaptic knob

A

many sodium ion channels to open
Many sodium ion channels opening will allow a large influx of sodium ions, increasing the likelihood of threshold being reached

68
Q

why are neurotransmitters then broken down

A

to prevent continued stimulation of the postsynaptic neurone

69
Q

explain movement of Ach after presynaptic vesicles fuse with membrane

A

diffuse across the synaptic cleft and bind with receptor molecules on the postsynaptic membrane

sodium ions diffuse through and postsynaptic membrane is depolarised ACh is broken down into Acetate and Choline and Choline is recycled into ACh

70
Q

what are three things synapses allow

A

one-way transmission of impulses

Divergence: One neurone can connect to several other neurones at a synapse, allowing nerve signals to be sent in several directions from a single presynaptic neurone

Amplification of nerve signals by summation as
a single impulse that arrives at a synaptic knob may be insufficient to generate an action potential in the post-synaptic neurone
- effect of multiple impulses can be added together to overcome this known as summation

71
Q

how can summation be achieved

A

Several presynaptic neurones converging to meet a single postsynaptic neurone

Many action potentials arriving at a postsynaptic knob in quick succession

72
Q

what are receptors

A

specialised cells that can generate an electrical impulse in a sensory neurone when stimulated by a particular stimulus

73
Q

where does light focus in the eye

what muscle controls how much light enters the eye

A

region of the retina called the fovea

muscles of the iris

74
Q

what focuses the light

A

the lens, the shape of which is controlled by ciliary muscles attached to the lens by suspensory ligaments

75
Q

where are rod cells located
what are rod cells sensitive to
colour of images by rod cells

A

outer retina

sensitive to light intensity so can detect presence and brightness of light

black and white images

76
Q

where are cone cells located
what are cone cells sensitive to
colour of images by cone cells

A

grouped together in the fovea

Sensitive to different wavelengths of visible light and so detect colour

77
Q

how are action potentials generated in photoreceptor transmitted to the brain

A

via the optic nerve
The optic nerve leaves the back of the eye from a region known as the blind spot

78
Q

what do photo receptors in the eye generate when stimulated by bright enough light or by light of a particular wavelength

A

action potentials

79
Q

what pigments do rod cells contain and explain what happens when light hits the pigment

A

light-sensitive pigment called rhodopsin

When light hits rhodopsin it breaks apart into constituent parts retinal and opsin

The breaking apart of rhodopsin is known as bleaching

80
Q

what does bleaching of light sensitive pigments cause

A

a chemical change in the photoreceptor that results in the generation of a nerve impulse

Nerve impulses travel along a bipolar neurone to the optic nerve, which carries information to the brain

81
Q

how are rod cells different to other nerve cells

A

rather than initiating an action potential when they are depolarised,

rod cells initiate action potentials in neighbouring bipolar neurones when they are hyperpolarised

82
Q

in the dark what occurs inside rod cells

A

Sodium ions are actively pumped out of rod cells, generating a concentration gradient

Sodium ions diffuse back down this concentration gradient into the rod cell via sodium channels

there is little difference in charge between the outside and inside of the rod cell, and the cell is said to be depolarised
In reality the inside of the rod cell is slightly negative in comparison to the outside

The depolarised rod cell releases neurotransmitters which diffuse across a synapse to a bipolar neurone

Rather than initiating an action potential in the bipolar neurone this neurotransmitter inhibits the generation of an action potential, preventing a nerve impulse from being sent to the optic nerve
This neurotransmitter is said to be an inhibitory neurotransmitter

83
Q

what happens inside rod cells in the light

A

Light bleaches rhodopsin, causing it to break apart into retinal and opsin

The bleaching of rhodopsin causes the sodium ion channels in the cell surface membrane of the rod cell to close, preventing sodium ions from diffusing back into the rod cell

The lack of positively charged ions entering the rod cell causes its interior to become more negative until it reaches a hyperpolarised state

The hyperpolarised rod cell stops releasing an inhibitory neurotransmitter, so the generation of an action potential in the neighbouring bipolar neurone is no longer inhibited

