Which gas molecules move from the region of their higher concentration to the region of their lower concentration inside the body of animals in the process of diffusion in animals?

Diffusion occurs when gas molecules move from a region of higher concentration to a region of lower concentration. 

Oxygen diffuses from the lungs into the bloodstream, where it is carried to cells throughout the body in animals. 

Carbon dioxide diffuses from the bloodstream into the lungs, where it is exhaled in the opposite direction. 

Although argon, krypton, and nitrogen are present in the atmosphere, they play no role in the diffusion process in animals.