Coordination, Response and Gene TechnologyEdexcel International A Level Biology: Topic test

1. 1
   A patient has Guillain-Barré syndrome. An immune reaction damages the Schwann cells of her peripheral neurones, and the myelin sheaths break down. She has weak limbs, and tests show that impulses travel along her motor neurones much more slowly than normal.

   (a)

   What is the normal function of Schwann cells?

   [1 mark]

   • AThey wrap around axons to form an insulating myelin sheath
   • BThey carry impulses from the central nervous system to the effectors
   • CThey release neurotransmitter into the synaptic cleft
   • DThey detect stimuli and generate impulses

   (b)

   In a spinal reflex arc, which neurone carries impulses from the spinal cord to a muscle?

   [1 mark]

   • AThe sensory neurone
   • BThe relay neurone
   • CThe motor neurone
   • DA relay neurone in the white matter

   (c)

   Suggest why impulses travel more slowly along the patient's motor neurones than they do in a healthy person.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A farmer sprays an organophosphate insecticide on a crop. Organophosphates inhibit the enzyme acetylcholinesterase in cholinergic synapses, and insects that eat the crop twitch uncontrollably and die.

   (a)

   What is the normal function of acetylcholinesterase at a cholinergic synapse?

   [1 mark]

   • AIt makes acetylcholine in the presynaptic neurone
   • BIt hydrolyses acetylcholine in the synaptic cleft, so that the postsynaptic membrane is not stimulated continuously
   • CIt opens sodium ion channels in the postsynaptic membrane
   • DIt transports acetylcholine across the synaptic cleft

   (b)

   How does the insecticide cause the insects to twitch?

   [1 mark]

   • AAcetylcholine cannot be released from the presynaptic neurone
   • BCalcium ion channels in the presynaptic neurone are blocked
   • CThe insecticide binds to acetylcholine receptors and prevents depolarisation
   • DAcetylcholine is not broken down, so the postsynaptic membrane is stimulated repeatedly

   (c)

   Describe how acetylcholine, once it has been released, causes an action potential in the postsynaptic neurone.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student studies pea plants. A dwarf variety grows to normal height when it is sprayed with gibberellin. In a second experiment she lays a germinating pea seedling on its side in the dark, and after one day its root tip has curved downwards.

   (a)

   Explain, with reference to auxin (IAA), why the root tip curved downwards.

   [3 marks]

   (b)

   Explain how gibberellin could cause the dwarf variety to grow to normal height, with reference to gene transcription.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biotechnology company wants yeast cells to make a viral surface protein for use in a vaccine. The gene for the protein is on a fragment of viral DNA. The company will insert the gene into a plasmid and then insert the plasmid into yeast cells. Only about one yeast cell in 10 000 takes up a plasmid. The plasmid also carries a gene for resistance to an antibiotic that normally kills yeast. The company later wants to find out which yeast genes are most active when the cells are making large amounts of the viral protein.

   (a)

   Explain how the recombinant plasmid is made and how the yeast cells that have taken it up are identified.

   [6 marks]

   (b)

   Explain how a microarray could be used to find out which yeast genes are most active when the cells are making large amounts of the viral protein, and how bioinformatics would help.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   MDMA is a recreational drug. It causes serotonin to be released from the presynaptic neurones of serotonergic synapses, and it blocks the reuptake of serotonin from the synaptic cleft. A user feels happy and energetic for several hours, but afterwards often feels low in mood for a few days.

   (a)

   How does MDMA increase the effect of serotonin at a synapse?

   [1 mark]

   • AIt hydrolyses serotonin in the synaptic cleft
   • BIt blocks serotonin receptors on the postsynaptic membrane
   • CIt increases the release of serotonin and blocks its reuptake, so serotonin stays in the cleft for longer
   • DIt prevents calcium ion channels in the presynaptic membrane from opening

   (b)

   What is the effect of MDMA on the postsynaptic neurone while the drug is active?

   [1 mark]

   • AIt is stimulated more often, so more action potentials are produced
   • BIt is hyperpolarised, so no impulses are produced
   • CIt is stimulated less often, because less serotonin is released
   • DIt is unaffected, because serotonin is not a neurotransmitter

   (c)

   Suggest why the user feels low in mood after the effects of MDMA wear off.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A man moves into a flat close to a railway line. For the first few nights each passing train wakes him, but after a few weeks he no longer wakes when the trains pass, although he still wakes when his alarm clock rings.

   (a)

   What is the term for this change in his response to the trains?

   [1 mark]

   • AA spinal reflex
   • BSensitisation
   • CReceptor fatigue
   • DHabituation

   (b)

   Which statement correctly compares nervous and hormonal coordination?

   [1 mark]

   • ANervous coordination is usually slower and its effects longer-lasting
   • BNervous coordination is usually faster and its effects are usually shorter-lived
   • CBoth rely on the blood to transport the signal
   • DHormones act only on neurones

   (c)

   Explain the advantage of habituation to an animal.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Researchers use functional MRI (fMRI) to find which regions of the brain are active in volunteers while they solve a puzzle and while they rest. They are also considering using PET scans with a radioactive form of glucose for the same study.

   (a)

   Explain how fMRI shows which regions of the brain are active.

   [3 marks]

   (b)

   Compare the use of fMRI with the use of PET scans in this research on healthy volunteers.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A woman looks at a faint star at night. Light from the star falls on rod cells in her retina, and information about the light is sent to her brain along optic neurones.

   (a)

   Explain how absorbing light in a rod cell leads to an action potential in an optic neurone.

   [6 marks]

   (b)

   Describe how an action potential is propagated along an optic neurone, and explain why it travels faster along a myelinated axon.

   [6 marks]

   Total for question 8: 12 marks

End of questions