Life’s Components Water, pH, and Biological Molecules The Importance of Water to Life •71 percent of Earth’s surface, 66 percent of weight of human body. •Important properties of water. –Required/generated by many cellular reactions (breaking down food). –Important solvent—hydrogen bonds with polar or charged molecules (NaCl). Important Properties of Water •Solid versus liquid densities, importance for marine organisms. •Specific heat (importance for insulating Earth, and for cooling living organisms by sweating). •Cohesion and surface tension. •Hydrophobic versus hydrophilic molecules. Acids and Bases •Common acids (vinegar) and common bases (lye). •Definition of an acid—substance that yields hydrogen ions in solution (HCl). •Definition of a base—substance that accepts hydrogen ions (NaOH).
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