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 3 billion years of evolution in water Search for water on other planets

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: The Molecule That Supports All of Life Water is the biological medium on Earth All living organisms require water more than any other substance Most cells are surrounded by water, & cells are ~ 70-95% water Water is the main reason the Earth is habitable

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Concept 3.1: The polarity of water molecules results in hydrogen bonding water molecule- polar molecule: opp ends have opp charges Polarity allows water molecules to form H-bonds w/ each other Animation: Water Structure Animation: Water Structure

LE 3-2 Hydrogen bonds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life 4 of water’s properties that facilitate an environment for life: I. Cohesive behavior II. Ability to moderate Tm III. Expansion upon freezing IV. Versatility as a solvent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cohesion Cohesion- H bonds hold H 2 O molecules together; helps transport of H 2 O against gravity in plants Adhesion of H 2 O 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- 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 H 2 O absorbs heat from warmer air & releases stored heat to cooler air H 2 O can absorb or release a lg amt of heat w/ only a slight change in its own Tm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heat and Temperature Kinetic energy- energy of motion Heat- measure of the total amt of kinetic energy due to molecular motion Tm measures intensity of heat due to the avg kinetic energy of molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water’s High Specific Heat The specific heat of a substance is the amt of heat that must be absorbed or lost for 1 g of that substance to change its Tm by 1ºC H 2 O’s high specific heat minimizes Tm changes to w/in limits that permit life – Heat is absorbed when H-bonds break – Heat is released when H-bonds form

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evaporative Cooling Evaporation- liquid to gas Heat of vaporization- heat a liquid must absorb for 1 g to be converted to gas As a liquid evaporates, its remaining surface cools, a process called evaporative cooling Evaporative cooling helps stabilize Tm’s in organisms & bodies of water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulation of Bodies of Water by Floating Ice Ice floats in liquid water b/c H bonds in ice are more “ordered,” making ice less dense – As the tm of water decreases, h- bonds are not broken as fast More hydrogen bonds  greater spacing The density of ice < liquid water If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

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The Solvent of Life Soln-liquid homogeneous mix of substances Solvent- dissolving agent of a soln Solute- substance dissolved Water is a versatile solvent due to its polarity An aqueous solution is one in which water is the solvent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water is an effective solvent because it readily forms hydrogen bonds When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water can also dissolve compounds made of nonionic polar molecules Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

LE 3-7a Lysozyme molecule in a nonaqueous environment.

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrophilic and Hydrophobic Substances Hydrophilic-“water loving” Hydrophobic-”water fearing”

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Solute Concentration in Aqueous Solutions Most biochemical reactions occur in water Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular mass - sum of all masses of all atoms in a molecule #’s of molecules are usually measured in moles, w/ one mole being 6.02 x molecules Molarity (M)- # of moles of solute per L of soln

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How would you make 1 liter of a 0.5 M solution of NaCl? 1 st find out the molecular mass of NaCl Na has a molecular mass of 23 Cl has a molecular mass of 35 Together the mass of NaCl is 58

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Weigh out 29 grams of NaCl and dissolve it in 1 L of distilled water.

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 H atom in a H bond b/w 2 water molecules can shift from 1 to the other: – The H atom leaves its e- behind & is transferred as a proton, or hydrogen ion (H + ) – The molecule w/ 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 The process can be described in a simplified way as the separation of a water molecule into a hydrogen ion (H + ) and a hydroxide ion (OH - ) Though statistically rare, the dissociation of water molecules has a great effect on organisms Changes in concentrations of H + and OH - can drastically affect the chemistry of a cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of changes in pH Concentrations of H + and OH - are equal in pure water Adding acids & bases, modifies the concentrations of H + & OH - Biologists use the pH scale to describe how acidic or basic a soln is

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acids and Bases Acid- any substance that ↑s the H + conc of a soln; pH < 7 Base- any substance that ↓s the H + conc of a soln; pH > 7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The pH Scale pH- relative concen of H+ ions in a soln Most biological fluids- pH b/w 6 & 8

LE 3-8 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 concen’s of H + & OH - in a soln Most buffers consist of an acid-base pair that reversibly combines with H +

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Threat of Acid Precipitation Acid precipitation (ppt)- rain, snow, or fog w/ a pH < 5.6; caused by mixing pollutants w/ water in the air Acid precipitation can damage life in lakes and streams Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

LE More basic Normal rain More acidic Acid rain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exam practice Buffers are substances that help resist shifts in pH by A) releasing H+ in acidic solutions. B) donating H+ to a solution when they have been depleted. C) releasing OH- in basic solutions. D) accepting H+ when the are in excess. E) both B and D

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exam practice Buffers are substances that minimize changes in the concentrations of H+ and OH- ions in a solution The answer is E

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exam practice Which of the following is responsible for the cohesive property of water? A. H-bonds b/w the oxygen atoms of 2 adjacent water molecules B. covalent bonds b/w Hydrogen atoms of 2 adjacent water molecules C. H-bonds b/w the oxygen atom of 1 water molecule and the hydrogen atom of another D. covalent bonds b/w O atom of 1 water molecule & H atom of another E. H-bonds b/w water molecules and other types of molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exam practice The cohesive property of water is due to the hydrogen bonding between water molecules, specifically the hydrogen bonds b/w the oxygen atom of one water molecule and the hydrogen atom of another water molecule The answer is C