Take the NUMS Biology — Nervous and Chemical Coordination, Immunity (Set 4): 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. A motor nerve is stimulated at two points 30 cm apart along its length. The muscle responses differ in latency by 3 ms. What is the conduction velocity?
- A. 1 m/s
- B. 10 m/s
- C. 1000 m/s
- D. 100 m/s ✓
Answer: D. 100 m/s
Explanation: Velocity = distance ÷ time difference = 0.30 m ÷ 0.003 s = 100 m/s, typical of a large myelinated axon.
Q2. A neuron needs 15 mV of depolarisation to reach threshold. Each excitatory input gives +6 mV and each inhibitory input −5 mV. Three excitatory inputs and one inhibitory input arrive simultaneously. What happens?
- A. Net +18 mV, so threshold is exceeded and an action potential fires
- B. Net +13 mV, so threshold is not reached and no action potential fires ✓
- C. Net +11 mV, so threshold is not reached and the neuron stays at rest
- D. Net +13 mV, which is above threshold, so an action potential fires
Answer: B. Net +13 mV, so threshold is not reached and no action potential fires
Explanation: Summation: 3 × 6 − 5 = +13 mV, below the 15 mV threshold. Without the inhibitory input, 18 mV would exceed it.
Q3. Tetrodotoxin blocks voltage-gated Na⁺ channels. When applied to an axon and the axon is stimulated, what is observed?
- A. The action potential lasts longer
- B. Hyperpolarisation is produced, but the action potential is unchanged
- C. A larger action potential is produced
- D. No action potential is generated, since depolarisation cannot reach the peak ✓
Answer: D. No action potential is generated, since depolarisation cannot reach the peak
Explanation: The rising phase depends on Na⁺ influx through voltage-gated channels; blocking them prevents regenerative depolarisation.
Q4. In multiple sclerosis, myelin sheaths are damaged by autoimmune attack. Which consequence best matches the cause?
- A. Increased number of nodes of Ranvier
- B. Faster conduction, due to exposed axon
- C. Failure of neurotransmitter synthesis in the cell body
- D. Slower or failed impulse conduction, as saltatory conduction is lost ✓
Answer: D. Slower or failed impulse conduction, as saltatory conduction is lost
Explanation: Myelin insulates the axon so that impulses jump between nodes; demyelination slows conduction and can block it.
Q5. An organophosphate insecticide inhibits acetylcholinesterase at neuromuscular junctions. What is the immediate result?
- A. Acetylcholine is not released from the presynaptic terminal, so the muscle becomes paralysed
- B. Muscle relaxes completely because acetylcholine is broken down too quickly in the cleft
- C. Acetylcholine receptors are destroyed on the muscle membrane, so contraction cannot occur
- D. Acetylcholine persists in the cleft, causing continuous muscle stimulation and spasm ✓
Answer: D. Acetylcholine persists in the cleft, causing continuous muscle stimulation and spasm
Explanation: Without the enzyme, ACh is not broken down, so the postsynaptic membrane stays depolarised, causing twitching and then paralysis.
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Q6. In myasthenia gravis, muscles weaken with repeated use. Antibodies against which target explain this?
- A. Acetylcholinesterase enzyme in the synaptic cleft
- B. Acetylcholine receptors at the neuromuscular junction
- C. Voltage-gated K⁺ channels in presynaptic nerve terminals
- D. Myosin heads in the sarcomeres of the muscle fibres
Q7. A patient treated with atropine, which blocks muscarinic acetylcholine receptors, will show
- A. increased heart rate, dilated pupils and dry mouth
- B. decreased blood pressure from vasodilation only
- C. decreased heart rate and constricted pupils
- D. increased salivation and slow digestion
Q8. A person walks into a dark room and, as their eyes adjust, becomes able to see dim objects. Which receptor property mainly explains vision at low light?
- A. Rods with rhodopsin, which are very sensitive to dim light
- B. Cones, because they give high acuity in the dark
- C. Optic nerve fibres changing their velocity
- D. Cones with iodopsin, which are most sensitive to dim light
Q9. After a stroke a patient walks with clumsy, uncoordinated movements and an unsteady gait, but understands speech and has normal sensation. Which brain region is most likely damaged?
- A. Hypothalamus
- B. Broca's area
- C. Cerebellum
- D. Medulla oblongata
Q10. A patient has lost the ability to form new long-term memories but old memories and skills are preserved. Which structure is most likely damaged?
- A. Hippocampus
- B. Thalamus
- C. Cerebellum
- D. Pons
Q11. In an experiment on a spinal reflex, the dorsal root of a spinal nerve is cut. After this, a pin-prick on the skin supplied by that nerve causes
- A. no reflex and no sensation, since sensory information cannot enter the cord
- B. normal reflex and sensation, because the motor neuron in the ventral root is intact
- C. sensation but no reflex, since sensory fibres still reach the brain through the ventral root
- D. a reflex but no sensation, because the motor fibres in the ventral root are intact
Q12. In the knee-jerk reflex, how many synapses lie in the reflex arc within the spinal cord?
- A. Three, with two relay neurons
- B. Two, with one relay neuron
- C. One, between the sensory neuron and the motor neuron
- D. None; the sensory neuron is the motor neuron
Q13. A patient has high blood glucose and also high plasma insulin. The most likely explanation is
- A. the β-cells have been destroyed by autoimmunity
- B. the α-cells secrete too little glucagon
- C. the kidneys fail to filter glucose
- D. target cells respond poorly to insulin (insulin resistance)
Q14. A patient has low thyroxine and high TSH. Which diagnosis fits best?
