Mechanism of Breathing — NEET Biology MCQs with Solutions
Free NEET Biology Mechanism of Breathing MCQs with step-by-step solutions (40 questions). Part of Breathing and Exchange of Gases. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Mechanism of Breathing · easy · theory
Inspiration (breathing in) occurs when the pressure inside the lungs (intra-pulmonary pressure) becomes:
A. Equal to atmospheric pressure
B. Less than atmospheric pressure ✓ Correct
C. Greater than atmospheric pressure
D. Zero
Solution: A drop in intrapulmonary pressure below atmospheric draws air into the lungs (inspiration).
Q2 — Mechanism of Breathing · easy · theory
During inspiration, the diaphragm ______ and the external intercostal muscles ______:
A. Relaxes; contract
B. Contracts (flattens); contract ✓ Correct
C. Contracts; relax
D. Relaxes; relax
Solution: Contraction of the diaphragm and external intercostals increases thoracic volume, lowering pressure for inspiration.
Q3 — Mechanism of Breathing · medium · theory
Expiration is normally a ______ process because:
A. Active; the diaphragm flattens
B. Passive; the lungs pump air
C. Passive; the diaphragm and intercostals relax, reducing thoracic volume ✓ Correct
D. Active; muscles contract forcefully
Solution: Quiet expiration is passive — muscle relaxation reduces thoracic/pulmonary volume, raising pressure to expel air.
Q4 — Mechanism of Breathing · medium · theory
The contraction of the external intercostal muscles raises the ribs and sternum, increasing the ______ of the thoracic chamber:
A. Vertical axis only
B. Antero-posterior (front-to-back) diameter ✓ Correct
C. Pleural fluid
D. Volume of the abdomen
Solution: External intercostals lift the ribs/sternum, increasing the antero-posterior dimension of the thorax.
Q5 — Mechanism of Breathing · hard · theory
The respiratory rhythm centre that controls breathing is located in the:
A. Hypothalamus
B. Medulla oblongata ✓ Correct
C. Cerebellum
D. Cerebrum
Solution: The medulla houses the respiratory rhythm centre; a pneumotaxic centre in the pons can moderate it.
Q6 — Mechanism of Breathing · hard · theory
A rise in CO₂ and H⁺ concentration in the blood is sensed by chemosensitive areas that then:
A. Have no effect
B. Stop breathing
C. Decrease the breathing rate
D. Signal the rhythm centre to increase the rate and depth of breathing ✓ Correct
Solution: CO₂/H⁺ (not O₂ primarily) are the main regulators; their rise stimulates faster, deeper breathing to expel CO₂.
Q7 — Mechanism of Breathing · easy · numerical
On average, a healthy adult human being breathes about how many times per minute?
A. 60 to 72 times
B. 12 to 16 times ✓ Correct
C. 4 to 6 times
D. 30 to 40 times
Solution: A normal healthy adult takes roughly 12-16 breaths per minute at rest.
Q8 — Mechanism of Breathing · easy · numerical
When the diaphragm contracts during inspiration, its dome:
A. becomes more dome-shaped, reducing thoracic volume
B. moves sideways without changing volume
C. flattens, increasing the volume of the thoracic cavity ✓ Correct
D. stays fixed while the ribs alone move
Solution: Contraction flattens the normally dome-shaped diaphragm, enlarging the thoracic chamber in the antero-posterior axis and aiding inspiration.
Q9 — Mechanism of Breathing · easy · numerical
The pneumotaxic centre, which can moderate the activity of the respiratory rhythm centre, is located in the:
A. medulla oblongata
B. cerebellum
C. pons region of the brain ✓ Correct
D. hypothalamus
Solution: The pneumotaxic centre lies in the pons and can reduce the duration of inspiration, thereby altering the breathing rate.
Q10 — Mechanism of Breathing · easy · numerical
A forceful (active) expiration, unlike quiet expiration, additionally involves contraction of the:
A. diaphragm and external intercostal muscles
B. pneumotaxic centre and the pons
C. internal intercostal muscles and abdominal muscles ✓ Correct
D. walls of the alveoli
Solution: Normal expiration is passive, but a forced expiration recruits the internal intercostals and abdominal muscles to push more air out.
Q11 — Mechanism of Breathing · medium · numerical
Assertion (A): Air moves into the lungs during inspiration. Reason (R): During inspiration the intra-pulmonary pressure becomes greater than the atmospheric pressure.
A. A is true but R is false ✓ Correct
B. Both A and R are true and R is the correct explanation of A
C. A is false but R is true
D. Both A and R are true but R is not the correct explanation of A
Solution: Air does enter during inspiration, but only because intra-pulmonary pressure falls BELOW atmospheric pressure; the reason as stated (higher than atmospheric) is false.
