Biological membranes

Biological membranes - Biological Membranes SOLUTES,...

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Biological Membranes SOLUTES, SOLVENTS, SOLUTIONS, TONICITY AND ENTROPY In order to understand how biological membranes function you need to know some basic and important concepts. A solution is a liquid that contains dissolved molecules. The liquid that dissolved the molecules (the “dissolver”) is known as the solvent and the substance that was dissolved (the “dissolvee”) is the solute. The most basic example of this concept is salt water. The solution is salt water, the solvent is water and the solute is salt. Another solution is blood. Can you think of other examples? The relative amount of solute in a solution is expressed in terms of a solution’stonicity. Notice that a solution’s tonicity is a relative term and is only used when comparing similar solutions (in other words these terms are not used to describe a single solution, only one solution relative to other solutions). If a solution contains less dissolved solute than another solution (salt water from the Pacific Ocean versus salt water from the Dead Sea, respectively) the first solution is said to be hypotonic to the second solution (think hypoglycemic, or low blood sugar). If we reverse this scenario we can say that Dead Sea water is hypertonic to Pacific Ocean water or contains more solute (think hyperactive child or a kid that has a lot of energy). If we compared two samples of Dead Sea water we can say that they are isotonic or equal in solute content to one another. Finally, entropy refers to the increasing randomness of molecules in a solution. Remember, molecules of a solute move randomly in solution. If you pour honey into hot water it is initially very concentrated in one area of the mug but given time the honey will dissolve and the sugar molecules will spread out randomly and evenly in the solution. Entropy is positively correlated with temperature. Recall your first lessons on matter from grade school. Solid elements are a barely-moving matrix of molecules. As temperature increases this matrix breaks down and the molecules move faster and faster; so a liquid contains little order and moving molecules, and
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Biological membranes - Biological Membranes SOLUTES,...

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