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Biology A level > 6.1 Stimulus and Response > Flashcards

6.1 Stimulus and Response Flashcards

1
Q

What is a tropism?

A

directional growth towards (positive) or away (negative) a stimulus

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2
Q

What is phototropism?

A

a directional growth in response to light

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3
Q

What is gravitropism?

A

directional growth in response to gravity

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4
Q

Where is IAA produced?

A

in the tips of roots and shoots

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5
Q

What is the effect of high conc of IAA in the shoots?

A

causes cell elongation and promotes growth

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6
Q

What is the effect of high conc of IAA in the roots?

A

inhibits growth

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7
Q

How does IAA cause positive phototropism in shoots?

A
  1. IAA is produced in the tip of the shoot
  2. light causes the movement of IAA
  3. IAA diffuses to the shady side of the shoot - a greater conc builds up on the shaded side
  4. IAA promotes cell elongation and growth occurs more on this side
  5. the shoot bends towards the light = positive phototropism
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8
Q

How does IAA cause positive gravitropism in roots?

A
  1. cells in the tip of the root produce IAA
  2. gravity influences the movement of IAA from the upper side of the root to the lower side of the root
  3. a greater conc of IAA builds up on the lower side
  4. IAA inhibits elongation of cells, the cells on the lower side grow less than the upper side
  5. causes the root to bend downwards towards gravity = positive gravitropism
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9
Q

What does a plant do in response to light when the shoot tip is removed?

A

it has no response to light = no IAA present in the shoots for phototropism

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10
Q

What is a taxis?

A

a directional response to a stimulus - the whole org either moves away (negative) or towards (positive) the stimulus

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11
Q

What is a kinesis?

A

when the org changes the speed and the rate it changes direction in order to find a more favourable environment
non-directional movement response, the rate that an organism changes direction is affected by the intensity of the stimulus

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12
Q

What are reflexes?

A

rapid involuntary responses
they are effective from birth and they do not need to be learned

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13
Q

Why are reflexes important to an organism?

A

protect against damge to body tissues
enables homeostatic control
enables escape from predators

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14
Q

What is the advantage of the reflex arc only having 3 neurons?

A

limits the number of synapses

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15
Q

What do sensory neurons do?

A

carry electrical nerve impulses from the receptor to the CNS

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16
Q

What are immediate neurons?

A

they synapse with the sensory neurone and the motor neurone - usually the coordinator

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17
Q

What are the stages of the reflex arc?

A

stimulus - receptor - sensory neurone -relay neurone - coordinator (immediate neurone) - motor neurone - effector - response

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18
Q

What are the features of all recpetors?

A

they respond to one specific stimulus
they act as a transducer - creating a generator potential
they convert energy of the stimulus into nervous impulses - generator potential

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19
Q

What is the structure of the pancinian corpuscle?

A
  • single sensory neurone at the centre of layers of tissue (lamellae)
  • each layer is separated by a gel
  • capsule surronds the layers
  • sensory neurone has strech mediated sodium channels in its membrane
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20
Q

What stimulus does the pacinian corpuscles respond to?

A

mechanical stimuli - changes in pressure

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21
Q

Describe how a pancinian corpuscle produces a generator potential in response to a specific stimulus

A
  1. increased pressure deforms the lamella
  2. deforms the strech-mediated sodium ion channels in the membrane of the sensory neurone
  3. sodium ion channels open
  4. sodium ions diffuse in
  5. causes the inside of the neurone to become more positive = depolarisation
  6. generator potential is produced
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22
Q

What pigment is in rod cells?

A

Rhodopsin

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23
Q

What pigment is in cone cells?

A

iodopsin

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24
Q

Which pigment from rod and cone cells is sensitive to low light intensity?

A

Rhodopsin - rod cells

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25
Q

Why do rod cells have low visual acutiy?

