Amoebas are single-celled eukaryotic organisms. Their defining characteristic is that they move by extending their cytoplasm into foot-like structures which are called pseudopodia.
Diffusion:
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.
Diffusion in Amoeba:
Amoeba gets oxygen gas dissolved in surrounding water through its plasma membrane by the process of diffusion. The oxygen gas diffused inside the body is used up by the amoeba. In the body, the oxygen gas absorbed is used to break down the complex food material into simple molecules.