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A Level Biology : Content > Topic 8A : Responding To The Environment > Flashcards

Topic 8A : Responding To The Environment Flashcards

1
Q

stimulus

A

any change in the internal or external environment

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2
Q

how is the nervous system split

A

central nervous system and peripheral nervous system

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3
Q

what makes up the central nervous system

A

brain and spinal cord

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4
Q

what makes up the peripheral nervous system

A

sensory neurones which carry sensory information from receptors to CNS and motor neurones which carry commands from CNS to effectors

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5
Q

neurotransmitters

A

neurone chemicals

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6
Q

why do organisms respond to changes in the environment

A

to increase their chance of survival (external)

to make sure conditions are always optimal for their metabolism (internal)

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7
Q

receptor

A

specialised cells or proteins on cell membranes that detect stimuli

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8
Q

effectors

A

cells that include muscle cells and gland cells that bring about a response to a stimulus to produce an effect.

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9
Q

describe the general stages that cause a response to stimulus

A

stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neurone to the CNS

neurotransmitters take information to the next neurone

CNS processes information and sends impulses along motor neurones to effectors

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10
Q

what makes up the hormonal system

A

glands and hormones

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11
Q

gland

A

group of cells that are specialised to secrete useful substances such as hormones

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12
Q

hormone

A

chemical messengers that are proteins or peptides or steroids

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13
Q

what does the peripheral nervous system divide into

A

autonomic (involuntary) and somatic (voluntary)

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14
Q

what does the autonomic nervous system divide into

A

sympathetic and parasympathetic systems

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15
Q

autonomic nervous system

A

heart muscle, smooth muscle and glands

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16
Q

somatic nervous system

A

voluntary skeletal muscles

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17
Q

parasympathetic division

A

rest and digest

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18
Q

sympathetic division

A

active and alert

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19
Q

pupil dilation

A

in low light intensity, nerve impulses are sent along the optic nerve at low frequency to the brain.

impulses are then sent down sympathetic motor neurones to the radial muscles of the iris.

this causes radial muscles to contract and pupil becomes dilated allowing more light to reach the retina.

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20
Q

pupil constriction

A

in high light intensity, nerve impulses are sent along the optic nerve at high frequency to the brain.

impulses are then sent down parasympathetic motor neurones to the circular muscles of the iris.

this causes circular muscles to contract and pupil becomes constricted allowing more less to reach the retina.

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21
Q

nervous communication features

A

use electrical impulses

faster response

localised response

short-lived response

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22
Q

hormonal communication features

A

uses chemicals

slower response

widespread response

long-lived response

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23
Q

what are the two types of photoreceptors

A

cones and rods

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24
Q

cones

A

allow colour vision in bright light and ate clustered in the centre of the retina (fovea)

red, green and blue sensitive

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25
Q

rods

A

black and white vision

more sensitive to light intensity

located in outer retina

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26
Q

name the bundle of neurones that links eye to the brain

A

optic nerve that carries nerve impulses from the photoreceptors from retina to the brain

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27
Q

blind spot

A

when optic nerve leaves the eye so there are not photoreceptors so its not sensitive to light

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28
Q

what controls the amount of light entering the eye

A

muscle of iris

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29
Q

what do photoreceptors convert light into

A

electrical impulses

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30
Q

how do photoreceptors convert light into electrical impulses

A

light enters the eye, hits the photoreceptors and is absorbed by light-sensitive pigments which then become bleached by the light resulting in a chemical change.

this triggers nerve impulses along a bipolar neutonr

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31
Q

bipolar neurones

A

neurones connecting photoreceptors to the optic nerve which takes impulses to the brain

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32
Q

monochromatic vision

A

black and white

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33
Q

trichromatic vision

A

colour

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34
Q

rhodopsin

A

light sensitive pigment in rods

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35
Q

what chemical make up rhodopsin

A

retinal and opsin

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36
Q

when are rods stimulated

A

when its light

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37
Q

when are rods not stimulated

A

when its dark

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38
Q

what happens when rods are not stimulated

A

sodium ions are pumped out of cell by active transport but they they do diffuse back in to the cell through open sodium channels.

this makes the inside of the cell only slightly negative so the cell membrane is said to be depolarised.

this triggers release of neurotransmitters (glutamate) which inhibit the bipolar neurone so bipolar neurone cant fire an action potential so information doesn’t reach the brain by binding to receptors on the neurone.