A

multiple rod cells are connected to a single bipolar neurone
it will generate a single impulse to the brain regardless of how many neurones are stimulated

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26
Q

Describe rod cells sensitivity to light

A

rhodopsin can be broken down in low light intensity to contribute to causing the generator potential
a threshold value must be exceeded before a generator potential is created in bipolar cells = many rod cells synapse with 1 bipolar cell - greater chance that threshold is reached through spatial summation

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27
Q

Why are images black and white from rod cells?

A

rhodopsin cannot distinguish different wavelengths = it is broken down by all wavelengths of light
only 1 type

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28
Q

How do rod cells create a generator potential?

A

rod cells absorb light energy and rhodopsin is broken down by the light energy
there is enough energy from low-intensity lght to cause the breakdown of rhodopsin
if enough pigment has been broken down = the threshold is met in the bipolar cell

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29
Q

Why can the threshold be reached by rod cells in low light intensities?

A

many rod cells are connected to a single bipolar cell = spatial summation

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30
Q

What is the issue with many rod cells joined to 1 bipolar cell?

A

low visual acuity = the brain cannot distinguish between the separate sources of light that stimulated the 1 bipolar cell

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31
Q

What are the 3 different colours of iodopsin?

A

red
green
blue

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32
Q

How are we able to see all colours due to iodopsin?

A

depends on the proportion of each cone cell that os stimulated

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33
Q

Why cant you see colours in the dark?

A

not enough light energy to break down iodopsin and overcome the thresold to generate an action potential
1 cone cell is conncted to 1 bipolar cell so there is no spatial summation

34
Q

What part of your eye recieves the highest light intensity?

A

the fovea

35
Q

Where are cone cells located in the eye?

A

the fovea

36
Q

Why do cone cells have a high visual acuity?

A

each cone cell is connected to a single bipolar neurone
the brain recieves separate impulses from each cone cell

37
Q

Describe cone cells sensitivity to light?

A

iodopsin can only be broken down in bright light
stimulation of each cone cell can also not be combined to reach threshold = each has their own bipolar cell

38
Q

Why are cone cells sensitive to colour?

A

there are 3 types of iodopsin
each is sensitive to different wavelengths of light

39
Q

What is a stimulus?

A

any detectable change in the environment that leads to a response

40
Q

What is the role of a coordinator?

A

formulates a suitable response

41
Q

What are the 2 effectors?

A

muscles and glands

42
Q

What is the role of IAA in plants?

A

controls plant cell elongation

43
Q

What are the 2 coordinators?

A

the brain and spinal cord

44
Q

What is the NS divided into?

A

the central NS
the peripheral NS

45
Q

What is the peripheral NS divided into?

A

sensory pathways and motor pathways

46
Q

What do sensory pathways of the peripheral NS do?

A

carries impulses from receptors to the CNS

47
Q

What do motor pathways of the peripheral NS do?

A

carries impulses away from the CNS to the effectors

48
Q

What is the motor pathway divided into?

A

somatic NS and autonomic NS

49
Q

Is the autonomic NS involuntary or voluntary?

A

involuntary

50
Q

What is the autonomic NS divided into?

A

sympathetic division and parasympathetic division

51
Q

What are reflexes?

A

rapid, involuntary responses that protects body tissues from damage and enables homeostatic control
they are effective from birth

52
Q

What is the process of a reponse generated from the refelx arc?

A
  1. stimulus
  2. receptor in skin
  3. sensory neurone pases nerve impulses to spinal cord
    4.intermediate neurone passes impulses across the spinal cord
  4. motor neuron passes impulses to effector
  5. effector reponds
  6. response
53
Q

What are the 2 features of all receptors?

A

all sensitive to 1 specific type of stimulus
act as transducers to produce a generated potential

54
Q

What does a transducer do?

A

changes 1 form of energy to another form

55
Q

Do you have more rod cells or cone cells?

A

rod cells

56
Q

Where are rod cells located?

A

the periphery of the retina

57
Q

What is an advantage of plants having positive phototropisms?

