StudyStore

Free MCAT-style practice, 3B

MCAT Respiratory System Practice Questions: Lung Volumes and Ventilation

By StudyStore · Published 2026-11-04 · 8 original questions · about 12 min

Eight free MCAT-style practice questions on lung volumes and capacities, inspiration and expiration mechanics, the diaphragm, surfactant and control of breathing, with explanations.

Email me free MCAT notes, practice sets and new packs from StudyStore. Double opt-in, unsubscribe in one click. Privacy

Quick concept primer

Humans use negative pressure breathing. When the diaphragm contracts and flattens and the external intercostals raise the ribs, thoracic volume increases, intrapleural and alveolar pressure fall below atmospheric pressure, and air flows in. Quiet expiration is passive elastic recoil; forced expiration uses the abdominal muscles and internal intercostals. Boyle's law (P1V1 = P2V2) explains the pressure changes.

Lung volumes: tidal volume (TV) is the air of a normal breath, inspiratory reserve volume (IRV) and expiratory reserve volume (ERV) are the extra air that can be inhaled or exhaled, and residual volume (RV) stays in the lungs after maximal exhalation. Vital capacity = TV + IRV + ERV, and total lung capacity = vital capacity + RV. Surfactant from type II pneumocytes lowers alveolar surface tension. Breathing is driven mainly by CO2 (through H+ in cerebrospinal fluid) sensed by medullary chemoreceptors; carotid and aortic bodies respond to low O2.

8 practice questions

Try each question before opening the explanation. Click "Show answer and explanation" to check yourself. All questions are original and written for study practice.

Question 1

During inspiration, which change occurs?

  1. The diaphragm relaxes and moves upward
  2. The diaphragm contracts and thoracic volume increases
  3. Intrapleural pressure rises above atmospheric pressure
  4. Alveolar pressure rises above atmospheric pressure
Show answer and explanation

Answer: B. The diaphragm contracts and thoracic volume increases

Contraction of the diaphragm flattens it and enlarges the thoracic cavity. By Boyle's law, pressure in the lungs falls below atmospheric pressure, so air flows in. Alveolar pressure becomes higher than atmospheric only during expiration.

Question 2

Which lung volume cannot be exhaled even with maximal effort?

  1. Tidal volume
  2. Expiratory reserve volume
  3. Residual volume
  4. Inspiratory reserve volume
Show answer and explanation

Answer: C. Residual volume

Residual volume is the air that remains in the lungs after a maximal exhalation, and it keeps alveoli from collapsing. It cannot be measured by simple spirometry. Tidal volume and the reserve volumes can all be moved by breathing.

Question 3

A patient has a tidal volume of 500 mL, an inspiratory reserve volume of 3,000 mL, an expiratory reserve volume of 1,100 mL and a residual volume of 1,200 mL. What is the vital capacity?

  1. 4,600 mL
  2. 3,500 mL
  3. 5,800 mL
  4. 4,100 mL
Show answer and explanation

Answer: A. 4,600 mL

Vital capacity is tidal volume plus inspiratory reserve volume plus expiratory reserve volume: 500 + 3,000 + 1,100 = 4,600 mL. Residual volume is not included. Adding it gives total lung capacity, which here is 5,800 mL.

Question 4

Premature infants can develop respiratory distress because they lack sufficient surfactant. How does surfactant normally help breathing?

  1. It increases surface tension so alveoli stay open
  2. It reduces surface tension so alveoli do not collapse
  3. It carries oxygen in the blood
  4. It thickens the respiratory membrane
Show answer and explanation

Answer: B. It reduces surface tension so alveoli do not collapse

Surfactant, secreted by type II alveolar cells, lowers the surface tension of the fluid lining the alveoli. Without it, the high surface tension causes alveoli to collapse and makes inflation require much more work, as in infant respiratory distress syndrome.

Question 5

Which stimulus is the strongest normal driver of an increase in breathing rate?

  1. A rise in arterial CO2 (and the resulting fall in pH)
  2. A fall in arterial CO2
  3. A rise in arterial O2
  4. A rise in blood pH
Show answer and explanation

Answer: A. A rise in arterial CO2 (and the resulting fall in pH)

Central chemoreceptors in the medulla respond to H+ in cerebrospinal fluid, which reflects arterial CO2. Increased CO2 raises ventilation rate, while peripheral chemoreceptors in the carotid and aortic bodies respond to a large fall in arterial O2.

Question 6

Which description of quiet expiration is correct?

  1. It is passive and results from elastic recoil of the lungs and relaxation of the diaphragm
  2. It requires strong contraction of the diaphragm
  3. It is driven by the external intercostal muscles
  4. It occurs when intrapleural pressure rises above alveolar pressure
Show answer and explanation

Answer: A. It is passive and results from elastic recoil of the lungs and relaxation of the diaphragm

At rest, the diaphragm and external intercostals relax, thoracic volume falls and the elastic lungs recoil, raising alveolar pressure above atmospheric pressure. No muscular effort is needed. Forced expiration uses the abdominal muscles and internal intercostals.

Question 7

The volume of the thoracic cavity is decreased in a sealed model while the temperature stays constant. According to Boyle's law, what happens to the pressure of the gas inside?

  1. It decreases
  2. It increases
  3. It stays the same
  4. It becomes zero
Show answer and explanation

Answer: B. It increases

Boyle's law states that pressure and volume are inversely proportional at constant temperature. A smaller volume gives a higher pressure, which in the body pushes air out during expiration. This is why expansion of the chest draws air in.

Question 8

A puncture in the chest wall lets air enter the pleural space, causing a pneumothorax. Why does the lung on that side collapse?

  1. The diaphragm stops contracting
  2. Surfactant is lost from the alveoli
  3. The elastic lung recoils because the negative intrapleural pressure is lost
  4. Carbon dioxide levels fall in the pleural space
Show answer and explanation

Answer: C. The elastic lung recoils because the negative intrapleural pressure is lost

Normally the pleural pressure is slightly below atmospheric, which holds the lung against the chest wall against its tendency to recoil. When air enters, pleural pressure equalizes with atmospheric pressure and the elastic lung collapses inward.

Free MCAT sampler

Free sample: MCAT cheat sheet (PDF)

Join the list and download a free sample from a paid pack: the 3-page Amino Acids, Proteins and Enzymes cheat sheet (PDF). We also email free MCAT notes and practice sets.

Free sampler, no signup needed: 51 study notes with original diagrams and 5-question quizzes, 80 practice sets (706 questions with full explanations) and the 2027 study schedule generator.

Email me free MCAT notes, practice sets and new packs from StudyStore. Double opt-in, unsubscribe in one click. Privacy

Keep practicing

Written by StudyStore from standard scientific facts as a study aid. These are not official exam questions and are not affiliated with or endorsed by any testing organization. Always check values against the reference provided with your exam or course.

Spotted a mistake in a question? Report a problem or suggest something