Chapter 3: Water and the Fitness of
the Environment
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Makes life on Earth possible
¾ of Earth’s surface
60- 90 % of cells mass
Cytoplasm and blood are mostly water
Small, simple molecule
Very common (occurrence)
Very uncommon (chemistry)
Several unique properties *** know these ***
Polar covalent molecule
• 2 hydrogen and 1 oxygen
• Mass of 18
• Strong zones of partial positive and partial
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negative – “poles”
Cooperates in MANY hydrogen bonds
Results in emergent properties
– Conditions or traits that appear (emerge) because of
the structure or relationships between components.
– Ex: molecules have different properties than elements
and a forest has different properties than a tree.
Cohesion and Adhesion
• Surface tension
• Cohesion means water “sticks” to other water
molecules….. “beads”
– This helps keep water liquid, the form we need most
as living organisms (cytoplasm to oceans)
• Adhesion means that water “sticks” to other
substances
– Meniscus in graduated cylinder
– Xylem and phloem in plant stems
– Necessary for PHOTOSYNTHESIS
Moderates temperature
• Heat => measure of total kinetic energy
• Temperature=> intensity of heat due to average
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kinetic energy
Kilocalorie =>food cal., 1000 calories
Calorie => amt of heat required to raise one
gram of water by one degree Celsius
Specific heat => amt of heat that must be
gained or lost in order to heat or cool one gram
of a substance by 1 degree Celsius
Water has relatively high specific heat
Specific Heat
• Because water has a high specific heat
compared to other molecules its size
– It take a long time to change temp.
– Lake stays warm in fall
– Ocean temperatures don’t vary much
– Body temp stays steady
Evaporative Cooling
• Heat of vaporization => quantity of heat
required to convert 1 gram of substance
from liquid to gas
• Evaporation of sweat (water) takes out a
lot of body heat
– Hottest molecules closest to phase change,
lowers overall kinetic energy….
– Sweat, drool, pant, large ears, capillaries, etc
Ice Floats
• Liquid water has H bonds that hold water in a
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very density collection
Solid water (ice) actually has longer bonds,
liquid water’s bonds are further apart, less dense
Floating ice
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Doesn’t overflow
Acts as insulation
Allows for bottom to stay liquid
Lake can “melt” completely in the summer
Weather because of cold polar water and warm
equatorial waters … flow and currents
Solvent of Life
• Solution =>homogenous liquid mixture of two or
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more substances
Solute=> what is dissolved, solid, smaller amt.
Solvent=> what did the dissolving, liquid, larger
amt.
Aqueous solution => solution where solvent is
water
Very common in nature
Solutions
• Blood is a solution that carries dissolved
nutrients, oxygen and waste to and from
cells
• Cytoplasm ( cytosol ) is a solution that is
mostly water and is the site of all chemical
reactions in cells
• Most biochemistry is carried out in
aqueous solutions
Solutions cont.
• Hydrophilic =>water loving
• Hydrophobic => water fearing
• Molarity => number of moles per liter of
solution (mole is atomic mass in grams)
– ** Be able to calculate molar solutions **
• Dissociation=> degree to which a substance
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separates when in solution.
Water separates into H+ and OH Acid => has more H+ than OH- available
Base => has more OH- than H+ available
pH
• pH is the negative log of the H+ concentration
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and is a measure of how much the water has
dissociated and how much H+ is available
Organisms are very sensitive to pH ranges.
Some acids include gastic acid, lemon juice,
soda, coffee, rain(6) and urine (6)
Pure water should be neutral (7)
Some bases would include sea water (8), blood
(7.4), Tums, ammonia/bleach and many
cleaners
Acid Precipitation
• Can be in any format (rain or snow)
• Also exists as exhaust and run off
• S and N in atmosphere bond to water creating
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acids
Changing pH of lakes or oceans is harmful to
plant and animal life there
Changing pH of soil changes the charge and
availability of ions and nutrients that are used by
plants
Both can have impacts on food webs and our
food/water/oxygen supply