Ch.3 Life on Earth is Aqueous

1
Ch.3 Life on Earth is Aqueous!
2
Predominance of Water -3/4 of earth covered with
water (liquid solid) -cells are 70-95
water -all organisms require water for
survival 1 week survival time for human
without water
3
LE 3-2
Hydrogen bonds
4
Key properties of water defines
behavior -Polarity partial positive and
negative charges -Hydrophilic nature attracted
to other water molecules and charged particles
5

• Four of waters properties
• Cohesive behavior
• Ability to moderate temperature
• Expansion upon freezing
• Versatility as a solvent

6
LE 3-3
Cohesion Adhesion During Transpiration
gt100 ft
Water-conducting cells
100 µm
H2O
7

• Cohesion
• Water molecules hold together through H-bonds to
  other water molecules
• Example
• Cohesion helps transport water against gravity
  in plants from roots to stems during
  transpiration
• Adhesion
• Waters attraction to other charged surfaces
• Example
• Waters attraction to cell walls helps upward
  transport against
• gravity

8
Surface Tension Strong ordered film-like
structure at interface of water and
atmosphere Held together through
H-bonds Strength creates surface for small
organisms to move across
9
High specific heat 1 cal/g/oC Amount of heat
gained or lost to change the temperature of 1g
of water by 1ºC Compare to alcohol specific heat
of 0.6 cal/g/oC

• Consequence
• Lessens temperature fluctuations to within limits
  that permit life
• Heat is absorbed to hydrogen bonds break
• Heat is released when hydrogen bonds form

10
Evaporative Cooling

• 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 (water 580 cal/g at 25oC)
• remaining surface cools during evaporation, a
  process called evaporative cooling
• Consequence
• Evaporative cooling of water helps stabilize
  temperatures in organisms and bodies of water
• Perspiration sensation?

11
Solid water (ice) less dense than liquid
because H-bonds more stable and ordered
expansion occurs Consequence Ice floats on
liquid water Insulates prevents temperature
fluctuations Example ponds and lakes in
wintertime aquatic organisms survive in the
liquid water beneath ice
12
(No Transcript)
13
Polar solvent
Dissolves other polar or charged
solutes Examples salts, polar proteins, nucleic
acids Creates an aqueous solution -through Hyd
ration shells H-bonds
14
LE 3-6
Hydration shells form around cations and
anions Causes salt crystals to dissolve In H2O

Na







Na



Cl
Cl








15
LE 3-7a
Lysozyme molecule in a nonaqueous
environment.
16
LE 3-7b
Lysozyme molecule in a aqueous environment.
17
Concepts of Hydrophilic and Hydrophobic

• Hydrophilic
• an affinity for water due to charged or polar
  nature
• e.g. salts (ionic)
• Hydrophobic
• -repelled by water due to nonpolar nature
• e.g. oils, fats (nonpolar)
• Important when considering the plasma membrane.

18
Aqueous chemistry in biological systems

• Most biochemical reactions occur in water
• Reactions require collisions of molecules -
  dependent on concentration of solutes in an
  aqueous solution
• Example increase the concentration of enzyme in
  an reaction and the rate of the reaction will
  increase.
• Cells can regulate how much enzyme they make to
  control reaction rates.

19
Water Dissociation -Hydrogens involved in
H-bonds in H2O can lose electrons -H (proton)
can bond with another H2O molecule

• Results
• molecule with the extra proton is now a hydronium
  ion (H3O)
• The molecule that lost the proton is now a
  hydroxide ion (OH-)

20
LE 3-UN53
Hydronium ion (H3O)
Hydroxide ion (OH)
Simplified to H
21

• Dissociation of water molecules
• Rare in pure water (25oC)
• H10-7 M
• OH-10-7 M
• Changes in concentrations of H and OH-
  drastically affect the chemistry of a cell
• Such changes alter the pH

22
pH -measures molar concentration of H in
solution pH -logH -adding acid to
a solution increases the H more acidic e.g.
HCl -adding base to a solution increases the
OH- more basic (alkali) e.g. NaOH -pH
scale measures level of acidity or alkalinity
23
The pH Scale

• pH 7 occurs when H OH-
• Acidic solutions pH lt 7
• Basic solutions pH gt 7
• Most biological fluids pH 6-8

24
LE 3-8
pH Scale
0
1
Battery acid
2
Digestive (stomach) juice, lemon juice
Vinegar, beer, wine, cola
3
Increasingly Acidic H gt OH
4
Tomato juice
Black coffee
5
Rainwater
Urine
6
Neutral H OH
Pure water
7
Human blood
8
Seawater
9
10
Increasingly Basic H lt OH
Milk of magnesia
11
Household ammonia
12
Household bleach
13
Oven cleaner
14
25
Calculating pH
Given pH -logH Water ion product
10-14 HOH-
What is the pH of a solution containing 10-7 M
H?
In the same solution, what is the concentration
of OH-?
Determine the concentration of H and OH- at pH 3.
26
Buffers

• pH of most living cells must remain close to pH 7
• Buffers minimize changes in H and OH- in a
  solution
• Most buffers consist of an acid-base pair that
  reversibly combines with H
• H2CO3
  HCO3- H
• carbonic acid
  bicarbonate

27
The Damage of Acid Precipitation

• Acid precipitation refers to rain, snow, or fog
  with a pH lower than 5.6
• Caused by the mixing of different pollutants with
  water in the air e.g. sulfur and nitrogen oxides
• Main source combusted fossil fuels
• Acid precipitation can damage life in lakes and
  streams
• Leaches geological buffers from soils
• Solubilizes toxic heavy metals e.g. aluminum

28
LE 3-9
0
More acidic
1
2
Acid rain
3
4
5
Normal rain
6
7
8
9
10
11
12
13
More basic
14