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Biology - Unit 6 > Chapter 14 - Response to Stimuli > Flashcards

Chapter 14 - Response to Stimuli Flashcards

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1
Q

Define stimulus

A

A detectable change in the environment that can be detected by an organisms. It is either internal in multicellular organisms or external in any organism

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2
Q

Define receptor

A

A specialised organ or cell that detects changes in the environment

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3
Q

Define response

A

As a result of the stimulus detected by the receptor, a change is caused which may be movement or a change in behaviour to increase chance of survival

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4
Q

Define taxes

A

A directional response that involves movement in a specific direction towards or away from a stimulus. Positive taxes is towards a stimulus and negative taxes is away from a stimulus

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5
Q

Give three examples of taxes

A

Algae move towards light (positive phototaxis)
Earthworms move away from light (negative phototaxis)
Bacteria move towards glucose (positive chemotaxis)

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6
Q

Define kinesis

A

A form of non-directional response from an unfavourable area to a favourable one by change of speed

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7
Q

When is kinesis important?

A

When the stimulus is less directional and no clear gradient is produced

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8
Q

How does kinesis work?

A

Organism moves into unfavourable area and increases movement to increase likelihood of moving into favourable area and vice versa

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9
Q

Define tropism

A

The directional growth of a plant in response to a directional stimulus

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10
Q

Give two examples of tropism

A
  • Plant shoots growing towards light (positive phototropism) and away from gravity (negative gravitropism)
  • Plant roots growing away from light (negative phototropism) and towards gravity (positive gravitropism)
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11
Q

State the three factors plants respond to and describe why

A

Light as needed for photosynthesis
Gravity as need water and must be firmly anchored
Water as needed for photosynthesis and other metabolic processes

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12
Q

What are plant growth factors?

A

Hormones that affect growth and the tissues that release them

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13
Q

Define the sequence that leads from a stimulus to a response

A

Stimulus - Receptor - Coordinator - Effector - Response

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14
Q

What is indoleacetic acid?

A

A plant hormone that is a type of auxin responsible for controlling plant cell elongation

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15
Q

Where is indoleacetic acid produced?

A

The tips and shoots of flowering plants

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16
Q

Summarise phototropism in a flowering plant

A
  • Cells in top produce IAA which is transported down shoot
  • Initially evenly distributed
  • Light causes movement of IAA from light side to dark side
  • Greater concentration of IAA on dark side
  • Causes elongation of shoot cells
  • Elongates faster than light side so tip bends towards light
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17
Q

Summarise gravitropism in a flowering plant

A
  • Cells in tip of root produce IAA which is transported along the root
  • Initially evenly distributed
  • Gravity influences movement of IAA from upper side to lower side of root
  • Greater of concentration on lower side of root
  • IAA inhibits elongation of root cells
  • Elongate less than upper side
  • Root bends towards the force of gravity
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18
Q

Why does IAA have a greater effect on cells that are not fully matured?

A

Mature cells develop greater rigidity and hence do not respond

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19
Q

What is the acid growth hypothesis

A

The explanation of how IAA increases plasticity of cells:

  • Active transport of hydrogen ions from cytoplasm into cell wall space
  • Causes cell wall to become more plastic allowing elongation by expansion
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20
Q

What is the central nervous system

A

A division of the nervous system comprised of the brain and spinal chord

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21
Q

What is the peripheral nervous system

A

A division of the nervous system made up of pairs of nerves that originate from the brain or spinal chord

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22
Q

What can the peripheral nervous system be divided into?

A
  • Sensory neurones which carry impulses from receptors to the central nervous system
  • Motor neurones which carry nerve impulses away from the central nervous system to effectors
23
Q

The motor neurone system can be divided into what?

A
  • Voluntary nervous system which carries nerve impulses to skeletal body muscles under conscious control
  • Autonomic nervous system which carries nerve impulses to glands, smooth muscle and cardiac muscle under subconscious control
24
Q

What is the spinal chord?

A

A column of nervous tissue that runs along the back inside the vertebral column for protection

25
Q

What are the properties of a reflex action

A

Rapid, short-lived, localised and involuntary

26
Q

Define reflex arc

A

The nerve pathway in the body taken by an action potential leading to a rapid, involuntary response to a stimulus

27
Q

Define reflex

A

An involuntary response to a sensory stimulus

28
Q

Summarise the reflex arc

A
  • Stimulus
  • Receptor detects this
  • Sensoru neurone passes impulse to spinal chord
  • Coordinator (intermediate neurone) links sensory neurone to motor neurone
  • Motor neurone carries impulse from spinal chord to effector
  • Effector such as muscle contracts
  • Response caused
29
Q

Why are reflex arcs important?

A
  • Involuntary so do not require decision making, allowing a more rapid and sometimes more complex response
  • Protect body from harm as do not need to be learnt
  • Fast as neurone pathway short with few synapses
30
Q

What can artificial IAA hormones be used as?

