Final answer:
The molecular weight of the gas is not an important factor in gas exchange, unlike the rate of blood flow, surface area, and partial pressures.
Step-by-step explanation:
Internal and external respiration depends on several factors important in gas exchange. The one factor that is NOT important is the molecular weight of the gas. Key factors that do influence gas exchange include the rate of blood flow through the tissue, the available surface area for gas exchange, and the partial pressure of the gases involved. Oxygen transport through the blood is facilitated by erythrocytes containing hemoglobin. This is driven by partial pressure differences between the blood and the tissues or alveoli, where internal and external respiration occur, respectively.