Mechanism of Breathing Practice Questions
20 free Mechanism of Breathing practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration occurs when:
- A Intra-pulmonary pressure is higher than atmospheric pressure
- B Intra-pulmonary pressure is lower than atmospheric pressure
- C Intra-pulmonary pressure is equal to atmospheric pressure
- D Intra-pleural pressure becomes positive
Correct answer: Intra-pulmonary pressure is lower than atmospheric pressure
Inspiration is initiated when the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure. This negative pressure gradient draws air from the outside into the alveoli.
Which of the following events occurs during the process of inspiration?
- A Relaxation of the diaphragm
- B Contraction of external intercostal muscles
- C Decrease in the volume of the thoracic chamber
- D Relaxation of the internal intercostal muscles only
Correct answer: Contraction of external intercostal muscles
Contraction of the external intercostal muscles lifts up the ribs and the sternum, causing an increase in the volume of the thoracic chamber in the dorso-ventral axis. This is a key step in increasing pulmonary volume for inspiration.
The diaphragm is a specialized muscle that helps in the generation of pressure gradients. Its contraction increases the thoracic volume in the:
- A Dorso-ventral (back-to-front) axis
- B Antero-posterior axis
- C Lateral (side-to-side) axis
- D Superior-inferior (vertical) axis
Correct answer: Antero-posterior axis
The contraction of the diaphragm causes it to flatten, which increases the volume of the thoracic chamber in the antero-posterior axis. This increase in volume leads to a decrease in intra-pulmonary pressure.
Expiration takes place when the intra-pulmonary pressure is ________ than the atmospheric pressure.
- A Lower than atmospheric
- B Higher
- C Equal to atmospheric
- D Zero or negligible
Correct answer: Higher
Expiration occurs when the relaxation of the diaphragm and intercostal muscles reduces the thoracic volume. This increase in intra-pulmonary pressure to a level slightly above atmospheric pressure forces air out of the lungs.
Which muscles are primarily responsible for the relaxation phase during normal quiet expiration?
- A Contraction of internal intercostal muscles
- B Active contraction of abdominal muscles
- C Passive recoil; no muscles actively contract
- D Sustained diaphragm contraction
Correct answer: Passive recoil; no muscles actively contract
Normal expiration is largely a passive process. It occurs when the diaphragm and external intercostal muscles relax, allowing the lungs and thoracic cage to recoil to their original positions.
Humans have the ability to increase the strength of both inspiration and expiration using additional muscles located in the:
- A Back and spine
- B Pelvic floor
- C Neck and throat
- D Abdominal wall
Correct answer: Abdominal wall
While normal breathing involves the diaphragm and external intercostals, humans can use abdominal muscles to increase the force of expiration. This is particularly evident during forceful breathing or exercise.
What happens to the sternum during the process of inspiration?
- A It moves downward and inward
- B It moves upward and outward
- C It remains stationary
- D It rotates laterally
Correct answer: It moves upward and outward
During inspiration, the contraction of external intercostal muscles pulls the ribs and the sternum upward and outward. This action expands the thoracic cavity in the dorso-ventral axis.
Anatomically, the lungs are situated in an air-tight thoracic chamber. This setup is essential because:
- A Lungs lack a muscular mechanism to change their own volume
- B It prevents airborne pathogens from entering the bloodstream directly
- C It maintains constant body temperature around the heart and lungs
- D It provides rigid structural support so the ribs can grow larger
Correct answer: Lungs lack a muscular mechanism to change their own volume
Since lung tissue is not muscular, it cannot expand or contract on its own. The air-tight thoracic chamber ensures that any change in the volume of the thoracic cavity is directly reflected in the pulmonary volume.
The relaxation of the diaphragm causes it to become:
- A Completely flattened out
- B Dome-shaped
- C Elongated downward
- D Concave from above
Correct answer: Dome-shaped
When the diaphragm relaxes, it returns to its natural dome-shaped position, arching upward into the thoracic cavity. This reduces the thoracic volume, contributing to expiration.
During forceful expiration, which of the following muscles contract?
- A The diaphragm contracting downward
- B Scalene and sternocleidomastoid muscles
- C External intercostal muscles acting on their own
- D Internal intercostals and abdominal muscles
Correct answer: Internal intercostals and abdominal muscles
Forceful expiration is an active process that involves the contraction of internal intercostal muscles (which pull the ribs down) and abdominal muscles (which push the diaphragm up), further reducing thoracic volume.
