NE

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