The Nervous System (Edexcel International A Level Biology)

Animals and plants can detect and respond to light.

Rod cells respond to light by producing action potentials in the optic nerve.

(i)

In which structure are rod cells located?

(1)

(3)

One cause of blindness is a mutation in the DNA coding for the enzyme RPE65.

The enzyme RPE65 converts trans-retinal to cis-retinal.

Explain why mutations in the RPE65 gene can result in blindness.

Scientists are investigating the use of gene therapy to treat blindness caused by mutations in the RPE65 gene.

In one investigation, different gene therapy doses containing functioning RPE65 genes were compared.

Two months after treatment, the trans-retinal and cis-retinal in each eye and the ability to follow a path were measured.

The graphs show the results of this investigation.


Describe the conclusions that can be made from this investigation.

Use the information in the graphs to support your answer.

Mutations in other genes can result in blindness.

Describe how these genes could be identified.

The eye is a sense organ specialised for detecting light stimuli.

Pupils of the eye react to light.

The effects of different light intensities from two light sources have been investigated.

The table shows the results of this investigation.

Describe the relationship between light intensity and pupil diameter.

(2)

(ii)

Calculate the amount of incandescent light that can pass through the pupil when the light intensity is 1400 a.u. per m².

Use a value of pi (π) = 3.14

(3)

(iii)

Describe how light entering the eye causes the pupil to respond.

(4)

Age-related macular degeneration (AMD) is a common cause of blindness in older people.

In AMD the epithelial layer behind the retina is damaged.

A new treatment for AMD uses induced pluripotent stem cells. These cells are grown in a culture to produce a retinal epithelial layer.

This retinal epithelial layer can then be used to replace the damaged layer of cells.

The procedure is outlined in the flow chart.

State what is meant by the term pluripotent stem cell.

(2)

(2)

Many predatory animals produce toxins to disable their prey. Some of these toxins inhibit nervous communication.

Nerve impulses are transmitted along axons. Some axons are myelinated.

(i)

Which type of cell produces myelin?

(1)

Which row correctly compares the conduction of an impulse along a myelinated neurone with conduction along a non-myelinated neurone?

(1)

Describe the role of ion transport in maintaining the resting potential of a neurone.

The pufferfish produces a neurotoxin called tetrodotoxin (TTX).

The graph shows the effect of TTX on the nerve impulse in an axon.

Deduce how TTX inhibits nerve impulses in an axon.

Parkinson’s disease occurs when dopamine-producing neurones die.

The most obvious motor symptoms of Parkinson’s disease include muscle tremors and muscle rigidity.

These motor symptoms are linked to the loss of dopamine-producing neurones in the brain.

(i)

One drug used to treat Parkinson’s disease is L-DOPA.

Which of the following statements explains why L-DOPA can be used to treat Parkinson’s disease?

(1)

Explain why the release of reduced quantities of dopamine by presynaptic neurones could result in motor symptoms.

(3)

It has been suggested that in Parkinson’s disease dopamine-producing neurones die because of a failure to release dopamine.

Suggest how the release of dopamine from presynaptic neurones could be inhibited.

Describe how microarrays and bioinformatics could be used to investigate the genetic basis of Parkinson’s disease.

Parkinson’s disease is a nervous system disorder that affects movement.

In people with Parkinson’s disease, some neurones in the brain die.

Many of the symptoms of Parkinson’s disease are due to a loss of neurones that produce a neurotransmitter called dopamine.

Describe how a neurotransmitter transmits a nerve impulse across a synapse.

One treatment for Parkinson’s disease is a drug called L-DOPA.

Describe how L-DOPA reduces some of the symptoms of Parkinson’s disease.

Scientists can induce pluripotent stem cells to produce transcription factors involved in the synthesis of dopamine.

(i)

Explain how transcription factors are involved in the synthesis of dopamine.

Some people with Parkinson’s disease have a DNA mutation called LRRK2.

Scientists studied the effect of this mutation on the dendrites of dopamine neurones produced from the stem cells of three groups of people.

The graphs show some of the results of their study.


Comment on these results.

The nervous system of an organism enables it to respond to a stimulus.

A reflex action is a rapid involuntary movement in response to a stimulus.

The response to a pinprick in a finger is an example of a reflex action.

(i)

Which component of the nervous system continues a reflex arc immediately after the receptor has been stimulated by the stimulus?

(1)

Which pathway shows a reflex arc?

(1)

Pacinian corpuscles are pressure receptors found in the skin of the fingertip.

The effect of different pressures applied to the finger tip, on electrode potentials across the axon membrane of the neurone of a Pacinian corpuscle was investigated.

