Water and the Fitness of the Environment

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Water and the Fitness of the Environment

• AP Biology
• Chapter 3

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Essential Questions?

• Why is water so essential to life?
• How do the properties of water affect its
  function?

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Water Rocks!

• No water no life
• The polarity of water molecules results in
  hydrogen bonding
• Polarity Review
• The slightly negative regions of one molecule are
  attracted to the slightly positive regions of
  nearby molecules, forming a hydrogen bond

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Cohesion
Adhesion

• The attraction of unlike particles

• The attraction of like particles
• Important to all organisms
• Surface tension

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Water and Temperature Moderation
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Heat and Temperature

• All atoms and molecules have kinetic energy
• energy of motion
• What is heat?
• Heat is a measure of the total quantity of
  kinetic energy due to molecular motion in a body
  of matter.
• Temperature measures the intensity of heat due to
  the average kinetic energy of molecules.

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How do we measure temperature?

• In most biological settings, temperature is
  measured on the Celsius scale (oC).
• At sea level, water freezes at O oC and boils at
  100oC.
• Human body temperature averages 37 oC.

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How do we measure heat energy?

• Calorie (cal).
• the amount of heat energy necessary to raise the
  temperature of one g of water by 1oC
• In many biological processes, the kilocalorie
  (kcal), is more convenient.
• A kilocalorie is the amount of heat energy
  necessary to raise the temperature of 1000g of
  water by 1oC.

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How does the polarity of water help in
temperature moderation?

• In order for water to change from a liquid to a
  gas, it had to absorb a lot of energy to first
  break the hydrogen bonds therefore absorbing a
  lot of energy before changing temperature
• In contrast, before water freezes it must release
  a lot of energy

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Specific Heat

• specific heat ? the amount of heat that must be
  absorbed or lost for 1g of that substance to
  change its temperature by 1oC
• the specific heat of water is 1 cal/g/oC.
• Water resists changes in temperature because it
  takes a lot of energy to speed up its molecules.
• Waters high specific heat is due to hydrogen
  bonding
• Heat must be absorbed to break hydrogen bonds and
  is released when hydrogen bonds form.

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How does waters high specific heat impact living
things?

• Large bodies of water
• Absorb heat during the day, release heat at night
• Influences temperature moderation, ex costal
  temperatures
• Water is the major component of all organisms
• Moderating organismal temperature

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Vaporization/evaporation

• The transformation of a molecule from a liquid to
  a gas, occurs when the molecule moves fast enough
  to overcome the attraction of other molecules
• Even in a low temperature liquid (low average
  kinetic energy), some molecules are moving fast
  enough to evaporate.
• Heating a liquid increases the average kinetic
  energy and increases the rate of evaporation.

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Heat of vaporization

• the quantity of heat that a liquid must absorb
  for 1 g of it to be converted from the liquid to
  the gaseous state.
• Water has a high heat of vaporization
• double the heat required to vaporize the same
  quantity of alcohol or ammonia.

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Evaporative Cooling

• As a liquid evaporates, the surface of the liquid
  that remains behind cools
• Moderates temperature in lakes and ponds and
  prevents terrestrial organisms from overheating.
• Evaporation of water from the leaves of plants or
  the skin of humans removes excess heat.

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Ice Floats pretty cool, ha!

• Water is less dense as a solid than a liquid
• Usually substances shrink as they cool
• Hydrogen bonding in water causes water molecules
  to form a lattice,
• making it less dense than
• liquid water
• Why is this helpful to life?

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Water is the solvent of life
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Water can dissolve other polar compounds, ionic
compounds and charged compounds

• Terms ? solution, solvent, solute, aqueous
  solution

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What types of substances dissolve in water? What
substances dont?

• Even large molecules, like proteins, can
  dissolve in water if they have ionic and polar
  regions.

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• hydrophilic
• Any substance that has an affinity for water
  water loving
• Contain many ionic or polar bonds
• includes substances that do not dissolve because
  their molecules are too large
• hydrophobic
• Substances that have no affinity for water water
  fearing
• Contain many by non-ionic and nonpolar covalent
  bonds.

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Other Chemical Reminders

• The mole, the chemistry counting unit
• number of molecules in a mole 6.02 x 1023
• How many grams in a mole of carbon?
• The concentration of a material in solution is
  called its molarity
• A one molar solution has one mole of a substance
  dissolved in one liter of solvent, typically
  water.M
• How many moles of solvent are dissolved in an 8.0
  molar solution?
• A 0.5 molar solution?

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The Dissociation of Water
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Sometimes, an H2O molecule loses a H ion that is
in turn accepted by another H2O
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• H leaves its electron behind and is transferred
  as a single proton - a hydrogen ion (H)
• The water molecule that lost a proton is now a
  hydroxide ion (OH-)
• The water molecule with the extra proton is a
  hydronium ion (H3O)

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H2O ltgt H OH-

• This reaction is reversible.
• At equilibrium the concentration of water
  molecules greatly exceeds that of H and OH-
• At equilibrium the concentration of H or OH- is
  10-7M (25C)
• Adding solutes (acids or bases) changes the
  concentration of H and OH-

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Acids
Bases

• base ? increases OH-
• Some bases accept H, ex. (NH3)
• NH3 H ltgt NH4
• Other bases reduce dissociate to OH- that
  combines with H to form water.
• NaOH -gt Na OH- OH- H -gt H2O

• acid ? increases H
• When hydrochloric acid (HCl) is added to water,
  hydrogen ions dissociate from chloride ions
• HCl -gt H Cl-
• Addition of an acid makes a solution more acidic

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Strength of Acids/Bases

• Some acids and bases (HCl and NaOH) are strong
  acids or bases.
• These molecules dissociate completely in water.
• Other acids and bases are weak acids or bases.
• the binding and release of hydrogen ions are
  reversible.
• ex. NH3,
• Carbonic acid (H2CO3) is a weak acid
• H2CO3 ltgt HCO3- H

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Measuring Acidity and Alkalinity

• In any solution H OH- 10-14
• In a neutral solution, H 10-7 M and OH-
  10-7 M
• Adding acid to a solution shifts the balance
  between H and OH- toward H and leads to a
  decline in OH-.
• If H 10-5 M, then OH- 10-9 M
• Practice one?

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pH

• In a neutral solution H 10-7 M, and the pH
  7.
• Values for pH decline as H increase.
• Most biological fluids???
• Each pH unit represents a tenfold difference in
  H and OH- concentrations.
• A small change in pH actually indicates a
  substantial change in H and OH- concentrations

Fig. 3.9
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Buffers

• resist changes to the pH of a solution
• typically consist of a weak acid and its
  corresponding base.
• Ex. carbonic acid/bicarbonate in human blood
• As H change, either add or remove H from the
  solution

Bicarbonate
Carbonic Acid
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Why do we care about pH?

• Organisms are sensitive to changes in pH
• Acid rain
• Rain is typically acidic because it combines with
  CO2
• Normal rain pH 5.6
• Acid rain pH lt5.6
• Result of pollution
• Burning of fossil fuels