Take the NUMS Biology — Homeostasis, Support and Movement (Set 6): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…
The first 5 questions of this test, with the correct answer and explanation.
Q1. A substance X is freely filtered, neither secreted nor reabsorbed. Its plasma concentration is 0.3 mg/mL, urine concentration 30 mg/mL and urine flow 1.2 mL/min. What is the glomerular filtration rate?
- A. 36 mL per minute
- B. 120 mL per minute ✓
- C. 12 mL per minute
- D. 1,200 mL per minute
Answer: B. 120 mL per minute
Explanation: GFR = U × V ÷ P = 30 × 1.2 ÷ 0.3 = 120 mL per minute.
Q2. In a glomerulus, blood hydrostatic pressure is 60 mmHg, capsular hydrostatic pressure 15 mmHg and blood oncotic pressure 25 mmHg. What is the net filtration pressure?
- A. 20 mmHg ✓
- B. 70 mmHg
- C. 45 mmHg
- D. 10 mmHg
Answer: A. 20 mmHg
Explanation: NFP = 60 − (15 + 25) = 20 mmHg.
Q3. A person forms 180 litres of filtrate a day and excretes 1.5 litres of urine. Approximately what percentage of the filtrate is reabsorbed?
- A. 90%
- B. 85%
- C. 95%
- D. 99% ✓
Answer: D. 99%
Explanation: (180 − 1.5)/180 × 100 ≈ 99.2%.
Q4. A diabetic patient's blood glucose is 15 mmol/L, above the renal threshold, and he passes large volumes of urine containing glucose. Which explanation is correct?
- A. ADH secretion is raised, so more water is reabsorbed in the collecting duct
- B. Glucose is secreted into the loop of Henle, so the urine is diluted by it
- C. Glomerular filtration of glucose has stopped, so it spills over into urine
- D. Tubular carriers are saturated, so leftover glucose holds water in urine ✓
Answer: D. Tubular carriers are saturated, so leftover glucose holds water in urine
Explanation: Tubular carriers are saturated, so glucose remains in the filtrate and its osmotic effect reduces water reabsorption.
Q5. A patient passes 15 litres of dilute urine a day. ADH levels are high in blood tests, and giving desmopressin (an ADH analogue) does not reduce urine volume. Which diagnosis is most likely?
- A. Central diabetes insipidus, with failure of ADH release from the pituitary
- B. Addison's disease, with loss of aldosterone from the adrenal cortex
- C. Diabetes mellitus, with raised blood glucose and glucose in urine
- D. Nephrogenic diabetes insipidus, with collecting ducts unresponsive to ADH ✓
Answer: D. Nephrogenic diabetes insipidus, with collecting ducts unresponsive to ADH
Explanation: ADH is plentiful and an analogue fails, so the target (collecting duct) is unresponsive.
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Q6. Furosemide, a loop diuretic, blocks Na⁺ and Cl⁻ transport out of the thick ascending limb. Why does it cause copious urine?
- A. The medullary gradient is lost
- B. The glomerular filtration rate falls to zero at once
- C. The descending limb stops being permeable to water altogether
- D. The proximal tubule begins secreting very large amounts of water
Q7. In Addison's disease the adrenal cortex fails. Which combination in the blood is expected?
- A. High Na⁺, low K⁺ and high blood pressure
- B. High Na⁺, high K⁺ and low blood pressure
- C. Low Na⁺, low K⁺ and high blood pressure
- D. Low Na⁺, high K⁺ and low blood pressure
Q8. Desert rodents can produce very concentrated urine. Compared with a freshwater mammal of similar size, their nephrons typically have:
- A. wider glomeruli that filter more water per minute
- B. no loops of Henle, relying on the collecting duct alone
- C. shorter loops of Henle with a much steeper medullary gradient
- D. longer loops of Henle, giving a steeper medullary gradient
Q9. Haemodialysis fluid contains glucose at the same concentration as normal plasma, but no urea. Why is glucose included?
- A. So that glucose diffuses from the blood into the dialysis fluid
- B. So that urea is converted to glucose
- C. So that the blood osmotic pressure is raised
- D. So that glucose does not diffuse out of the patient's blood
Q10. A patient's urine contains protein but no glucose. Which site of damage is most likely?
- A. The collecting duct, which fails to reabsorb water
- B. The proximal tubule, in which glucose cannot be reabsorbed
- C. The glomerular filter, which is leaking plasma proteins
- D. The loop of Henle, which cannot build a gradient
Q11. A person with a viral infection feels cold and shivers although the body temperature is 37.8 °C, and later feels hot and sweats as it falls. Which statement explains this?
- A. The sweat glands are damaged directly by the virus itself
- B. The body temperature is lower than the normal temperature
- C. Pyrogens raised the hypothalamic set point
- D. The skin thermoreceptors have stopped working during the infection
Q12. On a hot, very humid day, sweating cools the body less effectively than on a hot, dry day. The reason is that:
- A. sweat contains much more salt in humid conditions
- B. sweat evaporates slowly when the air is nearly saturated
- C. sweat glands produce no sweat at all in very humid air
- D. blood flow to the skin always falls sharply when the air is humid
Q13. A shrew has a much higher metabolic rate per gram than an elephant. This is mainly because the shrew:
- A. has a smaller number of mitochondria per gram
- B. has a thicker layer of fat than an elephant
- C. has a lower body temperature than an elephant
- D. has a greater surface area to volume ratio
Q14. In severe liver failure, patients may become confused. The most likely cause is that:
- A. ammonia is not converted to urea and builds up in blood
- B. bile pigments are not produced at all
- C. glycogen is converted to glucose too rapidly
- D. urea is produced in excess and is directly toxic to the brain
Q15. A patient has yellow skin, dark urine and pale stools. Which type of jaundice does this most suggest?
