Water and Its Value to Life

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Water and Its Value to Life

• Chapter 3

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Essential Characteristics of Water

• High surface tension
• --Capillary action
• Resists temperature change
• --High heat of vaporization
• --Low freezing point
• Water expands when it freezes
• Universal solvent

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Surface Tension of Water

• Force exerted by surface of water on particles
  below

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Capillary Action of Water

• Attributed to polar nature of molecules

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Capillary Action is Greater with Smaller Diameter
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High Heat of Vaporization of Water

• Helps cool animals that sweat

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or pant
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Water Resists Temperature Change

• Allows for living things to exist in an
  environment where ambient temperature varies
  dramatically

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Temperature Moderation

• High Specific Heat of Water
• Specific Heat amount of heat per unit mass
  needed to raise the temperature by one degree
  Celsius
• The specific heat of water is 1 calorie/gram C
  4.186 joule/gram C
• This is higher than any other common substance

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Temperature Moderation, continued

• Waters high Specific Heat
• Due to hydrogen bonding
• Heat is absorbed when hydrogen bonds break and is
  released when hydrogen bonds form,
• minimizes temperature fluctuations to within
  limits that permit life.

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Temperature Moderation, continued

• Evaporative cooling
• based on waters high heat of vaporization
• Water molecules require high kinetic energy to
  break hydrogen bonds
• evaporative loss of water molecules cools a
  surface.

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Density of Water

• Ice Floats
• Ice is less dense than liquid water
• Due to hydrogen bond formation
• Causes expansion into crystal formation
• Oceans and lakes dont freeze solid
• Floating ice allows life to exist under the
  frozen surfaces of lakes and polar seas.

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Water Expands When It Freezes

• In liquid water, the molecules move about freely

• In ice, the molecules assume a rigid lattice
  structure

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• Liquid Water

• Ice

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Water as a Solvent

• Polarity of water
• Water molecules attracted to charged and polar
  substances
• When ions or polar substances are surrounded by
  water molecules, they dissolve and are called
  solutes.

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Water as a Solvent, Continued

• Hydrophilic ? affinity for water.
• Hydrophobic ? repel water (because some things
  can and do repel water, it is not truly a
  universal solvent).
• Water most important solvent for living things
• Water about 70 to 95 of most organisms

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Acids Bases

• pH measure of how acidic or basic a solution is
• Ranges from 0 to 14
• Acid any substance that forms hydrogen ions
  (H) in water (H2O)
• pH lt 7
• Base any substance that forms hydroxide ions
  (OH-) in water (H2O)
• pH gt 7
• Neutral Substance pH 7

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The Dissociation of Water Molecules

• Organisms are sensitive to changes in pH (pH
  -log H)
• Water can dissociate into H and OH-
• The concentration of H is expressed as pH,
• Acids donate additional H in aqueous solutions
• Bases donate OH- or accept H.

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• In a neutral solution, H OH- 10-7, so pH
  7.
• In an acidic solution, H is greater than
  OH-, and the pH is less than 7.
• In a basic solution, H is less than OH-, and
  the pH is greater than 7.
• Buffers in biological fluids resist changes in
  pH. A buffer consists of an acid-base pair that
  combines reversibly with hydrogen ions.

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• Acid precipitation is rain, snow, or fog with a
  pH below 5.6.
• Due to reaction in air between water vapor and
  sulfur oxides and nitrogen oxides
• One source combustion of fossil fuels.