Final answer:
The exchange of oxygen and carbon dioxide across the respiratory membrane is facilitated by the process of diffusion, which is a passive transport mechanism that does not require energy.
Step-by-step explanation:
The exchange of oxygen and carbon dioxide across the respiratory membrane occurs through the process of diffusion. This is a passive transport mechanism in which gas molecules move from an area of higher concentration to an area of lower concentration, without the need for energy input. This process is vital for external respiration, where oxygen diffuses across the alveoli into the bloodstream while carbon dioxide diffuses in the opposite direction.
Diffusion is the dominant mechanism for gas exchange during respiration, which depends on a steep concentration gradient maintained by continuous blood flow and regular breathing. This mechanism is sufficient for delivering oxygen to tissues and removing carbon dioxide in humans and other large organisms thanks to their complex respiratory and circulatory systems. However, smaller or simple organisms may rely entirely on diffusion for their respiratory needs.
In summary, the correct answer to the question is B. diffusion, as this is the process that allows for the exchange of gases across cellular membranes in the lungs, without the need for energy.