The average breathing rate of a healthy human adult is:
- A 70-80 times/minute
- B 5-10 times/minute
- C 12-16 times/minute
- D 20-25 times/minute
Correct answer: 12-16 times/minute
A healthy human adult breathes approximately 12 to 16 times per minute under normal physiological conditions. This rate can increase significantly during physical exertion.
Which clinical instrument is used to estimate the volume of air involved in breathing movements?
- A Sphygmomanometer
- B Stethoscope
- C Spirometer (pulmonary function test)
- D Electrocardiograph
Correct answer: Spirometer (pulmonary function test)
A spirometer is used to measure the volume of air inspired and expired. Clinical assessment of pulmonary functions is often performed using spirometry to diagnose respiratory disorders.
What is the effect of an increase in thoracic volume on intra-pulmonary pressure?
- A Pressure rises proportionally
- B Pressure decreases proportionally
- C Pressure stays the same throughout
- D Pressure fluctuates unpredictably
Correct answer: Pressure decreases proportionally
According to Boyle's Law, as the volume of a container increases, the pressure of the gas inside decreases. Therefore, an increase in thoracic (and pulmonary) volume lowers the intra-pulmonary pressure.
The intra-pleural pressure is always ________ during normal quiet breathing.
- A Always positive and above atmospheric
- B Negative relative to atmospheric pressure
- C Exactly zero at all times
- D Higher than intra-pulmonary pressure always
Correct answer: Negative relative to atmospheric pressure
Intra-pleural pressure is the pressure within the pleural cavity. It remains negative (sub-atmospheric), which acts like a vacuum to keep the lungs expanded against the chest wall.
During expiration, the volume of the thoracic cavity decreases in the dorso-ventral axis due to:
- A Contraction of the diaphragm, which pushes air upward
- B Relaxation of external intercostal muscles
- C Passive recoil of the sternum toward the spine
- D Outward expansion of ribs driven by muscle pull
Correct answer: Relaxation of external intercostal muscles
As the external intercostal muscles relax, the ribs and sternum return to their original positions (moving downward and inward). This reduces the thoracic volume in the dorso-ventral axis.
Which of the following describes the correct sequence of events for inspiration?
- A Increased thoracic volume -> Decreased pulmonary pressure -> Air flows out
- B Decreased thoracic volume -> Increased pulmonary pressure -> Air flows in
- C Increased thoracic volume -> Decreased pulmonary pressure -> Air flows in
- D Decreased thoracic volume -> Decreased pulmonary pressure -> Air flows in
Correct answer: Increased thoracic volume -> Decreased pulmonary pressure -> Air flows in
Inspiration starts with an increase in thoracic volume, which leads to a corresponding increase in pulmonary volume. This causes pulmonary pressure to drop below atmospheric pressure, forcing air into the lungs.
The 'abdominal breathing' often observed in infants and relaxed adults is primarily driven by the:
- A Internal intercostal muscles
- B External intercostal muscles
- C Diaphragm
- D Accessory neck muscles
Correct answer: Diaphragm
In quiet, relaxed breathing, the diaphragm does the majority of the work. As it contracts and moves down, it pushes the abdominal contents outward, hence the term 'abdominal breathing'.
Which of the following is an auxiliary muscle used during deep or forced inspiration?
- A Rectus abdominis
- B Sternocleidomastoid
- C Internal intercostals
- D Gluteus maximus
Correct answer: Sternocleidomastoid
During forced or deep inspiration, accessory muscles like the sternocleidomastoid and scalenes in the neck help to further lift the rib cage and increase thoracic volume.
The pleural fluid helps in the mechanism of breathing by:
- A Increasing the weight of the lungs for stability
- B Reducing friction and keeping the pleural layers together
- C Providing direct oxygen supply to the alveolar surface
- D Buffering blood pH during rapid breathing episodes
Correct answer: Reducing friction and keeping the pleural layers together
The thin layer of pleural fluid between the parietal and visceral pleura reduces friction during lung expansion and creates surface tension that ensures the lungs follow the movements of the thoracic wall.
During expiration, the air is expelled from the lungs until:
- A The intra-pulmonary pressure equals the atmospheric pressure
- B The lungs reach a fully empty state with no residual volume
- C The diaphragm descends to its lowest anatomical position
- D The ribs rotate inward and press against adjacent structures
Correct answer: The intra-pulmonary pressure equals the atmospheric pressure
Air flows out of the lungs as long as the intra-pulmonary pressure is higher than the atmospheric pressure. The flow stops once the two pressures equilibrate.