1. Chapter 3 Water and the Fitness of the Environment 1

2. Why is water so important? 2

3. Importance of water Cell chemistry occurs in the watery cytoplasm Water moderates temperatures Universal solvent

4. How much of the earth is water? 4

5. Water Facts Three-quarters of the Earth’s surface is water The abundance of water is the main reason the Earth is habitable

6. What important fact about water have we already learned? 6

7. Water Facts The water molecule is polar The polarity results in hydrogen bonding 7

8. How does hydrogen bonding relate to the properties of water? 8 Hydrogen bonds + + H H + +  – –  – –  – –  – – Figure 3.2

9. Properties of water Six emergent properties of water contribute to Earth’s fitness for life 1.Cohesion/Adhesion 2.Surface tension 3.Temperature Moderation 4.High specific heat 5.Evaporative cooling 6.Universal solvent 9

10. Emergent Properties Emergent properties – result from the arrangement and interaction of parts within a system – may characterize nonbiological entities as well a functioning bicycle emerges only when all of the necessary parts connect in the correct way Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. The Power and Limitations of Reductionism Reductionism – the reduction of complex systems to simpler components that are more manageable to study Ex. the molecular structure of DNA Understanding biology – balances reductionism with the study of emergent properties Ex. new understanding comes from studying the interactions of DNA with other molecules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. What do we mean by cohesion of water molecules? 12

13. Cohesion – the bonding of a high percentage of the molecules to neighboring water molecules – Results from hydrogen bonding water attracting other water molecules 13

14. How does the cohesion of water affect living things? 14

15. Cohesion – Helps pull water up through the microscopic vessels of plants (capillarity) 15 Water conducting cells 100 µ m

16. What is surface tension? 16

17. Surface Tension – a measure of how hard it is to break the surface of a liquid – related to cohesion 17

18. Why do desert temperatures range from very hot during the day to very cold at night but areas near large bodies of water have a smaller temperature range? 18

19. Moderation of Temperature Water absorbs heat from air that is warmer and releases the stored heat to air that is cooler – heats up slowly and cools down slowly 19

20. Heat and Temperature Heat – a measure of the total amount of kinetic energy due to molecular motion Temperature – Measures the intensity of heat 20

21. Water’s High Specific Heat specific heat – the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC 21

22. Relate water’s molecular structure to its high specific heat. 22

23. Specific Heat When heat is absorbed, hydrogen bonds break When heat is released, hydrogen bonds form – Water’s high specific heat allows it to minimize temperature fluctuations within limits that permit life 23

24. Why is evaporation a cooling process? 24

25. 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 25

26. Evaporative Cooling due to water’s high heat of vaporization Sweating cools the body as heat energy from the body changes sweat into a gas 26

27. Insulation of Bodies of Water by Floating Ice Solid water, or ice – less dense than liquid water – Floats in liquid water – Insulates water & organisms below ice layer 27

28. Why is ice less dense than water? 28

29. Floating Ice The hydrogen bonds in ice – Are more “ordered” than in liquid water, making ice less dense (crystal lattice) 29 Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond Figure 3.5

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32. Floating Ice Since ice floats in water – Life can exist under frozen lakes and seas 32

33. Why do so many substances dissolve easily in water? 33

34. The Solvent of Life – Water is a solvent due to its polarity Forms aqueous solutions the universal solvent – because so many substances dissolve in it 34

35. Different regions of the polar water molecule interact with ionic compounds called solutes and dissolve them 35 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 –

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37. Water can also interact with polar molecules such as proteins 37 This oxygen is attracted to a slight positive charge on the lysozyme molecule. This hydrogen is attracted to a slight negative charge on the lysozyme molecule. (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva (c) Ionic and polar regions on the protein’s surface attract water molecules. ++ –– Figure 3.7

38. What kind of substances do not mix well with water? 38

39. Hydrophilic and Hydrophobic Substances A hydrophobic substance – No affinity for water – Nonpolar – Lipids – oil, fat, wax A hydrophilic substance – Has an affinity for water – Polar or ionic – Carbohydrates, salts 39

40. 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 40

41. Moles and Molarity A mole – Represents an exact number of molecules of a substance in a given mass Molarity – Is the number of moles of solute per liter of solution 41

42. Acids and Bases 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 42

43. Effects of Changes in pH Water can dissociate Into hydronium ions (H+ or H 3 O+) and hydroxide (OH-) ions Changes in the concentration of these ions Can have a great affect on pH in living organisms 43 H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + Figure on p. 53 of water dissociating

44. Acids and Bases An acid – any substance that increases the hydrogen ion concentration of a solution A base – any substance that reduces the hydrogen ion concentration of a solution (more OH- ions) 44

45. The pH Scale Scale goes from 0-14 with 7 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 solution Bases produce OH- ions in solution 45

46. 46 Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] Neutral [H + ] = [OH – ] Oven cleaner 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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 Figure 3.8

47. Buffers The internal pH of most living cells – Must remain close to pH 7 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 47

48. The Threat of Acid Precipitation Acid precipitation – Refers to rain, snow, or fog with a pH lower than pH 5.6 – Caused by the mixing of different pollutants with water in the air 48

49. Acid precipitation – Damages life in Earth’s ecosystems 49 0101 2323 4545 6767 8989 10 11 12 13 14 More acidic Acid rain Normal rain More basic Figure 3.9