Chemistry of Life

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Chemistry of Life

• Properties of Water

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The amazing molecule Water
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More about Water
Why are we studying water?

• All life occurs in water
• inside outside the cell

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Chemistry of water

• H2O molecules form H-bonds with each other
• attracted to
• creates a sticky molecule

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Elixir of Life

• Special properties of water
• cohesion adhesion
• surface tension, capillary action
• good solvent
• many molecules dissolve in H2O
• hydrophilic vs. hydrophobic
• lower density as a solid
• ice floats!
• high specific heat
• water stores heat
• high heat of vaporization
• heats cools slowly

I like the partabout the ice!
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Cohesion Adhesion

• H bonding between H2O molecules is cohesion
• water is sticky
• surface tension
• drinking straw
• H bonding between H2O other substances is
  adhesion
• capillary action
• meniscus
• water climbs uppaper towel or cloth

Can you sucksugar up a straw?
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How does H2O get to top of trees?

• Transpiration built on cohesion adhesion

How tall can a tree get?
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Water is the solvent of life

• Polarity makes H2O a good solvent
• polar H2O molecules surround ions
• solvents dissolve solutes creating solutions

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Do you dissolve in water?

• Hydrophilic
• substances have attraction to H2O
• polar or non-polar?

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Or dont you?

• Hydrophobic
• substances that dont have an attraction to H2O
• polar or non-polar?

fat (triglycerol)
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The special case of ice

• Most (all?) substances are more dense when they
  are solid, but
• Not water
• Ice floats!
• H bonds form a crystal

And this hasmade all the difference!
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Ice floats
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Why is ice floats important?

• Oceans lakes dont freeze solid
• surface ice insulates water below
• allowing life to survive the winter
• if ice sank
• ponds, lakes even oceans would freeze solid
• in summer, only upper few inches would thaw
• seasonal turnover of lakes
• cycling nutrients in autumn

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Specific heat

• H2O resists changes in temperature
• high specific heat
• takes a lot to heat it up
• takes a lot to cool it down
• H2O moderates temperatures on Earth

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Heat of vaporization
Evaporative cooling

• Organisms rely on heat of vaporization to remove
  body heat

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Ionization of water pH

• Water ionizes
• H splits off from H2O, leaving OH
• if H -OH, water is neutral
• if H gt -OH, water is acidic
• if H lt -OH, water is basic
• pH scale
• how acid or basic solution is
• 1 ? 7 ? 14

H2O ? H OH
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pH Scale

• In pure water only 1 water molecule in every 554
  million is dissociated.
• very small amount of ions
• H or OH- is 10-7M
• H OH- 10-14
• pH scale is based on this equation

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pH Scale
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Buffers cellular regulation

• pH of cells must be kept 7
• pH affects shape of molecules
• shape of molecules affect function
• pH affects cellular function
• Control pH by buffers
• reservoir of H
• donate H when H falls
• absorb H when H rises

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pH Biology

• pH of a neutral solution 7
• Acidic solutions pH lt 7 Basic solutions pH
  gt 7
• Most biological fluids have pH 6 8
• pH values in human stomach can reach 2
• Each pH unit represents a 10-fold difference in
  H OH- concentrations.
• small change in pH actually indicates a
  substantial change in H OH-

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Punchline

• Water is a polar molecule
• The special properties of water make life on
  Earth possible
• The chemical behavior of water governs how
  organisms function

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Hes gonnaearn a Darwin Award!
Do one brave thing todaythen run like hell!