1.	(a)	The figure below represents part of the axon of a neurone.

	Describe the structure of the feature labelled A.
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[2]
 
	The table below shows details of the diameter and speed of conduction of impulse along the neurones of different animal taxa.

type of neurone	axon diameter
(µm)	speed of
conduction
(m s–1)	animal taxon	
myelinated	4	25	mammal	
myelinated	10	30	amphibian	
myelinated	14	35	amphibian	
unmyelinated	15	3	mammal	
unmyelinated	1000	30	mollusc	

(b)	Using only the data in the table above, describe the effect of each of the following on the speed of conduction:
(i)	myelination,
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[2]
 
(ii)	axon diameter.
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[2]
 
(c)	The speed of conduction of a nerve impulse is also affected by temperature.
(i)	Suggest why an increase in temperature results in an increase in the speed of conduction.
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[1]

(ii)	As the temperature continues to increase, it reaches a point at which the conduction of the impulse ceases. Suggest why.
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[1]
[Total 8 marks]

2.	Outline the events following the arrival of an action potential at the synaptic knob until the acetylcholine has been released into the synapse.
	In your answer, you should use appropriate technical terms, spelt correctly.
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[Total 4 marks]

3.	(a)	Fig. 1 is a diagram of a neurone.

	Fig. 1
	Name the structures A and B.
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B ......................................................................................................................
[2]

	Fig. 2 shows a recording of the potential difference across the membrane of an axon as an action potential is transmitted.

	Fig. 2
(b)	Describe the events taking place in the neurone during stages X and Y.
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[4]

	The table below shows how the speed of conduction of an action potential varies with the diameter of myelinated and non-myelinated axons in different organisms.
organism	type of axon	axon diameter / µm	speed of conduction / ms-1	
crab	non-myelinated	30	5	
squid	non-myelinated	500	25	
cat	myelinated	20	100	
frog	myelinated	16	32	
(c)	Describe the effect of myelination on the rate of conduction of an action potential and explain how this effect is achieved.
	In your answer, you should use appropriate technical terms, spelled correctly.
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[5]
[Total 11 marks]

4.	Fig.1 represents some of the changes that occur across the membrane of the axon. Three protein complexes are shown to be present in the membrane:
•	sodium channels
•	potassium channels
•	sodium-potassium pumps.

Fig. 1

	Fig. 2 shows the change of membrane potential associated with an action potential.

	Fig. 2
(i)	State which of the three diagrams of the axon membrane in Fig. 1 match up to the phases labelled in Fig. 2. Write your answers in the table below.

phase	number	
A		
B		
C		
[1]

(ii)	With reference to Fig. 1, explain the changes in membrane potential in
Fig. 2.
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[5]
[Total 6 marks]

5.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	In order to transfer information from one point to another in the nervous system, it is necessary that action potentials be transmitted along axons. In humans, the rate of transmission is 0.5 m s–1 in a nonmyelinated neurone, increasing to 100 m s–1 in a myelinated neurone.

	Explain how action potentials are transmitted along a nonmyelinated neurone and describe which parts of this process are different in myelinated neurones.
	No credit will be given for reference to events at the synapse.
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[7]
Quality of Written Communication [1]
[Total 8 marks]

6.	In this question, one mark is available for the quality of the use and organisation of scientific terms.
	The medulla oblongata controls breathing, heart rate and blood pressure.
	Describe how the medulla oblongata responds to an increase in carbon dioxide concentration in the blood during exercise. Explain how this response leads to a decrease in the concentration of carbon dioxide in the blood.
[7]
Quality of Written Communication [1]
[Total 8 marks]

7.	The figure below shows a simplified diagram of a mammalian reflex arc.

(i)	Name S and T.
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T ......................................................................................................................
[2]

(ii)	Explain why the withdrawal of a hand, which has been subjected to pressure, is an example of a reflex action.
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[3]
 
(iii)	In this reflex, when pressure is applied to the receptor, impulses are generated in the sensory neurone.
	Outline what happens in the membrane of the sensory receptor in response to pressure.
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[3]
 
(iv)	Explain why, in the reflex arc shown in the figure above, impulses can only travel in the direction shown.
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[2]
[Total: 10 marks]

8.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	Mammals also rely on nerves to transfer information in the form of electrical impulses.
	Using the information shown in the figure below, outline how impulses are transmitted from receptor to effector.

[8]
Quality of Written Communication [1]
[Total 9 marks]

9.	Reflex actions are unlearned responses to a stimulus.
	Describe one advantage of reflex actions compared to learned responses in a mammal.
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[Total 1 mark]

10.	Alzheimer’s disease is a complex, degenerative disease that affects the brain. The risk of developing this disease increases with age, particularly over the age of 65. Symptoms include a gradual loss of memory, disorientation, difficulty with learning, loss of language skills and a decline in the ability to perform routine tasks. The areas of the brain that control memory and thinking skills are affected first.
	State the functions of acetylcholine and acetylcholinesterase in synapses in the brain.
acetylcholine ............................................................................................................
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acetylcholinesterase ................................................................................................
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[Total 2 marks]

11.	Parkinson’s disease is a disorder of the nervous system. People with this condition are unable to produce enough of the neurotransmitter substance dopamine. This chemical is required in neurone circuits in the brain that control movement.
(a)	Outline two roles of synapses in the nervous system.
1 ......................................................................................................................
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[2]

	The figure below illustrates the events at a synapse where the neurotransmitter is dopamine.

