Take the NUMS Biology — Digestion, Gaseous Exchange and Transport (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. At the end of diastole the left ventricle holds 120 mL of blood, and after contraction 50 mL remain. What is the stroke volume, and what is the ejection fraction (stroke volume ÷ end-diastolic volume)?
- A. 70 mL and about 42%
- B. 50 mL and about 42%
- C. 170 mL and about 58%
- D. 70 mL and about 58% ✓
Answer: D. 70 mL and about 58%
Explanation: Stroke volume = 120 − 50 = 70 mL. Ejection fraction = 70 ÷ 120 ≈ 0.58 = 58%.
Q2. On an ECG the time between two successive R waves is 0.8 s. What is the heart rate?
- A. 100 beats per minute
- B. 75 beats per minute ✓
- C. 60 beats per minute
- D. 80 beats per minute
Answer: B. 75 beats per minute
Explanation: Heart rate = 60 ÷ 0.8 = 75 beats per minute.
Q3. At one moment in the cardiac cycle the pressures are: left atrium 10 mmHg, left ventricle 8 mmHg, aorta 80 mmHg. What is the state of the left heart valves?
- A. The mitral valve is open and the aortic valve is closed ✓
- B. Both valves are closed
- C. Both valves are open
- D. The mitral valve is closed and the aortic valve is open
Answer: A. The mitral valve is open and the aortic valve is closed
Explanation: Atrial pressure exceeds ventricular pressure, so the AV (mitral) valve is open. Aortic pressure exceeds ventricular pressure, so the semilunar valve is shut.
Q4. A person's blood pressure is 120/80 mmHg. Using mean arterial pressure = diastolic + one-third of the pulse pressure, what is the MAP?
- A. 80 mmHg
- B. 100 mmHg
- C. 40 mmHg
- D. 93 mmHg ✓
Answer: D. 93 mmHg
Explanation: Pulse pressure = 120 − 80 = 40; MAP = 80 + 40/3 ≈ 93 mmHg.
Q5. The aorta has a cross-sectional area of 4 cm² with blood flowing at 25 cm/s. The total cross-sectional area of all capillaries is 2500 cm². What is the average capillary blood velocity?
- A. 4.0 cm/s
- B. 0.16 cm/s
- C. 0.4 cm/s
- D. 0.04 cm/s ✓
Answer: D. 0.04 cm/s
Explanation: Flow rate is constant: 4 × 25 = 100 cm³/s, so velocity in capillaries = 100 ÷ 2500 = 0.04 cm/s. Slow flow allows exchange.
Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.
Q6. At the venous end of a capillary, hydrostatic pressure is 15 mmHg and plasma colloid osmotic pressure is 25 mmHg. Taking net filtration pressure as hydrostatic minus osmotic, which statement is correct?
- A. Net pressure is 0 mmHg, so there is no net fluid movement
- B. Net pressure is −40 mmHg, so fluid leaves the capillary
- C. Net pressure is −10 mmHg, so fluid is drawn back in
- D. Net pressure is +10 mmHg, so fluid leaves the capillary
Q7. Children with severe protein deficiency develop swollen abdomens (oedema). Which change in the blood explains this?
- A. Low plasma albumin lowers osmotic pressure, so fluid stays in tissues
- B. High plasma albumin raises blood pressure, so fluid leaves the tissues
- C. Low haemoglobin lowers oxygen supply, so fluid enters the gut
- D. High red cell count thickens blood, so fluid cannot return
Q8. Blood is drawn into a tube containing sodium citrate. It does not clot, but clots when calcium chloride is added. Why?
- A. Citrate converts thrombin into prothrombin, which calcium reverses
- B. Citrate lyses platelets, which calcium chloride reforms
- C. Citrate destroys fibrinogen, which calcium chloride restores
- D. Citrate binds calcium ions, needed in the clotting cascade
Q9. A blood sample of 10 mL is centrifuged and the packed red cells measure 4.5 mL. Another sample from an anaemic patient has 2.5 mL of packed cells per 10 mL. What are the haematocrit (packed cell volume) values of the two samples?