An action potential is generated in the bipolar neurone attached to the rod cell and an impulse is sent to the optic nerve

84
Q

how can plants respond to stimuli

A

altering their growth (tropism)

85
Q

where are growth factors produced

A

in the growing parts of a plant before moving from the growing regions to other tissues where they regulate cell growth in response to a directional stimulus

86
Q

example of growth factor and what it does

A

auxin is a growth factor that stimulates cell elongation in plant shoots and inhibits growth in cells in plant roots

87
Q

what is the role of these plant hormones
gibberellin
cytokines
absicisic acid (ABA)
and ethene

A

Stem elongation / Flowering / Seed germination

Cell growth and division

Leaf loss / Seed dormancy

Fruit ripening / Flowering

88
Q

what is IAA (Indoleacetic acid)

A

a type of auxin

brings about plant responses such as phototropism by altering the transcription of genes inside plant cells

Altering the expression of genes that code for proteins involved with cell growth can affect the growth of a plant

89
Q

what is IAA produced by

A

cells in the growing parts of a plant before it is redistributed to other plant tissues

90
Q

what is redistribution of IAA affected by

A

environmental stimuli such as light and gravity, leading to an uneven distribution of IAA in different parts of the plant
This brings about uneven plant growth

91
Q

where does transport of IAA over long distances occur

A

in the phloem

92
Q

what happens if concentration of IAA isnt uniform across stem

A

then uneven cell growth can occur

93
Q

where does IAA move when light shines on a stem

A

IAA is transported from the illuminated side of a shoot to the shaded side
An IAA gradient is established, with more on the shaded side and less on the illuminated side

The higher concentration of auxin on the shaded side of the shoot causes a faster rate of cell elongation, and the shoot bends towards the source of light

94
Q

what is the response called in shoots/roots

A

shoots phototropism
roots geotropism

95
Q

how does IAA concentration affect cell elongation

A

higher concentrations result in a lower rate of cell elongation

as IAA is transported towards the lower side of plant roots

The resulting high concentration of auxin at the lower side of the root inhibits cell elongation

As a result, the lower side grows at a slower rate than the upper side of the root, causing the root to bend downwards

96
Q

what is the flowering in plants controlled by

A

stimulus of night length

When the nights reach a certain length, genes that control flowering may be switched on or off, leading to the activation or inhibition of flowering
Genes that are switched on are expressed, leading to production of the polypeptides for which they code, while genes that are switched off are not expressed, so the polypeptides for which they code are not produced

97
Q

what is Pr

A

inactive form of phytochrome, it absorbs light from the red part of the spectrum

98
Q

what is phytochrome

A

photosensitive leaf pigments which are used by the plant to detect periods of light and darkness.

99
Q

what is Pfr

A

active form of phytochrome, it absorbs light from the far red part of the spectrum

100
Q

What happens:

when Pr absorbs red light

when Pfr absorbs far red light

toPfr , In the absence of red light

A

it is converted into PFR

it is converted back to Pr

gradually converts back into PR

101
Q

what happens to Pfr during the day

A

During the day levels of PFR rise
Sunlight contains more wavelengths at 660 nm than 730 so the conversion from PR to PFR occurs more rapidly in the daytime than the conversion from PFR to PR

102
Q

what happens to Pr during the night

A

During the night levels of PR rise
Red light wavelengths are not available in the darkness and PFR converts slowly back to PR

103
Q

what happens in long day plants and why

A

high levels of the active form of phytochrome activate flowering

Days are long so PR is converted to PFR at a greater rate than PFR is converted to PR
The active form of phytochrome, PFR, is present at high levels
High levels of PFR activate flowering

PFR activates expression of genes that stimulate flowering
The active gene is transcribed and translated
The resulting protein causes flowers to be produced rather than stems and leaves

104
Q

how does low serotonin levels in an individual affect the transmission of impulses in the brain

A

serotonin is a neurotransmitter / there will be less neurotransmitter (1)

