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A Level - Biology > 14: Responses to stimuli > Flashcards

14: Responses to stimuli Flashcards

1
Q

What is a stimulus?

A

Detectable change in the internal or external environment of an organism that leads to a response

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2
Q

What is a receptor?

A

Something which detects the presence of a stimulus

Specific to a type of stimulus

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3
Q

What is a response produced by?

A

Effector

Response at molecular level or whole organism

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4
Q

What is a coordinator?

A

Formulates a suitable response to a stimulus

Coordination is at a molecular or organ level

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5
Q

What does the ability to respond to stimuli do?

A

Increases the chances of survival for an organism

Allows for alleles to be passed on and by natural selection

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6
Q

What are the two types of response to a stimuli?

A

Hormonal response

Nervous response

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7
Q

How does coordinators work?

A

Connects information from each receptor with appropriate effector

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8
Q

What is the sequence of events starting with a stimulus?

A

stimulus -> receptor -> coordinator -> effector -> response

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9
Q

What is a taxis?

A

Simple response whose direction is determined by moving its whole body

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10
Q

In which direction is a taxis done?

A

Either whole body is turned towards a favourable stimulus or away form an unfavourable stimulus

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11
Q

What are the simplest forms of response to stimuli?

A

Taxes
Kinesis
Tropisms

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12
Q

What is a positive taxis?

A

Movement of the organism towards the stimulus

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13
Q

What is a negative taxis?

A

Movement of the organism away from the stimulus

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14
Q

What is an example of positive phototaxis?

A

Single-celled algae move towards light, increases survival rate as they are photosynthetic cells

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15
Q

What does positive phototaxis mean?

A

Positive - towards stimulus

Phototaxis - response to light

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16
Q

What does positive chemotaxis mean?

A

Positive - towards stimulus

Chemotaxis - response to a chemical concentration

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17
Q

What is kinesis?

A

Form of response in which the rate of movement and rate of direction change is altered

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18
Q

What occurs in kinesis when an organism goes to an unfavourable environment?

A

Rate of turning increases

Increases chance of return to a favourable environment

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19
Q

What occurs to the rate of turning in kinesis after a long period of time in the unfavourable environment?

A

Rate of turning slowly decreases so it moves in a straight line before it turns very sharply
Brings into favourable conditions

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20
Q

When is kinesis important?

A

When the stimulus is less directional

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21
Q

What types of stimulus are thought as non-directional?

A

Temperature

Gradient

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22
Q

What occurs to woodlice when they move from damp to dry areas?

A

Move more rapidly and change direction more often

Once back in damp they move slower and change direction less often

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23
Q

What is a tropism?

A

Growth of part of a plant in response to a directional stimulus

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24
Q

What is positive and negative tropism?

A

Positive - plant grows towards the stimulus

Negative - plant grows away from the stimulus

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25
Q

What is a phototropism?

A

Tropism when light is involved

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26
Q

What tropism do plant shoots show?

A

Positive phototropism
Negative gravitotropism
Grow towards light and away from gravity
Allows leaves in most favourable position for photosynthesis

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27
Q

What tropism do plant roots show?

A

Negative phototropism
Positive gravitotropism
Increase probability the roots grow in the soil, where they can absorb water and mineral ions

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28
Q

Do plants have nervous systems?

A

None present

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29
Q

What do plants respond to?

A

Light
Gravity
Water

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30
Q

How do plants respond to light?

A

Shoots grow towards light
As light needed for photosynthesis
(positive phototropism)

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31
Q

How do plants respond to gravity?

A

Roots respond to gravity and grow in direction of its pull

positive gravitotropism

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32
Q

How do plants respond to water?

A

Almost all plant roots grow towards water to absorb for use in photosynthesis and other metabolic processes
(positively hydrotropic)

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33
Q

How do plants respond to external stimuli?

A

Involves hormone-like substances or plant growth factors

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34
Q

Why is the term plant growth factors descriptive?

A

Exert influence by affecting growth, made by cells throughout plant rather than particular organs
Can affect the tissues that release them rather than acting on specific organ (like animal organ)

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35
Q

How much of plant growth factors are produced?

A

Small quantities are produced

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36
Q

What is indoleacetic acid (IAA)?

A

Plant growth factor which is an auxin

Controls plant cell elongation

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37
Q

How does IAA affect phototropism in plants?

A

Cell in tip of shoot produces IAA which is transported down the shoot, which build up on shaded side of the shoot
Greater [IAA] causes shoot cells on shaded side to elongate
Shaded side elongates, causing shoot tip to bend towards the light

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38
Q

How does IAA work in the roots?

