Biology  5/e   Raven/Johnson
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Acids and bases: Acids are substances that dissociate to form H⁺ ions when they are dissolved in water. The higher the concentration of H⁺ ions, the stronger the acid. Acid strength is indicated by the pH scale, which is inversely proportional to the H⁺ concentration. Pure water has a pH of 7; the stronger the acid, the lower the pH value. Acids have pH values between 0 and 7. Bases act the opposite of acids. They decrease the concentration of H⁺ and have pH values between 7 and 14.

Glycogen: Organisms store glucose in an insoluble form by converting it to polysaccharides called starches. In animals, the starch molecule is composed of highly branched chains of amylose. Each amylose chain consists of hundreds of glucose molecules linked together. The specific name for this animal starch is glycogen. Glucose is converted to glycogen in the liver.

Lysosomes: Cells package their digestive enzymes in vesicles called lysosomes. These vesicles are formed from the Golgi complex and isolate the digestive enzymes so that they can be transported to where they are needed inside or outside the cell while at the same time preventing the enzymes from digesting the cell itself. Maintaining the lysosome membrane requires a constant expenditure of energy. If an adequate supply of ATP is not available, the lysosome membrane is digested and then the rest of the cytoplasm is attacked by the digestive enzymes, killing the cell.

Phagocytosis: During phagocytosis, a cell surrounds and engulfs solid particles such as other cells or food fragments. The particles wind up inside the cell, enfolded in a vesicle. This vesicle can then fuse with a lysosome, and particles can be digested. Phagocytosis is common in protists and in cells lining the digestive tracts of many animals.

Enzymes: Enzymes are biological catalysts. They catalyze or speed up chemical reactions in living organisms by lowering the activation energies of the reactions. Enzymes are globular proteins with complex three-dimensional shapes that determine their ability to function. An enzyme can only bind with a specific substrate if there is a match between the shape of the enzyme's active site and the shape of the substrate molecule. Any factor that changes or destroys the shape of the enzyme (e.g., such as pH or temperature changes, or inhibitors) decreases the ability of the enzyme to function properly.

Oxidative respiration: Oxidative respiration is the process that provides the energy that is required to keep living organisms alive. All organisms obtain energy to perform work by oxidizing organic compounds and using the energy released during the oxidation to synthesize ATP via proton pumps. Vertebrates eat food to obtain the necessary energy-rich organic compounds, such as sugars and fats, that will be oxidized.

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