Take the NUMS Biology — Nervous and Chemical Coordination, Immunity (Set 5): 30 multiple-choice questions (40 minutes) with instant scoring and a full…
The first 5 questions of this test, with the correct answer and explanation.
Q1. The threshold of a neuron is −55 mV. Two stimuli depolarise the membrane to −58 mV and to −40 mV respectively. Which statement is correct?
- A. Only the second stimulus triggers an action potential, of a larger size than normal
- B. Only the second stimulus triggers an action potential, of the usual full size ✓
- C. Neither stimulus triggers an action potential, because both exceed resting level
- D. Both stimuli trigger action potentials, the second one larger than the first
Answer: B. Only the second stimulus triggers an action potential, of the usual full size
Explanation: Action potentials are all-or-none: −58 mV does not reach threshold (−55 mV), while −40 mV does, producing a full-amplitude spike whose size does not depend on stimulus strength.
Q2. Two recording electrodes lie 12 cm apart along a nerve. An impulse reaches the second electrode 1 ms after the first. What is the conduction velocity?
- A. 120 m/s ✓
- B. 12 m/s
- C. 12 cm/s
- D. 1.2 m/s
Answer: A. 120 m/s
Explanation: v = distance ÷ time = 0.12 m ÷ 0.001 s = 120 m/s, typical of a large myelinated axon.
Q3. Tetrodotoxin (from pufferfish) blocks voltage-gated Na⁺ channels. When applied to an axon, what is the expected result?
- A. The resting potential is normal and action potentials are longer
- B. The resting potential is abolished and action potentials fail
- C. The resting potential is normal but action potentials fail ✓
- D. The resting potential is raised and action potentials are faster
Answer: C. The resting potential is normal but action potentials fail
Explanation: The resting potential depends mainly on K⁺ leak and the Na⁺/K⁺ pump, so it is unchanged, but depolarisation cannot develop without Na⁺ entry.
Q4. Extracellular K⁺ concentration in a patient's blood rises sharply (hyperkalaemia). What is the immediate effect on the resting potential of neurons?
- A. It becomes more negative, because the Na⁺ gradient into the cell is smaller
- B. It becomes less negative, because the K⁺ gradient out of the cell is smaller ✓
- C. It becomes more negative, because the K⁺ gradient out of the cell is larger
- D. It becomes less negative, because the Na⁺ gradient into the cell is larger
Answer: B. It becomes less negative, because the K⁺ gradient out of the cell is smaller
Explanation: Resting potential is close to the K⁺ equilibrium potential; raising outside K⁺ reduces the outward K⁺ flow and depolarises the membrane, which can disturb heart and nerve function.
Q5. A neuron with an absolute refractory period of 2 ms is stimulated continuously and strongly. What is the maximum number of action potentials it could fire per second?
- A. 500 ✓
- B. 2,000
- C. 200
- D. 1,000
Answer: A. 500
Explanation: One spike can occur every 2 ms at best, so 1000 ms ÷ 2 ms = 500 per second.
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Q6. Sarin and organophosphate pesticides inhibit acetylcholinesterase. Which result is expected at a neuromuscular junction?
- A. Acetylcholine receptors are blocked, so muscles remain relaxed
- B. Acetylcholine persists, so muscles are overstimulated, then paralysed
- C. Acetylcholine is not released, so muscles are relaxed and then paralysed
- D. Acetylcholine is destroyed faster, so muscles are weak and then spasm
Q7. A patient with Parkinson's disease is given L-DOPA, not dopamine itself. What is the reason?
- A. L-DOPA blocks dopamine breakdown, while dopamine cannot be absorbed
- B. L-DOPA binds receptors more strongly than dopamine does
- C. L-DOPA crosses the blood-brain barrier, while dopamine does not
- D. L-DOPA is a neurotransmitter, while dopamine is only a hormone
Q8. A postsynaptic neuron at −70 mV (threshold −55 mV) receives three excitatory inputs of +5 mV each and one inhibitory input of −8 mV at the same time. What happens?