The diagram shows the structure of a Pacinian corpuscle and the location of electrodes, X and Y, used to measure axon membrane potentials.

The table shows the results of the investigation.

Describe how the resting potential of −70 mV is maintained in the axon when no pressure is applied.

(3)

(ii)

Suggest how a change in pressure at the Pacinian corpuscle causes an action potential in the axon.

(3)

(iii)

Explain why the membrane potential at electrode Y was the same when medium or high pressure was applied to the fingertip.

(3)

Many neurones in the human nervous system are myelinated.

A myelinated axon conducts impulses faster than a non-myelinated axon of the same diameter.

Explain this difference.

Polyneuropathy is a disorder that damages the myelin sheath of neurones throughout the body.

One symptom is muscle weakness. Muscle weakness is the reduced strength in one or more muscles.

Suggest how damage to the myelin sheaths of neurones can lead to muscle weakness.

Dementia is a condition associated with the ongoing decline of brain functioning.

There are many types of dementia.

The relationship between myelin in brain tissue and types of dementia has been investigated.

The mean quantity of myelin in samples of brain tissue from groups of people with types of dementia and from a control group was measured.

The table shows the results of this investigation.

A student concluded that there was a relationship between the quantity of myelin in the brain of a person and whether or not they had dementia.

Comment on the validity of this conclusion.

The mammalian retina is a tissue that detects light.

Rod cells and bipolar neurones are cell types found in the retina.

(1)

(1)

An investigation studied the effects of light intensity on the mammalian retina.

Samples of retina were exposed to different light intensities and the mean potential difference of the bipolar neurones was recorded.

The results are shown in the table.

Answer ..............................................%

Which statement describes the response of the muscles in the iris to increasing light intensity?

The body length of the medicinal leech decreases when touched.

GlebK, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

The body length of the leech decreases less each time the leech is touched.

What is the name of this effect?

(1)

Why is it an advantage for the leech to respond in this way?

(1)

The photograph shows a fiddler crab.

Wilfredor, CC0, via Wikimedia Commons

In an experiment, the fiddler crab was used to investigate responses to a predator.
The responses by females and males were compared.

A predator approached a group of female crabs from one direction.

The percentage of crabs running home was recorded. This was repeated 20 times.

This experiment was repeated with a group of male crabs.

The graphs show the percentage of crabs running home for both groups of crabs against the total number of times each group of crabs encountered a predator.

Comment on the results of this experiment.

(3)

(ii)

Which statistical test would be used to analyse the effect of the increase in the number of predator encounters on the percentage of crabs running home?

(1)

Animals and plants can respond to light.

The photograph shows the front of a human eye.

ROTFLOLEB, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

The size of the pupil changes when moving from dim to very bright light.

Explain how this change occurs.

(3)

Describe the role of rhodopsin in causing changes in the polarisation of rod cells.

(4)

Whales are large mammals.

The photograph shows a humpback whale and a human diver.

NOAA's National Ocean Service, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

A humpback whale can become habituated to human divers.

How many of the following statements about habituation are correct?

(1)

• Habituation is an example of anatomical adaptation
• Habituation is only observed in mammals
• Habituation only occurs after repeated exposure to the same stimulus

A humpback whale can respond to a stimulus using a spinal reflex arc.

Which row is correct?

The heart rate of a whale changes when it is diving.

The graph shows the changes in heart rate that occur during dives of different durations.

The maximum heart rate at the surface is when the whale returns to the surface after a dive.

Comment on the changes in heart rate of the whale when it is diving.

(3)

(ii)

Explain how the changes in heart rate are controlled when the whale returns to the surface immediately after the dive.

The nervous system is a complex collection of neurones and specialised cells that transmit impulses between different parts of the body.

Which substance can transmit a nerve impulse from one neurone to the next one?

The diagram shows the change in membrane potential as an action potential is transmitted in a motor neurone.

Explain why the membrane potential changes between 1 and 2.

Myelinated neurones are surrounded by a fatty sheath.

The graph shows the speed of conduction in myelinated neurones and non‐myelinated neurones.

Calculate the percentage difference in the gradient of the myelinated and non‐myelinated neurones.

The gradient for non‐myelinated neurones is 0.5.

The equation for a straight line is y = mx + c .

(3)

(ii)

Explain why the speed of conduction differs in myelinated and non‐myelinated neurones.

(3)

The positron emission tomography (PET) images show the brain of an individual before (control) and after taking the drug cocaine.

Explain how positron emission tomography (PET) can be used to identify the change in activity in the brain after taking this drug.