Question

Select the incorrect statement from the following: (a) Diffusion of \(\mathrm{O}_{2}\) occurs from alveoli to tissue. (b) Diffusion of \(\mathrm{CO}_{2}\) occurs from tissue to alveoli. (c) Amount of \(\mathrm{CO}_{2}\) diffused through membrane is higher than that of \(\mathrm{O}_{2}\). (d) Partial pressure of \(\mathrm{O}_{2}\) is higher in pulmonary artery than that of pulmonary vein.

Short answer

The incorrect statement is (d): 'Partial pressure of \(\mathrm{O}_{2}\) is higher in pulmonary artery than that of pulmonary vein'. The correct statement would be that the partial pressure of \(\mathrm{O}_{2}\) is higher in pulmonary vein than that in pulmonary artery.

Step-by-step solution

Evaluate Statement (a)

Assess the statement 'Diffusion of \(\mathrm{O}_{2}\) occurs from alveoli to tissue': This is correct. During respiration, oxygen (\(\mathrm{O}_{2}\)) in the alveoli diffuses to the blood in the lung capillaries by simple diffusion, and it is further transported to cells in the tissues.

Evaluate Statement (b)

Assess the statement 'Diffusion of \(\mathrm{CO}_{2}\) occurs from tissue to alveoli': This statement is also correct. Carbon dioxide (\(\mathrm{CO}_{2}\)), which is a waste product of cellular respiration in the tissues, diffuses from the cells to the blood, and from the blood to the alveoli in the lungs, from where it is exhaled.

Evaluate Statement (c)

Assess the statement 'Amount of \(\mathrm{CO}_{2}\) diffused through membrane is higher than that of \(\mathrm{O}_{2}\)': Again, this statement is correct. The diffusion rate of \(\mathrm{CO}_{2}\) is approximately 20 times higher than that of \(\mathrm{O}_{2}\). This is because \(\mathrm{CO}_{2}\) is more soluble in cell membranes.

Evaluate Statement (d)

Assess the statement 'Partial pressure of \(\mathrm{O}_{2}\) is higher in pulmonary artery than that of pulmonary vein': This is incorrect. The opposite is true. The oxygen-rich blood in the pulmonary vein has a higher partial pressure of \(\mathrm{O}_{2}\) than the deoxygenated blood in the pulmonary artery. The discrepancy in this statement reveals it as the incorrect statement from the list.

Key concepts

Diffusion of Oxygen

Oxygen diffusion is a key process in respiratory physiology, where oxygen travels from high to low concentration areas. In the alveoli of the lungs, the concentration of oxygen is higher than in the blood in the lung capillaries. This difference creates a concentration gradient that allows oxygen to diffuse into the blood.
The journey begins as air enters the lungs, filling the alveoli, which are tiny air sacs providing a high surface area for gas exchange. Oxygen molecules move across the alveolar membrane and into the blood.
This process is essential for delivering oxygen to the body tissues, where it is used for cellular respiration. Without efficient oxygen diffusion, tissues would be deprived of oxygen, impacting cellular function and overall health.

• The process is passive—a result of the concentration gradient.
• No energy is required for this diffusion.
• Oxygen moves from higher to lower partial pressure areas.

Diffusion of Carbon Dioxide

Carbon dioxide diffusion is equally crucial in the respiratory system. It is the body's way of removing the byproduct of cellular respiration from the tissues. In tissue cells,
carbon dioxide levels are higher due to metabolism, creating a concentration gradient that drives it into the blood.
The blood carries carbon dioxide to the lungs, where it diffuses from the blood into the alveoli to be exhaled. This process occurs simply by the movement from an area of high concentration to an area of lower concentration.

• Carbon dioxide is highly soluble, facilitating its efficient diffusion across membranes.
• Even though it is produced throughout the body,
  its removal via the lungs prevents its accumulation.
• Unlike oxygen, carbon dioxide diffusion occurs in reverse—from tissues to lungs.

Partial Pressure in Circulatory System

Partial pressure refers to the pressure exerted by a single type of gas in a mixture. In the circulatory system, understanding the partial pressures of oxygen and carbon dioxide helps explain gas movement. The pulmonary artery carries deoxygenated blood from the heart to the lungs. Here, the partial pressure of oxygen
is lower compared to that in the pulmonary vein, which carries oxygenated blood back to the heart.
This relationship is crucial for efficient gas exchange.

• Oxygen partial pressure is higher in oxygen-rich areas, like the pulmonary veins.
• Carbon dioxide partial pressure, high in tissues, triggers its exhalation from the body.
• Maintaining these pressures supports the body’s homeostasis and efficient respiration.

When these pressures differ as expected, it ensures proper loading of oxygen and unloading of carbon dioxide,
facilitating effective respiratory function.