A

for more photoionisation of chlorophyll = more light absorbed

58
Q

What is the advantage of plants positive gravitropism?

A

more anchoring in the soil

59
Q

What is the role of the sino atrial node (SAN)?

A

it initiates the rhythm of the heart as a pacemaker

60
Q

What does it mean that the SAN is myogenic?

A

it is independant of the nervous system and doesnt require nervous stimulation to contract

61
Q

Where is the SAN located?

A

in the wall of the right atrium

62
Q

Describe how the SAN causes the atria to contract

A
  1. the SAN sends out broad waves of depolarisation across both atria
  2. this stimulates atrial systole
  3. blood is pushed into the ventricles through the open AV valves
63
Q

Why is there a delay of electriacl activity between atrial systole and ventricular systole?

A

allowing time for the ventricles to completely full before ventricular systole

64
Q

What is the role of the atrioventricular node (AVN)?

A

initiates ventricular systole

65
Q

Describe how the AVN causes ventricular systole

A
  1. AVN picks up wave of depolarisation from SAN
  2. transmits electrical activity as an impulse down the apex of the heart through the bundle of his
  3. impluses reaches the apex and spreads up the purkinje fibres
  4. spreads up through the walls of the ventricle
  5. ventricles contract upwards to force blood up to the arteries
66
Q

What motor pathway is the control of heart beat part of?

A

the autonomic nervous system

67
Q

What is the role of the sympathetic NS?

A

speeds up and stimulates effectors

68
Q

What is the role of the parasympathetic NS?

A

inhibits glands to release hormones and slows the activity of effectors when resting

69
Q

Describe the role of the sympathetic NS in controlling heart rate

A
  1. increased resp in cells increases CO2 conc so pH falls
  2. detected by chemoreceptors in the carotid arteries
  3. sends impulses to the cardiac centre in the medulla’s cardio-acceloratory centre
  4. acceleratory centre in the medulla sends more impulses to SAN by sympathetic nervous system
  5. increase in impulses sent out by the SAN = increase atrial systole
70
Q

Why does caffeine increase heart rate?

A

more action potentials along sympathetic nervous system pathway
to the SAN increasing the heart rate

71
Q

Describe the role of receptors in increasing heart rate

A
  1. chemoreceptors detect rise in CO2 / fall in pH
  2. Sends impulses to cardiac cente in medulla
  3. more impulses sent to SAN (higher frequency)
  4. by sympathetic nervous system
72
Q

Explain how both the ventricles contract at the same time after the initiation of the heartbeat by the SAN

A
  1. electrical activity only through Bundle of His
  2. wave of electrical activity passes over / through both ventricles at the same time
73
Q

Describe how the parasympathetic nervous system reduces heart rate

A
  1. decreased respiration in cells decreased CO2 conc in blood, increase in pH
  2. detected by chemoreceptors
  3. sends more impulses to the cardio-inhibitory centre in the medulla
  4. cardiac centre sends more impulses to the SAN by parasympathetic NS
  5. inhibits the SAN to intiate the heart beat
74
Q

What is the role of the cardio-acceleratory system?

A

responsible for speeping up heart rate

75
Q

What is the role of the cardio-inhibitory centre?

A

responsible for slowing down heart rate

76
Q

What is a baroreceptor?

A

a pressure receptor

77
Q

What happens when a baroreceptor deters high blood pressure?

A

the medulla sends impulses along the parasympathetic neurons to reduce heart rate

78
Q

What happens when a baroreceptor deters low blood pressure?

A

medulla sends impulses along sympathetic neurones to increase heart rate

79
Q

What happens when a chemoreceptor detects a low pCO2 / high pH?

A

medulla sends impulses along parasympathetic neurones to reduce heart rate

80
Q

What happens when a chemoreceptor detects a high pCO2 / low pH?

A

medulla sends impulses along sympathetic neurones to increase heart rate

81
Q

where are the chemoreceptors and the baroreceptors found?

A

in the wall of the carotid arteries

Biology A level (31 decks)

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