(b)	Using only the information above, list three ways in which the events occurring at this synapse are the same as at a cholinergic synapse.
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[3]
 
(c)	For the proper functioning of neurone circuits, neurotransmitters have to be removed from the receptors in the postsynaptic membrane and from the synaptic cleft. Explain why this is so.
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[2]
[Total 7 marks]

12.	The mammalian nervous system consists of the central and peripheral nervous systems.
	Describe how the central nervous system is protected from mechanical damage.
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[Total 3 marks]

13.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
	The autonomic nervous system contains neurones that carry impulses to the internal organs.
	Describe the role of the autonomic nervous system in the control of the heart beat.
[7]
Quality of Written Communication [1]
[Total 8 marks]

14.	Read the passage below and answer the questions that follow.
		Snake Venoms
	Some types of snake kill their prey and defend themselves by means of a poisonous bite.
	Fangs (hollow teeth) inject venom from specialised glands into the victim. The venom contains a protein, which is a toxin.
	Different species of snake have toxins that act in different ways. Haemolytic toxins are enzymes that hydrolyse phospholipids. They damage tissues, including heart muscle.
	Neurotoxins, such as the one produced by green mamba snakes, bind to acetylcholine receptors on the surface membranes of nerve cells or muscle fibres. This leads to muscle paralysis and heart failure.

	Some antibodies bind to toxins and inactivate them. These antibodies are known as antitoxins.
	The human immune response is far too slow to be effective in making antitoxins against snake venom.
	Injecting a very small, non-lethal quantity of venom into a horse produces antitoxin. The horse produces antitoxins that can be extracted from horse blood and used as an emergency treatment for those bitten by the same species of snake.
	Each time the horse is injected with venom, it is able to tolerate larger doses and the concentration of the specific antitoxin in its blood is greater.
 
(a)	State how enzymes which hydrolyse phospholipids damage tissues.
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[1]
 
(b)	Suggest how a neurotoxin which binds to acetylcholine receptors on muscle fibres would produce paralysis.
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(c)	Explain why the human immune response is too slow to protect a person from a snake bite.
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(d)	Explain why a horse is injected more than once with a small amount of venom when it is being prepared for use as a source of antitoxin.
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[3]
 
(e)	Why would treatment with horse antitoxin produce no long-term protection against snake bites?
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[2]
[Total 10 marks]

15.	The table below shows how the speed of nerve impulse conduction varies with the diameter of myelinated and non-myelinated axons in different organisms.
organism	type of axon	axon diameter /μm	speed of impulse /m s–1	
crab	non-myelinated	30	5	
squid	non-myelinated	500	25	
cat	myelinated	20	100	
frog	myelinated	16	32	
	Describe the trends shown in the table above.
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[Total 2 marks]

16.	Explain the term refractory period and outline its importance in nerve impulse conduction.
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[Total 4 marks]

17.	(a)	During winter, the brown bear, Ursus arctus, enters a long period of inactivity. Whilst inactive, the brown bear undergoes various physiological changes, for example a decrease in core body temperature and a decrease in resting heart rate. There are also changes in the brown bear’s metabolism of protein and lipids.
	Explain the role of the autonomic nervous system in achieving a decrease in resting heart rate.
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[3]
 
	During periods of inactivity, the brown bear reabsorbs all urea molecules from the filtrate in its kidneys and from the bladder. Urea is then transported in the bloodstream to the large intestine. Bacteria in the large intestine convert urea to ammonia and carbon dioxide, which diffuse back into the blood. When the ammonia reaches the liver, it is converted into amino acids. These newly produced amino acids are then used to synthesise proteins in the body, especially in the liver and muscle cells.
(b)	Name two plasma proteins that will be produced by the liver.
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[2]

(c)	Describe the similarities and differences between the metabolism of nitrogen-containing compounds in inactive brown bears, as described in the passage, and in humans.
similarities
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differences
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[5]

	The blood plasma cholesterol concentration of inactive brown bears rises to twice the concentration found in normally active bears and in humans. However, brown bears do not suffer any of the cardiovascular diseases associated with high cholesterol concentrations in humans, as their liver produces a protective substance, which prevents these diseases from developing.
(d)	Explain the importance of cholesterol in the metabolism of mammals.
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[3]
 
(e)	Suggest how the protective substance produced by their liver prevents brown bears developing cardiovascular diseases.
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[2]
[Total 15 marks]