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Biology > 14. Response to stimuli > Flashcards

14. Response to stimuli Flashcards

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1
Q

Define a stimulus

A

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

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2
Q

Define a taxis

A

A directional response to a directional stimulus

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3
Q

Define kinesis

A

A response to a change in stimulus by changing the amount of activity (speed/ rate of change of direction)

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4
Q

Define tropism

A

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

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5
Q

Name 3 stimuli that plants respond to

A
  • light
  • gravity
  • water
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6
Q

Name the plant growth factor that causes tropism

A

IAA (indoleacetic acid)

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7
Q

Describe phototropism in flowering plants

A
  • Cells in shoot tips produce IAA which is then transported down the shoot, initially it is spread evenly
  • Light causes the movement of IAA from the light to dark side of the plant
  • A greater concentration builds on the dark side of the shoot relative to the light side
  • IAA causes elongation of cells in shoots, so the cells on the dark side elongate more
  • The shaded side grows quicker than on the light side which causes the shoot tip to bend towards the light
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8
Q

Describe gravitropism in flowering plants

A
  • Cells in root tips produce IAA which is then transported along the shoot, initially it is spread evenly
  • Gravity causes the movement of IAA from the upper side to lower side of the plant
  • A greater concentration builds on the lower side of the root relative to the upper side
  • IAA causes inhibition growth in of cells in roots so the cells on the lower side elongate less than the upper side
  • The upper side grows quicker than on the lower side which causes the shoot tip to bend downward towards the light
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9
Q

Name the steps in a reflex arc

A
  • Stimulus
  • Receptor
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • Effector
  • Response
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10
Q

Why are reflex arcs important

A
  • They are involuntary, does not require decision making of brain so does not overload with stimuli in which their responses are always the same
  • They protect you from harm
  • Fast, as the neurone pathway is very short, typically 1 or two synapses and there is no decision making process (impulse being sent to brain)
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11
Q

What are the qualities of a reflex

A
  • immediate
  • innate
  • protect you from harm
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12
Q

Name 2 features of receptors

A
  • specific to one type of stimulus

- produces an action potential (transducer- converts energy of stimulus into electrical energy)

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13
Q

What is the receptor in the skin that responds to pressure

A

Pacinian corpuscle

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14
Q

Describe how the Pacinian corpuscle works

A
  • At resting sate the stretch mediated sodium ion channels on the membrane of the corpuscle are too narrow to allow Na+ ions through. In this state the Pacinian corpuscle has a resting state
  • When pressure is applied to the Pacinian corpuscle it is deformed
  • This widens the stretch mediated sodium ion channels and sodium ions can diffuse into the neurone.
  • This causes the membrane to depolarise, producing a generator potential
  • This creates an action potential which passes along the neurone
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15
Q

Where are light receptors found

A

The retina

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16
Q

Name the two kinds of cells that are light receptors

A
  • Rod cells

- Cone cells

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17
Q

Describe the structure of a Pacinian corpuscle

A
  • sensory neurone at the centre
  • surrounded by layers of connective tissue
  • blood capillary then capsule layer
  • sensory neurone has stretch-mediated sodium channel in the centre
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18
Q

What are the colour of the images produced by rod cells

A

Black and white

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19
Q

In what way are rod cells connected to sensory neurones

A

Many rod cells are connected to a single sensory neurone

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20
Q

What kind of light conditions are rod cells used to detect

A

Light of very low intensity

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21
Q

How rod rod cells see in lower light

A
  • a number of rod cells are connected to a single bipolar cell (retinal convergence)
  • due to summation there a much larger chance that the threshold value will be exceeded for rod cells
22
Q

What must occur in order to create an action potential in rod cells

A
  • pigment in the rod cells (rhodopsin) must be broken down

- there is enough energy in low intensity light to cause this breakdown

23
Q

What is visual acuity

A

How clear eye sight is

24
Q

Why do rod cells give low visual acuity

A
  • many rod cells link to one sensory neurone
  • rod cells sharing the same neurone will only generate a single impulse
  • the brain cannot separate sources of light
  • two close together dots cannot be resolved giving low visual acuity
25
Q

How many different cone cells are there

A

3, each responding to a different range of wavelengths

26
Q

Why do cone cells only respond to high intensity light

A
  • each cone cell is connected to their own separate bipolar cell connected to a sensory neurone
  • there is no summation to exceed the threshold value and create an action potential
27
Q

