Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 3 Water and the Fitness of the Environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Overview: The Molecule That Supports All of Life All living organisms require water more than any other substance – cells themselves are about 70-95% water The abundance of water is the main reason the Earth is habitable

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen bonds Concept 3.1: The polarity of water molecules results in hydrogen bonding Polarity allows water molecules to form hydrogen bonds with each other Animation: Water Structure Animation: Water Structure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life Four of water’s properties that facilitate an environment for life: Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cohesion Cohesion helps the transport of water against gravity in plants Adhesion of water to plant cell walls also helps to counter gravity Animation: Water Transport Animation: Water Transport

LE 3-3 Water-conducting cells 100 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is related to cohesion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Moderation of Temperature High Heat Capacity – Water can absorb or release a large amount of heat with only a slight change in its own temperature

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heat and Temperature Kinetic energy is the energy of motion Heat - total amount of kinetic energy Temperature - intensity of heat due to the average kinetic energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 absorbed when hydrogen bonds break released when hydrogen bonds form

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evaporative Cooling Evaporation is transformation of a substance from liquid to gas – evaporative cooling

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulation of Bodies of Water by Floating Ice

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Solvent of Life A solution is a liquid that is a homogeneous mixture of substances – solvent – solute An aqueous solution is one in which water is the solvent

LE 3-6 Na + Cl – – – – – – – – – – – –

LE 3-7b Lysozyme molecule in a aqueous environment.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrophilic and Hydrophobic Substances A hydrophilic substance is one that has an affinity for water A hydrophobic substance is one that does not have an affinity for water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular mass = sum of all masses of all atoms in a molecule (Measured in Daltons) Numbers of molecules are usually measured in moles, with one mole being 6.02 x molecules -Avogadro’s Number Molarity is the number of moles of solute per liter of solution

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molarity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molarity Calculate: 1 mol of ethyl alcohol (C 2 H 6 O) Calculate: 1 mol of sucrose (C 12 H 22 O 11 )

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molarity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 3.3: Dissociation of water molecules leads to acidic and basic conditions that affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: – hydrogen atom is transferred as a proton, or hydrogen ion (H + ) – The molecule with the extra proton is now a hydronium ion (H 3 O + ) – The molecule that lost the proton is now a hydroxide ion (OH - )

LE 3-UN53 Hydronium ion (H 3 O + ) Hydroxide ion (OH – )

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of changes in pH Concentrations of H + and OH - are equal in pure water acids and bases modify the concentrations of H + and OH -

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acids and Bases acid increases the H + concentration base reduces the H + concentration pH Scale Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Pure water Human blood Urine Rainwater Black coffee Tomato juice Vinegar, beer, wine, cola Digestive (stomach) juice, lemon juice Battery acid Neutral [H + ] = [OH – ] Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ]

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Buffers The internal pH of most living cells must remain close to pH 7 – Buffers minimize changes in concentrations of H + and OH - in a solution Most buffers consist of an acid-base pair that reversibly combines with H + – Carbonic Acid Bicarbonate ion + Hydrogen ion – H 2 CO 3 HCO H +

LE More basic Normal rain More acidic Acid rain