Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AP Biology Ch. 3 Water and the Fitness of the Environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Importance of Water: – Living cells are 70-95% water – Water covers ¾ of the Earth – Life evolved in water – Water exists in all 3 states in nature

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polarity of Water Polar covalent bonds hold 1 oxygen and 2 hydrogens together Hydrogen bonds hold 1 water molecule to another Water can form up to 4 bonds with neighboring water molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 3.2 Hydrogen bonds between water molecules Hydrogen bonds  + + ++ H H ++ ++ –– –– –– ––

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Properties of Water due to H bonds 1. Cohesion 2. Adhesion 3. Temperature moderator 4. Evaporative Cooling 5. Insulation of Bodies of Water by Floating Ice 6. Versatile solvent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Cohesion – hydrogen bonds holds water together 2. Adhesion – hydrogen bonds hold a substance to another polar substance Water conducting cells 100 µ m Figure 3.3 Water transport in plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Surface tension – -a measure of how hard it is to break the surface of a liquid -resists stretching/breaking Figure 3.4 Walking on water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3. Temperature Moderator High Specific Heat Water resists temperature changes when it absorbs or releases heat Temp. on Earth is stable (3/4 covered by water) Coast is milder than inland Marine environments are stable 4. Evaporative cooling - due to water’s high heat of vaporization Sweating cools mammals specific heat of a substance is defined at the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1º C.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5. Insulator - forms crystalline structures creating floating barriers -p rotects aquatic organisms – oceans and lakes don’t freeze solid b/c ice floats Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4.Versatile Solvent - dissolves polar & ionic substances due to it’s polarity Negative Oxygen regions of polar water molecules are attracted to sodium cations (Na + ) Cl – – – – – Na + Positive hydrogen regions of water molecules cling to chloride anions (Cl – ) – – – – – – Na + Cl – Figure 3.6 A crystal of table salt dissolving in water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molarity - Moles of solute per liter of solution Mole – molecular weight of a substance scaled from daltons to grams – How many grams of lactic acid (C 3 H 6 O 3 ) are in a.5 M solution of lactic acid? Answer: C 3 H 6 O 3 C 3 x 12g = 36g H 6 x 1g = 6g O 3 x 16g = 48g 90g x.5M = 45g – How many grams of salt (NaCl) must be dissolved in water to make 2 liters of a 2 M salt solution? (find molecular weight of each element and use in the equation) Answer:NaCl Na 23g x 2L = 46g Cl 34g x 2L = 68g 114g x 2M = 228g

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Difference b/t hydrophilic & hydrophobic Hydrophilic – “water loving” – Ionic & polar molecules dissolve in water Hydrophobic – “water fearing” – nonionic/nonpolar covalent bond molecules don’t dissolve in water Equal sharing of e- prevents hydrogen bonding – (ex. Lipids) Application: Major components of cell membranes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dissociation of Water – - Reaction producing hydroxide and hydronium ions -Water molecules when bump into one another transfer a single proton (H+) + H Hydronium ion (H 3 O + ) acid H Hydroxide ion (OH – ) base H H H H H H – + Changes in the concentration of these ions affect cell chemistry Pure water – concentration of H+ or OH- is M (at 25 o C)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 3.8 The pH scale and pH values of some aqueous solutions Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] Neutral [H + ] = [OH – ] Oven cleaner pH Scale Battery acid Digestive (stomach) juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach pH Scale - Describes how acidic or basic a solution is Each pH represents a 10 fold difference in hydronium and hydroxide ion concentration Buffers: biological fluids that accept/donate hydrogen ions from/to solution Applications: Most biological fluids – 6-8 pH *Exception: human stomach pH 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Difference b/t acid and base: – Acid – substance that increases the [H + ] of a sol’n – pH < 7 – Base – substance that reduces the [H + ] of a sol’n – pH > 7 pH Scale: – -log [H + ] – In any aqueous sol’n: [H + ] x [OH - ] = – Neutral sol’n: if [H + ] = & [OH - ] = – Acidic sol’n: if [H + ] = then [OH - ] = – Basic sol’n: if [H + ] = then [OH - ] = – What is the difference in [H + ] between sol’ns of pH 2 & pH 6 ? pH 2 has 10,000 more H + than pH 6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 3.9 Acid precipitation and its effects on a forest More acidic Acid rain Normal rain More basic Application: Impacts eggs/early developmental stages of aquatic organisms Wash away soil buffers/minerals Damages trees