Final answer:
Inspiration occurs when the intra-alveolar pressure is less than the atmospheric pressure (Ppul < Patm), which allows air to flow into the lungs according to Boyle's Law.
Step-by-step explanation:
The question is asking which pressure relationship best illustrates when inspiration will occur. Inspiration, or inhalation, occurs when air flows into the lungs from the atmosphere. According to Boyle's Law, in a gas, pressure increases as volume decreases, and vice versa. For inspiration to take place, the intra-alveolar pressure (Ppul), which is the pressure within the alveoli of the lungs, must be lower than the atmospheric pressure (Patm). This creates a pressure gradient, allowing air to flow into the lungs.
The correct answer is A) Ppul < Patm. This indicates that the pressure inside the alveoli is lower than the pressure of the outside atmosphere, which is the condition necessary for inspiration. When Ppul is less than Patm, air naturally moves down the pressure gradient from the outside environment into the lungs to equalize the pressure.