Water and the Fitness of the Environment


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Water and the Fitness of the Environment

  1. 1. Chapter 3 Water and the Fitness of the Environment
  2. 2. Overview: The Molecule That Supports All of Life <ul><li>Water is the biological medium on Earth </li></ul><ul><li>All living organisms require water </li></ul><ul><li>cells are about 70-95% water </li></ul><ul><li>water is the main reason the Earth is habitable </li></ul>
  3. 3. Structure of Water <ul><li>Water is a polar </li></ul><ul><li>Polarity allows water molecules to form hydrogen bonds with each other </li></ul>Animation: Water Structure
  4. 4. Four emergent properties of water <ul><li>Water’s properties that contribute to an environment for life: </li></ul><ul><ul><ul><li>Cohesive behavior </li></ul></ul></ul><ul><ul><ul><li>Ability to moderate temperature </li></ul></ul></ul><ul><ul><ul><li>Expansion upon freezing </li></ul></ul></ul><ul><ul><ul><li>Versatility as a solvent </li></ul></ul></ul>
  5. 5. Cohesion <ul><li>Cohesion = attraction of water molecules for each other due to H-bonding </li></ul><ul><ul><li>Ex: transport of water against gravity in plants </li></ul></ul><ul><li>Adhesion & Surface tension are related </li></ul>Animation: Cohesion of Water
  6. 6. Moderation of Temperature <ul><li>Water has a high specific heat </li></ul><ul><ul><li>can absorb/release a large amount of heat to/from the air with only a slight change in its own temperature </li></ul></ul><ul><ul><li>Temperature = a measure of the average kinetic energy of molecules </li></ul></ul><ul><li>Water also has a high heat of vaporization </li></ul><ul><ul><li>Allows for evaporative cooling </li></ul></ul><ul><ul><li>Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water </li></ul></ul>
  7. 7. Insulation of Bodies of Water by Floating Ice <ul><li>Ice floats (less dense) </li></ul><ul><li>Makes aquatic life possible in winter! </li></ul>
  8. 8. The Solvent of Life <ul><li>“ Likes Dissolve Likes” </li></ul><ul><li>Aqueous solution: solvent (water) dissolves solute </li></ul><ul><li>Water is a versatile solvent due to its polarity </li></ul>
  9. 9. LE 3-6 Na + Na + Cl – Cl – + + + + + + + + – – – – – – – – – – – When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell
  10. 10. LE 3-7b Lysozyme molecule in a aqueous environment. 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
  11. 11. Hydrophilic and Hydrophobic Substances <ul><li>A hydrophilic substance is one that has an affinity for water </li></ul><ul><li>A hydrophobic substance is one that does not have an affinity for water </li></ul>
  12. 12. Solute Concentration in Aqueous Solutions <ul><li>Chemical reactions depend on collisions of molecules </li></ul><ul><li>Molarity (M) = moles solute per L solution </li></ul><ul><ul><li>1 mole = 6.02 x 10 23 molecules </li></ul></ul>0.1 M 1.0 M
  13. 13. Dissociation of water <ul><li>Water reacts with itself - transfers a proton, or hydrogen ion (H + ) </li></ul><ul><ul><li>The molecule with the extra proton is now a hydronium ion (H 3 O + ~ has an extra H + ) </li></ul></ul><ul><ul><li>The molecule that lost the proton is now a hydroxide ion (OH - ) </li></ul></ul>H 2 O + H 2 O  H 3 O + + OH - Animation: Dissociation
  14. 14. Effects of changes in pH <ul><li>Concentrations of H + and OH - are equal in pure water </li></ul><ul><li>Adding certain solutes, called acids and bases, modifies the concentrations of H + and OH - </li></ul><ul><li>Biologists use something called the pH scale to describe how acidic or basic (the opposite of acidic) a solution is </li></ul>
  15. 15. Acids and Bases & pH <ul><li>Acid = increases the H + concentration of a solution </li></ul><ul><li>Base = reduces the H + concentration of a solution </li></ul><ul><li>pH of a solution is determined by the relative concentration of H + ions </li></ul><ul><ul><li>Acidic pH < 7 </li></ul></ul><ul><ul><li>Basic pH > 7 </li></ul></ul><ul><li>Most biological fluids have pH values in the range of 6 to 8 </li></ul>Animation: Acids, Bases & pH
  16. 16. LE 3-8 pH Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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 – ]
  17. 17. Buffers <ul><li>The internal pH of most living cells must remain close to pH 7 </li></ul><ul><li>Buffers are substances that minimize changes in concentrations of H + and OH - in a solution </li></ul><ul><li>Most buffers consist of an acid-base pair that reversibly combines with H + </li></ul>
  18. 18. The Threat of Acid Precipitation <ul><li>Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6 </li></ul><ul><li>Acid precipitation is caused mainly by the mixing of different pollutants with water in the air </li></ul><ul><li>Acid precipitation can damage life in lakes and streams </li></ul><ul><li>Effects of acid precipitation on soil chemistry are contributing to the decline of some forests </li></ul>Investigation: Acid Rain
  19. 19. LE 3-9 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 More basic Normal rain More acidic Acid rain