Chapter
3 - Water and the Fitness of the Environment
Life exists on
earth because of water and its amazing properties
Concept 3.1 The polarity of water molecules results in
hydrogen bonding
-
water
is polar and therefore has partial positive and negative charges
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this
polarity causes hydrogen bonding to occur
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Concept 3.2 Four emergent properties of water contribute to Earth′s fitness for life
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4
key properties make water important for life on Earth
o Cohesion
o Moderation of Temperature
o Insulation of bodies of water
by floating ice
o Water as a solvent
Cohesion
-
remember
back to hydrogen bonding, water molecules stick together
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cohesion
helps water and dissolved minerals travel up a plant
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adhesion
helps the water “stick” to the sides of tubes (xylem) as the water is traveling
upward
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cohesion
is also the cause of surface tension
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Moderation of
Temperature
-
temperature
review
o kinetic energy – energy of
motion
o heat vs
temperature
o calorie = heat required to
raise 1 g of water by 1 degree C
o water has a high specific
heat (related to a calorie)
o water can absorb and store
large amounts of heat
o a body of water will heat up
or cool down much faster than an area of land
o oceans keep nearby land
temperatures from fluctuating too much
o organisms are made of lots of
water – helps maintain homeostasis
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evaporative
cooling
o Heat of vaporization is the
quantity of heat a liquid must absorb for 1 g of it to be converted from the
liquid to the gaseous state.
o lots of heat is needed to
vaporize a volume of water compared to other substances
o as water evaporates, the
liquid that remains is cooled down
o evaporative cooling helps
cool many living things and keep Earth’s environments relatively stable
Ice Floats in
Water
-
water
is less dense as a solid than it is as a liquid
-
hydrogen
bonding
-
greatest
density at 4deg. c
-
ability
of ice to float keeps ponds and oceans from freezing
o allows life to continue
during winter months
o insulates water below
The solvent of
life
-
review
definitions: solvent, solute, solution, aqueous solution
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water
is not a universal solvent, but is very versatile
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hydrophilic
vs hydrophobic
o hydrophilic – water loving (
soluble in water)
o hydrophobic – water fearing
(insoluble in water)
§
important
for cell membranes
-
solute
concentrations
o find molecular mass
o add one mole of solute and
dissolve in water – continue adding water until total volume reaches 1 liter –
this gives a 1 molar solution
Concept 3.3 Dissociation of water molecules leads to acidic
and basic conditions that affect living organisms
hydrogen can shift from one water molecule to the
other
to simplify life, we think of it as water
splitting to form a hydrogen ion and a hydroxide ion
Effects of Changes
in pH
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acids
– donate H+ to the solution
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bases
– reduce H+ concentration (raise
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pH
scale 0 to 14
o 0 – 6 = base
o 7 = neutral
o 8 – 14 = acid
[H+][OH−]
= 10−14
pH = −log[H+]
most biological solutions are between pH 6 – 8
buffers help to keep pH in that range
-
they
minimize the changes in pH
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A
buffer works by accepting hydrogen ions from the solution when they are in
excess and donating hydrogen ions to the solution when they have been depleted.
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Read
“The threat of acid precipitation” on your own