Final answer:
The ideal ventilation and perfusion ratio in the alveolus is 1:1 to achieve equal partial pressures of O₂ and CO₂ between the alveoli and capillaries at the end of gas exchange, ensuring efficient gas exchange.
Step-by-step explanation:
The ideal ratio of ventilation and perfusion in the alveolus is 1:1 so that at the end of gas exchange, the capillaries and alveolus have equal partial pressure of O₂ and CO₂. The correct answer to the student's question is a) 1:1, equal. In the lungs, the partial pressure of oxygen (Po₂) in the alveoli is about 104 mm Hg, while in the capillaries it is about 40 mm Hg. This pressure gradient allows oxygen to move down its gradient and diffuse into the blood where it binds to hemoglobin found in red blood cells (RBCs).
The partial pressure of carbon dioxide (Pco₂), although different, has a smaller pressure gradient between the alveolar air (about 40 mm Hg) and the blood of the capillary (about 45 mm Hg). However, because carbon dioxide is significantly more soluble than oxygen, the relative concentrations that diffuse across the respiratory membrane are similar, allowing for efficient gas exchange.
Proper gas exchange depends on this tight regulation of the ventilation/perfusion ratio and pressure gradients. If ventilation is insufficient, the partial pressure of oxygen in the alveoli drops, prompting the body to redirect blood flow to better-ventilated alveoli. This physiological response helps to maintain the ideal ventilation/perfusion ratio and to ensure efficient gas exchange.