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03 water text

  1. 1. Chapter 3 Water and the Fitness of the Environment
  2. 2. Importance of water <ul><li>Overview: The Molecule That Supports All of Life on Planet Earth </li></ul><ul><li>In one way or another, all life forms are dependent on water for life processes to occur. </li></ul><ul><li>Water is the biological medium here on Earth </li></ul><ul><li>All living organisms require water more than any other substance </li></ul>
  3. 3. Water Facts <ul><li>Three-quarters of the Earth’s surface is submerged in water </li></ul><ul><li>The abundance of water is the main reason the Earth is habitable </li></ul>Figure 3.1
  4. 4. Water Facts <ul><li>The polarity of water molecules results in hydrogen bonding </li></ul><ul><li>The water molecule is a polar molecule </li></ul>
  5. 5. Water’s Polarity <ul><li>The polarity of water molecules </li></ul><ul><ul><li>Allows them to form hydrogen bonds with each other </li></ul></ul><ul><ul><li>Contributes to the various properties water exhibits </li></ul></ul>Hydrogen bonds + + H H + +  –  –  –  – Figure 3.2
  6. 6. Properties of water <ul><li>Four emergent properties of water contribute to Earth’s fitness for life </li></ul><ul><ul><li>Cohesion / Adhesion </li></ul></ul><ul><ul><li>Surface Tension </li></ul></ul><ul><ul><li>Thermal Properties </li></ul></ul><ul><ul><li>Universal Solvent </li></ul></ul>
  7. 7. Cohesion / Adhesion <ul><li>Water molecules exhibit cohesion </li></ul><ul><li>Cohesion </li></ul><ul><ul><li>Is the bonding of molecules to neighboring molecules </li></ul></ul><ul><ul><li>Is due to hydrogen bonding </li></ul></ul><ul><ul><li>Like molecules bonding to each other (water attracting other water molecules) </li></ul></ul><ul><li>Adhesion – is the act of two different substances “sticking” to each other. Example: water will “adhere” to the sides of a test tube or the “vein” (xylem) cells of a plant </li></ul>
  8. 8. <ul><li>Cohesion </li></ul><ul><ul><li>Helps pull water up through the microscopic vessels of plants </li></ul></ul>Water conducting cells (xylem) 100 µ m Figure 3.3
  9. 9. Surface Tension <ul><li>Surface tension </li></ul><ul><ul><li>Is a measure of how hard it is to break the surface of a liquid </li></ul></ul><ul><ul><li>Is related to cohesion </li></ul></ul>Figure 3.4
  10. 10. Thermal Properties Moderation of Temperature <ul><li>Water moderates air temperature </li></ul><ul><li>By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler </li></ul>
  11. 11. Thermal Properties Heat and Temperature <ul><li>Kinetic energy is the energy of motion </li></ul><ul><li>Heat </li></ul><ul><ul><li>Is a form of energy </li></ul></ul><ul><ul><li>Is a measure of the total amount of kinetic energy due to molecular motion </li></ul></ul><ul><ul><li>Is the lowest form of energy </li></ul></ul><ul><ul><li>As energy is converted from one form to another it will always end up as heat – Entropy </li></ul></ul><ul><ul><li>Maintaining “Life” is about preventing our body systems from reaching a state of “entropy” – because there is no other energy transformation that can take place – the flow stops! </li></ul></ul><ul><li>Temperature measures the intensity (amount) of heat </li></ul>
  12. 12. Thermal Properties Water’s High Specific Heat <ul><li>The specific heat of a substance </li></ul><ul><ul><li>Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC </li></ul></ul>
  13. 13. Thermal Properties Specific Heat <ul><li>Water has a high specific heat (1), which allows it to minimize temperature fluctuations to within limits that permit life </li></ul><ul><ul><li>Heat is absorbed when hydrogen bonds break </li></ul></ul><ul><ul><li>Heat is released when hydrogen bonds form </li></ul></ul>
  14. 14. Thermal Properties Evaporative Cooling <ul><li>Evaporation </li></ul><ul><ul><li>Is the transformation of a substance from a liquid to a gas </li></ul></ul><ul><ul><li>Requires energy </li></ul></ul><ul><li>Heat of vaporization </li></ul><ul><ul><li>Is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas </li></ul></ul>
  15. 15. Thermal Properties Evaporative Cooling <ul><li>Is due to water’s high heat of vaporization </li></ul><ul><li>Allows water to cool a surface </li></ul><ul><li>Sweating cools the body as heat energy from the body changes sweat into a gas and allows heat to escape (entropy) </li></ul>
  16. 16. Thermal Properties Insulation of Bodies of Water by Floating Ice <ul><li>Solid water, or ice </li></ul><ul><ul><li>Is less dense than liquid water </li></ul></ul><ul><ul><li>Floats in liquid water </li></ul></ul>
  17. 17. Thermal Properties Insulation of Bodies of Water by Floating Ice <ul><li>The hydrogen bonds in ice are more “ordered” than in liquid water, making ice less dense </li></ul>Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Figure 3.5