A

High [IAA] results in inhibition of elongation of shaded side
Causes light side to grow more and bends away from the light

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39
Q

How is IAA used in gravitotropism?

A

Cells in root tip produce IAA
Gravity causes IAA to move from the upper to lower side of the root
IAA inhibits elongation so greater elongation on upper side causes root to bend downwards to force of gravity

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40
Q

What happens to IAA in shoots for gravitotropism?

A

Greater [IAA] on lower side increases cell elongation
Causes this side to elongate more than upper side
Shoots grow upwards away from the force of gravity

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41
Q

How is IAA transported?

A

IAA always transported away from shoots and roots where its produced

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42
Q

When does IAA work?

A

Only works on young cell walls where cells can elongate

Known to increase the cells ability to stretch

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43
Q

Why do older cells of plants not respond to IAA?

A

Rigidity of cells increase

So cannot stretch/elongate

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44
Q

What is the theory by which IAA increases plasticity of cells?

A

Acid growth hypothesis

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45
Q

What is the acid growth hypothesis?

A

Active transport of hydrogen ions from cytoplasm into spaces in the cell wall
This causes cell wall to become more plastic and allows elongation

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46
Q

Do plants respond to stimuli quickly?

A

Elongation occurs rapidly

Due to IAA uneven distribution

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47
Q

What are the two major divisions of the nervous system?

A

Central nervous system (CNS)

Peripheral nervous system (PNS)

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48
Q

What are the constituents of the CNS?

A

Brain and spinal cord

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49
Q

What are the constituents of the PNS?

A

Made of pairs of nerves that originate from either the brain or spinal cord

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50
Q

What does the peripheral nervous system consist of?

A

Sensory neurones

Motor neurones

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51
Q

What is a sensory neurone?

A

Carries nerve impulse (electrical signals) from receptors to the CNS

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52
Q

What is a motor neurone?

A

Carries nerve impulses away from the CNS to the effectors

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53
Q

What is the motor nervous system divided into?

A

Somatic nervous systems

Autonomic nervous system

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54
Q

What is the somatic nervous system?

A

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

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55
Q

What is the autonomic nervous system

A

Carries nerve impulses to glands, smooth and cardiac muscle

Involuntary (subconscious)

56
Q

What is the spinal cord?

A

Column of nervous tissue that runs along the back and lies inside the vertebral column for protection

57
Q

What is the characteristic of a reflex?

A

Rapid, short-lived, localised and totally involuntary

58
Q

What is a reflex arc?

A

Pathway of neurones involved in a reflex

59
Q

How many neurones are involved in a reflex?

A

Three neurones

60
Q

What is the alternative name of a reflex and why?

A

Spinal reflex

One of the 3 neurones is in the spinal cord

61
Q

What is an examples of a stimulus which causes a spinal reflex arc?

A

Withdrawing hand from a hot object

62
Q

What are the stages of a spinal reflex arc?

A 
Stimulus
Receptor
Sensory neurone
Coordinator (intermediate neurone)
Motor neurone
Effector
Response
63
Q

What are examples of the stages of the reflex arc?

A

Stimulus - heat from hot object
Receptor - temp receptor in skin which generates nerve impulse in sensory neurone
Sensory neurone
Coordinator (intermediate neurone)
Motor neurone - carries nerve impulses from spinal cord to a muscle in the upper arm
Effector - muscle in upper arm is caused to contract
Response - hand pulled away from hot object

64
Q

What is the function of a sensory neurone in a spinal reflex?

A

Passes nerve impulse to spinal cord

65
Q

What is the function of the coordinator/intermediate neurone in a spinal reflex?

A

Links sensory neurone to motor neurone in spinal cord

66
Q

What is the function of the motor neurone in a spinal reflex?

A

Carries nerve impulse to muscle/effector

67
Q

Why are reflex actions important?

A

Involuntary - doesn’t require brain to decide, meaning it can do more complex responses. Brain not overloaded when the response is the same
Protect body from harm - don’t have to be learnt, there from birth
Fast - short neurone pathway (1 or 2 synapses)
Absence of any decision making process means action is rapid

68
Q

Why are few synapses important in a reflex arc?

A

Synapses are the slowest link in a neurone pathway

69
Q

How is sensory information from internal and external environments?

A

Variety of receptors

Each type responds to different and specific type of stimulus

70
Q

What is sensory reception?

A

Function of the receptor - broadcast of a nerve impulse

71
Q

What is sensory perception?