Q12 — Mechanism of Breathing · medium · numerical
The pneumotaxic centre chiefly influences breathing by:
A. generating the basic rhythm of breathing on its own
B. directly detecting changes in blood CO₂ levels
C. reducing the duration of inspiration and thereby altering the respiratory rate ✓ Correct
D. stimulating the diaphragm to remain permanently contracted
Solution: The pneumotaxic centre in the pons signals the rhythm centre to shorten inspiration, which changes the respiratory rate; it is not the primary rhythm generator or a chemoreceptor.
Q13 — Mechanism of Breathing · medium · numerical
The chemosensitive area near the respiratory rhythm centre is highly sensitive to CO₂ and H⁺ ions, but the role of ______ in the regulation of respiratory rhythm is quite insignificant.
A. bicarbonate ions
B. hydrogen ions
C. oxygen ✓ Correct
D. carbon dioxide
Solution: Breathing regulation is driven mainly by CO₂ and H⁺ acting on the chemosensitive area; oxygen plays only a minor, insignificant role in this control.
Q14 — Mechanism of Breathing · medium · numerical
Arrange the following events of inspiration in the correct sequence: (i) diaphragm and external intercostal muscles contract (ii) volume of the thoracic chamber increases (iii) intra-pulmonary pressure falls below atmospheric pressure (iv) air rushes into the lungs.
A. ii → i → iii → iv
B. i → ii → iii → iv ✓ Correct
C. iii → i → ii → iv
D. i → iii → ii → iv
Solution: Muscle contraction increases thoracic (and pulmonary) volume, which lowers intra-pulmonary pressure below atmospheric, and air then flows in.
Q15 — Mechanism of Breathing · medium · numerical
Assertion (A): Normal (quiet) expiration is a passive process. Reason (R): Relaxation of the diaphragm and intercostal muscles returns them to their resting position, decreasing the thoracic volume.
A. Both A and R are true and R is the correct explanation of A ✓ Correct
B. A is true but R is false
C. Both A and R are true but R is not the correct explanation of A
D. A is false but R is true
Solution: Quiet expiration needs no active muscular effort; simple relaxation of the inspiratory muscles reduces thoracic and pulmonary volume, raising pressure and forcing air out.
Q16 — Mechanism of Breathing · medium · numerical
Which of the following statements about the mechanism of breathing is INCORRECT?
A. Normal expiration is always an active process that requires muscular energy ✓ Correct
B. During inspiration the intra-pulmonary pressure is less than the atmospheric pressure
C. Inspiration is initiated by contraction of the diaphragm
D. Relaxation of the diaphragm and intercostal muscles helps in normal expiration
Solution: Normal expiration is passive, driven by relaxation of inspiratory muscles; only forced expiration is active. The other three statements are correct.
Q17 — Mechanism of Breathing · easy
The lungs expand in inspiration/inhalation because
A. External intercostal muscles relax
B. The volume of thoracic cavity increases ✓ Correct
C. Diaphragm contracts upward
D. Diaphragm relaxes
Solution: During inspiration the diaphragm contracts and flattens and the external intercostals contract, increasing the volume of the thoracic cavity, which lets the lungs expand.
Q18 — Mechanism of Breathing · easy
The process of exhalation / expiration is mainly due to –
A. The contraction of intercostal muscles
B. The contraction of the diaphragm
C. Low pressure in thoracic cavity
D. The relaxation of intercostal muscles ✓ Correct
Solution: Expiration occurs mainly when the diaphragm and intercostal muscles relax, reducing thoracic volume and forcing air out.
Q19 — Mechanism of Breathing · medium
Which of the following statements about the mechanism of ventilation/breathing is false?
A. As the diaphragm relaxes, air is expelled from the respiratory system
B. For quiet breathing external intercostal muscles and diaphragm play an important role.
C. Inspiration is a passive and expiration is an active process. ✓ Correct
D. During inspiration the lungs act as suction pump
Solution: It is the reverse: during quiet breathing inspiration is the active process (muscle contraction) while expiration is passive (muscle relaxation).
Q20 — Mechanism of Breathing · medium
Inspiration occurs when there is a negative pressure in the lungs with respect to atmospheric pressure. This negative pressure is achieved when
A. Intrapulmonary pressure is less than the atmospheric pressure ✓ Correct
B. Intrapulmonary pressure is equal to the atmospheric pressure
C. Intrapleural pressure becomes more than the intra-alveolar pressure
D. Intra pulmonary pressure is greater than the atmospheric pressure
Solution: Inspiration happens when intrapulmonary (intra-alveolar) pressure falls below atmospheric pressure, so air rushes into the lungs.