- A. Obstructive jaundice, with conjugated bilirubin blocked from the gut
- B. Haemolytic jaundice, with excess unconjugated bilirubin from red cell breakdown
- C. Physiological jaundice of the newborn, which fades without treatment
- D. Jaundice caused by a lack of vitamin K in the diet
Q16. A child in a poor, dark housing area has bowed legs and soft bones. The most likely deficiency is of:
- A. vitamin A, needed for making rhodopsin in rods
- B. vitamin K, needed for blood clotting factors
- C. vitamin D, needed for calcium uptake
- D. vitamin C, needed for making collagen fibres
Q17. A torn cartilage in the knee heals very slowly compared with a broken bone. The best explanation is that cartilage:
- A. is made of dead cells that contain no matrix, so it cannot heal
- B. has no cells at all, so it cannot repair itself or grow
- C. has no blood vessels, so nutrients arrive only by diffusion
- D. is repaired only by osteoclasts, which are slow to arrive
Q18. A footballer twists his ankle and a band connecting two bones is torn, but the muscle attachments are intact. What has been injured?
- A. A tendon, which joins muscle to cartilage
- B. A ligament, which joins muscle to bone
- C. A tendon, which joins bone to bone
- D. A ligament, which joins bone to bone
Q19. A relaxed muscle fibre is 2.4 cm long and has 10,000 sarcomeres in series, each 2.4 µm long. On maximal contraction each sarcomere shortens to 1.8 µm. By how much does the fibre shorten?
- A. 1.8 cm
- B. 0.6 cm
- C. 6 cm
- D. 0.06 cm
Q20. When a skeletal muscle fibre contracts, which band remains the same length?
- A. The distance between Z lines
- B. The A band
- C. The I band
- D. The H zone
Q21. Muscles become stiff soon after death (rigor mortis). The molecular reason is that:
- A. calcium ions leave the sarcoplasmic reticulum permanently
- B. no ATP is available to detach myosin heads from actin
- C. actin filaments become shorter
- D. troponin is converted into tropomyosin
Q22. Botulinum toxin blocks acetylcholine release at neuromuscular junctions. What is the effect on the muscle?
- A. Cramp, because acetylcholinesterase is blocked
- B. Spastic paralysis, because muscle contracts continuously
- C. Increased muscle tone, since calcium is retained
- D. Flaccid paralysis, because the end-plate is not depolarised
Q23. In myasthenia gravis, muscles weaken as the day goes on, and antibodies are found against acetylcholine receptors. Which explanation is correct?
- A. Acetylcholine is no longer made in the motor neurons
- B. Fewer working receptors on the fibres
- C. The muscle fibres have lost all of their sarcomeres
- D. Sodium channels in the motor axons stay permanently open
Q24. A marathon runner's leg muscle is compared with a weightlifter's. Which feature is more typical of the runner's muscle fibres?
- A. Thicker fibres that fatigue fast but contract fast
- B. More glycogen granules and fewer capillaries, giving a white colour
- C. Fewer mitochondria and less myoglobin, giving a pale colour
- D. More mitochondria and myoglobin, giving a red colour
Q25. During a 100 m sprint, the first few seconds of muscle contraction are supported mainly by:
- A. amino acid breakdown in the liver
- B. glycogen stored in the brain
- C. aerobic oxidation of fatty acids
- D. stored ATP and creatine phosphate
Q26. A thin section of a hollow organ shows long, spindle-shaped cells, each with one central nucleus and no striations. The tissue is most likely:
- A. cardiac muscle
- B. skeletal muscle
- C. smooth muscle
- D. dense connective tissue
Q27. Which plant tissue is dead at maturity and gives a stem rigid support because of heavily lignified walls?
- A. Parenchyma
- B. Sclerenchyma
- C. Collenchyma
- D. Phloem sieve tubes
Q28. A salmon moves from the sea into fresh water to breed. Which change in its osmoregulation is expected?
- A. It drinks large volumes of seawater and excretes excess salt through the gills
- B. It produces large volumes of dilute urine and absorbs salts through gills
- C. It produces concentrated urine and secretes salts through the gills
- D. It stops producing urine altogether and retains all of its salts
Q29. After the menopause, many women develop osteoporosis. The most likely reason is that:
- A. calcium is stored in excess in bone
- B. falling oestrogen lets bone resorption exceed formation
- C. vitamin D can no longer be made in the skin from sunlight at all
- D. rising oestrogen increases osteoclast activity
Q30. Birds and reptiles excrete uric acid instead of urea. The main advantage of this to the embryo in a shelled egg is that uric acid:
- A. is converted into protein before hatching
- B. is less toxic than ammonia but uses more water
- C. is more soluble than urea, so it dissolves in the egg white fluid
- D. non-toxic and insoluble, so it is stored with little water