Gas Exchange

Which structure in the respiratory system is primarily responsible for gas exchange?

• A. Trachea

• B. Bronchus

• C. Alveoli

• D. Larynx

Answer explanation

Alveoli are tiny air sacs in the lungs where gas exchange occurs. Oxygen diffuses into the blood, and carbon dioxide diffuses out of the blood into the alveoli.

What role does haemoglobin play in oxygen transport?

• A. Produces oxygen

• B. Binds to oxygen and transports it in the blood

• C. Converts oxygen to carbon dioxide

• D. Expels oxygen from the body

Answer explanation

Haemoglobin is a protein in red blood cells that binds to oxygen and transports it from the lungs to the tissues.

How does negative pressure breathing facilitate inspiration?

• A. By increasing air pressure in the lungs

• B. By decreasing air pressure in the lungs

• C. By producing oxygen in the lungs

• D. By expelling carbon dioxide from the lungs

Answer explanation

Negative pressure breathing involves decreasing air pressure within the lungs, causing air to flow into the lungs to equalise the pressure, facilitating inspiration.

Which muscles are primarily involved in the process of inspiration?

• A. Abdominal muscles

• B. Intercostal muscles and diaphragm

• C. Pectoral muscles

• D. Trapezius muscles

Answer explanation

The intercostal muscles and the diaphragm contract during inspiration, increasing the volume of the thoracic cavity and decreasing air pressure in the lungs.

How is most of the carbon dioxide transported in the blood?

• A. Bound to hemoglobin

• B. Dissolved in plasma as bicarbonate ions

• C. As carbon monoxide

• D. Attached to oxygen molecules

Answer explanation

Most of the carbon dioxide in the blood is transported as bicarbonate ions in the plasma, which are formed through a reaction with water.

a) Describe the structure and function of the alveoli in the respiratory system. [3]

b) Explain how the principles of diffusion apply to gas exchange in the alveoli. [3]

Answer explanation

a) Alveoli are tiny, sac-like structures in the lungs where gas exchange occurs. They have thin walls surrounded by a network of capillaries, allowing for an efficient exchange of oxygen and carbon dioxide between the air and the blood.

b) In the alveoli, oxygen diffuses from the air into the blood due to a concentration gradient, while carbon dioxide diffuses from the blood into the air to be exhaled. This process is facilitated by the thin walls of the alveoli and the large surface area available for exchange.

a) Discuss the roles of the diaphragm and intercostal muscles in inspiration and expiration. [4]

b) How does negative pressure breathing facilitate the movement of air into and out of the lungs? [2]

Answer explanation

a) During inspiration, the diaphragm contracts and flattens, and the intercostal muscles contract, expanding the ribcage. This increases the volume of the thoracic cavity, reducing the pressure inside, allowing air to flow into the lungs. During expiration, these muscles relax, decreasing the thoracic volume, increasing the pressure, and forcing air out of the lungs.

b) Negative pressure breathing involves the creation of a lower (negative) pressure inside the lungs compared to the atmospheric pressure, causing air to flow into the lungs. When exhaling, the pressure inside the lungs becomes higher than the atmospheric pressure, pushing the air out.

a) Explain the role of haemoglobin in oxygen transport in the blood. [3]

b) Discuss how carbon dioxide is transported in the blood from the body tissues to the lungs. [3]

Answer explanation

a) Hemoglobin is a protein in red blood cells that binds to oxygen in the lungs and transports it to the body's tissues. Each haemoglobin molecule can carry four oxygen molecules, allowing for efficient oxygen transport. In the tissues, oxygen is released from haemoglobin due to lower oxygen concentration.

b) Carbon dioxide is transported in the blood in three main ways: dissolved in plasma, bound to haemoglobin, and as bicarbonate ions. The majority is converted to bicarbonate ions in red blood cells, which then move into the plasma. In the lungs, the reactions are reversed, releasing carbon dioxide to be exhaled.

a) Explain the concept of negative pressure breathing. [3]

b) How do intercostal muscles contribute to this process? [2]

c) Discuss the role of haemoglobin in transporting oxygen and carbon dioxide. [3]

Answer explanation

a) Negative pressure breathing involves increasing the thoracic cavity's volume, decreasing the internal pressure below atmospheric pressure, causing air to flow into the lungs. During expiration, the volume decreases, pressure increases, and air is expelled.

b) Intercostal muscles contract to expand the ribcage during inspiration and relax to reduce the thoracic volume during expiration, contributing to the pressure changes necessary for breathing.

c) Hemoglobin in red blood cells binds to oxygen in the lungs and transports it to tissues. It also binds to carbon dioxide, a waste product from cellular respiration, and transports it back to the lungs for exhalation.

What is the primary function of the trachea in the respiratory system?

• A. Gas exchange

• B. Producing sound

• C. Conducting air to the lungs

• D. Filtering air

Answer explanation

The trachea, or windpipe, is a tube that conducts air from the larynx to the bronchi, leading to the lungs.