Water and the Fitness of The
Environment
Polarity
Effect on Environment
Effect on Living Things
Water as a Solvent
pH and Living Things
Polarity
Opposite ends of the water molecule have
opposite charges
Oxygen region has a partial negative
charge and the hydrogen atoms have a
partial positive charge
Two water molecules are held together by
a hydrogen bond which gives water some
of its unique properties
Hydrogen Bonding and Water’s
Properties
Water molecules attract one another and
“stick” together and this gives water the
property of Cohesion.
Cohesion helps in:
the transport of water against the force of
gravity in plants
Hydrogen bonding also results in Adhesion
Adhesion results in water sticking to the sides of
the tube-like cells in plants, helping them rise
as a unit to the leaves.
Effects on the Environment
Water absorbs and releases heat to moderate
the temperature of Earth’s environment. This
makes areas of the earth more habitable than
they otherwise would be without this property.
This results from its relatively high Specific
Heat, or the amount of heat that must be
absorbed or lost for one gram of that substance
to raise its temperature 1oC.
Its temperature changes less than other
substances when it absorbs or loses a given
amount of heat. (It absorbs or loses a relatively
large amount of heat for each degree it goes up
or down.)
Effects on The Environment 2
Many areas near ocean waters can
sustain populations because their coastal
areas are much warmer than interior
areas at that latitude.
Ocean temperatures remain much more
stable than land temperatures which
allows for diverse marine life to thrive.
Effects on The Environment 3
Water also has a high Heat of Vaporization or
quantity of heat a liquid must absorb for 1 gram
of it to be converted to a gas.
This evaporation causes the surface of the
liquid to cool causing something called
Evaporative cooling.
This contributes to the stability of temperature
in lakes and ponds .
Effects on The Environment 4
Water actually loses density when it takes
solid form.
As water becomes a solid crystal the
hydrogen atoms become locked a bit
further apart which results in it becoming
10% less dense than it is as a liquid.
This allows life to continue at depth in
lakes and ponds through the winter.
Effects on Living Things
Evaporative cooling allows animals to cool
their body temperature in warmer climates,
preventing them from overheating.
Cohesion and adhesion allow water to flow
against the force of gravity in plants.
Water is an important part of animal and plant
tissues and allows substances to be dissolved in
and move with it.
Water as a Solvent
Water is a solvent or a dissolving agent due to
its polarity
It dissolves many things but is not a “universal
solvent”
See example in your text pages 45-6
Negatively charged part of the water molecule
attracts positive ions and vice versa-Water
forms a hydration shell around each dissolved
ion
Substances that have a love for water are called
hydrophilic and those that seem to repel water
are called hydrophobic
Solute Concentrations
Solute concentrations are important as
controllers of what goes into and out of cells.
Molarity is a measure of solute concentration
based on moles of solute per liter of solution.
To obtain one mole of a substance you measure
out its molecular weight in grams.
Remember that one mole is equal to 6.02 X 1023
molecules
pH and living things 1
Remember that acids are solutions that increase
the hydrogen ion concentration of a solution
and bases reduce the hydrogen ion
concentration of a solution, usually by
accepting hydrogen ions.
The concentration of hydrogen ions in pure
water is 10-7M at 25oC
Therefore water has a pH of 7 because the pH
is the negative log of the concentration of
hydrogen ions in any solution.
pH and Living Things 2
In addition remember that the product of
hydrogen ions and hydroxide ions in a
solution is always 10-14
Most living things exist in a very narrow
pH range, usually from 5-7.
Buffers are substances that minimize
changes in pH to maintain a favorable
pH range (see examples page 48-9).
pH and Living Things 3
Acid rain or acid precipitation seriously
affects plants because pH affects the
solubility of minerals in the soil
necessary for plants.
If the pH does not allow soil and water to
combine to dissolve needed minerals,
trees and plants are stressed and can die
easily.