(less serotonin) results in fewer
depolarisations of post synaptic membranes (1)

threshold not achieved / less chance of action potential being produced

105
Q

how does nicotine cause an action potential in the post synaptic neurone that released noradrenaline

A

nicotine similar in shape to acetylcholine

increases permeability of membrane to sodium ions / changes shape of (receptors / channel proteins } (1)

nicotine causes the depolarisation of the post-synaptic membrane (1)

depolarisation reaches threshold level (1)

106
Q

process that occur at synapse that leads to habituation

A

(repeated stimulus) decreases {sensitivity / permeability} of pre-synaptic membrane / calcium channels not opening
(1)

so {fewer / no} Ca?+ ions move into pre-synaptic neurone
(1)

so {fewer / no} vesicles {move towards / fuse with} (pre-synaptic) membrane
(1)

so {less / no} neurotransmitter {released / can diffuse across gap}
(1)

{action potential / depolarisation} less likely to occur in post-synaptic neurone

107
Q

role of sodium ions in the functioning of mammalian rod cell

A

sodium ions are pumped out of the rod calls.

in the light they do not move back into the rod cell

in the dark sodium ions move back into rod cells

in light when the sodium ions dont move back into rod cell they are hyperpolarised and in the dark they are depolarised when sodium ions move back in

108
Q

explain how IAA affects growth

A

it diffuses from the tip of the …
taken up by cells in the zone of elongation
causing cells to elongate
leads to lowering in pH of cell wall
causes the … to grow towards the light

109
Q

explain effect of light intensity on current produced by rod cell

A

increasing light intensity decreases the current (1)

  • because (rhodopsin is broken down / opsin is released} (1)
  • therefore, more opsin binds to the channel proteins in the outer segment (1)
  • sodium-gated voltage channels close (1)
  • (reducing / stopping) the influx of sodium ions / making membrane impermeable to sodium ions (1)
110
Q

Explain what happens at the synapse to cause a decrease in saliva production
when the child was shown a cheeseburger on more than six occasions.

A

reduced permeability of presynaptic membrane to calcium ions / fewer calcium ions enter the pre-synaptic neurone (1)

(so fewer) vesicles { move towards / fuse with } the presynaptic membrane (1)

(therefore) less neurotransmitter binds to receptors on the post-synaptic membrane (1)

action potential may not occur in the post-synaptic neurone / membrane may not be depolarised (1)

111
Q

role of dendrites

A

{ form synapses / connections } with other neurones (1)

{ integrate / receive } impulses from other neurones (1)

involved in summation
{ propagate a signal / initiate an action potential } to the {cell body / axon?

112
Q

compare contrast structure of sensory and motor neurones

A

Similarities
* both have a cell body containing a nucleus (1)
* both have an axon (1)

  • both have dendrites at one end of neurone and terminal branches at the other end (1)
    Difference
  • location of cell body (1)
113
Q

describe the interaction of the muscles in the eye that led to the dilation of the pupils

A
  • antagonistic (interaction) of muscles (1)
  • in the iris (1)
    radial muscles contract and circular muscles
    relax (1)
114
Q

explain why the neurone gets hyperpolarised

A

potassium ions (continue) leaving the {axon / cytoplasm} (1)
* (therefore) preventing another depolarisation occurring / it is the refractory period (1)
* allowing time for the neurone to reset (1)
* so that nerve impulses travel in one direction only (1)

115
Q

describe the process that occur at a synapse that lead to habituation

A

(repeated stimulus) decreases {sensitivity / permeability} of pre-synaptic membrane / calcium channels not opening
(1)
so {fewer / no} Ca?+ ions move into pre-synaptic neurone (1)
so {fewer / no} vesicles {move towards / fuse with} (pre-synaptic) membrane
(1)
so {less / no} neurotransmitter {released / can diffuse across gap}
(1)
{action potential / depolarisation} less likely to occur in post-synaptic neurone

Biology Mock AS 2 (23 decks)

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