- A. 4.5% for the normal and 2.5% for the anaemic sample
- B. 45% for the normal and 75% for the anaemic sample
- C. 45% for the normal and 25% for the anaemic sample
- D. 55% for the normal and 75% for the anaemic sample
Q10. Blood from an exercising muscle has higher CO₂ and lower pH than at rest. How does this affect the oxygen–haemoglobin dissociation curve, and what is the benefit?
- A. The curve shifts left, so haemoglobin holds more oxygen in the muscle
- B. The curve shifts right, so haemoglobin takes up more oxygen in the muscle
- C. The curve shifts right, so haemoglobin releases more oxygen to the muscle
- D. The curve is unchanged, so oxygen release depends only on volume
Q11. Each gram of fully saturated haemoglobin carries 1.34 mL of oxygen. Blood has 15 g Hb per 100 mL and is 97% saturated. Ignoring dissolved oxygen, what is the oxygen content per 100 mL?
- A. 13.0 mL
- B. 19.5 mL
- C. 20.1 mL
- D. 14.6 mL
Q12. A drug inhibits carbonic anhydrase in red blood cells. What is the most direct effect on CO₂ transport from tissues?
- A. More chloride moves into red cells, so blood pH falls
- B. Less CO₂ is converted to bicarbonate, so blood carries less CO₂ away
- C. More CO₂ is converted to bicarbonate, so blood carries more CO₂ away
- D. Less O₂ is bound to haemoglobin, so blood pH rises
Q13. A stab wound lets air enter the pleural cavity on one side and that lung collapses. What is the cause?
- A. Alveolar surfactant is dissolved by the air, so alveoli collapse
- B. Intrapleural pressure rises to atmospheric, so the lung recoils inwards
- C. Intrapleural pressure falls below atmospheric, so the lung over-expands
- D. The diaphragm paralyses at once, so the lung cannot move
Q14. A person hyperventilates deliberately for a minute and then holds the breath. Why can the breath be held for longer than usual?
- A. Blood O₂ has risen enormously, so tissues store much more oxygen
- B. Blood pH has fallen, so the respiratory centre is switched off
- C. Haemoglobin has become saturated with CO₂, so it needs no oxygen
- D. Blood CO₂ has fallen, so the urge to breathe returns later
Q15. Assume 70% of the CO₂ released by tissues is carried as bicarbonate, 23% as carbaminohaemoglobin and 7% dissolved in plasma. If tissues add 400 mL of CO₂ per minute to the blood, how many mL per minute travel as carbaminohaemoglobin?
- A. 120 mL
- B. 280 mL
- C. 28 mL
- D. 92 mL
Q16. Rate of diffusion across a gas-exchange surface is proportional to surface area × pressure difference ÷ thickness. In a lung disease, the surface area is halved and the barrier thickness doubles. By what factor does the diffusion rate change?
- A. It stays the same
- B. It falls to one quarter
- C. It falls to one half
- D. It falls to one eighth
Q17. In a potometer, the capillary has a radius of 0.5 mm and the air bubble moves 24 mm in 10 minutes. Using π = 3.14, what is the water uptake rate per hour?
- A. 18.8 mm³ per hour
- B. 226 mm³ per hour
- C. 452 mm³ per hour
- D. 113 mm³ per hour
Q18. Tree trunk diameter measured with a sensitive gauge shrinks slightly at midday and recovers at night. This supports which idea?
- A. Pressure flow, where sugar is pushed through the phloem
- B. Capillarity, where narrow xylem vessels raise water by adhesion alone
- C. Cohesion–tension, in which transpiration pulls on xylem water
- D. Root pressure, where roots push water up the xylem at midday
Q19. A ring of bark (including phloem) is removed from a woody stem. After some weeks, what is observed?
