The Movement Of Substances Into And Out Of Cells

THE MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS

All cells are separated from their surroundings by a surface membrane—the plasma membrane; eukaryotic cells are further divided internally by a variety of membranes, including those of the endoplasmic reticulum, dictyosomes, and the bounding membranes of organelles. These cellular membranes are not impenetrable barriers, for cells are able to regulate the amount, kind, and often the direction of movement of substance that pass across membranes. This is an essential capacity of living cells because few metabolic process could occur at reasonable rates if they depended upon the concentration of necessary substances found in the cell’s surroundings. Control of the exchange of substance across membranes depends on the physical and chemical properties of the membranes and of the ions or molecules that move through the. Water is the most important of the molecules moving into and out of cells. (Peter H. Raven, 1986: 58) The function of cell membrane include as a regulator of entry and exit of substances. That settings allows the cell to obtain the appropriate pH and concentration of substances to be controlled. Cells also can obtain the input of substances and ions required and dispose of substances that are not needed. All control is depending on transport through the membrane. Displacement of molecules or ions across the membrane there are 2 kinds, they are passive transport and active transport. 1. Passive transport is the movement of molecules or ions without the use of cellular energy. Molecular displacement occurs spontaneously. Examples of passive transport are diffusion, osmosis, and facilitated diffusion. 2. Active Transport is the movement of molecules or ions by using the energy of that cell. Displacement can occur even against concentration. Examples of active transport are the pumping of sodium, potassium, endocytosis, and exocytosis. (Syamsuri Istamar, 2007 : 20)

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