- A. Hyperthyroidism due to a thyroid tumour secreting excess thyroxine
- B. Primary hypothyroidism, a failure of the thyroid gland itself
- C. Hyperthyroidism due to excess TSH secreted by a pituitary tumour
- D. Secondary hypothyroidism, a failure of the pituitary gland
Q15. In a region with iodine-deficient soil, people often develop an enlarged thyroid (goitre). Which sequence explains this?
- A. High thyroxine → raised TSH → thyroid enlargement from overstimulation
- B. Low thyroxine → raised negative feedback on the pituitary → low TSH → no enlargement
- C. Low thyroxine → reduced negative feedback → raised TSH → thyroid enlargement
- D. Low TSH → reduced stimulation → thyroid atrophy and lower thyroxine output
Q16. After removal of the thyroid gland, a patient develops muscle spasms and tetany because the parathyroid glands were accidentally removed. What is the cause of tetany?
- A. High plasma potassium, due to lack of ADH
- B. Low plasma sodium, due to lack of aldosterone
- C. Low plasma calcium, due to lack of parathyroid hormone
- D. High plasma calcium, due to lack of calcitonin
Q17. A patient takes high-dose oral cortisol-like steroids for months. What happens to the patient's own adrenal cortex?
- A. It is unchanged, because steroids do not affect the pituitary
- B. It enlarges, because ACTH rises
- C. It makes more aldosterone only
- D. It shrinks, because ACTH secretion is suppressed by negative feedback
Q18. After surgical removal of the anterior pituitary, which hormone is still released normally?
- A. ACTH
- B. Oxytocin
- C. TSH
- D. Growth hormone
Q19. A tumour of the pituitary secretes large amounts of ADH. Which blood and urine changes are expected?
- A. High plasma sodium and large urine volume because collecting ducts become impermeable to water
- B. Concentrated plasma and large volumes of dilute urine because water reabsorption is blocked
- C. Normal plasma volume and glucose in the urine because the kidneys cannot reabsorb it
- D. Dilute plasma with low sodium concentration and small volumes of concentrated urine
Q20. Adrenaline acts on liver cells by binding to a membrane receptor and raising cAMP. Why is a second messenger needed?
- A. Adrenaline cannot cross the membrane, so cAMP relays the signal and amplifies it inside
- B. cAMP is the hormone that is secreted into the blood and carries the signal to the liver
- C. cAMP binds directly to DNA to switch on genes and so stops glycogenolysis in the liver
- D. Adrenaline is a steroid that must enter the nucleus, so cAMP is needed to carry it there
Q21. A coleoptile tip is covered with an opaque cap and illuminated from one side. What is observed after a day, and why?
- A. It grows straight, because the tip cannot sense the light to redistribute auxin
- B. It bends away from the light
- C. It stops growing because auxin is blocked from the base
- D. It bends toward the light
Q22. The terminal bud of a plant is removed and lateral buds start to grow. Applying auxin paste to the cut stump prevents this. What does this show?
- A. Cytokinin is made in the apical bud and inhibits lateral buds there
- B. Auxin promotes the growth of lateral buds directly once it reaches them
- C. Auxin from the apical bud suppresses lateral buds (apical dominance)
- D. Gibberellin from the stump prevents lateral buds from growing
Q23. Unripe bananas are stored in a closed room with a few ripe ones and ripen faster than those stored separately. Which hormone is responsible?
- A. Auxin
- B. Abscisic acid
- C. Gibberellin
- D. Ethylene
Q24. In a drought, a plant's leaf cells produce a hormone that triggers K⁺ loss from guard cells. What is the result?
- A. Stomata close to reduce water loss
- B. Seed dormancy is broken
- C. Cell elongation increases
- D. Stomata open wider to cool the leaf
Q25. A person is infected with a virus twice, months apart. How does the antibody response to the second exposure differ from the first?
- A. It is faster and larger, because memory B cells were formed
- B. It is faster but smaller, because antibodies are diluted
- C. It is slower, because plasma cells are depleted
- D. It is the same, because antibodies are not stored
Q26. Immunoglobulin G has two identical antigen-binding sites. How many antigen molecules can be bound at most by 6 IgG molecules if each antigen has only one epitope?
Q27. A person is bitten by a dog and is given ready-made rabies antibodies immediately. This is
- A. natural passive immunity
- B. artificial active immunity
- C. natural active immunity
- D. artificial passive immunity
Q28. A child lacking a thymus from birth is most likely to suffer from
- A. loss of innate immunity only, since phagocytes and complement depend on the thymus
- B. absence of red blood cells, because the thymus is the main site of erythropoiesis
- C. defective cell-mediated immunity and poor antibody responses requiring T helper cells
- D. normal immunity, because B cells mature in the thymus and make antibodies without help
Q29. A virus-infected body cell is destroyed by a lymphocyte that recognises viral peptides displayed on the infected cell's surface. Which pairing is correct?
- A. B cell recognising peptide on MHC class II to release perforin
- B. Cytotoxic T cell (CD8⁺) recognising peptide on MHC class I
- C. Plasma cell recognising peptide on MHC class I
- D. Helper T cell recognising peptide on MHC class I
Q30. A person stung by a bee develops swelling, hives and a sharp fall in blood pressure within minutes. Which mechanism and treatment fit best?
- A. IgG-mediated killing of cells by complement; antibiotics are the emergency treatment
- B. IgE-mediated mast cell release of histamine; adrenaline is the emergency treatment
- C. Complement deficiency in the plasma; a plasma transfusion is the emergency treatment
- D. Delayed T-cell response to the venom; a vaccine is required as emergency treatment