  18. 18. Thermal Properties Insulation of Bodies of Water by Floating Ice <ul><li>Since ice floats in water life can exist under the frozen surfaces of lakes and polar seas </li></ul>
  19. 19. The Solvent of Life <ul><li>Water is a versatile solvent due to its polarity </li></ul><ul><li>It can form aqueous solutions </li></ul><ul><li>Called the universal solvent because so many substances dissolve in water </li></ul>
  20. 20. <ul><li>The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them </li></ul>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
  21. 21. <ul><li>Water can also interact with polar molecules such as proteins </li></ul>Lysozymes are a group of enzymes which damage bacterial cell walls by destroying the 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. It is abundant in a number of secretions, such as tears, saliva, and mucus. Large amounts of lysozymes are also found in egg whites. Figure 3.7 This oxygen is attracted to a slight positive charge on the lysozyme molecule. This oxygen 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.  +  –
  22. 22. Hydrophilic and Hydrophobic Substances <ul><li>A hydrophobic substance </li></ul><ul><ul><li>Does not have an affinity for water </li></ul></ul><ul><li>A hydrophilic substance </li></ul><ul><ul><li>Has an affinity for water </li></ul></ul>
  23. 23. Solute Concentration in Aqueous Solutions <ul><li>Since most biochemical reactions occur in water </li></ul><ul><ul><li>It is important to learn to calculate the concentration of solutes in an aqueous solution </li></ul></ul>
  24. 24. Moles and Molarity <ul><li>A mole </li></ul><ul><ul><li>Represents an exact number of molecules of a substance in a given mass </li></ul></ul><ul><li>Molarity </li></ul><ul><ul><li>Is the number of moles of solute per liter of solution </li></ul></ul><ul><ul><li>A 1M solution has 1 mole of solute in 1 L of water. (Remember: 1 mole of any substance is equal to its molecular weight in grams) </li></ul></ul>
  25. 25. Acids and Bases <ul><li>Dissociation of water molecules leads to acidic and basic conditions that affect living organisms </li></ul><ul><li>Organisms must maintain homeostasis in the pH of their internal and external environments </li></ul>
  26. 26. <ul><li>Water can dissociate Into hydronium ions (H+ or H 3 O+) and hydroxide (OH-) ions </li></ul><ul><li>Changes in the concentration of these ions Can have a great affect on pH in living organisms </li></ul>Effects of Changes in pH H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + Figure of water dissociating
  27. 27. Acids and Bases <ul><li>An acid </li></ul><ul><ul><li>Is any substance that increases the hydrogen ion concentration of a solution </li></ul></ul><ul><li>A base </li></ul><ul><ul><li>Is any substance that reduces the hydrogen ion concentration of a solution </li></ul></ul>
  28. 28. The pH Scale <ul><li>Scale goes from 0-14 with 7 neutral </li></ul><ul><li>The pH of a solution is determined by the relative concentration of hydrogen ions </li></ul><ul><li>Difference of 10X in hydrogen ion concentration between any two pH values </li></ul><ul><li>Acids have a higher number of H+ ions than a base </li></ul><ul><li>Acids produce H+ ion in solution </li></ul><ul><li>Bases produce OH- ions in solution </li></ul>
  29. 29. The pH scale and pH values of various aqueous solutions 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
  30. 30. Buffers <ul><li>The internal pH of most living cells </li></ul><ul><ul><li>Must remain close to pH 7 </li></ul></ul><ul><li>Buffers </li></ul><ul><ul><li>Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution </li></ul></ul><ul><ul><li>Consist of an acid-base pair that reversibly combines with hydrogen ions </li></ul></ul><ul><ul><li>Made by organisms </li></ul></ul>
  31. 31. The Threat of Acid Precipitation <ul><li>Acid precipitation </li></ul><ul><ul><li>Refers to rain, snow, or fog with a pH lower than pH 5.6 </li></ul></ul><ul><ul><li>Is caused primarily by the mixing of different pollutants with water in the air </li></ul></ul>
  32. 32. <ul><li>Acid precipitation </li></ul><ul><ul><li>Can damage life in Earth’s ecosystems </li></ul></ul>0 1 2 3 45 6 7 8 9 10 11 12 13 14 More acidic Acid rain Normal rain More basic Figure 3.9
  33. 33. <ul><li>Make sure you have read Chapter 3 in Campbell </li></ul><ul><li>“ Water and the Fitness of the Environment” </li></ul><ul><li>You should also read Chapter 4 </li></ul><ul><li>“ Carbon and the Molecular Diversity of Life” </li></ul><ul><li>We are starting this section – NOW ! </li></ul>

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