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39
Q

what happens when rods cells are stimulated

A

light bleaches rhodopsin causing it to break apart into retinal and opsin so sodium ion channels close (cause of opsin) leading to them being actively transported out of the cell and they cant diffuse back in.

sodium ions build up on the outside of the cell making the outside of membrane more negative so membrane is said to be hyperpolarised.

glutamate is not released so generation of action potential in neighbouring bipolar neurone so no longer inhibited.

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

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40
Q

when its dark, is a bipolar neurone inhibited or uninhibited

A

inhibited

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41
Q

when its light, is a bipolar neurone inhibited or uninhibited

A

uninhibited

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42
Q

axons

A

carry nerve impulses away from cell body

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43
Q

dendrites and dendrons

A

carry nerve impulses towards the cell body

44
Q

list the events happening during an action potential

A

stimulus

depolarisation

repolarisation

hyperpolarisation

resting potential

45
Q

stimulus as a part of action potential

A

stimulus excites neurone cell membrane causing sodium ion channels to open.

membrane becomes more permeable to sodium so sodium diffuses into neurone down the sodium ion electrochemical gradient making the inside less negative.

46
Q

depolarisation as a part of action potential

A

if potential reaches the threshold value (-55mV) more sodium ion channels open so more sodium ions diffuse into neurone.

47
Q

repolarisation as a part of action potential

A

at potential difference of 30mV sodium ion channels close and potassium ion channels open so membrane is more permeable to potassium so potassium ions diffuse out of neurone down the potassium ion concentration gradient bringing the membrane back its resting potential.

48
Q

hyperpolarisation as a part of action potential

A

potassium ion channels slowly close so too many potassium ions diffuse out of the neurone.

potential difference becomes more negative than resting potential (-70mV).

49
Q

what happens after action potential

A

refractory period

50
Q

refractory period

A

channels are recovering

sodium ion channels closed during repolarisation

potassium ion channels closed during hyperpolarisation

it ensures action potential travels in one direction

51
Q

resting potential

A

nerve cells are polarised as a result of imbalance better sodium ions and potassium ions so inside of nerve cell is more negative.

sodium ion pumps remove sodium ions from cell cytoplasm and potassium ions diffuse out of cell along their concentration gradient.

52
Q

describe how an action potential moves along a neurone

A

when action potential happens, some of sodium ions that enter neurone diffuse sideways.

this causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part.

this causes wave of depolarisation to travel along the neurone

wave moves away from the parts of membrane in refractory period because these parts cant fire an action potential.

53
Q

give one function of refractory period in nervous transmission

A

ion channels are recovering and can’t be opened so refractory period acts as time delay between one action potential and the next so that action potentials don’t overlap but pass along as discrete impulses.

so action potentials are unidirectional

54
Q

how does a biggee stimulus affect the size of action potential

A

makes them fire more frequently

55
Q

how do local anaesthetics prevent action potential from being conducted

A

they bind to sodium ion channels in membrane of neurones which stops sodium ions from moving into neurones resulting in membranes not becoming depolarisated

action potentials are prevented and information doesn’t reach the brain.

56
Q

myelin sheath

A

electrical insulator

57
Q

what makes up myelin sheath

A

schwann cells

58
Q

nodes of ranvier

A

gaps between schwann cells

sodium ion channels are concentrated there

59
Q

in a myelinated neurone, where does depolarisation occur

A

nodes of ranvier

60
Q

conduction velocity

A

the speed at which an impulse moves along a neurone

61
Q

saltatory conduction

A

when the neurone’s cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node

62
Q

synapse

A

junction between a neurone and another neurone

63
Q

synaptic cleft

A

tint gap between cells at a synapse

64
Q

synaptic knob

A

swelling of presynaptic neurone

65
Q

what does the synaptic knob contain

A

synaptic vesicles filled with neurotransmitters

66
Q

what happens after neurontransmitters bind to receptors on postsynaptic membrane

A

action potential is triggered causing muscle contraction or hormone to be secreted

