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AQA A Level Biology Paper 2 > Topic 6.1 - Survival, Response, and Receptors > Flashcards

Topic 6.1 - Survival, Response, and Receptors Flashcards

Includes response mechanisms in plants

1
Q

What do receptors do?

A

Detect stimuli

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2
Q

What can receptors be?

A

Cells or proteins on cell surface membranes

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3
Q

What are effectors?

A

Cells that bring about a response to stimulus to produce an effect

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4
Q

Give examples of types of effectors cells

A

Muscle cells and cells found in glands e.g. pancreas

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5
Q

How do receptors communicate with effectors?

A

Via nervous system and/or hormonal system

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6
Q

Name 3 types of neurones

A
  1. Sensory neurones
  2. Motor neurones
  3. Intermediate/relay neurones
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7
Q

What do sensory neurones do?

A

Transmit electrical impulses from receptors to the CNS - the brain and spinal cord

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8
Q

What do motor neurones do?

A

Transmit electrical impulses from CNS to effectors

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9
Q

What do relay neurones do?

A

Transmit electrical impulses between sensory neurones and motor neurones

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10
Q

State the 5 stages of a response to a stimulus

A
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11
Q

What the central nervous system (CNS) made up of?

A

Brain and spinal cord

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12
Q

What is the peripheral nervous system (PNS) made up of?

A

Neurones that connect the CNS to the rest of the body

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13
Q

What does the somatic nervous system control?

A

Conscious activities e.g running and playing video games

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14
Q

What does the autonomic nervous system control?

A

Controls unconscious activities e.g. digestion

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15
Q

What does the sympathetic nervous system do?

A

Gets the body ready for action - ‘flight or fight’ system

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16
Q

What does the parasympathetic nervous system do?

A

Calms the body down - ‘rest and digest’ system

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17
Q

What is a reflex?

A

When body responds to stimulus without making a conscious decision to respond

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18
Q

What is a reflex arc?

A

Pathway of neurones linking receptors to effectors in a reflex

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19
Q

Describe the simple reflex arc for a hand-withdrawal response to heat

A
  1. Thermoreceptors in skin detect heat stimulus
  2. Sensory neurone carries impulses to relay neurone
  3. Relay neurone connects to motor neurone
  4. Motor neurone sends impulses to effector
  5. Muscle contracts to withdraw your hand and stop it being damaged
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20
Q

Explain how nervous communication is localised

A

When electrical impulse reaches end of neurone = neurotransmitters are secreted directly onto target cells

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21
Q

Explain how nervous communication is short-lived

A

Neurotransmitters are quickly removed once they’ve done their job

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22
Q

State the 2 types of responses that simple mobile organisms have to keep them in a favourable environment

A
  • Tactic (taxes)
  • Kinetic (kineses)
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23
Q

Define taxes

A

Organisms move towards or away from a directional stimulus e.g. light

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24
Q

Define kineses

A

Organisms’ movement is affected by non-directional stimulus e.g. humidity

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25
Q

Give an example of taxes

A
  • e.g. woodlice show tactic response to light (phototaxis)
  • Move away from light source
  • Helps them to survive because it keeps them concealed under stones during the day (where they’re safe from predators) & keeps them in damp conditions (reduces water loss)
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26
Q

Give an example of kineses

A
  • e.g. woodlice show kinetic response to humidity
  • In high humidity they move slowly and turn less often so they stay where they are
  • When air gets drier they move faster and turn more often so more likely to move into new area
  • Response increases chance woodlouse will move to area with higher humidity
  • Improves survival chances of organisms by reducing their water loss & keeps them concealed
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27
Q

Explain the importance of relfex actions (3)

A
  • Automatic / involuntary
  • Prevents injury
  • Role in homeostasis
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28
Q

Why do flowering plants respond to changes in their environment?

A

Increases their chances of survival

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29
Q

Give examples of how flowering plants respond to changes in environment

A
  • They sense direction of light and grow towards it to maximise light absorption for photosynthesis
  • Sense gravity so roots and shoots grow in right direction
  • Climbing plants have a sense of touch = find things to climb up and reach sunlight
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30
Q

What is tropism?

A

Response of plant to directional stimulus

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31
Q

How do plants respond to stimuli?

A

By regulating their growth

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32
Q

What is positive tropism?

A

Growth towards stimulus

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33
Q

What is negative tropism?

A

Growth away from stimulus

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34
Q

Name 4 types of tropisms

A
  • Phototropism
  • Gravitropism
  • Hydrotropism
    • Responds to water
  • Chemotropism
    • Responds to chemicals
35
Q

What is phototropism?

A

Growth of plant in response to light

36
Q

Describe how the shoots and roots respond to light

A
  • Shoots are positively phototropic and grow towards light
  • Roots are negatively phototropic and grow away from light
37
Q

What is gravitropism (aka geotropism)?

A

Growth of plant in response to gravity

38
Q

Describe how the shoots and roots respond to gravity

A
  • Shoots are negatively gravitropic and grow upwards
  • Roots are positively gravitropic and grow downwards
39
Q

What do plants use to respond to directional stimuli?

A

growth factors

40
Q

What are growth factors?

A

Hormone-like chemicals that speed up or slow down plant growth

41
Q

Where are growth factors produced?

A

In growing regions of plant (e.g. shoot tips, leaves)

& move to where they’re needed in other parts of plant

42
Q

What do auxins (growth factors) do?

A
  • Stimulate growth of shoots by cell elongation
    • Where cell walls become loose and stretchy so cells get longer
43
Q

What is indoleacetic acid (IAA)?

