Active and Passive Transport of Molecules Through Plasma Membrane

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The movement of molecules have two forms of transport through the plasma membrane: active transport and passive transport. Active processes require energy, such as ATP, in order for the molecules to be transported. In active transport, the cell administers ATP.i Within passive processes no energy is required and changes n pressure and concentration are the driving forces. Processes such as simple diffusion, facilitated diffusion, osmosis, and filtration are characterized as passive transport, while solute pumps are a form of active transport. Each of these form of transports occur in the cells of all living organisms and are essential to life.
The process of diffusion occurs in and out of a cell when molecules travel from areas of higher
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iii Due to the fact that water can move freely in and out of most membrane pores, it is also considered a passive process.
Filtration is the process of which both water and solutes permeate a membrane from a region of higher fluid (hydrostatic) pressure to an area of lower fluid pressure. iv Due to the fact that filtration is based on pressure and the size of membrane pores, it is a passive process. Within the human body filtration occurs in the kidney and encompasses both blood and the fluid in the kidney tubule pressures.
Active transport is a process that requires ATP in order for molecules to move. There are several reasons why active transport is required as oppose to passive transport: substances may be too large to pass through the membrane, substances may move against the concentration gradient as oppose to with it, or some substances may not be lipid soluble. v Amino acids and some sugars are transported into cells by solute pumps. An example of a solute pump is a sodium-potassium pump. Within a sodium-potassium pump, both K+ and Na+ are pushed into opposite regions across the cell membrane. Other processes that require ATP are pinocytosis and phagocytosis. Both pinocytosis and phagocytosis occurs when the cell membrane descends beneath the material in order to create a small vesicle, then pinches off into the cell. vi Phagocytosis is the process of cell eating, and phagocytic cells work
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