Take the NUMS Biology — Nervous and Chemical Coordination, Immunity (Set 7): 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 giant axon is bathed in a solution with the sodium concentration reduced to one-third of normal. Compared with normal, how will a single action potential change?
- A. Its peak is smaller because less K⁺ enters during repolarisation
- B. Its peak is the same because the resting potential is unchanged
- C. Its peak is larger because more K⁺ leaves during depolarisation
- D. Its peak is smaller because less Na⁺ enters during depolarisation ✓
Answer: D. Its peak is smaller because less Na⁺ enters during depolarisation
Explanation: The rising phase is caused by Na⁺ inflow down its gradient. A smaller external Na⁺ concentration reduces the gradient and the size of the spike.
Q2. Tetrodotoxin from puffer fish blocks voltage-gated sodium channels. After it is applied to a nerve axon, what happens when the axon is stimulated?
- A. The resting potential collapses to zero before stimulation
- B. The action potential is faster, because the Na⁺ pump is blocked
- C. No action potential forms, although the resting potential remains ✓
- D. The action potential is longer, because the K⁺ channels stay shut
Answer: C. No action potential forms, although the resting potential remains
Explanation: Without voltage-gated Na⁺ channels the membrane cannot depolarise to produce a spike, while resting potential (K⁺ leak and the pump) remains.
Q3. An impulse travels along a myelinated sensory axon at 100 m/s from the foot to the spinal cord, a distance of 1.2 m. How long does conduction take?
- A. 12 ms ✓
- B. 1.2 ms
- C. 83 ms
- D. 120 ms
Answer: A. 12 ms
Explanation: Time = distance ÷ speed = 1.2 ÷ 100 = 0.012 s = 12 ms.
Q4. A neuron has an absolute refractory period of 2 ms. What is the maximum frequency at which it can fire?
- A. 200 impulses per second
- B. 50 impulses per second
- C. 500 impulses per second ✓
- D. 2000 impulses per second
Answer: C. 500 impulses per second
Explanation: The maximum rate is 1 ÷ 0.002 s = 500 impulses per second.
Q5. As the strength of a stimulus to a single neuron is increased well above threshold, what change is recorded?
- A. The impulses become larger but their frequency does not change
- B. The impulses become larger and more frequent together
- C. The impulses become more frequent, with the same size ✓
- D. The impulses become slower but their size does not change
Answer: C. The impulses become more frequent, with the same size
Explanation: Action potentials are all-or-none. Stimulus intensity is coded by firing frequency and the number of neurons recruited.
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Q6. Botulinum toxin prevents the release of acetylcholine at the neuromuscular junction. What is the result?
- A. Loss of sensation, because sensory neurons stop firing
- B. Fast heartbeat, because adrenaline is released instead
- C. Spastic paralysis, because muscle fibres receive continuous stimulus
- D. Flaccid paralysis, because muscle fibres receive no stimulus
Q7. An organophosphate insecticide inhibits acetylcholinesterase. In an exposed person which effect is expected at cholinergic synapses?
- A. Acetylcholine is reabsorbed faster, so the synapse is blocked
- B. Acetylcholine is not released at all, so the membrane is at rest
- C. Acetylcholine is destroyed rapidly, so the stimulation is lost
- D. Acetylcholine stays in the cleft, so the stimulation is continuous
Q8. A postsynaptic neuron rests at −70 mV and fires at −55 mV. Each excitatory input causes a depolarisation of +5 mV and each inhibitory input −5 mV, all arriving at the same moment. How many excitatory inputs are needed to reach threshold while one inhibitory input is active?
Q9. In a frog, the dorsal root of a spinal nerve is cut, and then the skin of the foot is pinched. What is expected?
- A. Withdrawal without feeling, because the interneuron is cut
- B. No withdrawal, because the motor output cannot leave the spinal cord
- C. Withdrawal as normal, because the brain controls the reflex
- D. No withdrawal, as sensory input cannot enter the spinal cord
Q10. A patient has no paralysis but cannot touch the nose accurately with the finger and shows unsteady, shaky movements when attempting precise tasks. Which brain region is damaged?
- A. The cerebellum
- B. The medulla oblongata
- C. The thalamus
- D. The hypothalamus
Q11. Propranolol, a drug that blocks β-adrenergic receptors, is given to a person who then runs up several flights of stairs. Compared with the same exercise without the drug, how will the heart rate response be?
- A. Larger rise, because adrenaline binds the receptors more strongly
- B. Larger rise, because the vagus nerve is more active than usual
- C. No rise at all, because the SA node is not nerve-controlled
- D. Smaller rise, because noradrenaline and adrenaline cannot act through β receptors on the SA node
Q12. A person tries to see a very faint star at night. The star disappears when looked at directly but is seen when gazing slightly to one side. Why?
- A. The lens focuses dim light only on the periphery of the retina
- B. The fovea has only rods, while cones outside it are more sensitive in dim light
- C. The blind spot is sensitive to dim light but not to bright light
- D. The fovea has only cones, while rods outside it are more sensitive in dim light
Q13. When a person shifts from looking at a distant mountain to reading a book, what happens in the eye?
- A. The ciliary muscles relax, the suspensory ligaments slacken and the lens becomes more convex
- B. The ciliary muscles relax, the suspensory ligaments tighten and the lens becomes flatter
- C. The ciliary muscles contract, the suspensory ligaments slacken and the lens becomes more convex
- D. The ciliary muscles contract, the suspensory ligaments tighten and the lens becomes flatter
Q14. Dopamine cannot cross the blood–brain barrier but L-DOPA can. Why is L-DOPA given to patients with Parkinson's disease?
