Materials enter or leave the cells in the following ways: Diffusion: It is the movement of substances from the region of the higher concentration to the region of their lower concentration. Osmosis: Movement of water molecules from their higher concentration to lower concentration through a semi-permeable membrane. (a) Movement of ions and molecules across a membrane against the concentration gradient, i.e. from lower to higher concentration. (b) It requires energy (ATP). (a) Transport of large quantities of micro-molecules, macro-molecules and food particles through the membrane. (b) They are of two types:Pinocytosis: Bulk intake of fluid, ions and molecules across the cell membrane by forming small endocytic vesicles of 100-200 nm in diameter. Also called ‘Cell drinking’. Phagocytosis: Ingestion of large particles by living cells. Also called ‘Cell eating’.