Water and the Fitness of the Environment

• Importance of Water   * The molecule that supports all of life   * Water is the biological medium here on Earth   * All living organisms require water more than any other substance
• Water Facts   * ¾ of the Earth’s surface is submerged in water   * The abundance of water is the main reason the Earth is habitable   * The polarity of water molecules results in hydrogen bonding   * Water is a polar molecule
• Water’s Polarity   * The polarity of water molecules     * Allows them to form hydrogen bonds with each other     * Contributes to the various properties' water exhibits
• Properties of water   * Cohesion/adhesion     * Is the bonding of a high percentage of the molecules to neighboring water molecules     * Is due to hydrogen bonding     * Like molecules bonding to each other       * Water attracting other water molecules     * Helps pull water up though the microscopic vessels of plants       * capillarity   * Surface tension     * It is a measure of how hard it is to break the surface of a liquid     * Is related to cohesion   * Temperature moderation     * Water moderates air temperature     * By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler     * Kinetic energy       * Energy of motion     * Heat       * Measure of the total amount of kinetic energy due to molecular motion     * Temperature       * Measures intensity of heat   * High specific heat     * The amount of heat that must be absorbed or lost for 1 gram of the substance to change its temperature by 1℃     * Water has a high specific heat, which allows it to minimize temperature fluctuation to within limits that permit life       * Heat is absorbed when hydrogen bonds break       * Heat is released when hydrogen bonds form   * Evaporative cooling     * Evaporation       * The transformation of a substance from a liquid to a gas       * Requires energy     * Heat of vaporization       * The quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas       * 100℃ steam has more heat than 100℃ boiling water     * Due to the water’s high heat of vaporization     * Allows water to cool a surface     * Sweating cools the body as heat energy from the body changes sweat into gas     * Insulation of Bodies of Water by Floating Ice       * The hydrogen bonds in the ice are more “ordered: than in liquid water, making the ice less dense       * Since ice floats in water, life can exist under the frozen surfaces of lakes and polar seas   * Universal solvent     * Water is a versatile solvent due to its polarity     * It can form aqueous solutions     * Called the universal solvent because so many substances dissolve in water     * The different regions of the polar water molecules can interact with ionic compounds called solutes and dissolve them     * Water can also interact with polar molecules such as proteins   * Hydrophilic and Hydrophobic Substances     * Hydrophobic       * Does not have an affinity for water       * Nonpolar       * Ex: lipids     * Hydrophilic       * Has an affinity for water       * Polar or ionic       * Ex: carbohydrates, salts
• Solute Concentration in Aqueous Solutions   * Since most biochemical reactions occur in water inside cells, it is important to learn to calculate the concentration of solutes in an aqueous solution
• Moles and Molarity   * A mole     * Represents the exact number of molecules of a substance in a given mass   * Molarity     * Number of moles of solutes per liter of solution
• Acids and Bases   * Acid     * Any substance that increases the hydrogen ion concentration of a solution   * Base     * Any substance that reduced the hydrogen ion concentration of a solution   * Dissociation of water molecules leads to acidic and basic conditions that affect living organisms   * Organisms must maintain homeostasis in the pH of their internal and external environments
• The pH Scale   * Scale goes from 1-14, where 7 is neutral   * The pH of a solution is determined by the relative concentration of hydrogen ions   * Difference of 10x in hydrogen ion concentration between any two pH values   * Acids have a higher number of H+ ions than a base   * Acids produce H+ ion in a solution   * Bases produce OH- in a solution
• Effects of Changes in pH   * Water can disassociate into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions   * Changes in the concentration of these ions can have a great effect on the pH in living organisms
• Buffers   * Substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution   * Consist of an acid-base pair that reversibly combines with hydrogen ions   * Made by organisms
• The Threat of Acid Precipitation   * Refers to rain, snow, or fog with a pH lower than pH 5.6   * It is caused primarily by the mixing of different pollutants with water in the air   * Can damage life in Earth’s ecosystems

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