- A. The roots below swell, as sugars arrive from the leaves
- B. A swelling forms just above the ring, as sugars accumulate there
- C. The leaves above wilt at once, as the xylem is cut
- D. A swelling forms just below the ring, as water accumulates there
Q20. On a warm, humid night, droplets of water appear at the leaf margins of a grass seedling. This is best explained by:
- A. transpiration pull drawing water out through stomata
- B. active secretion of salts through the cuticle
- C. evaporation of dew from the leaf surface
- D. root pressure forcing water out through hydathodes
Q21. A child lacks enterokinase (enteropeptidase) in the duodenum. Which digestive problem is expected?
- A. Poor fat digestion, as bile salts are not secreted
- B. Poor protein digestion, as trypsinogen is not activated
- C. Poor lactose digestion, as lactase is not secreted
- D. Poor starch digestion, as salivary amylase is inhibited
Q22. After a protein-rich meal, the pyloric antrum releases gastrin. Which statement describes the effect and its regulation?
- A. It stimulates HCl secretion, which is shut off when stomach pH falls
- B. It stimulates bile release, which is shut off when fat is absorbed
- C. It stimulates pepsin inhibition, which is shut off when pH rises
- D. It stimulates bicarbonate release, which is shut off when pH falls
Q23. A drug inhibits the Na⁺/K⁺ pump on the basal side of intestinal epithelial cells. What is the effect on glucose absorption from the lumen?
- A. It rises, because sodium builds up and attracts more glucose
- B. It falls, as the sodium gradient driving the symport is lost
- C. It falls, because glucose cannot be converted to starch
- D. It is unchanged, because glucose uses simple diffusion only
Q24. A person lacks lactase. After drinking milk, which result is most likely?
- A. Fatty stools, as lactose blocks the secretion of bile
- B. Constipation, as lactose cannot be fermented by bacteria
- C. High blood glucose, as lactose is absorbed unchanged
- D. Gas and watery diarrhoea, as lactose is fermented in the colon
Q25. A person eats a carbohydrate-rich meal. Compared with blood in the hepatic vein, how is the glucose level in the hepatic portal vein?
- A. The same, as the liver does not alter the blood sugar level
- B. Higher, as the liver takes up glucose and stores it as glycogen
- C. Higher, as the liver converts glycogen back to blood glucose
- D. Lower, as the liver releases glucose into the portal vein
Q26. Helicobacter pylori survives in the stomach by producing urease. How does this help it?
- A. Pepsin is broken down to ammonia, which neutralises mucus
- B. Ammonia is broken down to urea, which feeds the stomach lining
- C. Urea is broken down to ammonia, which neutralises nearby acid
- D. Urea is broken down to HCl, which kills competing bacteria
Q27. A drug that blocks the vagus nerve's action on the heart (atropine) is given to a resting person. What is the expected change in heart rate?
- A. It rises, because the slowing effect on the SA node is removed
- B. It is unchanged, because the SA node is not nerve controlled
- C. It rises, because the sympathetic nerves are blocked
- D. It falls, because the speeding effect on the SA node is removed
Q28. A premature baby has laboured breathing because the alveoli collapse at the end of each breath. Which substance is deficient?
- A. Lysozyme, which digests bacterial walls in the alveoli
- B. Surfactant, which lowers surface tension in the alveoli
- C. Haemoglobin, which carries oxygen across the alveolar wall
- D. Mucin, which traps dust in the airways
Q29. At sea level, air is 21% oxygen and the total pressure is 760 mmHg. At the summit of a very high mountain the total pressure is 250 mmHg. What is the partial pressure of oxygen there?
- A. About 26 mmHg, because oxygen percentage halves at altitude
- B. About 160 mmHg, because oxygen pressure does not change with altitude
- C. About 10 mmHg, because oxygen falls faster than other gases
- D. About 52 mmHg, because the oxygen fraction is still 21%
Q30. After surgical removal of the stomach, a patient develops anaemia with large red cells after some years. Which loss explains this?
- A. Loss of mucus, needed for absorption of folic acid in the ileum
- B. Loss of intrinsic factor, needed for absorption of vitamin B₁₂
- C. Loss of pepsin, needed for absorption of vitamin C
- D. Loss of gastrin, needed for absorption of iron in the colon