Life on Earth Exists because of H2O
1. Cells are mostly water 70-95%.
2. 3/4th of Earth’s surface is covered by
water.
3. Water is a polar molecule:
a.opposite ends of the molecule have
opposite charges
b.opposite charges attract the molecules
to H-bond (each H2O molecules can
form H-bonds with at least 4 others)
c.this accounts for the properties of
water
4. Properties of Water:
a. Cohesion:
Hydrogen bonds hold individual
water molecules together  it acts
as one substance. (attraction that
water has for itself)
b. Adhesion:
Clinging of water to another
substance (the attraction that water
has for other molecules)
c. Surface Tension:
(Is due to cohesion) it is a measure
of the force necessary to stretch or
break the surface of a liquid.
d. Specific Heat:
The amount of heat that must be
absorbed or lost for 1g of that
substance to change its temperature
by 10C.
1. Heat is a measure of the total
kinetic energy in a system.
2. Temperature measures the
intensity of heat due to the
average kinetic energy in
molecules.
a. Temperature is measured on the
Celsius scale (Celsius = C)
-H2O freezes at 00C
-H2O boils at 1000C
b. A calorie is a measure of
heat.
-One calorie (cal) is the
amount of heat energy
necessary to raise the
temperature of one g of
water by 10C
- A kilocalorie (kcal) is the
amount of heat energy
necessary to raise the
temperature of 1000 g of
water by 10C
-The specific heat of H2O is:
1cal per gram per degree Celsius:
1cal/g/0C
-water has a high specific heat
-water can absorb or release relatively
large amounts of heat with only a slight
change in its own temperature.
-water can stabilize temperature
3. Water’s high specific heat is due
to H-bonding
a. heat is absorbed to break
hydrogen bonds
b. heat is released when H-bonds
form
e. Heat of Vaporization- the quantity of heat
that a liquid must absorb for 1g of it to be
converted from liquid to gas.
-H2O has a high Heat of Vaporization due to
(H-bonds which must be broken)
-moderates environmental and body temp.
1. Evaporation: water molecule
is energized, breaks H-bond, and
turns into gas. Energy is taken
from the system.
a. convection cells-water absorbs
heat in tropics through
evaporation and releases it
through condensation
and precipitation
Ex. – Tropics have moderate temp
fluctuations, poles have extremes
-Biomes
- oceans same temp day & night vs.
dessert with temperature extreme
-Kendall vs. Mia Beach
- sweating cools off animals
- transpiration cools off plants
f. Ice- water is less dense as a solid than as a
liquid (at 40C, ice is 10% less dense than
H2O liquid)
1. water expands as it solidifiesa. H-bonds do not have enough energy
to break at 00C
b. ice is a crystal lattice with each water
molecule bonded to 4 others
2. Ice floats
a. prevents ponds, lakes, oceans from
freezing solid
b. insulates
g. Water is the ‘universal’ solvent of life
1. solution=homogeneous mixture
composed of solute (subs, that is
dissolved) and the solvent (the
dissolving agent)
a. aqueous solution = (water =
solvent)
2. polarity of water allows it to form Hbonds with charged and polar mol.
-ex. NaCl
3. hydrophilic substances have an affinity
(form H-bonds) and/or dissolve in
water. (ionic/polar subs.)
hydrophobic substances do not have
an affinity for water.
(covalent/nonpolar/non-ionic subs.)
ex. Lipids
h. dissociation of water an H atom shared by two water
molecules shifts from one molecule to
the other.
1. Hydrogen ion –
the Hydrogen atom leaves its electron
behind and is transferred as a single
proton (H+ )
2. Hydroxide ion –
the water molecule that lost the proton
is an (OH-)
3. Hydronium ion –
the water molecule with the extra
proton is an ( H3O+)
H2O ------- H+ + OH-
4. Hydrogen and hydroxide ions are very
reactive and their concentrations can
affect proteins and other molecules in
a cell.
5. The pH scaledescribes how acidic or basic a
solution is
a. Acid – (proton donor)
increases the H+concentration in a
solution
b. Base- ( proton acceptor)
Reduces the H+ concentration
c. in any solution the product of the
H+ and OH- concentrations is
constant at 10-14.
[H+] [OH-] = 10-14
(1) in a neutral solution
[H+] = 10-7 M
[OH-] = 10-7 M
(2) adding acid to a solution shifts
the balance toward H+ conc.
(3) adding base to a solution shifts
the balance toward OH- conc.
d. The pH scale is used to express
the concentrations of Hydrogen
and the Hydroxide ions.
(1) neutral solution
pH = 7
(2) Acidic solutions have pH
values less than 7
(3) Basic solutions have pH
values greater than 7
e. Most biological substances have
pH values between 6 to 8, therefore
neutral.
(1) homeostasis requires optimum
pH ranges ex. Acid Rain
(2) Buffers resist change in pH
when H+ or OH- are added
a. buffers accept H+ ions from
the solution when they are in
excess and donate H+ when
they are depleted.
b. buffers usually consist of a
weak acid and its
corresponding base.