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Chapter 3. Water and the Environment. The Molecule That Supports All of Life. Can exist in 3 forms at once Main reason Earth is habitable Life on earth probably evolved in water Living organisms require water more than any other substance Most cells are surrounded by water
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Chapter 3 Water and the Environment
The Molecule That Supports All of Life • Can exist in 3 forms at once • Main reason Earth is habitable • Life on earth probably evolved in water • Living organisms require water more than any other substance • Most cells are surrounded by water • Cells are compose of 70–95% water
The polarity of water results in hydrogen bonds • polar molecule • Oxygen very electronegative • Attractions exist between partially charged poles
Emergent properties of water contribute to life on Earth • Properties of water that support life: • Cohesive and Adhesive • Ability to moderate temperature • Solid form lighter than liquid form • Versatility as a solvent
Cohesion • Water molecules tend to stick to each other • Surface tension
Adhesion • Water molecules stick to other polar molecules • Counteracts gravity
Moderation of Temperature • Heat is transferable energy • Objects exchange heat until they are achieve an equal temperature • Water has a high heat capacity • Absorbs/releases great amounts of heat
Heat is a form of energy and temperature is a measure of the kinetic energy of an object or solution • Heat energy increases the movement of molecules • Water has high specific heat • Can absorb and release great amounts of heat, influencing the temperature
Water has a high heat of vaporization • Evaporative cooling
Water Expands when it freezes • Ice floats in liquid water • Hydrogen bonds are more “ordered,” making ice less dense • Floating ice insulates bodies of water
Water is the solvent of life • Solution • Solvent • Solute • Aqueous solution
Hydrophilic substances • Hydrophobic substances Hydrogen Shell Salt, an ionic compound, dissociates in water
(b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein’s surface attract water molecules. (a) Lysozyme molecule in a nonaqueous environment • Even large polar molecules such as proteins can dissolve in water but maybe not completely
Acids and Bases • Changes in hydrogen ion concentration results in acidic and basic solutions • Measured as pH
Acid • substance that increases H+ of a solution • Base • substance that reduces H+ of a solution • Salt • substance that has no impact on H+ of a solution
pH calculated by: • pH = -log [H+] • For a neutral solution • [H+] is 10–7 = –(–7) = 7 • Each number represents a tenfold difference in ion concentrations
Buffers • Buffers • minimize changes in H+ and OH– concentration • accept or donate H+ to maintain consistent pH • pH of living cells maintained close to 7
Blood always contains a combination of some carbonic acid and some bicarbonate ions. When hydrogen ions (H+) are added to blood: When hydroxide ions (OH−) are added to blood: Prevents any significant change in blood pH
Threats to Earth’s Water Quality Acid Precipitation Reduction of CO32- in Oceans