Biology. The Movement of Molecules

Every cell is surrounded by a plasma membrane. The cell membrane is selectively permeable- only certain substances can cross it freely. The structure of the membrane allows materials to move across it by 2 main means: active and passive transport. Password transport involves two processes: Diffusion and Osmosis. Passive transport allows some substances such gases and water to move into and out of the cell without using energy. Active transport includes processes such as "ion pumps", "exocytosis" and "phagocytosis". …