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AP Biology
Why are we studying Why are we studying water?water?
All life occurs in waterAll life occurs in water– inside & outside the cellinside & outside the cell
AP Biology
Chemistry of waterChemistry of water
Water is polar moleculeWater is polar molecule– remember polar covalent bondsremember polar covalent bonds– + & – poles+ & – poles
AP Biology
Chemistry of waterChemistry of water HH22O molecules form H bonds with O molecules form H bonds with
each othereach other– + attracted to –+ attracted to –– creates a sticky creates a sticky
molecule molecule
AP Biology
CohesionCohesion
H bonding between HH bonding between H22O creates O creates cohesioncohesion– water is “sticky”water is “sticky”– surface tensionsurface tension– drinking strawdrinking straw
can you suck can you suck sugar up a sugar up a straw?straw?
AP Biology
How does HHow does H22O get to O get to top of tree?top of tree? Transpiration Transpiration
AP Biology
AdhesionAdhesion
HH22O molecules form H bonds with O molecules form H bonds with other substances other substances – capillary actioncapillary action– meniscusmeniscus– water climbs up fiberwater climbs up fiber
ex. paper towelex. paper towel
AP Biology
Water is the solvent of Water is the solvent of lifelife
HH22O is a good solvent due to its O is a good solvent due to its polaritypolarity– polar Hpolar H22O molecules surround + & – O molecules surround + & –
ionsions– solvents dissolve solutes creating solvents dissolve solutes creating
aqueous solutionsaqueous solutions
AP Biology
HydrophilicHydrophilic HydrophilicHydrophilic
– substances have affinity for Hsubstances have affinity for H22OO
– polarpolar or or non-polarnon-polar??– ionicionic
AP Biology
HydrophobicHydrophobic Hydrophobic Hydrophobic
– substances do not have affinity for Hsubstances do not have affinity for H22OO– polarpolar or or non-polarnon-polar??– non-ionicnon-ionic
fat (triglycerol)
AP Biology
The special case of iceThe special case of ice
Most (all?) substances are more Most (all?) substances are more dense when they are soliddense when they are solid
But not water…But not water… Ice Ice floatsfloats!!
– H bonds form a crystal with H bonds form a crystal with loose structure loose structure
AP Biology
Ice floatsIce floats
AP Biology
Why is “ice floats” Why is “ice floats” important?important?
Oceans & lakes don’t freeze solidOceans & lakes don’t freeze solid– if ice sank…if ice sank…
eventually all ponds, lakes & even ocean eventually all ponds, lakes & even ocean would freeze solidwould freeze solid
during summer, only upper few inches during summer, only upper few inches would thawwould thaw
– surface ice insulates water belowsurface ice insulates water below allowing life to survive the winterallowing life to survive the winter
– seasonal turnover of lakesseasonal turnover of lakes cycling nutrientscycling nutrients
AP Biology
Specific heatSpecific heat HH22O has high specific heatO has high specific heat
– due to H bondingdue to H bonding
HH22O resists changes in temperatureO resists changes in temperature– takes a lot to heat it uptakes a lot to heat it up– takes a lot to cool it downtakes a lot to cool it down
HH22O moderates temperatures on O moderates temperatures on EarthEarth
AP Biology
AP Biology
Evaporative coolingEvaporative cooling
Organisms rely on Organisms rely on heat of vaporization heat of vaporization to remove heatto remove heat
AP Biology
Water forms ionsWater forms ions
Hydrogen ion (HHydrogen ion (H++) splits off from water to ) splits off from water to leave a hydroxide ion (leave a hydroxide ion (--OH) OH)
HH220 ----> H0 ----> H++ + + --OHOH
If concentration of 2 ions is equal, If concentration of 2 ions is equal, water is water is neutralneutral
If [If [HH++]] > [> [--OHOH], water is ], water is acidicacidic If [If [--OHOH] > [] > [HH++],], water is water is basicbasic pH scalepH scale = how acidic or basic a solution is = how acidic or basic a solution is
AP Biology
pH ScalepH Scale
In pure water only 1 water molecule In pure water only 1 water molecule in every 554 million is dissociated.in every 554 million is dissociated.– very small amount of ionsvery small amount of ions– [H[H++] or [OH] or [OH--] is 10] is 10-7-7MM
[H[H++] [OH] [OH--] = 10] = 10-14-14
pH scale is based on this equationpH scale is based on this equation
AP Biology
pH ScalepH Scale In neutral solution In neutral solution
[H[H++] = 10] = 10-7-7 pH = 7 pH = 7 Values for pH Values for pH declinedecline as [H as [H++] ] increaseincrease
Acids Acids – adding acid adding acid
increases [Hincreases [H+]+] BasesBases
– adding base adding base increases [OHincreases [OH--]]
AP Biology
pH & BiologypH & Biology
pH of a neutral solution = 7pH of a neutral solution = 7 Acidic solutions Acidic solutions == pH < 7 pH < 7
Basic solutionsBasic solutions = = pH > 7pH > 7 Most biological fluids have pH 6 – 8Most biological fluids have pH 6 – 8
– pH values in human stomach can reach 2pH values in human stomach can reach 2 Each pH unit represents a Each pH unit represents a 10-fold10-fold
difference in Hdifference in H++ & OH & OH-- concentrations. concentrations.– small change in pH actually indicates a small change in pH actually indicates a
substantial change in [Hsubstantial change in [H++] & [OH] & [OH--]]
AP Biology
Water is a polar moleculeWater is a polar molecule The special properties of water The special properties of water
make life on Earth possiblemake life on Earth possible The chemical behavior of water The chemical behavior of water
governs how organisms functiongoverns how organisms function
PunchlinePunchline
AP Biology
Any Questions??Any Questions??