This chapter describes the structure of the water molecule and explores the many ways that polar covalent bonds and hydrogen bonds among water molecules affect organisms and their interactions with their environments. In addition, this chapter discusses topics including concentrations of solutions, hydrogen ion concentration (pH), and buffer solutions. | Chapter 3 Water and the Fitness of the Environment Overview: 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 Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable Figure Concept : The polarity of water molecules results in hydrogen bonding The water molecule is a polar molecule The polarity of water molecules Allows them to form hydrogen bonds with each other Contributes to the various properties water exhibits Hydrogen bonds + + H H + + – – – – Figure Concept : Four emergent properties of water contribute to Earth’s fitness for life Cohesion Water molecules exhibit cohesion Cohesion Is the bonding of a high percentage of the molecules to neighboring molecules Is due to hydrogen bonding Cohesion Helps pull water up through the microscopic vessels of plants Water conducting cells 100 µm Figure Surface tension Is a measure of how hard it is to break the surface of a liquid Is related to cohesion Figure Moderation of Temperature Water moderates air temperature By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler Heat and Temperature Kinetic energy Is the energy of motion Heat Is a measure of the total amount of kinetic energy due to molecular motion Temperature Measures the intensity of heat Water’s High Specific Heat The specific heat of a substance Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC Water has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit life Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form Evaporative Cooling Evaporation Is the transformation of a substance from a liquid to a gas Heat of vaporization Is the quantity of heat a liquid must absorb for 1 gram | Chapter 3 Water and the Fitness of the Environment Overview: 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 Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable Figure Concept : The polarity of water molecules results in hydrogen bonding The water molecule is a polar molecule The polarity of water molecules Allows them to form hydrogen bonds with each other Contributes to the various properties water exhibits Hydrogen bonds + + H H + + – – – – Figure Concept : Four emergent properties of water contribute to Earth’s fitness for life Cohesion Water molecules exhibit cohesion Cohesion Is the bonding of a high percentage of the molecules to neighboring molecules Is due to hydrogen bonding Cohesion Helps pull water up through the microscopic vessels of plants Water conducting cells 100 µm Figure
