Define. diffusion. endocytosis. exocytosis. phagocytosis. osmotic pressure.

Diffusion is the movement of the molecule (in gaseous form) from a region of high concentration to a region of low concentration until equilibrium is achieved.  The movement of these molecules is always down the gradient and the movement of the molecules is stochastic

Endocytosis is the uptake of large molecule, that can't pass through the pores of the cell membrane, by a cell. It involves the invagination of the cell membrane engulfing the materials and budding off into a vesicle. The materials are therefore internalized and are transported into the cell.

Exocytosis is the reverse of endocytosis. The material comes from inside of the cell and carried in a vesicle. The vesicle binds with the cell membrane and the part in contact with the cell membrane diffuses off. The contents of the vesicle are therefore emptied outside of the cell.  

Phagocytosis is the ingestion of an organism such as bacteria by another cell such as a phagocytic immune cell or amoeba. The process of phagocytosis is similar to that of endocytosis. However, this process is aided by cell membrane receptors on the surface of the phagocyte that recognizes and binds the epitopes of the bacteria.

Osmotic pressure is the bare minimum pressure required to be exerted to prevent the movement of water, by osmosis, from a low concentrated solution to a higher concentrated solution through a semipermeable membrane.