Another physical requirement is the extent of acidity or alkalinity

Another physical requirement is the extent of acidity or alkalinity

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Another physical requirement is the extent of acidity or alkalinity, referred to as the pH of  a solution. For most bacteria, the optimum pH is between 6.5 and 7.5. Since the pH of  most human tissue is 7.0 to 7.2, these neutrophilic bacteria usually grow well in the body.  Certain bacteria, such as those in sauerkraut and yogurt, prefer acidic environments of  6.0 or below. These bacteria are said to be acidophilic. Molds and yeasts are among  other common acidophilic microorganisms.  Microbial growth proceeds best when the osmotic pressure is ideal. Normally, the salt  concentration of microbial cytoplasm is about 1 percent. When the external environment  also has a 1 percent salt concentration, then the osmotic pressure is optimum. Should 
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Unformatted text preview: the external salt concentration rise, as when food is salted, water will flow out of the microbial cytoplasm by osmosis through the cell membrane into the environment, thereby causing the microorganisms to shrink and die. By comparison, if exterior water is free of salt, it will flow through the cell membrane into the cytoplasm of the cell, causing the organism to swell and burst. Microorganisms that live in marine environments can tolerate high salt concentrations. These organisms are said to be halophilic. They include diatoms and dinoflagellates, two types of unicellular algae that lie at the base of oceanic food chains. There are many other species of halophilic bacteria, fungi, protozoa, and algae....
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