A

Herbicides by causing the plant to grow itself to death

31
Q

Define effector

A

A cell tissue, organ or system that carries out a response

32
Q

Define coordinator

A

Connects information between receptor and appropriate effector

33
Q

What is the pacinian corpuscle

A

A type of receptor that responds to mechanical pressure

34
Q

What are the two features of the pacinian corpuscle?

A
  • Specific to a single type of stimulus
  • Produces a generator potential by acting as a transducer (transduces mechanic energy of stimulus into generator potential)
35
Q

Where do pacinian corpuscles occur?

A

Fingers, soles of feet and on external genitalia. They also occur in ligaments and tendons

36
Q

Why are pacinian corpuscles located in tendons?

A

To enable the organism to know which joints are changing direction

37
Q

Summarise the structure of a pacinian corpuscle

A

Sensory neurone lays in the centre of tissues with each tissue layer separated by gel

38
Q

What is a stretch mediated sodium channel

A

A sodium channel whose permeability changes when deformed

39
Q

Define transducer

A

Cells that convert a non electrical stimulus into an electrical signal

40
Q

Define generator potential

A

Depolarisation of the membrane of a receptor cell due to stimuli

41
Q

Summarise how a pinion corpuscle works

A
  • Resting state means channels too narrow for sodium
  • Pressure applied causing membrane around neurone to deform
  • Widens sodium channels
  • Influx causes depolarisation and hence generator potential
  • Creates an action potential
42
Q

Summarise rod cells of the eye

A
  • Cannot distinguish between wavelengths of light so see black/white
  • More numerous than cone cells
  • Many link to one bipolar neurone (retinal convergence) resulting in low visual acuity
  • Greater chance of generator potential as many to one (spatial summation)
  • One type
  • Sensitive to low intensity light
  • More at the periphery of the retina and absent at the fovea
43
Q

How do rod cells create a generator potential and what does this allow?

A
  • Pigment in rod cells called rhodopsin must be broken down
  • There is enough energy from low level light to enable this
  • Hence rod cells can respond to low intensity light
44
Q

Summarise cone cells

A
  • Three types for different wavelengths of light (colour)
  • Fewer number that rod cells
  • Fewer at periphery of retina and concentrated at fovea
  • Good visual acuity due to each cell have one bipolar
    neurone but only respond to high intensity light
45
Q

Why are rod cells located at the retinal periphery and cone cells at the fovea?

A

Fovea is opposite pupil where light intensity high and hence cone cells located here. Rod cells at retinal periphery as light intensity low

46
Q

What are the two divisions of the autonomic nervous system?

A

Sympathetic - stimulates effectors and speeds up activity

Parasympathetic - Inhibits effectors and so slows down activity

47
Q

Define sinoatrial node

A

An area of heart muscle in the right atrium that controls and coordinates contraction of the heart

48
Q

Distinguish between myogenic and neurogenic muscles

A

Myogenic muscles contract from within whereas neurogenic muscle contracts due to nervous impulses from the outside

49
Q

Summarise the sequence of events that controls heart rate

A
  • Wave of electrical excitation spreads from SAN across atria causing them to contract
  • Atrioventricular septum is nonconductive and prevents the wave crossing to the ventricles
  • Wave of excitation enters second group of cells called atrioventricular node between atria
  • This conveys electrical excitation between ventricles along fibres called purkyne tissue which collectively make the bundle of His
  • Bundle of His conducts wave through atrioventricular septum to the base of ventricles
  • Wave of excitation released from Purkyne tissue causing both ventricles to contract form the bottom of the heart upwards
50
Q

What is the medulla oblongata?

A

Area of the brain that causes change in heart rate. It has two centres:

  • One increases heart rate and is linked to the SAN by the sympathetic nervous system
  • One decreases heart rate which is linked to the senatorial node by the parasympathetic nervous system
51
Q

What are the two receptors that detect changes in the heart?

A

Chemoreceptors and pressure receptors

52
Q

Summarise how control by chemoreceptors work

A
  • When blood has higher CO2 conc, pH lower
  • Chemoreceptors in wall of carotid arteries detect this and increase frequency of nerve impulses to medulla oblongata
  • This increases frequency of nerve impulse via sympathetic nervous system to SAN increasing production of electrical waves
  • Increased blood flow leads to more CO2 removed from lungs
  • pH falls and chemoreceptors reduce frequency of nerve impulses
  • Medulla oblongata reduces impulses to sinoatrial node
53
Q

How do pressure receptors in the heart operate when blood pressure is too high

A
  • Pressure receptors in the carotid arteries and aorta transmit more nervous impulses to centre of medulla oblongata that decreases heart rate
  • Impulses sent to SAN via parasympathetic nervous system to decrease heart rate
54
Q

How do pressure receptors in the heart operate when blood pressure is too low

A
  • Pressure receptors in the carotid arteries and aorta transmit more nervous impulses to centre of medulla oblongata that increases heart rate
  • Impulses sent to SAN via sympathetic nervous system to increase heart rate

Biology - Unit 6 (6 decks)

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