- A. It is converted to acetylcholine in the brain, replacing the lost transmitter
- B. It destroys the damaged neurons, removing the abnormal signals
- C. It blocks dopamine receptors, reducing excess transmitter
- D. It is converted to dopamine in the brain, replacing the lost transmitter
Q15. A peptide hormone is attached to large beads that cannot enter cells. Even so, it triggers a response in target cells. What does this suggest?
- A. The hormone acts on a receptor inside the nucleus
- B. The hormone acts only after it enters by endocytosis
- C. The hormone must be broken down before it acts
- D. The hormone acts on a receptor on the cell surface
Q16. A virus-infected cell secretes interferon. What is the main effect of interferon on nearby uninfected cells?
- A. They stop all protein synthesis and are digested by lysosomes
- B. They are killed by perforin before the virus can enter them
- C. They display viral antigens that are bound by free interferon
- D. They make antiviral proteins that interfere with viral replication
Q17. A patient has low blood thyroxine (T₄) and a high level of TSH. What is the most likely site of the problem?
- A. The hypothalamus, which does not make enough TRH
- B. The anterior pituitary, which does not make enough TSH
- C. The thyroid gland, which fails to respond to TSH
- D. The adrenal cortex, which does not make enough cortisol
Q18. An adult has enlarged hands, feet and jaw, and a tumour is found in the anterior pituitary. Which hormone is in excess?
- A. Thyroid-stimulating hormone
- B. Oxytocin
- C. Antidiuretic hormone
- D. Growth hormone
Q19. During thyroid surgery, the parathyroid glands are accidentally removed. Which signs may follow?
- A. Low blood glucose and tremor of hands
- B. Low blood calcium and muscle spasms (tetany)
- C. High blood calcium and weak, flabby muscles
- D. High blood sodium and retention of fluid
Q20. A decapitated oat coleoptile is given an agar block containing auxin placed on its left side only, in the dark. What happens?
- A. It bends to the right, because the right side elongates more
- B. It bends to the right, because the left side elongates more
- C. It bends to the left, because the left side elongates less
- D. It grows straight up, because the tip is absent
Q21. Barley seeds without an embryo do not mobilise starch in the endosperm unless gibberellin is added. What does this suggest?
- A. Gibberellin makes starch from sugars in the endosperm
- B. Gibberellin acts only on the roots of the embryo
- C. Gibberellin destroys the aleurone layer in the seed
- D. Gibberellin induces the aleurone layer to make amylase
Q22. A single overripe banana placed in a bag with green bananas makes them all ripen faster. Which plant hormone is responsible?
- A. Gibberellin, which is released from roots
- B. Auxin, which is transported in phloem
- C. Ethylene, which is a gas
- D. Abscisic acid, which is made in the leaf
Q23. A child receives a vaccine and the blood antibody level is measured. After a booster dose weeks later, the antibody level rises sooner and higher. This is explained by:
- A. phagocytes that remember the shape of the antigen
- B. antibodies that are retained from the first dose
- C. memory B cells that respond rapidly to the antigen
- D. plasma cells that survive and live for many years
Q24. An Rh-negative woman delivers her first Rh-positive baby and is given anti-D antibodies within 72 hours. Why does this protect her next Rh-positive baby?
- A. The anti-D stimulates her plasma cells to make more anti-D for later pregnancies
- B. The anti-D blocks the placenta, so no maternal antibody can cross to the fetus
- C. The anti-D destroys fetal Rh-positive cells in her blood before she makes memory cells
- D. The anti-D makes her blood Rh-positive, so a later baby is no longer foreign
Q25. Seasonal influenza vaccines are updated almost every year, whereas the measles vaccine has stayed essentially the same for decades. Which explanation is best?
- A. Influenza viruses make bacterial toxins whose type changes every year
- B. Measles viruses infect only memory cells, because they cannot be seen by antibodies
- C. Measles vaccine contains live bacteria, because these never mutate at all
- D. Influenza surface proteins mutate often, because old antibodies then fit them poorly
Q26. A newborn mouse has its thymus removed. As an adult it will be unable to:
- A. mount cell-mediated responses, as T cells do not mature
- B. digest food, as intestinal enzymes are not made
- C. clot blood, as platelets do not form
- D. make red blood cells, as stem cells are lost
Q27. A person develops hives within minutes of eating peanuts. Which sequence describes what happens?
- A. IgG on red cells binds the allergen and haemoglobin is released
- B. IgE on mast cells binds the allergen and histamine is released
- C. IgM on neutrophils binds the allergen and histamine is destroyed
- D. IgA on T cells binds the allergen and perforin is released
Q28. In myasthenia gravis, patients develop muscle weakness that worsens with activity. Antibodies are found against acetylcholine receptors. This is an example of:
- A. an autoimmune disorder at the neuromuscular junction
- B. an inherited loss of calcium channels in muscle
- C. a viral infection of the motor neurons
- D. an allergy caused by IgE in skeletal muscle
Q29. The connection between the hypothalamus and the posterior pituitary (the pituitary stalk) is cut surgically. Which hormone supply is lost?
- A. ADH and oxytocin, made in the hypothalamus and released by the posterior lobe
- B. Growth hormone and prolactin, as they are made in the hypothalamus
- C. Oxytocin and growth hormone, as both are stored in the posterior lobe
- D. TSH and ACTH, as they are made in the hypothalamus
Q30. A kidney transplant between identical twins does not need immunosuppressant drugs. Why?
- A. The donor and recipient have the same MHC antigens
- B. The donor kidney produces antibodies against rejection
- C. The kidney has no antigens at all on its cells
- D. The recipient has no T cells to react