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AQA Biology: A Level > Paper 3: Stimuli and Response > Flashcards

Paper 3: Stimuli and Response Flashcards

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1
Q

Stimuli [definition]:

A

A change in the internal or external environment of an organism that brings about a response

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2
Q

Examples of stimuli [6]:

A
  • Light/light intensity
  • Temperature
  • Humidity/ moisture levels
  • Pressure changes
  • Sound
  • Chemicals
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3
Q

Why do organisms need to detect and respond to stimuli [3]:

A
  • To prevent organism from harm
  • To help them find more favourable conditions (to mate, eat, live)
  • Ultimately its for survival
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4
Q

What do receptors do? [2]:

A
  • They detect the stimulus

- They convert energy of a stimulus into electrical energy/impulses

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5
Q

Taxes [definition]:

A

A directional response where an animal moves towards or away from a stimulus

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6
Q

Positive taxis =

A

Organism moves towards stimulus

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7
Q

Negative Taxis =

A

Organism moves away from stimuli

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8
Q

Taxis =

A

Singular

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9
Q

Taxes =

A

Plural

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10
Q

Tropisms [definition]:

A

Response of a plant to a directional stimulus

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11
Q

Phototropism [definition]:

A

The growth of a plant in response to light

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12
Q

Gravitropism/ Geotropism [definition]:

A

The growth of plants in response to gravity

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13
Q

What type of tropisms do the shoots and leaves of a plant show? [2]:

A
  • Positively phototropic

- Negatively gravitropic

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14
Q

Positive phototropism =

A

Plant grows towards light

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15
Q

Negative phototropism =

A

Plant grows away from light

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16
Q

Positive gravitropism =

A

Plant grows in the direction of gravity

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17
Q

Negative gravitropism =

A

Plant grows AGAINST the direction of gravity

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18
Q

What type of tropisms do the roots of the plant show?

[2]:

A
  • Negatively Phototropic

- Positively gravitropic

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19
Q

Why do roots need to be positively gravitropic?

A

They need to grow downwards towards the soil to get water and mineral ions

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20
Q

What is a auxin? [2]:

A
  • A Growth factor

- Plant hormone

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21
Q

What is an example of an auxin?

A

IAA

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22
Q

Where in the plant is IAA made?

A

In the TIPS of the SHOOTS of a plant

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23
Q

How does IAA move across short distances? [2]:

A
  • Moves by diffusion at first

- Then through active transport

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24
Q

How does IAA move across long distances?

A

IAA is transported by the phloem

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25
Q

How is IAA distributed in a normal plant shoot?

A

Distributed evenly

26
Q

What does light on a shoot do to the distribution of IAA?

[2]:

A
  • IAA moves by diffusion + active transport to the SHADED side of the shoot
  • IAA is distributed unevenly
27
Q

Light on a shoot dododododo [4]:

A
  • IAA moves to shaded side
  • IAA causes cells on shaded side to elongate and become stretchy
  • Cells on shaded side now growing at a faster rate than cells on lit side
  • Causes shoot to bend/curve downwards towards the light
28
Q

Shoots below the soil [3]:

A
  • IAA unevenly distributes on lower side of shoot
  • IAA causes lower surface cells elongate and become stretchy
  • Rate of growth of cells on lower surface is faster than upper surface causing shoot to curve upwards
29
Q

What’s gravity’s effect on IAA?

A

In response to gravity IAA conc increases on the lower side of the shoot

30
Q

In what direction does a shoot grow without light?

A

Upwards

31
Q

How do roots grow downwards? [4]:

A
  • IAA distributes itself unevenly on the lower side of root
  • IAA INHIBITS cell elongation and slows down growth rate in lower surface cells
  • Cells on upper surface of root continue to grow at normal rate
  • Root bends/ curves downwards
32
Q

Thigmotropism [definition]:

A

A plant response to touch

33
Q

What factors affect IAA distribution?

A
  • Light

- Gravity

34
Q

What is a property of receptors?

A

They are specific

35
Q

Reflex actions are…[2]:

A
  • Rapid

- Automatic

36
Q

Pacinian corpuscle [definition]:

A

A mechanical receptor that detect changes in vibrations and pressure

37
Q

Where is the pacinian corpuscle found?

A

In the skin

38
Q

What is the structure of the pacinian corpuscle?

A

Layers of connective tissue (lamellae) are wrapped around the end of a sensory neuron

39
Q

What are charges in a neuron when it is at rest? [2]:

A
  • Inside neuron = -ve

- Outside neuron = +ve

40
Q

What happens when a pacinian corpuscle detects a stimuli? [4]:

A
  • Lamellae are deformed
  • Causes stretch-mediated Na ion channels to open in the membrane of sensory neuron
  • Na ions diffuse into nerve cell, depolarising the neuron and creating a P.D across the cell
  • When generator potential reaches a certain threshold it will trigger an action potential along the neuron
41
Q

Action Potential =

A

Electrical impulse

42
Q

Generator potential [definition]:

A

A change caused by a stimulus

43
Q

The bigger the stimulus…

A

the bigger the generator potential

44
Q

What is the same in all action potentials?

A

Size/Same P.D

45
Q

What is the P.D in a nerve cell measured in?

A

mV

46
Q

Electrical impulses only occur when a lot of ….. occurs

A

depolarisation

47
Q

What is depolarisation?

A

When the charges are switched

48
Q

What is the name given to the value at which an action potential will be triggered?

A

The threshold value

49
Q

Myelin sheath [function]:

A

It is an electrical insulator

50
Q

Dendrites [function]:

A

These are all extensions of the cell body which connect with other dendrites

51
Q

Scwann cell [definition]:

A

Cells wrapped around the axon of the nerve cell

52
Q

Nodes of ravier [definition]:

A

Gaps between the scwann cells where bare membranes can be seen

53
Q

Axon [function]:

A

There are a lot of sodium channels here

54
Q

Cell body [definition]:

A

Where the nucleus and cell organelles are found

55
Q

Why do positive charges diffuse into neurons at rest? [

A

There is an electrochemical gradient

56
Q

What maintains the resting stage/potential of a neuron?

[2]:

A
  • sodium-potassium ion pump

- Sodium ions cannot move across the membrane back into the axon

57
Q

At what voltage is a neuron at rest maintained at?

A

-70 mV

58
Q

How does sodium-potassium maintain neuron charges at rest? [2]:

A
  • 3 Na+ ions are pumped out using ACTIVE TRANSPORT

- At the same time, 2 K+ ions are pumped in by FACILITATED DIFFUSION

59
Q

Why can sodium not move back into the axon?

A

Na+ ions cannot move across the membrane back into the axon cus at rest are CLOSED

60
Q

Why can potassium move back out of the axon? [2]:

A

There are many K+ ion channels that are open and allow K+ ions out
- also helping to maintain the resting potential

61
Q

The ‘All or Nothing’ principle:

A

As long as the generator potential reaches the threshold value then an action potential will be triggered, REGARDLESS of the strength of the stimulus

62
Q

How does a strong stimuli differ from weak stimuli?

A

frequency of action potentials will increase/ be higher with a strong stimulus
- so less action potentials for weaker stimulus

AQA Biology: A Level (18 decks)

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