WATER AND THE FITNESS OF THE ENVIRONMENT CHAPTER 3 WATER AND THE FITNESS OF THE ENVIRONMENT

WATER’S POLARITY AND ITS EFFECTS WATER IS A POLAR MOLECULE ITS POLAR BONDS AND ASSYMMETRICAL SHAPE GIVE WATER MOLECULES OPPOSITE CHARGES ON OPPOSITE SIDES

HYDROGEN BONDING IN WATER MOLECULES The polar molecules of water are held together by H+ bonds Positively charged H of one molecule is attracted to negatively charged O of another water molecule Each water molecule can form four H bonds

PROPERTIES OF WATER HAS COHESIVE BEHAVIOR RESISTS CHANGES IN TEMPERATURE HAS A HIGH HEAT OF VAPORIZATION AND COOLS SURFACES AS IT EVAPORATES EXPANDS WHEN IT FREEZES IS A VERSATILE SOLVENT

COHESIVE PROPERTIES OF WATER COHESION- phenomenon of a substance being held together by hydrogen bonds In water, enough molecules are H+ bonded together at one time to give it amazing structure not found in any other liquid Contributes to the upward transport in plants

SURFACE TENSION SURFACE TENSION- measure of how difficult it is to stretch or break the surface of a liquid Water has a greater surface tension than most liquids due to all of the H+ bonds it forms S.T. causes water to bead also due to H+ bonds

WATER MODERATES TEMPERATURES ON EARTH KINETIC ENERGY-the energy of motion HEAT- total kinetic energy due to molecule motion in a body of matter TEMPERATURE-measure of heat intensity due to the average kinetic energy of molecules in a body of matter CALORIE- amount of heat it takes to raise the temperature of one gram of water by one degree Celsius

CELSIUS SCALE AT SEA LEVEL 100°C (212°F) = WATER BOILS 37°C (98.6°F) = HUMAN BODY TEMP 23°C (72°F) = ROOM TEMP 0°C(32°F) = WATER FREEZES

WATER’S HIGH SPECIFIC HEAT Water has a high specific heat, which means that it resists temperature changes when it absorbs or releases heat ** SPECIFIC HEAT-amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by one degree Celsius.

BIG BODIES OF WATER Water covers 3/4’s of the planet, keeps temp. fluctuations within a range suitable for life Coastal areas have milder climates than inland The marine environment has a relatively stable temperature

EVAPORATIVE COOLING Vaporization(evaporation) - transformation from liquid to gas For water molecules to evaporate, hydrogen bonds must be broken which requires heat energy WATER’S HIGH HEAT OF VAPORIZATION: Moderates the Earth’s climate Stabilizes temp. in aquatic ecosystems Helps organisms from overheating by evaporative cooling

WATER’S HIGH SPECIFIC HEAT WATER HAS A HIGH SPECIFIC HEAT - THIS MEANS THAT IT TAKES A LOT OF ENERGY TO CHANGE THE TEMPERATURE OF WATER AS THE ENVIRONMENT GETS COLDER, THE MOLECULES HAVE LESS KINETIC ENERGY AND MOVE CLOSER TOGETHER FORMING H+ BONDS THAT RELEASE ENERGY AS THEY FORM DUE TO A DECREASE IN FREE ENERGY (DG)

OCEANS AND LAKES DON’T FREEZE SOLID BECAUSE ICE FLOATS Because of hydrogen bonding, water is less dense as solid than it is as a liquid, therefore ice floats Water is densest at 4°C Water contracts as it cools to 4°C As water cools from 4°C to freezing (0°C) it expands and becomes less dense

WATER MOLECULES FORMING ICE NOTICE THE LAYERS AND SPACING OF THE WATER MOLECULES

FORMATION OF ICE AS ICE FORMS, EACH WATER MOLECULE FORMS A MAXIMUM OF 4 H+ BONDS, WHICH KEEPS WATER MOLECULES FURTHER APART THAN THEY ARE IN A LIQUID STATE

HOW EXPANSION OF WATER HELPS THE ENVIRONMENT Prevents deep bodies of water from freezing solid from the bottom up Since ice is less dense, it forms on the surface first. As water freezes it releases heat to the water below and insulates it Makes the transitions between seasons less abrupt. As water freezes, H+ bonds form releasing heat. As ice melts, H+ bonds break absorbing heat

WATER IS THE SOLVENT OF LIFE SOLUTION- a liquid that is a completely homogenous mixture of two or more substances SOLVENT- dissolving agent of a solution SOLUTE- substance dissolved in a solution AQUEOUS SOLUTION - solution in which water is the solvent ***WATER IS A VERSATILE SOLVENT DUE TO THE POLARITY OF THE WATER MOLECULE

HYDROPHILIC AND HYDROPHOBIC HYDROPHILIC-means water loving; ionic and polar substances HYDROPHOBIC-means water fearing;are not water-soluble ***MOST BIOCHEMICAL RXNS INVOLVE SOLUTES DISSOLVED IN WATER; THERE ARE 2 IMPORTANT PROPERTIES OF AQUEOUS SOLUTIONS 1) SOLUTE CONCENTRATION 2) pH

SOLUTE CONCENTRATIONS MOLECULAR WEIGHT-sum of the weight of all atoms in a molecule (expressed in daltons) MOLE- amount of substance that has a mass in grams equivalent to its molecular weight in daltons MOLARITY- number of moles of solute per liter of solution

THE DISSOCIATION OF WATER WHAT HAPPENS: A hydrogen ion (proton with +1 charge) is transferred from one water molecule to another, creating a hydronium ion (H30+) H2O + H20 <--> H30+ + OH- ***THIS REACTIONS IS REVERSIBLE

DISSOCIATION OF WATER

ACIDS AND BASES ACID BASE Substance that increases the [ H+] of a solution Also removes OH- because it tends to combine with H+ to form water BASE Substance that reduces the relative[ H+] of a solution May also increase [OH-]

THE pH SCALE pH < 7 = acid Presence of H+ ions pH of 7 = neutral pH > 7 = base Presence of OH- ions ** most biological fluids are within the pH range of 6 to 8 **stomach acid - 1.5

BUFFERS HOW BUFFERS WORK: By minizing wide pH fluctuations, buffers help organisms maintain a healthy pH of body fluids Buffers are combinations of H+ donor and H+ acceptor forms in a solution of weak acids or bases They work by accepting H+ ions from solutions when they are in excess and donating them when they have been depleted

ACID PRECIPITATION WHAT IS IT??? Rain, snow, or fog more strongly acidic than pH 5.6 Occurs when sulfur oxides and nitrogen oxides in the atmosphere react with water in the air to form acids which fall to Earth in precipitation Major oxide source is the combustion of fossil fuels by industry and cars Acid rain affects the fitness of the environment to support life