Download powerpoint

CHAPTER 3
WATER AND THE FITNESS
OF THE ENVIRONMENT
I. Water’s Polarity and Its
Effects
• A. The polarity of water molecules results
in hydrogen bonding
– A HYDROGEN BOND FORMS WHEN THE
OXYGEN OF ONE WATER MOLECULE IS
ELECTRICALLY ATTRACTED TO THE
HYDROGEN OF A NEARBY MOLECULE.
– HYDROGEN BONDING BETWEEN WATER
MOLECULES IS THE BASIS OF WATER’S
UNUSUAL PROPERTIES.
Figure 3.0 Earth
SPECIAL PROPERTIES OF WATER
• COHESION
• ADHESION
• HIGH SURFACE
TENSION
• HIGH HEAT
CAPACITY
• DENSITY
• VERSATILE
SOLVENT
Figure 3.1 Hydrogen bonds between water molecules
Figure 3.1 Hydrogen bonds between water molecules
B. Organisms depend on the cohesion of
water molecules
• HYDROGEN BONDING MAKES WATER MOLECULES STICK
TOGETHER, AND THIS COHESION HELPS PULL WATER
UPWARD IN THE MICROSCOPIC VESSELS OF PLANTS.
Figure 0301 HYDROGEN BONDS B/W MOLECULES
• HYDROGEN BONDING IS ALSO RESPONSIBLE FOR WATER’S
SURFACE TENSION.
• SURFACE TENSION: A measure of how difficult it is to stretch or
break the surface of a liquid.
C. Water moderates temperatures on Earth
• HYDROGEN BONDING GIVES WATER A HIGH
SPECIFIC HEAT.
– SPECIFIC HEAT = The amount of heat that must be
absorbed or lost for 1 g of a substance to change its
temperature 1° C.
• HEAT IS ABSORBED WHEN H+ BONDS BREAK AND
IS RELEASED WHEN H+ BONDS FORM,
MINIMIZING TEMP. FLUCTUATIONS TO WITHIN
LIMITS THAT PERMIT LIFE.
Figure 3.4 Evaporative cooling
D. Oceans and lakes don’t freeze solid
because ice floats
• ICE IS LESS DENSE THAN LIQUID WATER B/C ITS
MORE ORGANIZED H+ BONDING CAUSES
EXPANSION INTO A CRYSTAL FORMATION.
• FLOATING ICE ALLOWS LIFE TO EXIST UNDER
THE FROZEN SURFACES OF LAKES AND POLAR
SEAS.
Figure 0305 THE STRUCTURE OF ICE
Figure 3.5 The structure of ice (Layer 1)
Figure 3.5 The structure of ice (Layer 2)
Figure 3.5x1 Ice, water, and steam
Figure 3.6 Floating ice and the fitness of the environment
Figure 3.6x1 Floating ice and the fitness of the environment: ice fishing
Figure 3.6x2 Ice floats and frozen benzene sinks
E. Water is the solvent of life
• WATER IS AN UNUSUALLY VERSATILE SOLVENT
B/C ITS POLARITY ATTRACTS IT TO CHARGED
POLAR SUBSTANCES.
• WHEN IONS OR POLAR SUBSTANCES ARE
SURROUNDED BY WATER MOLECULES, THEY
DISSOLVE AND ARE CALLED SOLUTES.
– HYDROPHYLIC = “LIKE” WATER
– HYDROPHOBIC = “FEAR” WATER
Figure 0307 A CRYSTAL OF TABLE SALT DISSOLVING IN WATER
Figure 0308 A WATER SOLUBLE PROTEIN
II. The Dissociation of Water
A. Organisms are sensitive to changes in pH
•
•
•
•
•
WATER CAN DISSOCIATE INTO H+ AND OHTHE CONCENTRATION OF H+ IS EXPRESSED AS pH.
ACIDS DONATE ADDITIONAL H+ IN AQUEOUS SOLN’S.
BASES DONATE ADDITIONAL OH- IN AQUESOUS SOLN’S.
pH SCALE: A measure of hydrogen ion concentration ranging in
value from 0 to 14.
– ACID = 0-7
– NEUTRAL = 7
– BASE = 7 – 14
Figure 0309 THE pH OF SOME AQUEOUS SOLUTIONS
Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift