Introduction
Body cells are surrounded by plasma membrane that controls the movement of substances into and out of the cells. Plasma membrane is a semi-permeable. Consequently, it can only allow certain substances to move across it into the cells or out of the cell. Three main processes are involved in the movement of substances across the plasma membrane: diffusion, active transport, and osmosis. Diffusion refers to the movement of molecules down a concentration gradient (Chiras, 1999). However, there are two main types of diffusion: Simple and facilitated diffusion. In simple diffusion, molecules pass through the semi permeable membrane without assistance. Continue reading...