Q21 — Mechanism of Breathing · easy
Expiration takes place when the intrapulmonary pressure is –
A. Equal to intrapleural pressure
B. Lesser than the atmospheric pressure
C. Equal to atmospheric pressure
D. Greater than the atmospheric pressure ✓ Correct
Solution: Expiration occurs when intrapulmonary pressure rises above atmospheric pressure, pushing air out of the lungs.
Q22 — Mechanism of Breathing · hard
Which of the following sequences is correct to initiate inspiration?
I. The contraction of external intercostal muscles raises the ribs and sternum
II. Volume of thorax increases in the dorso-ventral axis
III. Intrapulmonary pressure decreases
IV. Diaphragm contraction
V. Air rushes into lungs
VI. Volume of thorax increases in the antero-posterior axis
A. I, II, IV, VI, III, V
B. I, II, III, IV, V
C. IV, VI, I, II, III, V ✓ Correct
D. VI, I, II, III, V
Solution: Diaphragm and external intercostals contract to raise the ribs, increasing thoracic volume in both axes, which lowers intrapulmonary pressure so air rushes in.
Q23 — Mechanism of Breathing · hard
Which of the following sequences is correct to initiate expiration?
I. Relaxation of external intercostal muscles and return of diaphragm and sternum to their normal position
II. Air expelled from lungs
III. Volume of thorax decreases
IV. Intrapulmonary pressure increases
A. I, II, III, IV
B. II, IV, III, I
C. I, III, IV, II ✓ Correct
D. IV, III, II, I
Solution: Muscles relax and the diaphragm/sternum return to normal, thoracic volume decreases, intrapulmonary pressure rises and air is expelled.
Q24 — Mechanism of Breathing · easy
On an average, a healthy human breathes ______ times /minute
A. 16 – 25
B. 20 – 40
C. 1 – 6
D. 12 – 16 ✓ Correct
Solution: A healthy adult human on average breathes 12–16 times per minute.
Q25 — Mechanism of Breathing · medium
Additional muscles for forceful breathing are –
A. Diaphragm and abdominal muscles
B. Abdominal muscles and internal intercostal muscles ✓ Correct
C. External and internal intercostal muscles
D. Diaphragm and external intercostal muscles
Solution: Forceful (forced) breathing recruits additional muscles such as the abdominal muscles and internal intercostal muscles.
Q26 — Mechanism of Breathing · medium
Which one of the following is a possibility for most of us with regard to breathing by making a conscious effort?
A. One can breathe out air through Eustachian tube by closing both nose and mouth.
B. One can consciously breathe in and breathe out by moving the diaphragm alone, without moving the ribs at all. ✓ Correct
C. One can breathe out air totally without oxygen.
D. The lungs can be made fully empty by forcefully breathing out all air from them.
Solution: Diaphragmatic (abdominal) breathing lets one consciously breathe using the diaphragm alone without moving the ribs; the lungs can never be fully emptied due to residual volume.
Q27 — Mechanism of Breathing · medium
Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because
A. There is a negative intrapleural pressure pulling at the lung walls ✓ Correct
B. Pressure in the lungs is higher than the atmospheric pressure
C. There is a positive intrapleural pressure
D. There is a negative pressure in the lungs
Solution: A negative intrapleural pressure keeps the lungs pulled against the thoracic wall, preventing collapse and retaining residual air.
Q28 — Mechanism of Breathing · hard
A person suffers punctures in his chest cavity in an accident, without any damage to the lungs. Its effect could be
A. Reduced breathing rate
B. Cessation of breathing
C. Rapid increase in breathing rate ✓ Correct
D. No change in respiration
Solution: A puncture lets air into the pleural cavity, disturbing the negative intrapleural pressure needed for lung expansion, leading to a rapid increase in breathing rate.
Q29 — Mechanism of Breathing · easy
Mark the true statement among the following with reference to normal breathing
A. Inspiration and expiration are passive processes.
B. Inspiration and expiration are active processes
C. Inspiration is an active process whereas expiration is passive ✓ Correct
D. Inspiration is a passive process whereas expiration is active
Solution: Normal inspiration requires active contraction of the diaphragm and external intercostals, while normal expiration is passive due to elastic recoil.
Q30 — Mechanism of Breathing · easy
Mark the correct pair of muscles involved in the normal breathing in humans
A. Diaphragm and abdominal muscles
B. Diaphragm and internal intercostal muscles.
C. External and internal intercostal muscles
D. Diaphragm and external intercostal muscles ✓ Correct
Solution: Normal inspiration is driven by contraction of the diaphragm and the external intercostal muscles.