Biology 1020 Lecture 2 Water as a vehicle for life

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  1. Properties of water that support life (on Earth)
    • - Versatility
    • - Expansion upon freezing
    • - Cohesive Behaviour
    • - Moderation of temperature
  2. Hydrogen Bonding
    Attraction between H atom in a polar covalent bond and another electronegative atom (like a oxygen atom).
  3. Solution
    Liquid that is a homogeneous mixture of substances
  4. Aqueous Solution
    Solutes dissolved in water (the solvent).
  5. Hydration Shell
    • Each ion of an aqueous solution is surrounded by a hydration shell.
    • - Cations (+ve ions) oxygen closet
    • - Anions (+ve ions) hydrogen closet
  6. Water as a solvent
    • Can dissolve many types of solutes
    • - ionic molecules
    • - compounds made of non-polar molecules
    • - Large polar molecules (ex. proteins) if they have ionic and polar regions
  7. Hydrophilic Substance
    • Has an affinity for water
    • (relatively polar bonds)
  8. Hydrophobic Substance
    • Does not have an affinity for water
    • (relatively nonpolar bonds)
  9. H-bonding in ice is more ordered that in liquid water
    Ice is less dense and has a larger volume
  10. Freezing Point Depression
    • Presence of solutes decreases the freezing point of a solvent.
    • - Freezing point of seawater lower than freshwater (-1.8 c)
    • - Solutes disrupts H bonding
    • - High concentration of solutes in some organisms in colder climate can prevent body fluids from freezing.
  11. Cohesion
    • - Sticking together
    • - Water molecules form hydrogen bonds with other polar molecules and each other
  12. Cohesion of Water
    • - Water moves by capillary action - "wicks"
    • - Cohesion (with each other) and adhesion (other surfaces) important in water transport in plants
  13. Cohesion of Water: Surface Tension
    • - How hard it is to break the surface of a liquid
    • - High in water in part due to its cohesive behaviour
  14. Temperature moderation by water
    • - Water has a high specific heat. (H bonding)
    • - Amount of heat to change temperature
    • 1g, raised by 1 degree celsius
  15. Heat
    amount of KE due to molecular motion
  16. Temperature
    intensity of heat
  17. Evaporative Cooling
    • - Large quantity of heat must be absorbed to make liquid -> Gas
    • - Remaining surface cools as liquid evaporates -> evaporative cooling
    • * helps stabilize temp. in organisms and bodies of water.
  18. Temperature moderation by water
    • - Ocean absorbs heat from warmer air
    • - Releases stored heat to cooler air
    • - Only slight change in water temperature
    • (Temp. more moderate near oceans than prairies).
  19. Equilibruim of Water
    • - H atom in a H-bond between two water molecules can shift from one to the other.
    • - H2O  molecules dissociate at the same rate at which they are being reformed.
  20. Equilibruim of Water #2
    • H atom leaves its e- behind
    • -> transformed as a proton (H+ ion)

    => H3O+ ion (hydronuim ion) molecules that lost H+ => OH- Hydroxide
  21. Acid
    donates a proton to a solution, increases H+ concentration of a solution.
  22. Base
    accepts a proton from the solution, decreases H+ concentration of a solution
  23. pH and biological systems
    Most biological fluids - pH 6-8

    - Changes in pH can drastically affect the chemistry of a cell
  24. Buffers
    Minimize changesin concentration of H+ and OH-  in a solution.

    Acid-base pair that reversibly combines with H+
  25. pH buffering in biological systems
    • CO2 + H2O --> H2CO3 or HCO3- + H+
    • ---------------------------------------------
    • H2CO3 <---> HCO3- + H+
    • Acid                    Base
  26. Acidification of Biological Systems
    • -  Air pollutants mix with water in atmosphere: decrease pH
    • - Can fall at some distance from the source
    • - Lakes and streams, soil chemistry
  27. Ocean water quality:
    Coral Bleaching
    and a decrease in the ability of corals to form calcified reefs.

    - Algae dies, (with higher pH).
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Biology 1020 Lecture 2 Water as a vehicle for life
2013-09-28 07:07:32
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