Take the NUMS Biology — Nervous and Chemical Coordination, Immunity (Set 6): 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. An axon is treated with tetrodotoxin, which blocks voltage-gated Na⁺ channels. A stimulus normally strong enough to trigger an impulse now produces only a small local change. What does this show?
- A. The rising phase of the impulse depends on Na⁺ entry ✓
- B. Repolarisation requires these Na⁺ channels to open again
- C. The rising phase of the action potential depends on K⁺ entry
- D. Resting potential depends mainly on Cl⁻ pumps in the membrane
Answer: A. The rising phase of the impulse depends on Na⁺ entry
Explanation: Blocking Na⁺ channels prevents depolarisation from reaching and exceeding threshold, so no action potential can be generated.
Q2. On an action potential recording, the membrane potential briefly falls below the resting level (to about −80 mV) before returning to −70 mV. The usual explanation is:
- A. The sodium–potassium pump has stopped working
- B. voltage-gated K⁺ channels close slowly ✓
- C. Na⁺ channels reopen after repolarisation
- D. Cl⁻ ions enter the axon in large numbers
Answer: B. voltage-gated K⁺ channels close slowly
Explanation: Slow closing of K⁺ channels allows continued K⁺ efflux, causing hyperpolarisation or undershoot.
Q3. A myelinated axon conducts at 60 m/s and an unmyelinated axon of the same length at 2 m/s. For an axon 0.6 m long, how long does the impulse take in the myelinated axon?
- A. 1 ms
- B. 10 ms ✓
- C. 0.3 s
- D. 100 ms
Answer: B. 10 ms
Explanation: Time = distance ÷ speed = 0.6 ÷ 60 = 0.01 s = 10 ms (the unmyelinated one would take 0.3 s).
Q4. How does the brain distinguish a strong stimulus from a weak one if every action potential has the same size?
- A. By the amount of myelin on the sensory neuron
- B. By impulse frequency and the number of neurons activated ✓
- C. By the size of each impulse, which varies with the stimulus
- D. By the speed of the impulse along the axon
Answer: B. By impulse frequency and the number of neurons activated
Explanation: Action potentials obey the all-or-none law; intensity is coded by firing rate and recruitment of more neurons.
Q5. A neuron has an absolute refractory period of 2 ms. What is the theoretical maximum number of impulses per second?
- A. 500 ✓
- B. 2
- C. 1,000
- D. 200
Answer: A. 500
Explanation: Maximum frequency = 1 ÷ 0.002 s = 500 per second.
Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.
Q6. A farm worker exposed to an organophosphate insecticide shows muscle twitching, excessive salivation and slow heart rate. The insecticide acts by:
- A. inhibiting acetylcholinesterase
- B. blocking the release of acetylcholine from nerve endings
- C. destroying the myelin sheath around the motor axons
- D. blocking all of the sodium channels in motor axons
Q7. A neuron has a resting potential of −70 mV and a threshold of −55 mV. Each excitatory input depolarises it by 6 mV and a simultaneous inhibitory input hyperpolarises it by 4 mV. What is the smallest number of simultaneous excitatory inputs needed to fire it, with one inhibitory input present?
Q8. In the spinal cord of an experimental animal, the ventral root of a spinal nerve is cut. What is the expected result?
- A. Loss of movement in the muscles supplied; sensation intact
- B. Loss of both sensation and movement in that area
- C. Loss of the reflex only, with voluntary movement also intact
- D. Loss of sensation from the area, with movement intact
Q9. A patient is given atropine before surgery. Which set of effects is expected?
- A. Dry mouth, constricted pupils and slower heart rate
- B. Excess saliva, constricted pupils and slower heart rate
- C. Dry mouth, dilated pupils and a faster heart rate
- D. Excess saliva, dilated pupils and faster heart rate
Q10. A patient after a stroke has intention tremor, a wide-based staggering gait and difficulty touching his nose, but normal understanding and speech. Which brain region is most likely damaged?
- A. Cerebral cortex of the frontal lobe
- B. Cerebellum
- C. Hypothalamus
- D. Medulla oblongata
Q11. In Parkinson's disease, patients are given L-DOPA rather than dopamine itself. The reason is that L-DOPA:
- A. crosses the blood–brain barrier and is converted to dopamine
- B. is a blocker of dopamine receptors on postsynaptic neurons
- C. stimulates the production of myelin around the axons of neurons
- D. is an inhibitor of acetylcholine reuptake in brain synapses
Q12. A patient has high blood glucose and high blood insulin. Which diagnosis best fits?
- A. Type 1 diabetes with beta-cell destruction
- B. Hypoglycaemia caused by excess insulin
- C. Type 2 diabetes with insulin resistance
- D. Diabetes insipidus with ADH lack
Q13. Blood tests show low T₄ and high TSH. Which interpretation is most appropriate?