A

Involves making sense of the info from the impulse from the receptor

72
Q

Where is sensory perception done?

A

Mostly a function of the brain

73
Q

What are Pacinian corpuscles?

A

Receptors in the skin which respond to changes in mechanical pressure

74
Q

How do Pacinian corpuscles show they are sensory neurones?

A

Specific to a single type of stimulus - only responds to mechanical pressure
Produces a generator potential by acting as a transducer

75
Q

What is a transducer?

A

Convert one form of energy into another

E.g. heat,light,sound,mechanical energy to electrical nervous impulse

76
Q

How do receptors act as a transducer?

A

Converts one form of energy to the nerve impulse

Nerve impulse called a generator potential

77
Q

What is a generator potential?

A

Nerve impulse created by a receptor

78
Q

What does the Pacinian corpuscle respond to?

A

Responds to mechanical stimuli such as pressure

79
Q

Where are the Pacinian corpuscles found?

A

Deep in the skin
Most abundant on fingers, soles of feet and external genitalia
Joints, ligaments, tendons

80
Q

Why are Pacinian corpuscles found in joints, ligaments and tendons?

A

Enables organism to know which joints are changing directions

81
Q

Where is the sensory in the Pacinian corpuscle?

A

Centre of layers of tissue

Each layer is separated by a gel

82
Q

How does a Pacinian corpuscle function?

A

Stretch mediated sodium channels in membrane of sensory neurone
Permeability increases when pressure applied as stretches membrane
Na+ flow in and changes the potential of the membrane, creates a generator potential
Generator potential creates action potential that passes along neurones to CNS

83
Q

Where are the light receptors of the eye found?

A

Innermost layer - the retina

84
Q

What are the types light receptors in the eye?

A

Rod cells

Cone cells

85
Q

How do light receptors work as transducers?

A

Transduces light energy into electrical energy of a nerve impulse

86
Q

What does visual acuity mean?

A

Clarity of the image seen by the eye

Measured by an eye chart 20 feet away

87
Q

What is the pupil?

A

Black dot - hole through which light can enter the eye

88
Q

What is the iris?

A

Colour in the eye - muscle that controls how much light enters the eye

89
Q

What is the cornea?

A

Colourless curved front of the eye that helps to diffract light onto the retina

90
Q

Why can rod cells only contribute B&W images?

A

Cannot distinguish different λ of light

91
Q

How many light receptors are there compared to each other?

A

More rod cells than cone cells

92
Q

How are light receptors connected?

A

Light receptors are connected to bipolar cells
Bipolar cells are connected to a sensory neurone
Sensory neurone sends impulse to the brain

93
Q

How are rod cells connected to a single sensory neurone?

A

Many rod cells connected to a single bipolar and sensory neurone

94
Q

What is required for a light receptor to create an impulse?

A

Threshold value has to be exceeded before a generator potential is created in the bipolar cell

95
Q

What is retinal convergence?

A

Many rod cells are connected to a single bipolar cell

96
Q

Why are rod cells sensitive to very low intensity of light?

A

Many rod cells connected to a bipolar cell

Greater chance the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell

97
Q

What is the photopigment in rod cells?

A

Rhodopsin

98
Q

How is a generator potential induced in a rod cell?

A

Rhodopsin broken down by even low-intensity light

Breakdown causes a potential difference to form and a generator potential is formed in a bipolar cell

99
Q

Why do rods give low visual acuity?

A

Many rod cells linking to a single bipolar cell
Therefore only one impulse created regardless of number of neurones stimulated
Brain cannot distinguish between separate sources of light that stimulated them
Two dots close together cannot be resolved

100
Q

How many types of cone cells are there?

A

Three different types

Respond to: short, medium and long wavelengths of light

101
Q

How are full colour images formed?

A

Different proportions of different stimulation of different cone cells

102
Q

How are cone cells connected to the CNS?

A

One cone cell connected to one bipolar cell

Bipolar cell is connected to sensory neurone to the brain

103
Q

Why can cone cells only respond to high light intensity?

A

Stimulation of cone cells cannot be combined to exceed threshold variable to create generator potential
One cone cell connected to one bipolar cell

104
Q

What pigments are found in cone cells?

A

Iodopsin

Each type of cone cell has a specific type of pigment

105
Q

What is a feature of iodopsin?

A

Requires higher light intensity for breakdown

Only responds to a specific λ of light

106
Q

Why do cone cells have a high visual acuity?

A

One cone connected to one bipolar cell
Brain receives separate impulses from adjacent cone cells, can distinguish as two separate sources
Two dots can be resolved

107
Q

What is the fovea?

