Final answer:
The direction of gas movements in internal respiration is determined by partial pressure differences, as gases move from high to low pressure areas to reach equilibrium.
Step-by-step explanation:
The direction of gas movements in internal respiration is determined by A. Partial pressure differences. This is because gases tend to migrate from areas where their partial pressure is high to areas where the partial pressure is low, moving down their concentration gradient. Dalton's law explains that each gas in a mixture exerts its own partial pressure, contributing to this movement. Oxygen diffuses from the high partial pressure in the alveoli to the lower partial pressure in the blood, while carbon dioxide moves in the opposite direction to maintain equilibrium.