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Biology: AQA A-Level > Survival, Response To Stimuli & Neurons > Flashcards

Survival, Response To Stimuli & Neurons Flashcards

(80 cards)

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1
Q

What is a taxis?

A

A directional movement toward or away from a stimulus.

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2
Q

What is a positive taxis?

A

Movement toward a stimulus.

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3
Q

What is a negative taxis?

A

Movement away from a stimulus.

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4
Q

What is kinesis?

A

A non-directional, random movement in response to a stimulus.

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5
Q

What makes kinesis different from taxis?

A

Kinesis has no specific direction, taxis does.

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6
Q

When does kinesis typically occur?

A

When an organism is in unfavorable conditions.

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7
Q

What is a tropism?

A

A plant’s growth response to a directional stimulus.

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8
Q

How is tropism different from taxis?

A

Tropism = growth of a plant part; taxis = movement of an organism.

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9
Q

How is tropism similar to taxis?

A

Both are directional responses to stimuli.

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10
Q

Where is IAA produced in shoots?

A

In the shoot tips.

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11
Q

How does light affect IAA in shoots?

A

IAA moves to the shaded side of the shoot.

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12
Q

What does IAA cause on the shaded side of a shoot?

A

More cell elongation, causing the shoot to bend toward light.

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13
Q

Where is IAA produced in roots?

A

In the root tips.

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14
Q

What does IAA do on the underside of roots?

A

Inhibits cell elongation.

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15
Q

What is the result of more IAA on the root underside?

A

Root bends downward (positive gravitropism).

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16
Q

What is a simple reflex?

A

A rapid, automatic response to a stimulus.

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17
Q

Why are reflexes fast?

A

They bypass the brain and use spinal cord reflex arcs.

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18
Q

Why are reflexes important?

A

They protect the body from harm and aid survival.

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19
Q

Are reflexes learned?

A

No — they are innate (automatic and unlearned).

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20
Q

What is a resting potential?

A

The voltage across a neurone’s membrane when not transmitting an impulse (around –70 mV).

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21
Q

How is the resting potential maintained?

A

By the sodium-potassium pump.

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22
Q

What does the sodium-potassium pump do?

A

It actively transports 3 Na⁺ out and 2 K⁺ in.

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23
Q

Which ions accumulate outside the neurone during rest?

A

Sodium ions (Na⁺).

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24
Q

Which ions are more concentrated inside the neurone at rest?

A

Potassium ions (K⁺).

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25
Is the membrane permeable to sodium at rest?
No — it’s less permeable to Na⁺ than to K⁺.
26
Why is the inside of the axon negative?
Due to more positive ions outside and anions inside.
27
What triggers an action potential?
A stimulus that reaches threshold potential.
28
What is the threshold?
The minimum voltage required to trigger an action potential (usually –55 mV).
29
What happens when threshold is reached?
Voltage-gated Na⁺ channels open.
30
What enters the neurone during depolarisation?
Na⁺ ions rush in by diffusion.
31
What happens to membrane potential during depolarisation?
It becomes more positive, up to +40 mV.
32
What happens after depolarisation?
Na⁺ channels close, K⁺ channels open.
33
What leaves the neurone during repolarisation?
K⁺ ions diffuse out.
34
What does this do to the membrane potential?
Returns it to negative (resting) potential.
35
What is hyperpolarisation?
When the membrane potential becomes more negative than resting.
36
What is the refractory period?
A short time where the neurone can’t be stimulated again.
37
Why is the refractory period important?
Ensures unidirectional transmission and limits frequency of impulses.
38
What is saltatory conduction?
Action potentials jump from node to node in myelinated neurones.
39
Why is saltatory conduction faster?
Fewer depolarisations — ions only enter at nodes of Ranvier.
40
What does myelin do?
Acts as electrical insulation and increases speed of conduction.
41
Why do unmyelinated neurones need more ATP?
They pump ions along the entire axon, not just at nodes.
42
What is a neuromuscular junction (NMJ)?
A synapse between a motor neurone and a muscle fibre.
43
How is NMJ similar to a cholinergic synapse?
Uses acetylcholine, Ca²⁺-dependent vesicle release, and Na⁺ entry for depolarisation.
44
How is NMJ different from a synapse between neurones?
NMJ always causes an excitatory response. Postsynaptic membrane = sarcolemma, which is highly folded for more ACh receptors. A muscle fibre, not a neurone, is stimulated.
45
What triggers ACh release at an NMJ?
Action potential arrives at motor neurone terminal.
46
What does Ca²⁺ influx trigger?
Vesicles fuse with presynaptic membrane, releasing ACh.
47
What happens when ACh binds to receptors on the sarcolemma?
Na⁺ channels open, sarcolemma depolarises, triggering a muscle action potential.
48
What happens first when a muscle fibre is activated?
Action potential spreads across sarcolemma and down T-tubules.
49
What do T-tubules stimulate?
Release of Ca²⁺ from the sarcoplasmic reticulum.
50
What does calcium do?
Binds to troponin, which causes tropomyosin to move, exposing myosin binding sites on actin.
51
What happens after binding sites are exposed?
Myosin heads bind to actin, forming cross-bridges.
52
What provides energy for this process?
ATP.
53
How does the power stroke occur?
Myosin head pulls actin, ADP is released → filament slides inward.
54
How is the myosin head detached?
New ATP binds, causing detachment.
55
What happens if ATP is not available?
Myosin remains attached → rigor mortis.
56
What stops the contraction signal?
ACh broken down by acetylcholinesterase at NMJ.
57
What happens to calcium?
Actively pumped back into sarcoplasmic reticulum.
58
What does tropomyosin do when calcium is removed?
Covers binding sites, preventing further cross-bridge formation.
59
What is a tropism?
The gross response of a flowering plant to directional stimuli.
60
What is the result of IAA accumulation in different plant parts?
Shoots → stimulates elongation; Roots → inhibits elongation.
61
What are the advantages of simple reflex arcs?
They are rapid.
62
How do reflex arcs protect the body?
They protect against damage to body tissues.
63
How do reflex arcs help survival?
They help escape from predators.
64
How are reflex arcs involved in regulation?
They enable homeostatic control.
65
How is sodium involved in maintaining resting potential?
Sodium ions are actively transported out of the neurone.
66
Where is the sodium concentration higher during resting potential?
Outside the neurone.
67
How does membrane permeability affect ion distribution?
The membrane is more permeable to K⁺ than Na⁺ ions.
68
What happens to sodium channels during an action potential?
Sodium ion channels open.
69
What causes depolarisation in an action potential?
Na⁺ ions rapidly diffuse in.
70
What is the threshold in a neurone?
The point at which a stimulus causes an action potential.
71
What happens if a stimulus is below threshold?
No action potential is triggered.
72
What is the all-or-nothing principle?
A stimulus at or above threshold always produces an action potential.
73
What is the refractory period?
The time after an action potential when a new one can't be generated.
74
What does the refractory period limit?
The number of impulses per second (frequency of transmission).
75
Why does information not increase above a certain stimulus strength?
Because all (higher) stimuli produce the same response — all-or-nothing.
76
How does myelination affect conduction?
Myelination provides electrical insulation.
77
How does an action potential travel in a myelinated axon?
By saltatory conduction — jumping from one node of Ranvier to another.
78
How else can conduction speed increase?
Larger axon diameter = less resistance to ion flow.
79
Why does a demyelinated neurone use more ATP than a myelinated one?
Because more Na⁺/K⁺ ions enter/leave along its full length.
80
Why does oxygen use increase when a neurone fires?
More oxygen is needed to make ATP for active transport.

Biology: AQA A-Level (48 decks)

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