Some organisms, probably including the earliest forms of life, live in and have adapted to solutions with extremes of pH. However, most organisms control the pH of the separate compartments within their cells. The normal pH of human red blood cells, for example, is 7.4, and deviations of even a few tenths of a pH unit can be fatal. The control of pH is made possible in part by buffers: chemical mixtures that maintain a relatively constant pH even when substantial amounts of an acid or base are added.
A buffer is a mixture of a weak acid and its corresponding base—for example, carbonic acid (H2CO3) and bicarbonate ions (HCO3-). If an acid is added to a solution containing this buffer, not all the H+ ions from that acid stay in solution. Instead, many of them combine with the bicarbonate ions to produce more carbonic acid. This reaction uses up some of the H+ ions in the solution and decreases the acidifying effect of the added acid:
If a base is added, the reaction essentially reverses. Some of the carbonic acid ionizes to produce bicarbonate ions and more H+, which counteracts some of the added base. In this way, the buffer minimizes the effects of an added acid or base on pH. This is what happens in the blood, where this buffering system is important in preventing significant changes in
Digital pH meter
Digital pH meter
Acidic pH value O
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.