A

Important auxin that’s produced in tips of shoots in flowering plants

44
Q

Describe how IAA is moved around a plant

A

Moves by diffusion and active transport over short distances & via phloem over long distances

45
Q

Describe where IAA moves to control phototropism

A

IAA moves to more shaded parts of shoots and roots so there’s uneven growth

46
Q

Phototropism

State what happens to IAA and its effect in a shoot

A
  • IAA concentration increases on the shaded side
    • cells elongate and the shoot bends towards the light
47
Q

Phototropism

State what happens to IAA and its effect in a root

A
  • IAA concentration increases on the shaded side
    • Growth is inhibited so root bends away from light
48
Q

Describe where IAA moves to control gravitropism

A

IAA moves to the underside of shoots and roots, so there’s uneven growth

49
Q

Gravitropism

State what happens to IAA and its effect in a shoot

A
  • IAA concentration increases on lower side
    • cells elongate so shoot grows upwards
50
Q

What is a potential difference?

A

The difference in charge across a membrane due to the movement and isolation of different

51
Q

Receptors only detect …

A

one particular stimulus

52
Q

Describe a receptor in its resting state (not being stimulated)

A

There’s a difference in charge between inside and outside of cell

53
Q

What is the difference in charge between inside and outside of receptor cell generated by and what does this mean?

A
  • Difference is generated by ion pumps and ion channels
  • Means there’s a potential difference (voltage) across the membrane
54
Q

Describe how a generator potential is created

A
  1. When stimulus is detected, cell membrane is excited and becomes more permeable
  2. Allows more ions to move in & out = alerting potential difference
  3. Change in potential difference due stimulus = generator potential
55
Q

Explain how a bigger stimulus results in a bigger generator potential being produced

A

Bigger stimulus excites membrane more = bigger movement of ions and bigger change in potential difference.

56
Q

State when an action potential is generated

A

If generator potential is big enough i.e. reaches threshold level, it’ll trigger an action potential

57
Q

Describe the size of action potentials

A

Action potentials are all same size (all or nothing theory)

58
Q

How is the strength of a stimulus measured?

A

By frequency of action potentials

59
Q

What type of receptors are Pacinian corpuscles?

A

Mechanoreceptors

(Detect mechanical stimuli e.g. pressure, vibrations)

60
Q

Pacinian corpuscles the contain end of a _____ neurone

A

Pacinian corpuscles contain the end of a sensory neurone

(Called sensory nerve ending)

61
Q

What is the sensory nerve ending wrapped in?

A

Lamellae

62
Q

Describe what happens when a Pacinian corpuscle is stimulated

A
  1. When the Pacinian corpuscle is stimulated the lamellae are deformed and press on the sensory nerve ending
    • = the sensory neurone’s cell membrane to stretch
  2. This deforms (stretch-mediated) sodium ion channels
  3. This opens the channels = greater pressure & allows for Na+ to diffuse into the cell creating a generator potential
63
Q

Where are photoreceptors found?

A

Retina

64
Q

What is the fovea?

A

An area of retina where there’s loads of photoreceptors

65
Q

Nerve impulses from photoreceptor cells are carried from retina to brain by ___ ___ (bundle of neurones)

A

Optic nerve

66
Q

What do photoreceptors do?

A

Convert light into electrical impulse

67
Q

What happens when light enters the eye?

A

It hits photoreceptors and is absorbed by light-sensitive pigments

68
Q

What happens when light bleaches pigments?

A
  1. Causes chemical change and alters membrane permeability to sodium ions
  2. Generator potential is created & if it reaches threshold = nerve impulse is sent along bipolar neurone
69
Q

What do bipolar neurones do?

A

Connect photoreceptors to optic nerve, which takes impulses to brain

70
Q

Name the 2 types of photoreceptor the human eye has

A
  • Rods
  • Cones
71
Q

Where are rods found?

A

Found in peripheral parts of retina

72
Q

Where are cones found?

A

Cones packed together in fovea

73
Q

Why do rods and cones give information in different colours?

A

Rods and cones contain different optical pigments making them sensitive to different wavelengths of light

74
Q

Rods give information in ____

A

Black and white (monochromatic vision)

75
Q

Cones give information in ____

A

Colour (trichromatic vision)

76
Q

Name the 3 types of cones (each containing a different pigment)

A
  1. Red-sensitive
  2. Green-sensitive
  3. Blue-sensitive

When stimulated in different proportions = see different colours

77
Q

State which one is more sensitive to light: rods or cones?

A

Rods

78
Q

Explain why rods are very sensitive to light (work well in dim light)

A
  • because many rods join one neurone, so many weak generator potentials combine to reach threshold and trigger action potential
  • & rhodopsin can be broken down easily (pigment needs to be broken down in order to create an action potential) (called spatial summation)
79
Q

Explain why cones are less sensitive than rods (work best in bright light)

A
  • because one cone joins one neurone
  • Takes more light to reach threshold and trigger action potential
  • & requires lots of light intensity to breakdown iodopsin
80
Q

Which one gives a higher visual acuity (ability to tell apart points
that are close together): rods or cones?

A

Cones

81
Q

Explain why cones give a high visual acuity

A
  • because cones are close together and one cone joins one neurone
  • When light from 2 points hits 2 cones, 2 action potentials (one from each cone) go to the brain
  • Can distinguish 2 points that are close together as 2 separate points
82
Q

Explain why rods give a low visual acuity

A
  • Give low visual acuity because many rods join same neurone
  • Which means light from 2 points close together can’t be told apart
83
Q

Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness. (2)

A
  • rhodopsin bleached / broken down by light
  • time for resynthesis

AQA A Level Biology Paper 2 (16 decks)

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