NEET 2025 MCQ with Answer Explanation : Breathing and Exchange of Gases.

Here below some basic MCQ’s of “Breathing and Exchange of Gases” with answer which is well explained. Let’s check one by one which is given below.

MCQ 1:
Which of the following statements about the respiratory system is correct?

A) The trachea is a muscular tube that can expand and contract.

B) Alveoli are the primary sites for gas exchange in the lungs.

C) The diaphragm is located above the lungs.

D) The bronchioles have a thick muscular wall to facilitate gas exchange.

Answer: B) Alveoli are the primary sites for gas exchange in the lungs.

Explanation: The alveoli are tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged. They are lined with a thin layer of cells, allowing efficient gas exchange. The trachea is a rigid structure, not muscular; the diaphragm is below the lungs, and bronchioles have thin walls for gas exchange, not thick ones.

MCQ 2:
What is the primary muscle involved in the process of breathing?

A) Intercostal muscles

B) Diaphragm

C) Abdominal muscles

D) Pectoral muscles

Answer: B) Diaphragm

Explanation: The diaphragm is the main muscle responsible for breathing. When it contracts, it flattens, increasing the thoracic cavity’s volume and drawing air into the lungs. The intercostal muscles assist in expanding and contracting the ribcage but are secondary to the diaphragm.

MCQ 3:
Which of the following gases is primarily responsible for the stimulus to breathe in healthy individuals?

A) Oxygen

B) Carbon dioxide

C) Nitrogen

D) Hydrogen

Answer: B) Carbon dioxide

Explanation: The primary stimulus for breathing in healthy individuals is the level of carbon dioxide in the blood. When CO2 levels rise, it leads to an increase in respiratory rate to expel excess CO2 and maintain pH balance.

MCQ 4:
In the human body, the exchange of gases occurs primarily in the:

A) Bronchi

B) Trachea

C) Alveoli

D) Pharynx

Answer: C) Alveoli

Explanation: The alveoli are the functional units of the lungs where oxygen and carbon dioxide are exchanged. The bronchi and trachea are involved in conducting air but do not participate in gas exchange.

MCQ 5:
What is the role of surfactant in the lungs?

A) To transport oxygen

B) To reduce surface tension in the alveoli

C) To facilitate the movement of cilia

D) To filter out dust particles

Answer: B) To reduce surface tension in the alveoli

Explanation: Surfactant is a substance that reduces surface tension in the alveoli, preventing their collapse and making it easier for them to expand during inhalation. This is crucial for maintaining proper lung function.

MCQ 6:
Which part of the brain is primarily responsible for the regulation of breathing?

A) Cerebrum

B) Cerebellum

C) Medulla oblongata

D) Thalamus

Answer: C) Medulla oblongata

Explanation: The medulla oblongata is responsible for the automatic control of breathing. It detects changes in blood CO2 and O2 levels and adjusts the rate and depth of breathing accordingly.

MCQ 7:
Which of the following is the primary component of inhaled air?

A) Carbon dioxide

B) Nitrogen

C) Oxygen

D) Argon

Answer: B) Nitrogen

Explanation: Inhaled air is composed of about 78% nitrogen, 21% oxygen, and trace amounts of other gases, including carbon dioxide.

MCQ 8:
During inhalation, the pressure in the thoracic cavity:

A) Increases

B) Decreases

C) Remains the same

D) Fluctuates

Answer: B) Decreases

Explanation: During inhalation, the diaphragm contracts, expanding the thoracic cavity and lowering the pressure, which allows air to flow into the lungs.

MCQ 9:
What is the role of hemoglobin in the blood?

A) To transport nutrients

B) To carry oxygen

C) To regulate pH

D) To aid in digestion

Answer: B) To carry oxygen

Explanation: Hemoglobin is a protein in red blood cells that binds to oxygen in the lungs and transports it to tissues throughout the body.

MCQ 10:
The partial pressure of oxygen in the alveoli is approximately:

A) 40 mmHg

B) 100 mmHg

C) 760 mmHg

D) 21 mmHg

Answer: B) 100 mmHg

Explanation: The partial pressure of oxygen in the alveoli is around 100 mmHg, which facilitates the diffusion of oxygen into the blood.

MCQ 11:
What is the primary site of carbon dioxide exchange in the lungs?

A) Trachea

B) Bronchioles

C) Alveoli

D) Pleura

Answer: C) Alveoli

Explanation: The alveoli are the main sites where carbon dioxide is exchanged for oxygen during respiration.

MCQ 12:
Which of the following factors decreases the affinity of hemoglobin for oxygen?

A) Decreased temperature

B) Decreased pH

C) Decreased carbon dioxide concentration

D) Increased oxygen concentration

Answer: B) Decreased pH

Explanation: A decrease in pH (increased acidity) decreases hemoglobin’s affinity for oxygen, facilitating oxygen release in tissues where it is needed most.

MCQ 13:
Which structure prevents food from entering the trachea during swallowing?

A) Larynx

B) Pharynx

C) Epiglottis

D) Uvula

Answer: C) Epiglottis

Explanation: The epiglottis is a flap of cartilage that covers the trachea during swallowing, preventing food from entering the airway.

MCQ 14:
The primary function of the cilia in the respiratory tract is to:

A) Exchange gases

B) Filter and move mucus

C) Assist in vocalization

D) Provide structural support

Answer: B) Filter and move mucus

Explanation: Cilia are tiny hair-like structures that help to trap and move mucus and debris out of the respiratory tract, keeping the airways clear.

MCQ 15:
What is the tidal volume during normal resting breathing?

A) 150 mL

B) 500 mL

C) 1000 mL

D) 2500 mL

Answer: B) 500 mL

Explanation: Tidal volume is the amount of air inhaled or exhaled during normal breathing, which is approximately 500 mL in adults.

MCQ 16:
In which part of the respiratory system does gas exchange occur?

A) Nasal cavity

B) Lungs

C) Alveoli

D) Bronchi

Answer: C) Alveoli

Explanation: Gas exchange occurs specifically in the alveoli, where oxygen and carbon dioxide are exchanged between air and blood.

MCQ 17:
Which condition is characterized by inflammation of the bronchi?

A) Asthma

B) Pneumonia

C) Bronchitis

D) Emphysema

Answer: C) Bronchitis

Explanation: Bronchitis is the inflammation of the bronchial tubes, which can cause coughing and difficulty breathing.

MCQ 18:
The primary gas transported by hemoglobin is:

A) Nitrogen

B) Carbon monoxide

C) Oxygen

D) Carbon dioxide

Answer: C) Oxygen

Explanation: Hemoglobin’s primary function is to carry oxygen from the lungs to the tissues.

MCQ 19:
Which of the following conditions is most likely to result from smoking?

A) Asthma

B) Chronic bronchitis

C) Lung cancer

D) All of the above

Answer: D) All of the above

Explanation: Smoking can lead to various respiratory conditions, including asthma, chronic bronchitis, and lung cancer.

MCQ 20:
What is the main function of the respiratory system?

A) To circulate blood

B) To exchange gases

C) To regulate temperature

D) To digest food

Answer: B) To exchange gases

Explanation: The primary function of the respiratory system is to facilitate the exchange of oxygen and carbon dioxide between the body and the environment.