- A. The potential reaches −78 mV and no impulse is fired
- B. The potential reaches −48 mV and an impulse is fired
- C. The potential reaches −55 mV and an impulse is fired
- D. The potential reaches −63 mV and no impulse is fired
Q9. In an experiment on a spinal animal, the ventral root of the spinal nerve is cut. Which result is expected when the skin supplied by that nerve is pinched?
- A. Sensation is intact, but no reflex movement occurs
- B. Sensation and reflex movement are both lost
- C. Sensation and reflex movement are both intact
- D. Sensation is lost, but the reflex movement occurs
Q10. A patient staggers when walking, misses the nose when asked to touch it with a finger, and has tremor on purposeful movement. Which region of the brain is damaged?
- A. Cerebellum
- B. Corpus callosum
- C. Hypothalamus
- D. Medulla oblongata
Q11. Atropine blocks muscarinic acetylcholine receptors. Which set of effects does it cause?
- A. Constricted pupils, dry mouth and a decreased heart rate
- B. Constricted pupils, watery mouth and an increased heart rate
- C. Dilated pupils, dry mouth and an increased heart rate
- D. Dilated pupils, watery mouth and a decreased heart rate
Q12. In a glucose tolerance test, a patient's blood glucose rises from 5 mM to 12 mM after a glucose drink and is still 11 mM two hours later, whereas a normal person's value returns to about 5 mM. What is the most likely cause?
- A. Insufficient glucagon action, so the liver stores too little glucose
- B. Excess insulin action, so cells take up too much glucose
- C. Excess adrenaline action, so the liver stores too much glucose
- D. Insufficient insulin action, so cells take up too little glucose
Q13. A patient with a swollen neck from a goitre has low blood thyroxine and very high TSH. This pattern suggests
- A. iodine deficiency, with TSH falling by loss of positive feedback
- B. iodine deficiency, with TSH rising by loss of negative feedback
- C. iodine excess, with TSH rising by loss of negative feedback
- D. pituitary failure, with TSH falling by excess negative feedback
Q14. A woman has weight loss, heat intolerance, tachycardia and protruding eyes. Her blood has high thyroxine and a very low TSH. Which explanation fits best?
- A. A pituitary tumour secretes TSH, and feedback raises TSH
- B. Antibodies stimulate the TSH receptor, and feedback suppresses TSH
- C. Antibodies block the TSH receptor, and feedback raises TSH
- D. Iodine deficiency lowers thyroxine, and feedback suppresses TSH
Q15. A patient has taken prednisolone (a glucocorticoid) for a year and stops it suddenly. Why is this dangerous?
- A. Long-term negative feedback raised TSH, so the thyroid is underactive
- B. Long-term positive feedback raised ACTH, so the adrenal cortex is overactive
- C. Long-term negative feedback suppressed ACTH, so the adrenal cortex is underactive
- D. Long-term positive feedback suppressed ACTH, so the adrenal medulla is underactive
Q16. An adult develops enlarged hands, feet and jaw, caused by a pituitary tumour. Which hormone is in excess?
- A. Prolactin, secreted before the growth plates have closed
- B. Growth hormone, secreted before the growth plates have closed
- C. Growth hormone, secreted after the growth plates have closed
- D. Thyroid-stimulating hormone, secreted after the growth plates have closed
Q17. Adrenaline acts within seconds on liver cells, while oestrogen takes hours to cause its effects. What is the main reason?
- A. Adrenaline enters the nucleus directly, while oestrogen uses a surface receptor
- B. Adrenaline uses a surface receptor and second messenger, while oestrogen alters gene expression
- C. Adrenaline is a lipid hormone, while oestrogen is a peptide hormone
- D. Adrenaline alters gene expression, while oestrogen uses a surface receptor and second messenger
Q18. The tip of an oat coleoptile is cut off and an agar block that contains auxin is placed on the right side of the cut surface. The seedling is kept in complete darkness. What will happen?
- A. The coleoptile bends to the left, because the right side elongates more
- B. The coleoptile does not bend, because the light is absent
- C. The coleoptile bends to the right, because the right side elongates more
- D. The coleoptile bends to the left, because the left side elongates more
Q19. A dwarf pea variety grows to normal height after being sprayed with a plant hormone. Which hormone is it?
