Water and the Fitness of the Environment Chapter 3

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Water and the Fitness of the EnvironmentChapter 3
Principles of Biology I BSC 1010 Associate
Professor Pamela L. Pannozzo
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Water
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Hydrogen Bonds

• Between water molecules
• Based on polarity
• Weak and highly directional
• Last trillionths/second
• Constantly breaking and re-forming

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Types of Molecules

• Hydrophilic polar molecules
• Water-soluble
• Hydrophobic nonpolar molecules
• Insoluble in water

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Hydrogen Bonds Result in Unique Properties of
Water that Facilitate Life

• Cohesion/adhesion
• Ability to moderate temperature
• Ice formation
• Versatility as a solvent

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Cohesion /Adhesion

• Cohesionattraction of water molecules to other
  water molecules
• Due to hydrogen bonding
• Water more structured than other liquids
• Surface tension of water
• Transport of water against gravity in plants
• Adhesionattraction of water molecules to other
  non-water polar molecules
• Wetness

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Water-conducting cells
100 µm
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Moderation of Temperature

• Water minimizes large air temperature
  fluctuations through
• Absorbing heat from warm air
• Releasing heat to cool air
• Due to
• High specific heat
• High heat of vaporization

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Heat and Temperature

• Kinetic energy the energy of motion
• Heat the total amount of kinetic energy due to
  molecular motion in a body of matter
• Temperature measurement of the intensity of
  heat due to the average kinetic energy of
  molecules in a body of matter

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Waters 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
• Higher specific heat than other substances
• Water requires a large input or loss of heat to
  change its temperature slightly
• Stabilizes water body temperatures

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High Specific Heat (cont)

• Water resists temperature change
• When water temperature does occur, water loses or
  absorbs large amounts of heat
• Why?
• Heat is absorbed when hydrogen bonds break
• Heat is released when hydrogen bonds form

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Waters High Heat of Vaporization

• Evaporation transformation of a substance from
  liquid to gas
• Heat of vaporization the heat a liquid must
  absorb for 1 gram to be converted to gas
• Why?
• Hydrogen bonds
• Stabilizes Earths climate

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Evaporative Cooling

• As a liquid evaporates, molecules with greatest
  kinetic energy become vaporized
• Remaining surface temperature decreases
• Helps stabilize temperatures in organisms and
  bodies of water

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Ice Formation

• Ice is less dense than liquid water--floats
• Maintains liquid water in freezing temperatures
• Insulates liquid water

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Versatile Solvent

• Solution liquid that is a homogeneous mixture
  of substances
• Solvent the dissolving agent of a solution
• Solute the substance that is dissolved
• Aqueous solution solution in which water is the
  solvent
• Water is a versatile solvent due to its polarity
• Ions, polar molecules, molecules with ionic or
  polar regions dissolved in water surrounded by
  hydration sphere

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Human lysozyme, water-soluble protein
Lysozyme molecule in a aqueous environment.
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Solute Concentration in Aqueous Solutions

• Most biochemical reactions occur in water
• Chemical reactions depend on collisions of
  molecules and therefore on the concentration of
  solutes in an aqueous solution

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Ionization Dissociation of Water Molecules

• A hydrogen atom in a hydrogen bond between two
  water molecules can shift from one to the other
• H2O ? H OH-
• 2H2O ? H3O OH-

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Hydronium ion (H3O)
Hydroxide ion (OH)
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Acids and Bases

• Pure water concentrations of H and OH- are
  equal
• Adding certain solutes, called acids and bases,
  modifies the concentrations of H and OH-
• Acid any substance that increases the H
  concentration of a solution
• Base any substance that reduces the H
  concentration of a solution

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pH Scale

• pH scale (0-14) describes how acidic or basic a
  solution is
• pH of a solution determined by the relative
  concentration of hydrogen ions
• ph 7 H OH-
• Acidic solutions pH lt 7
• Basic solutions pH gt 7
• Most biological pH 6 to 8

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pH of Biological Fluids

• Cell cytoplasm 7.0
• Blood 7.35-7.45
• Urine 5.5-6.9
• Gastric juice 1.6-1.8
• Tissue fluid 7.35-7.45
• Bile 7.8-8.6
• Saliva 5.5-6.9
• Pancreatic juice 7.5-8.0

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Biological Metabolism

• Constantly produces acids
• Anaerobic fermentationlactic acid
• Nucleic acid catabolismphosphoric acid
• Fat catabolismfatty acids
• Respirationcarbonic acid
• Body must maintain acid-base balance by
  counteracting acids produced by metabolism with
  buffers

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Buffers

• Internal pH of most living cells must remain
  close to pH 7
• Buffers substances that minimize changes in
  concentrations of H and OH- in a solution
  (intracellular fluid, extracellular fluid, blood,
  lymphatic fluid)
• Most buffers consist of an acid-base pair that
  reversibly combines with H
• H2CO3 ? HCO3- H
• H donor H acceptor
• (acid) (base)
  

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pH Homeostasis

• Slight changes in pH can
• Disrupt chemical reactions
• Cause conformational shape change in enzymes
• Disrupt physiological functions
• Tremors, fainting, paralysis, death

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Acid Precipitation

• Acid precipitation rain, snow, or fog pH lt 5.6
• Caused by air pollutants
• Sulfur dioxide (SO2) from coal-burning
• Damages life in lakes and streams
• Effects on soil chemistry causing forest decline

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Acid Rain