Human Respiratory System Practice Questions
20 free Human Respiratory System 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.
Which of the following structures is known as the 'sound box' and helps in sound production?
- A Pharynx
- B Larynx (voice box)
- C Trachea
- D Epiglottis
Correct answer: Larynx (voice box)
The larynx is a cartilaginous box which helps in sound production and is hence called the sound box. During swallowing, the glottis can be covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx.
The trachea divides into two primary bronchi at the level of which thoracic vertebra?
- A 4th thoracic vertebra
- B 5th thoracic vertebra
- C 6th thoracic vertebra
- D 7th thoracic vertebra
Correct answer: 5th thoracic vertebra
The trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of the 5th thoracic vertebra into right and left primary bronchi. These bronchi undergo repeated divisions to form secondary and tertiary bronchi.
Which of the following structures in the respiratory system are supported by incomplete cartilaginous rings?
- A Trachea and primary bronchi only
- B Trachea, primary and secondary bronchi only
- C Trachea, all bronchi and initial bronchioles
- D Trachea, all bronchi and terminal bronchioles
Correct answer: Trachea, all bronchi and initial bronchioles
Trachea, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings. These rings prevent the airway from collapsing during breathing.
What is the primary function of the 'conducting part' of the respiratory system?
- A Diffusion of oxygen and carbon dioxide
- B Clearing the air of foreign particles and humidifying it
- C Actual exchange of gases between blood and atmospheric air
- D Production of pleural fluid
Correct answer: Clearing the air of foreign particles and humidifying it
The conducting part transports atmospheric air to the alveoli, clears it from foreign particles, humidifies it, and also brings the air to body temperature. It includes the external nostrils up to the terminal bronchioles.
The lungs are situated in an anatomically air-tight chamber known as the:
- A Abdominal cavity
- B Pericardial cavity
- C Thoracic cavity
- D Pelvic cavity
Correct answer: Thoracic cavity
The lungs are situated in the thoracic chamber which is anatomically an air-tight chamber. The anatomical setup of lungs in the thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung (pulmonary) cavity.
Which membrane covers the lungs and reduces friction on the lung-surface?
- A Peritoneum
- B Pericardium
- C Pleural membrane
- D Meninges
Correct answer: Pleural membrane
Each lung is covered by a double-layered pleura, with pleural fluid between them. This fluid reduces friction on the lung-surface and the outer pleural membrane is in close contact with the thoracic lining.
Which of the following represents the actual diffusion site of oxygen and carbon dioxide between blood and atmospheric air?
- A Trachea and larynx
- B Primary and secondary bronchi
- C Terminal and respiratory bronchioles
- D Alveoli and their ducts
Correct answer: Alveoli and their ducts
The alveoli and their ducts form the respiratory or exchange part of the respiratory system. This is where the actual diffusion of $O_2$ and $CO_2$ between blood and atmospheric air occurs.
The thoracic chamber is formed dorsally by the ________ and ventrally by the ________.
- A Sternum, vertebral column
- B Vertebral column, sternum
- C Ribs, diaphragm
- D Diaphragm, ribs
Correct answer: Vertebral column, sternum
The thoracic chamber is formed dorsally by the vertebral column and ventrally by the sternum. Laterally it is bounded by the ribs and on the lower side by the dome-shaped diaphragm.
Inspiration can occur if the intra-pulmonary pressure is:
- A Higher than the atmospheric pressure
- B Equal to the atmospheric pressure
- C Lower than the atmospheric pressure
- D Double the atmospheric pressure
Correct answer: Lower than the atmospheric pressure
Inspiration occurs when there is a negative pressure in the lungs with respect to atmospheric pressure. This means the intra-pulmonary pressure is less than the atmospheric pressure, allowing air to flow in.
Which of the following muscles are primarily involved in generating pressure gradients during normal quiet breathing?
- A Diaphragm and internal intercostals
- B Diaphragm and external intercostals
- C Abdominal muscles and internal intercostals
- D Internal and external intercostals
Correct answer: Diaphragm and external intercostals
The diaphragm and a specialized set of muscles—external and internal intercostals between the ribs—help in generation of pressure gradients. Specifically, the diaphragm and external intercostals are essential for normal inspiration.