- A. Abscisic acid
- B. Cytokinin
- C. Gibberellin
- D. Ethylene
Q20. A gardener removes the apical bud of a shrub and finds that many side branches grow. Which explanation is correct?
- A. Gibberellin from the apical bud normally promotes lateral buds
- B. Auxin from the apical bud normally inhibits lateral buds
- C. Ethylene from the apical bud normally inhibits lateral buds
- D. Cytokinin from the apical bud normally inhibits lateral buds
Q21. A child receives a vaccine and the antibody level in the blood is measured. After a booster dose six weeks later, the antibody level rises faster and higher than after the first dose. What is the cause?
- A. Memory B cells formed after the first dose respond rapidly
- B. Plasma cells made after the first dose persist forever
- C. Phagocytes retain antigen and secrete antibodies on re-exposure
- D. Memory T cells make antibodies directly on second exposure
Q22. A child bitten by a venomous snake is given horse-derived antivenom. Which type of immunity does this provide?
- A. Natural active immunity, which gives memory cells
- B. Natural passive immunity, which gives memory cells
- C. Artificial passive immunity, which gives no memory
- D. Artificial active immunity, which gives no memory
Q23. An IgG antibody and an IgM antibody (a pentamer of IgG-like units) are compared. Which pair shows the number of antigen-binding sites on each?
- A. IgG has 4, and IgM has 20
- B. IgG has 2, and IgM has 10
- C. IgG has 1, and IgM has 5
- D. IgG has 2, and IgM has 5
Q24. A child is born without a thymus. Which finding is expected?
- A. Few mature B cells, and a poor graft rejection by the T cells
- B. Few mature T cells, and a poor antibody response to many antigens
- C. Few mature B cells, and a normal cell-mediated killing of virus-infected cells
- D. Few mature T cells, and a normal antibody response to all antigens
Q25. A person stung by a wasp develops itching and hives within minutes. Which sequence describes the main events?
- A. IgE on mast cells binds the antigen, and histamine is released
- B. IgG on mast cells binds the antigen, and complement is released
- C. IgM on mast cells binds the antigen, and histamine is absorbed
- D. IgE on basophils binds the antigen, and perforin is released
Q26. A woman has muscle weakness that worsens with activity, and her blood contains antibodies against nicotinic acetylcholine receptors. Which condition is it?
- A. Multiple sclerosis, an autoimmune disorder
- B. Myasthenia gravis, an autoimmune disorder
- C. Botulism, a bacterial toxin disorder
- D. Parkinson's disease, a degenerative disorder
Q27. After a bacterial skin cut, pus forms at the site within a day. Which cells make up most of the pus?
- A. Dead plasma cells and antibodies
- B. Dead red blood cells and platelets
- C. Dead neutrophils and bacteria
- D. Dead lymphocytes and mast cells
Q28. In producing monoclonal antibodies, spleen B cells from an immunised mouse are fused with myeloma cells. What does each type of cell contribute?
- A. B cell gives antibody specificity, and myeloma cell gives complement
- B. B cell gives antibody specificity, and myeloma cell gives unlimited division
- C. B cell gives antibody memory, and myeloma cell gives cytokines
- D. B cell gives unlimited division, and myeloma cell gives antibody specificity
Q29. A tumour of pancreatic β cells (insulinoma) secretes insulin without control. Which symptom is expected?
- A. Low blood glucose with sweating and confusion
- B. Low blood glucose with excess urine and dehydration
- C. High blood glucose with sweating and confusion
- D. High blood glucose with thirst and weight loss
Q30. A person is suddenly frightened and the adrenal medulla releases adrenaline. Which group of changes follows?
- A. Slower heart rate, narrower airways and less glucose in the blood
- B. Slower heart rate, wider airways and less glucose in the blood
- C. Faster heart rate, narrower airways and more glucose in the blood
- D. Faster heart rate, wider airways and more glucose in the blood