67
Q

how do synapsed ensure that nerve impulses are unidirectional

A

receptors are only present on postsynaptic membranes

68
Q

how do synapses ensure response is not constantly happening

A

neurotransmitters are removed from the cleft by acethylcholineestarase

69
Q

how do neurotransmitters transmit nerve impulses between neurones

A

action potential arrives at the synaptic knob of presynaptic neurone and this stimulated voltage-gated calcium ion channels in presynaptic neurone to open.

calcium ions diffuse into the synaptic knob.

the influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane which then fuse with presynaptic membrane.

vesicles release the neurotransmitter into the synaptic cleft (exocytosis)

neurotransmitter diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane causing sodium ion channels in postsynaptic neurone to open

depolarisation caused by influx of sodium ions into postsynaptic membrane, action potential generated if the threshold value is reached.

70
Q

synaptic divergence

A

when one neurone connects to many neurones and so information can be dispersed to different parts of the body.

71
Q

synaptic convergence

A

when many neurones connect to one neurone so information can be amplified (made stronger)

72
Q

summation

A

where the effects of neurotransmitter released from many neurones is added together.

73
Q

why do plants need to respond to stimuli

A

to increase their chance of survival

74
Q

tropism

A

response of a plant to a directional stimulus (coming from a particular direction)

75
Q

how do plants respond to directional stimuli

A

they regulate their growth

76
Q

positive tropism

A

growth towards stimulus

77
Q

negative tropism

A

growth away from stimulus

78
Q

phototropism

A

growth of a response to light

79
Q

are shoots positively or negatively phototropic

A

positively and grow towards light

80
Q

are roots positively or negatively phototropic

A

negatively and they grow away from light

81
Q

geotropism

A

growth of a plant in response to gravity

82
Q

are shoots negatively or positively geotropic

A

negatively and grow upwards

83
Q

are roots negatively or positively geotropic

A

positively and grow downwards

84
Q

what do plants use to respond to stimuli

A

growth factors

85
Q

growth factors

A

chemicals that speed up or slow down plant growth

86
Q

where are growth factors produced

A

growing regions of plants and they move to where they are needed

87
Q

which growth factor stimulates growth of shoots

A

auxin by cell elongation

88
Q

cell elongation

A

cell walls become loose and stretchy

89
Q

what do high concentrations of auxin cause

A

growth inhibition of roots

90
Q

list other growth factors

A

gibberellins

cytokinis

ethene

abscisic acid

91
Q

gibberellins

A

stimulate flowering and see germination

92
Q

cytokinins

A

stimulate cell division and cell differentiation

93
Q

ethene

A

stimulates fruit ripening and flowering

94
Q

abscisic acid (ABA)

A

involved in leaf fall

95
Q

indoleacetic acid (IAA)

A

important auxin produced in the tips of shoots in flowering plants

96
Q

chemotropism

A

response to chemicals

97
Q

hydrotropism

A

response to water

98
Q

cation

A

sodium ions

99
Q

cation channels

A

sodium channels

100
Q

when do rod cells initiate action potentials in neighbouring bipolar neurones

A

when they are hyperpolarised

101
Q

sensory neurones (afferent)

A

specialised to detect stimuli from the external environment or internal body conditions

they transmit sensory information from sensory receptors to the central nervous system

102
Q

relay neurones (intermediate)

A

faciliate communication and coordination within CNS by relaying information between sensory and motor neurones

103
Q

which neurone doesnt have dendrons

A

sensory

104
Q

which neurone doesnt have myelin sheath

A

relay

105
Q

another word for cell body

A

soma

106
Q

events of reflex arc

A

potential harmful stimulus is detected by receptors

electrical impulse generated and carried by sensory neurones to relay neurones in CNS

response coordinated in spinal cord so impulse doesnt travel to the brain

the impulse then passes to a motor neurone which carries the impulses to an effector which carries out the response

107
Q

what enzyme breaks down acetylcholine

A

acetylcholinestarase

A Level Biology : Content (18 decks)

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