The volume of air inspired or expired during a normal respiration is called:
- A Inspiratory Reserve Volume (IRV)
- B Expiratory Reserve Volume (ERV)
- C Tidal Volume (TV) — normal breath
- D Residual Volume (RV)
Correct answer: Tidal Volume (TV) — normal breath
Tidal Volume (TV) is the volume of air inspired or expired during a normal respiration. It is approximately 500 mL in a healthy man.
Total Lung Capacity (TLC) is the total volume of air accommodated in the lungs at the end of a forced inspiration. It includes:
- A RV + ERV + TV + IRV
- B RV + ERV + TV only
- C ERV + TV + IRV only
- D RV + IRV only
Correct answer: RV + ERV + TV + IRV
Total Lung Capacity (TLC) includes Residual Volume (RV), Expiratory Reserve Volume (ERV), Tidal Volume (TV), and Inspiratory Reserve Volume (IRV). It can also be defined as Vital Capacity + Residual Volume.
Which of the following is NOT part of the 'respiratory membrane' through which diffusion of gases occurs?
- A Thin squamous epithelium of alveoli
- B Endothelium of alveolar capillaries
- C Basement substance between epithelium and endothelium
- D Ciliated columnar epithelium of bronchioles
Correct answer: Ciliated columnar epithelium of bronchioles
The diffusion membrane is made up of three layers: the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries, and the basement substance in between. Ciliated columnar epithelium is part of the conducting zone, not the diffusion membrane.
The solubility of carbon dioxide is ________ times higher than that of oxygen across the diffusion membrane.
- A 2-5
- B 10-15
- C 20-25
- D 50-100
Correct answer: 20-25
As the solubility of carbon dioxide is 20-25 times higher than that of oxygen, the amount of carbon dioxide that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher than that of oxygen.
The partial pressure of oxygen ($pO_2$) in the alveolar air and deoxygenated blood is respectively:
- A 104 mm Hg and 40 mm Hg
- B 40 mm Hg and 104 mm Hg
- C 95 mm Hg and 40 mm Hg
- D 45 mm Hg and 40 mm Hg
Correct answer: 104 mm Hg and 40 mm Hg
In the alveoli, the $pO_2$ is 104 mm Hg, which is higher than the $pO_2$ in deoxygenated blood (40 mm Hg). This gradient allows oxygen to diffuse from the alveoli into the blood.
The 'Pneumotaxic center' which can moderate the functions of the respiratory rhythm center is located in:
- A Medulla oblongata and brain stem
- B Pons region of the brain
- C Cerebellum and its cortex
- D Cerebral cortex of the brain
Correct answer: Pons region of the brain
The respiratory rhythm center is primarily located in the medulla. However, another center present in the pons region of the brain called the pneumotaxic center can moderate the functions of the respiratory rhythm center.
What is the volume of air that remains in the lungs even after a forcible expiration?
- A Tidal Volume
- B Expiratory Reserve Volume
- C Residual Volume
- D Vital Capacity
Correct answer: Residual Volume
Residual Volume (RV) is the volume of air remaining in the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL and ensures that gas exchange continues even between breaths.
Vital Capacity (VC) can be defined as:
- A TV + IRV alone
- B TV + ERV alone
- C ERV + TV + IRV
- D ERV + RV alone
Correct answer: ERV + TV + IRV
Vital Capacity is the maximum volume of air a person can breathe in after a forced expiration. It includes Expiratory Reserve Volume (ERV), Tidal Volume (TV), and Inspiratory Reserve Volume (IRV).
During expiration, the diaphragm and external intercostal muscles ________, and the diaphragm becomes ________.
- A Contract, flat
- B Relax, dome-shaped
- C Contract, dome-shaped
- D Relax, flat
Correct answer: Relax, dome-shaped
Relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to their normal positions and reduces the thoracic volume. The diaphragm returns to its original dome-shaped position during expiration.
Which of the following is an occupational respiratory disorder characterized by inflammation and leading to fibrosis (proliferation of fibrous tissues)?
- A Asthma
- B Emphysema
- C Silicosis
- D Bronchitis
Correct answer: Silicosis
Silicosis and asbestosis are occupational respiratory disorders. In certain industries involving stone-breaking or grinding, long-term exposure to dust can give rise to inflammation leading to fibrosis (proliferation of fibrous tissues), causing serious lung damage.