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The Essential Role of Water in Biology: Properties and Functions

Chapter 3 explores the foundational role of water (H2O) in biology, highlighting its unique properties such as polarity, cohesion, and adhesion. It explains how hydrogen bonding contributes to phenomena like transpiration in plants and surface tension in water. The chapter also discusses water's ability to moderate temperature due to its high specific heat, making it vital for sustaining life. Lastly, it addresses how water interacts with different substances, emphasizing its role as a solvent for polar and ionic compounds, while also discussing its limitations with nonpolar substances.

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The Essential Role of Water in Biology: Properties and Functions

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Presentation Transcript

  1. Chapter 3 Water & Biology

  2. H2O is why we are here • H2O molecules are polar • What does their polarity contribute to? • Each H2O molecule can form __ Hydrogen bonds?

  3. Cohesion & Adhesion • Caused by Hydrogen bonding • Cohesion – Water-to-water • Adhesion – water-to-something other than water • When water travels upward in a straw, is that cohesion or adhesion? Why? • Diameter of straw: small or large? Why?

  4. Transpiration (Plants)

  5. Structure & Function in water transport • What structural feature of water enables it to be transported upward? • Hydrogen bonding  Cohesion + Adhesion • What structural feature of plant vessels enables water to be transported upward? • Hydrophilic walls to enable adhesion • Narrow walls to maximize adhesive forces

  6. Surface Tension • Surface Tension – water can stand above the rim of a glass due to hydrogen bonds • Is surface tension a result of cohesion or adhesion? • Why?

  7. Water Moderates Temperature Temperature – measure of average kinetic energy of molecules Water does this because it has a high specific heat  Water can absorb large amounts of heat but change little in temperature  Guess what type of bonding is responsible for high specific heat?

  8. Sea Breeze? (cranberry juice & …) • Day, land heats up faster (low specific heat) • Air over land rises • Onshore breeze • Night, lands cools faster • Hot air rises over water • Offshore breeze

  9. Evaporative Cooling • Water has high specific heat due to? • Responsible for cooling • Heat is released as liquid is vaporized into gas • Highest energy molecules are vaporized first • Vaporization involves the breaking of which bonds?

  10. Hydrogen Bonding

  11. Like dissolves like… • Water is polar so it dissolves polar substances • Also dissolves ionic solids (salts) • Polar substances = hydrophilic • Hydro = water • -philic = to like (Dendrophiliac – one who likes trees) • Water does not dissolve nonpolar substances • NonPolar substances = hydrophobic • Hydro = water • -phobe = to fear (Triskaidekaphobe – one who fears the number 13)

  12. Remember… • Hydrophilic = polar molecule • Will dissolve in water • Hydrophobic = nonpolar molecule • Will NOT dissolve in water • What about ionic compounds?

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