- A. The pituitary is failing to secrete enough TSH for the thyroid
- B. The thyroid itself is underactive; the pituitary is responding
- C. The patient has excess iodine intake causing hyperthyroidism
- D. The thyroid is overactive and has suppressed the pituitary's TSH
Q14. A patient on long-term high-dose steroid tablets for asthma stops them suddenly and becomes weak with low blood pressure. The best explanation is that:
- A. the adrenal medulla has stopped making adrenaline altogether
- B. ACTH secretion had been increased by the steroid drug
- C. the steroids had permanently raised aldosterone output
- D. feedback had suppressed ACTH
Q15. A patient has sudden episodes of pounding headache, sweating and palpitations, and has a tumour of the adrenal medulla. The tumour most likely secretes excess:
- A. aldosterone and angiotensin
- B. cortisol and corticosterone
- C. thyroxine and triiodothyronine
- D. adrenaline and noradrenaline
Q16. An excess of growth hormone in a 40-year-old adult, after growth plates have closed, most likely leads to:
- A. cretinism, with mental and growth retardation
- B. gigantism, with greatly increased adult height
- C. pituitary dwarfism, with short stature in adults
- D. acromegaly, with enlarged hands, feet and jaw
Q17. After thyroid surgery, a patient develops muscle spasms and tingling around the mouth. The most likely cause is damage to:
- A. the adrenal glands, causing low blood sodium levels
- B. the pancreas, causing a fall in blood sugar after meals
- C. the pituitary, causing a fall in blood water content
- D. the parathyroid glands, causing low blood calcium
Q18. A peptide hormone is attached to large beads that cannot enter cells. The beads still trigger the usual response in target cells. What does this suggest?
- A. The receptor for this hormone is on the cell surface
- B. The hormone acts only after being digested by the cell
- C. The hormone must enter the nucleus to produce its effect
- D. The receptor is cytoplasmic like that of the steroids
Q19. A coleoptile tip is cut off in the dark and replaced on one half of the cut surface. After some hours the coleoptile bends. Which statement is correct?
- A. It bends towards the side where the tip was placed
- B. It bends away from the tip side, since that side grows faster
- C. It stays straight, since auxin spreads evenly across the cut surface
- D. It does not bend, because the tip is needed for light
Q20. Barley seeds without embryos do not break down their starch. When gibberellic acid is added, α-amylase is produced and starch is digested. This indicates that the embryo normally:
- A. stores amylase that spreads out into the endosperm tissue
- B. releases auxin that makes the endosperm layer waterproof for storage
- C. releases gibberellin that induces enzyme synthesis in the aleurone
- D. produces ethylene that digests the starchy endosperm directly
Q21. In plant tissue culture, a callus placed on medium with a high auxin to cytokinin ratio mostly forms:
- A. roots
- B. shoots
- C. flowers
- D. fruits
Q22. Unripe bananas ripen faster when sealed in a bag with a ripe apple. The hormone responsible is:
- A. ethylene, a gas
- B. cytokinin, a protein
- C. abscisic acid, a vapour
- D. auxin, a liquid
Q23. A person is exposed to a pathogen for the first time and again six months later. Compared with the first exposure, the second antibody response is:
- A. absent, because antibodies from the first exposure remain
- B. slower and lower, as the first exposure used up the cells
- C. faster and higher, because memory cells are present
- D. equal, because plasma cells live permanently in the blood
Q24. A vaccine against tetanus uses an inactivated toxin (toxoid) rather than the killed bacteria. This is effective because:
- A. the toxoid kills the bacterium on direct contact
- B. the bacteria themselves can never be killed by antibodies
- C. the disease is caused by the toxin
- D. the toxin is the only antigen the body can recognise
Q25. A person bitten by a venomous snake is given antivenom prepared in horses. This provides:
- A. immediate, long-lasting active immunity
- B. delayed, short-lived passive immunity
- C. delayed, long-lasting active immunity
- D. immediate, short-lived passive immunity
Q26. Which immunoglobulin class crosses the placenta, and which is the main class found in colostrum?
- A. IgA crosses the placenta; IgG is in colostrum
- B. IgE crosses the placenta; IgM is in colostrum
- C. IgM crosses the placenta; IgE is in colostrum
- D. IgG crosses the placenta; IgA is in colostrum
Q27. Each B cell makes antibodies of only one specificity. This is explained by:
- A. the antigen moulding the shape of each antibody as it is made
- B. B cells swapping antibody genes during activation
- C. all of the B cells having identical antigen receptors
- D. each B cell carrying one receptor type that antigen selects
Q28. A kidney transplant is rejected by the recipient within weeks. Which cell type is mainly responsible?
- A. Cytotoxic T cells recognising foreign MHC
- B. Plasma cells forming IgE against the graft
- C. Red blood cells that attack and destroy the graft
- D. Platelets that clot the blood in the graft vessels
Q29. During an allergic reaction to pollen, histamine release from mast cells causes sneezing and a runny nose. What triggers this release?
- A. Cytotoxic T cells attacking the mast cells in the nasal lining
- B. Antibody IgG from a previous infection binding the mast cells
- C. Complement activation by bacteria
- D. Allergen binding to IgE already attached to mast cells
Q30. Cells infected with a virus secrete interferon. What is its role?
- A. It acts as an antibody against the viral coat proteins
- B. It directly kills free virus particles
- C. It signals nearby cells to make antiviral proteins
- D. It converts virus particles into harmless forms