A

Location on the retina where light is focused the most

Receives the highest intensity of light

108
Q

What is the distribution of cone cells?

A

High intensity of cone cells found at the fovea

Concentration of cone cells diminishes further away from the fovea

109
Q

What is the distribution of rod cells?

A

No rod cells at the fovea

Conc of rod cells increase further from fovea, only rod cells at the peripheries

110
Q

What part of the nervous system is responsible for the control of heart rate?

A

Autonomic nervous system

111
Q

What is the two divisions of the autonomic nervous systems?

A

Sympathetic nervous system

Parasympathetic nervous system

112
Q

What is the sympathetic nervous system?

A

Motor neurones that stimulate effectors so speeds up activity
Used in emergency controller or in stressful situations as heightening awareness (fight or flight)

113
Q

What is the parasympathetic nervous system?

A

Motor neurones that inhibits effectors so slows down any activity
Controls activity in normal resting conditions, conserves energy

114
Q

Why is the parasympathetic and sympathetic nervous system said to be antagonistic?

A

Actions normally oppose one another

115
Q

What muscles control heart rate?

A

Cardiac muscles

116
Q

Why is contraction of muscles said to be myogenic?

A

Contraction is initiated from within the muscle itself

117
Q

What is neurogenic?

A

Contractions caused by nervous impulses from outside

118
Q

What is the sinoatrial node (SAN)?

A

Group of cells responsible for producing initial stimulus for contraction of cardiac muscles
Found in the wall of the right atrium

119
Q

Why is the SAN known as a pacemaker?

A

Has a basic rhythm of stimulation that determines the beat of the heart

120
Q

What are the sequences of events which controls the basic heart rate?

A

Wave of electrical excitation from SAN moves across both atria, causing atrial systole
Atrioventricular septum prevents wave crossing to the ventricles
Wave of excitation moves to AVN
AVN produces electrical excitation along ventricles after a short delay
Wave passes along Purkyne tissue which make up the Bundle of His
Bundle conducts wave through atrioventicular septum to base of ventricles, where the bundle branches off
Wave of excitation causes ventricular systole from bottom upwards

121
Q

What is the normal resting heart rate of an adult?

A

~70 bpm

122
Q

What is the equation for cardiac output?

A

Cardiac output = Stroke volume * Heart rate (beats per minute)

123
Q

What are chemoreceptors?

A

Receptors which can detect concentrations of different chemicals

124
Q

Where are chemoreceptors found which control heart rate?

A

Carotid arteries and aortic arteries

125
Q

What are the carotid arteries?

A

Arteries that serve the brain

126
Q

What are the chemoreceptors in the carotid arteries sensitive to?

A

pH of the blood as a result of [CO2]

127
Q

How does [CO2] affect pH?

A

Increased [CO2] lowers the pH

128
Q

How are chemoreceptors used to control heart rate?

A

Decrease in pH causes chemoreceptors to send nervous impulse to centre in brain that increases heart rate
Center increases frequency of impulses the sympathetic nervous system to the SAN
This increases rate of production of electrical waves, therefore heart rate
Increased blood flow causes more CO2 removed by lungs
[CO2] goes back to normal, chemoreceptors detect this
Then leads to reduction of nerve impulses so back to normal

129
Q

Where is the center for the control of both the increase and decrease of heart rate?

A

Medulla oblongata

130
Q

What are the two nervous systems which are used to control heart rate?

A

Sympathetic - increases heart rate

Parasympathetic - decreases heart rate

131
Q

How do responses from chemoreceptors affect heart rate?

A

Controls rate

Doesn’t control whether it beats

132
Q

Where are pressure receptors to control the heart rate?

A

Walls of the carotid arteries and aorta

133
Q

How is blood pressure controlled if it is too high?

A

Pressure receptors transmit nervous impulses to centre that decreases heart rate
Center sends impulses via parasympathetic nervous system to SAN
Leads to decrease in rate at which heart beats

134
Q

How is blood pressure controlled if it is too low?

A

Pressure receptors transmit nervous impulses to centre that increases heart rate
Center sends impulses via sympathetic nervous system to SAN
Leads to increase in rate at which heart beats

135
Q

Define fibrillation

A

When the contraction of the heart is not synchronised

136
Q

Why is the SAN referred to as the pacemaker?

A

Sets the rhythm of the heart rate

137
Q

What are the names of pressure receptors in the carotid artery and aorta?

A

Baroreceptors

A Level - Biology (22 decks)

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