the pH scale measures the acidity or the basicity of a solution. Solutions that have a pH below 7 are acids. Solutions that have a low pH are more acidic than solutions that have a higher pH . The graph below shows shows the pH of four common fruit juices .

the sphincter muscles at the end of the digestive tract is the anus.

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not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.