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

Paper 3: Stimuli and Response Flashcards

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
How is IAA distributed in a normal plant shoot?
Distributed evenly
26
What does light on a shoot do to the distribution of IAA? | [2]:
- IAA moves by diffusion + active transport to the SHADED side of the shoot - IAA is distributed unevenly
27
Light on a shoot dododododo [4]:
- 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
Shoots below the soil [3]:
- 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
What's gravity's effect on IAA?
In response to gravity IAA conc increases on the lower side of the shoot
30
In what direction does a shoot grow without light?
Upwards
31
How do roots grow downwards? [4]:
- 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
Thigmotropism [definition]:
A plant response to touch
33
What factors affect IAA distribution?
- Light | - Gravity
34
What is a property of receptors?
They are specific
35
Reflex actions are...[2]:
- Rapid | - Automatic
36
Pacinian corpuscle [definition]:
A mechanical receptor that detect changes in vibrations and pressure
37
Where is the pacinian corpuscle found?
In the skin
38
What is the structure of the pacinian corpuscle?
Layers of connective tissue (lamellae) are wrapped around the end of a sensory neuron
39
What are charges in a neuron when it is at rest? [2]:
- Inside neuron = -ve | - Outside neuron = +ve
40
What happens when a pacinian corpuscle detects a stimuli? [4]:
- 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
Action Potential =
Electrical impulse
42
Generator potential [definition]:
A change caused by a stimulus
43
The bigger the stimulus...
the bigger the generator potential
44
What is the same in all action potentials?
Size/Same P.D
45
What is the P.D in a nerve cell measured in?
mV
46
Electrical impulses only occur when a lot of ..... occurs
depolarisation
47
What is depolarisation?
When the charges are switched
48
What is the name given to the value at which an action potential will be triggered?
The threshold value
49
Myelin sheath [function]:
It is an electrical insulator
50
Dendrites [function]:
These are all extensions of the cell body which connect with other dendrites
51
Scwann cell [definition]:
Cells wrapped around the axon of the nerve cell
52
Nodes of ravier [definition]:
Gaps between the scwann cells where bare membranes can be seen
53
Axon [function]:
There are a lot of sodium channels here
54
Cell body [definition]:
Where the nucleus and cell organelles are found
55
Why do positive charges diffuse into neurons at rest? [
There is an electrochemical gradient
56
What maintains the resting stage/potential of a neuron? | [2]:
- sodium-potassium ion pump | - Sodium ions cannot move across the membrane back into the axon
57
At what voltage is a neuron at rest maintained at?
-70 mV
58
How does sodium-potassium maintain neuron charges at rest? [2]:
- 3 Na+ ions are pumped out using ACTIVE TRANSPORT | - At the same time, 2 K+ ions are pumped in by FACILITATED DIFFUSION
59
Why can sodium not move back into the axon?
Na+ ions cannot move across the membrane back into the axon cus at rest are CLOSED
60
Why can potassium move back out of the axon? [2]:
There are many K+ ion channels that are open and allow K+ ions out - also helping to maintain the resting potential
61
The 'All or Nothing' principle:
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
How does a strong stimuli differ from weak stimuli?
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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