PASSIVE TRANSPORT

=Passive Transport= Passive transport is the movement of substances across the membrane. Unlike active transport substances move down their concentration gradient and the process does not require energy, relying solely on diffusion. [image:http://i.imgur.com/QhIYQKI.png?1] Diffusion is the movement of particles down a concentration gradient. Diffusion is the result of random particle movement and results in the '''net''' movement of particles from an area of high concentration to low concentration. Individuals particles do not move in any particular direction, but overall there are more particles moving down the concentration gradient. The word diffusion is actually derived from the Latin word, "diffundere", which means "to spread out" (if a substance is “spreading out”, it is moving from an area of high concentration to an area of low concentration). ==Diffusion across the membrane== [image:http://i.imgur.com/Et0qZHn.gif] Some substances, especially smaller & non-polar molecules, are able to diffuse directly through the membrane. For instances dissolved gasses such as oxygen and carbon dioxide can diffuse directly through the membrane. ==Facilitated Diffusion== [image:http://i.imgur.com/m6MGm5w.png] The membranes hydrophobic layer (formed by the lipid tails) can prevent the diffusion of charged molecules across the membrane. Thus, cells will often incorporate specialised proteins called '''ion channels''' into the membrane that act that like a tunnel, allowing specific ions to diffuse through them. This is driven solely by diffusion, it does not require cellular energy and the molecules will move down their concentration gradient.