CELL TRANSPORT

=Cell Transport= The movement of materials into and out of the cell is essential for: *the uptake of nutrients *the elimination of wastes *the exchange of oxygen and carbon dioxide for cellular respiration *cell signalling [image:http://i.imgur.com/BEElO4a.png?1] The movement of materials across the cell membrane is highly regulated. This regulation is possible because the membrane is ''selectively permeable'' -not all substances are capable of moving across it. Some smaller hydrophobic (non-polar / fat soluble) molecules are able to diffuse directly through the membrane. Many charged molecules (ions) are unable to diffuse through the lipid layers of the membrane, while other molecules may simply be too large. The transport of most substances is mediated by specialised carrier proteins embedded in the membrane. These proteins not only regulate what crosses the membrane, but also when substances are able to cross the membrane. For instance during vigorous exercise more glucose must be released into the blood-stream and absorbed by our muscle cells. ==Passive & Active Transport== [image:http://i.imgur.com/hAnOALG.png?2] '''PASSIVE TRANSPORT:''' *Substances are moved ''down their concentration gradient'', from an area of high to low concentration *''Does not require energy'' (ATP) *May involve specialised proteins that facilitate the movement of materials across the membrane '''ACTIVE TRANSPORT:''' *Substances are moved ''against their concentration gradient'', from an area of low to high concentration *''Requires energy'' (ATP) *Requires specialised proteins that force materials across the membrane