Types Of Transport Within A Cell

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There are many different types of transport within a cell that can end up being very complex. On the outside of the cell is the plasma membrane that protects it from the outside environment. The plasma membrane is very picky about what it allows through it. It wants to let in oxygen and nutrients, but keep out harmful bacteria. It also wants to keep in the proteins and nutrients that are already in the membrane. Because of this property, the plasma membrane is called a selectively permeable membrane and it has two basic transport processes. In passive transport processes it is the concentration differences that drives the movement. The two passive transports are diffusion and filtration. In active transport processes the cell provides energy in the form of Adenosine Triphosphate (ATP) to power the process. The two active transport processes are primary which is driven directly by ATP or secondary which is driven indirectly by ATP (Marieb P61). For the most part, molecules will diffuse passively through the plasma membrane if they are small enough, but they must be aided by a concentration gradient. A concentration gradient is when there is a difference in concentration of a substance from one area to another (Amerman P75). This property of the plasma membrane is critical to the cell. Without this property the cell would not be able to exchange the oxygen and nutrients it needs to with the extracellular fluid (the fluid located in the spaces between the cells). The
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