a2 04 nervous communication

8/2/2019 A2 04 Nervous Communication

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A2 Biology Exam DoctorNERVOUS COORDINATION

Question

2

Question

3

Question

1


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QUESTION 1


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The diagram below shows a recording of an action potential passing along a

nerve axon.

(a) (i) What is meant by the term threshold stimulus?

[1]

(ii) By means of an arrow, indicate on the diagram the probable time when the

stimulus was applied. [1](iii) What is the state of the axon membrane from A to B?

[1]

(b) (i) Describe the changes that are occurring in the axon during the period B to D.

[2]


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nerve axon.


[1]


stimulus was applied. [1](iii) What is the state of the axon membrane from A to B?

[1]


[2]

e in

tensity of stimulus needed to get a nerve impulse generat

Resting.

brane becomes permeable to sodium ions and they rush in.

inside becomes positively charged.


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nerve axon.

(a) (i) What is meant by the term threshold stimulus? [1]

(ii) By means of an arrow, indicate on the diagram the probable time when thestimulus was applied. [1]

(iii) What is the state of the axon membrane from A to B? [1]


[2]

(a)(i) the smallest stimulus that is capable of setting up an action potential; 1

(ii) put arrow on or near to 0.7 millisecond; 1

(iii) at the resting potential; 1

(b)(i) stimulus makes axon membrane become permeable to sodium ions;

these flood into the axon along the diffusion gradient;

thus polarity of membrane reverses to give action potential; max 2

TOTAL 5

MARK SCHEME


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[1]


nerve axon.

e in

tensity of stimulus needed to get a nerve impulse generat

Resting.

brane becomes permeable to sodium ions and they rush in.

inside becomes positively charged.

Need minimum

Not precise enough, need reference to action potential.

It isnt instantaneous

A wasted mark. The student clearly knows what is going on

but isnt answering the questions carefully enough.


stimulus was applied. [1]

(iii) What is the state of the axon membrane from A to B?

[1]

(b) (i) Explain the changes that are occurring in the axon during the period B to D.

[2]

Why?

So what? Need to mention diffusiongradient. This is a good example of a student throwing marks away.

MP 1Total 1 out of 5


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QUESTION 2


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(a) (i) Why do synaptic knobs contain many mitochondria?

[2]

The diagram below illustrates the structure of a cholinergic synapse between a

voluntary motor nerve ending and the sarcolemma of a striated muscle fibre.

(ii) Briefly describe how the arrival of an impulse at the synapse causes

depolarisation of the post-synaptic membrane.

[5]


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[2]





[5]

To make ATP to provide energy for makingtransmitter substances like acetylcholine.

The vesicles release their transmittersubstances (acetylcholine) out of the pre-synaptic membrane. The acetylcholinediffuses across the gap and causes the

membrane the sarcolemma to change.If there is enough acetylcholine the


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(a)(i) provide ATP;

to provide energy for active absorption of acetate/choline into the knobs;

for combining acetate and choline/to make acetylcholine/synthesis of

acetylcholine; max 2

(ii) calcium ions enter synaptic knobs;

and attract vesicles to the pre-synaptic membrane;

these fuse with the membrane and release acetylcholine;

this attaches to receptors on post synaptic membrane;

making it become permeable to sodium ions;

these rush into the muscle fibre along the concentration gradient;

this alters the potential across the sarcolemma/membrane resulting in an action

potential; max 5

TOTAL 7

MARK SCHEME

(a) (i) Why do synaptic knobs contain many mitochondria? [2]



(ii) Briefly describe how the arrival of an impulse at the synapse causesdepolarisation of the post-synaptic membrane. [5]


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Good concise answer with two

separate points well made.

The student

has forgotten,

or does not

know about

the role of

calcium ions

Great! But how?

Lacking in detailhere, they fuse with

the membrane

MP 1

Total 2 out of 7




[2]

To make ATP to provide energy for makingtransmitter substances like acetylcholine.

The vesicles release their transmittersubstances (acetylcholine) out of the pre-synaptic membrane. The acetylcholinediffuses across the gap and causes the

membrane the sarcolemma to change.If there is enough acetylcholine the



[5]

MP 3

Too vague!Questions on this topic demand precise detail, vaguedescriptions of membranes changing are no use.

Disappointing after a

good start.


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QUESTION 3


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Read through the following passage on neurones and nerve impulses and then fill in the spaces

with the most appropriate word or words.

The nervous system contains several types of neurones. neurones carry

impulses to muscles and glands but neurones carry impulses from

receptors to the central nervous system. The interior of a resting nerve fibre has a lower

concentration of ions than its surroundings, due to the actions of a

in its membrane. This leads to a resting potential on the

inside relative to the outside. Depolarisation occurs when the membrane permeability is

changed by a allowing ions to flood in. If the depolarisation

reaches a value it is propagated along the fibre as an . In some

fibres an insulating layer of allows the depolarisation to jump betweenmaking impulse transmission much . Impulses are propagated across synapses by

release of from vesicles in the synaptic knobs. This release is triggered by

an inflow of ions. [14]


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Motor

sensory

sodium

pump

large

stimulus

potassium

critical

axonpotentialmylin

nodesquicker

hormonessodium


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MARK SCHEMEMotor;

sensory;

sodium;

sodium pump; negative;

stimulus; sodium;

threshold; action potential;

myelin; nodes;

faster;

acetylcholine/eq;

calcium;


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sodium

sensoryMotor

quicker

nodes

stimulus

mylinAccepted wrong spelling.

pump

Specifically need sodium pump.

largeNegative required.

potassium

Sodium

critical

Threshold/minimum value wanted.axonpotential

Action not axon.

hormones

Need acetylcholine/nor-adrenaline/

transmitter substance.

sodium

Calcium ions are involved here.Total 7 out of 14

a2 04 nervous communication

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