What must occur in order to create an action potential in cone cells

A
  • pigment in the cone cells (iodeosin) must be broken down

- only light of high intensity will provide enough energy to break it down

28
Q

Why do cone cells give good visual acuity

A
  • one cone cells link to one sensory neurone
  • when two adjacent cone cells are stimulated the brain receives two separate impulses
  • the brain can distinguish between sources of light
  • two close together dots can be resolved giving good visual acuity
29
Q

Describe the distribution of rod and cone cells on the retina

A
  • cone cells are found on the fovea (which receives the highest intensity of light)
  • 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
30
Q

What is the benefit of having both types of light receptor

A

Mammals have good all-round vision in both day and night

31
Q

Name the two divisions of the autonomic nervous system

A
  • the sympathetic nervous system

- the parasympathetic nervous system

32
Q

What is the sympathetic nervous system

A
  • stimulates effectors so speeds up any activity

- helps us cope with stressful situations by heightening our awareness and preparing us for activity

33
Q

What is the parasympathetic nervous system

A
  • inhibits effectors and so slows down any activity
  • controls activities under normal resting conditions
  • concerned with conserving energy and replenishing the body’s reserves
34
Q

What word can be used to describe how the sympathetic and parasympathetic systems work together

A

Antagonistic

35
Q

What is an example of how the sympathetic and parasympathetic nervous systems work together

A

The control of heart rate

36
Q

Why is the heart muscle known as myogenic

A

Its contractions are initiated from within rather than by nervous impulses from outside

37
Q

What does the SAN stand for

A

Sinoatrial node

38
Q

Where is the SAN located

A

Within the wall of the right atrium

39
Q

Why is the SAN referred to as the pacemaker

A

It is where the initial stimulus for contraction originates. It has a basic rhythm of stimulation that determines the beat of the heart

40
Q

Describe the sequence of events that controls the heart rate

A
  • a wave of electrical excitations spreads out from the SAN across both atria causing them to contract
  • the atrioventricular septum prevents the wave from crossing to the ventricles as it is non-conductive
  • the wave of excitation enters a second group of cells called the AVN
  • after a short delay the AVN produces a wave of electrical excitation between the ventricles along the bundle of His
  • the bundle of his conducts the wave through the atrioventricular septum to the base of the ventricles where the bundle branches to smaller fibres of Purkyne tissue
  • the wave of excitation is released from the Purkyne tissue causing the ventricles to contract quickly at the same time
41
Q

What is the atrioventricular septum

A

A layer of non-conductive tissue between the ventricles and the atria

42
Q

What does the AVN stand for

A

Atrioventricular node

43
Q

Where is the AVN located

A

Lies between the atria and the ventricles

44
Q

What is the bundle of His

A

A structure made of specialised fibres called Purkyne tissue

45
Q

Through what structure does the electrical excitation produced by the AVN travel through

A

bundle of His, made from Purkyne tissue

46
Q

In what region of the brain is the heart rate controlled by

A

Medulla oblongata

47
Q

Describe two centres in the medulla oblongata that are concerned with heart rate

A
  • one centre increases heart rate (linked to the sinoatrial node by the sympathetic nervous system)
  • one centre decreases heart rate (linked to the sinoatrial node by the parasympathetic nervous system)
48
Q

How do chemoreceptors detect changes of CO2 in the blood

A
  • when the blood has higher concentration of CO2 its pH is lowered
  • the chemoreceptors in the wall of the carotid arteries and the aorta detect this
49
Q

How does impulses from the chemoreceptors increase heart rate

A
  • the centre in the medulla oblongata increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node
  • this increases the rate of production if the electrical waves by the SAN and therefore increasing heart rate
50
Q

How does the heart rate return to normal via chemoreceptors after heart rate has increased

A
  • this increased blood flow leads to more CO2 being removed by the the lungs so CO2 levels return to normal
  • pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and the aorta reduce the frequency of nerve impulses to the medulla oblongata
  • the medulla oblongata reduces the frequency of impulses to the sinoatrial node which therefore leads to a reduction in the heart rate
51
Q

How is heart rate controlled by pressure receptors when blood pressure is higher than normal

A
  • pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate
  • this centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart
  • leads to a decrease in the rate at which the heart beats
52
Q

How is heart rate controlled by pressure receptors when blood pressure is lower than normal

A
  • pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate
  • this sends impulses via the sympathetic nervous system to the sinoatrial node
  • increases the rate at which the heart beats

Biology (23 decks)

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