Neuronal Communication (OCR A Level Biology)

Exam Questions

1 hour27 questions
1a
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2 marks

FURA-2 is a fluorescent dye that can be used to measure the concentration of Ca2+ ions inside cells.

The structure of FURA-2 is shown below.

q18a-paper-1-nov-2020-ocr-a-level-biology
Use the information in the figure to explain why FURA-2 is unable to cross cell membranes.

1b
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5 marks

Scientists have used FURA-2 to study the role of Ca2+ ions in the synapses of living nerve tissue.

FURA-2 was injected into a single sensory neurone that was connected by a synapse to a relay neurone.

FURA-2 fluorescence inside the neurone was observed using a confocal microscope.

(i)

Explain one advantage of using a confocal microscope in this study.

 [1]

(ii)

The sensory neurone was stimulated electrically and the FURA-2 fluorescence in the synaptic bulb was measured. At the same time, an electrode recorded the membrane potential in a postsynaptic neurone.

The results of this study are shown in the table.

Strength of electrical
stimulation
FURA-2 fluorescence in
synaptic bulb
Highest membrane
potential in postsynaptic
neurone (mV)
Low Low –60
Medium Medium +40
High High +40


The intensity of FURA-2 fluorescence is proportional to the concentration of Ca2+ ions.
The scientists concluded that changes in the concentration of Ca2+ ions in the presynaptic neurone caused an action potential in the postsynaptic neurone.

Evaluate and explain the scientists’ conclusion.

[4]

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2a
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9 marks

The greater blue-ringed octopus, Hapalochlaena lunulata, is one of the most venomous of all animals.

Its bite contains tetrodotoxin (TTX), a neurotoxin that can cause paralysis and death within minutes. 

(i)

The following information has been discovered about the effects of TTX on nerve cells:

    • TTX binds to the external surface of the voltage-gated sodium ion channels in the axon membrane.
    • Binding of TTX changes the tertiary structure of the channel.
    • This means the channel cannot open.

Using the information provided, explain how TTX affects the activity of neurones.

[4] 

(ii)

A common cause of death from TTX poisoning is suffocation (not getting enough oxygen) as a result of paralysis of the diaphragm.

Explain how paralysis of the diaphragm could lead to suffocation.

[2] 

(iii)

TTX is also known to reduce the speed of conduction in the Purkyne fibres of the heart.

Suggest and explain what effect this would have on the heart rate.

[3]
2b
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1 mark

Molluscs such as H. lunulata have unmyelinated neurones. Saltatory conduction cannot occur in these neurones.

Why is transmission of action potentials along the axon slower in the absence of saltatory conduction?

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3a
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3 marks

A student looked at slides of different tissues under a light microscope.

The four viewed images are labelled W, X, Y and Z in Fig. 23.1 below.

ocr-a-alevel-paper-1-june-2018-q23

Fig. 23.1

Identify tissues W, X and Y.

3b
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4 marks

The student wrote the following summary about the control of heart rate.

When the heart rate is too low the level of carboxylic acid in the blood becomes higher than normal. The vagus nerve sends action potentials to the AVN to increase the contraction rate of the heart muscle. The baroreceptors in the walls of the blood vessels then detect that the pH of the blood is normal, so heart rate can return to resting.

The endocrine system can also change heart rate. Release of the hormone adrenaline from the adrenal medulla causes the smooth muscle of the heart to contract more frequently.

Identify and correct any biological errors in the student’s summary.

3c
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5 marks

Reflex actions are rapid responses that protect the body from harm.

The Moro reflex is found in babies up to five months of age, and occurs when the baby feels its head is suddenly no longer supported. The Moro reflex is made up of the following responses:

  • The baby spreads out its arms then brings them together rapidly.
  • The baby cries.
(i)

Suggest how the Moro reflex helps to prevent harm to a newborn baby.

[2]

(ii)

The Moro reflex gradually disappears and usually stops completely after babies reach nine months. Other reflexes develop as children grow older.

Describe a reflex response a 3-year-old child would make to an object moving towards their eyes and explain the advantage of this response.

[3]

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4a
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4 marks

Fig. 1 below shows some structures inside the ear.

Within the cochlea of the ear, fluid surrounds thousands of mechanoreceptor cells that transmit nerve impulses to the brain via the cochlear nerve. These receptor cells are called sensory hairs.


sensory-hairs-sq

Fig. 1

(i)

Identify the stimulus for these sensory hairs.

[1]

(ii)

Sensory hair cells are highly specialised cells shown to contain many voltage gated Ca2+ channels within the cell membrane and many clusters of vesicles tethered to the internal cell membrane.

Suggest why these cells are specialised in this way. 

[3]

4b
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7 marks

Fig. 2 shows the changes in membrane potential across the membrane of the cochlear nerve over a period of time.

The membrane was stimulated after a quiet sound at A and after a louder sound at B.


enkzyr4-action-potential-graph-sq

Fig. 2

(i)

Explain why the quiet sound at A did not result in an action potential being produced.

[2]

(ii)

State which of the letters C, D and E on Fig. 2 correspond to each of the events below.

You may use each of the letters C, D or E once, more than once or not at all.

  • The Na+/K+ pump is operating
  • The voltage gated Na+ channels are open
  • The voltage gated K+ channels are open

[3]

(iii)

The period between around 2.9 ms and 3.3 ms in Fig. 2 is known as the refractory period

Describe the importance of the refractory period in the transmission of action potentials.

[2]

4c
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4 marks

Exposure to loud sounds can result in damage to the sensory hairs found in the cochlea of the ear due to breakage of the cell tips and disruption of the synapses, resulting in varying degrees of hearing loss.

Suggest how damage to hairs may result in hearing loss for individuals.

4d
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2 marks

Stem cell therapy provides one potential treatment for sensory hair damage.

Describe how stem cells could provide a successful treatment

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5a
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2 marks

Table 1 shows the speed of impulse transmission in neurones of different type and diameter.

Neurone source Myelinated Axon diameter / μm Speed of impulse transmission / m s-1
Cat Yes 5 27
Rabbit No 7 6
Frog Yes 16 36
Newt Yes 7 27

Table 1

Calculate the percentage increase in impulse transmission speed in myelinated neurones when the axon diameter is increased from 7 μm to 16 μm.

5b
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2 marks

Describe the effect of myelination on the speed of impulse transmission in neurones shown in Table 1.

5c
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4 marks

Explain the following from Table 1:

(i)

The effect of myelination on speed of nerve impulse transmission.

[3]

(ii)

The effect of axon diameter on speed of nerve impulse transmission.

[1]

5d
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4 marks

Scientists investigated the relationship between myelin in brain tissue and the different types of dementia.

The scientists measured the mean myelin content in brain tissue samples from 3 different groups:

  • A control group of 15 people without dementia
  • 22 people with vascular dementia (VD)
  • 18 people with Alzheimer's dementia (AD)

Their results are shown in Fig. 1 below. The smaller vertical bars represent standard deviation.

15-1-fig-3-1Fig. 1

A research assistant reviewing Fig. 1 concluded that there was a relationship between the concentration of myelin present in an individual’s brain and the likelihood of dementia.

Evaluate this conclusion.

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