Ch. 3 Water and Fitness of Environment BIOL 222

Transcription

1 Ch. 3 Water and Fitness of Environment BIL 222 verview: The Molecule That Supports All of Life Importance of water Water is the biological medium on Earth All living organisms require water more than any other substance Most cells are surrounded by water, and cells themselves are about 7095% water Makes Earth habitable nly substance to exist in three states at once Fig. 3 2 δ δ δ δ δ δ δ ydrogen bond δ

2 Emergent proper?es of water Four properes of water Cohesive behavior As well as adhesive Ability to moderate temperature Expansion upon freezing Versality as a solvent Cohesion Cohesion Water molecules (co)hering to one another through hydrogen bonds helps the transport of water against gravity in plants Adhesion Water molecules (ad)hering to other substances via hydrogen bonds Fig. 3 3 Adhesion Water-conducting cells Direction of water movement 150 µm Cohesion

3 Emergent proper?es of water Surface tension measure of how hard it is to break the surface of a liquid due to cohesion Modera?on of Temperature Water is a powerful temperature buffer Absorbs heat from warmer air and releases stored heat to cooler air because Water can absorb or release a large amount of heat with only a slight change in its own temperature Due to a high specific heat capacity eat and Temperature Kine?c energy eat energy of moon, energy doing work measure of the total amount of kinec energy due to molecular moon Temperature measures the amount of heat due to the average kinec energy of molecules

4 eat and Temperature Celsius scale measure of temperature using Celsius degrees ( C) Fahrenheit not used in sciences calorie (cal) amount of heat required to raise the temperature of 1 g of water by 1 C The calories on food packages are actually kilocalories (kcal), where 1 kcal = 1,000 cal joule (J) another unit of energy where 1 J = cal, or 1 cal = J Water s igh Specific eat specific heat amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC specific heat of water 1 cal/g/ºc or joules/g/ºc Therefore Water resists changing its temperature because of its high specific heat Water s igh Specific eat Water s high specific heat can be traced to hydrogen bonding eat is absorbed when hydrogen bonds break eat is put in and much is used to break bonds before the molecules can move faster eat is released when hydrogen bonds form When bonds form molecules slow down The high specific heat of water minimizes temperature fluctuaons to within limits that permit life

5 Fig. 3 5 Santa Barbara 73 70s ( F) 80s 90s 100s Los Angeles (Airport) 75 Pacific cean Burbank 90 San Diego 72 San Bernardino 100 Riverside 96 Santa Ana 84 Palm Springs miles Evapora?ve Cooling Evaporaon transformaon of a substance from liquid to gas eat of vaporiza?on heat a liquid must absorb for 1 g to be converted to gas Evapora?ve cooling as a liquid evaporates, its remaining surface cools highest kinec energy molecules escape stabilize temperatures in organisms and bodies of water Insula?on of Bodies of Water by Floa?ng Ice Ice is less dense than liquid water hydrogen bonds in ice are more ordered results in lower molecular density Water reaches its greatest density at 4 C Lower molecular kinec energy Molecules can pack ghter together higher density If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

6 Fig. 3 6 ydrogen bond Ice ydrogen bonds are stable Liquid water ydrogen bonds break and re-form The Solvent of Life Solu?on liquid that is a homogeneous mixture of substances Solvent dissolving agent of a soluon Solute substance that is dissolved aqueous solu?on water is the solvent Solu?ons Polarity of water Form hydrogen bonds easily () () () () () () () () versale solvent Ionic compounds dissolve in water each ion surrounded by a sphere of water molecules hydra?on shell

7 Fig. 3 7 Na Na Cl Cl The Solvent of Life Nonionic polar molecules also dissolved by water Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions They are water soluble Fig. 3 8 (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein s surface attract water molecules.

8 ydrophilic and ydrophobic Substances hydrophilic affinity for water Polar or ionic Readily dissolve hydrophobic no affinity for water Difficult or impossible to dissolve il molecules nonpolar bonds Solute Concentra?on in Aqueous Solu?ons Most biochemical reacons occur in water Aqueous environments to aqueous cytosol Chemical reacons Due to collisions of molecules therefore depend on the concentraon of solutes in an aqueous soluon Molecular mass Mole Solute Concentra?on in Aqueous Solu?ons sum of all masses of all atoms in a molecule Typical unit of measure for number of molecules Counng molecules impraccal 1 mole (mol) = 6.02 x molecules Molarity (M) Avogadro s number A s n and the unit dalton were defined such that 6.02 x daltons = 1 g number of moles of solute per liter of soluon

9 Acidic and basic condi?ons affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can shil from one to the other: hydrogen ion ( ) hydrogen atom leaves electron behind transferred as a proton hydronium ion ( 3 ) The molecule with the extra proton represented as hydroxide ion ( ) molecule that lost the proton Acids and Bases Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed 2 2 ydronium ion ( 3 ) ydroxide ion ( ) Effects of Changes in p Concentraons of and are equal in pure water Dynamic equilibrium Acids and bases are solutes alter concentraons of and p scale describe whether a soluon is acidic or basic Direct measure of ion concentraon

10 Acids and Bases Acid substance that increases concentraon of a soluon CL Cl 2 C 3 C 3 Base substance that reduces the concentraon of a soluon Na Na N 3 N 4 The p Scale In any aqueous soluon at 25 C the product of and is constant and can be wrioen as [ ][ ] = The p of a soluon is defined by the negave logarithm of concentraon, wrioen as p = log [ ] For a neutral aqueous soluon [ ] is 10 7 = (7) = 7 The p Scale Acidic p below 7 Basic p above 7 Most biological fluids have p values in the range of 6 to 8

11 Fig. 3 9 p Scale 0 Acidic solution Neutral solution Basic solution Increasingly Acidic [ ] > [ ] Neutral [ ] = [ ] Increasingly Basic [ ] < [ ] 1 Battery acid Gastric juice, 2 lemon juice 3 Vinegar, beer, wine, cola 4 Tomato juice Black coffee 5 Rainwater 6 Urine Saliva 7 Pure water uman blood, tears 8 Seawater 9 10 Milk of magnesia 11 ousehold ammonia 12 ousehold 13 bleach ven cleaner 14 Buffers The internal p of most living cells must remain close to p 7 Buffers minimize and concentraon changes consist of an acid base pair that reversibly combines with Bicarbonate buffer system 2 C 3 C 3 Acid precipita?on Threats to Water Quality on Earth rain, snow, or fog with a p lower than 5.6 caused mainly by the mixing of different pollutants with water in the air S 2 (g) ½ 2 (g) ==> S 3 (g) 2 (l) S 3 (g) ==> 2 S 4 (aq) can fall at some distance from the source of pollutants Acid precipitaon can damage life in lakes and streams Effects of acid precipitaon on soil chemistry are contribung to the decline of some forests

12 Fig More acidic Acid rain Normal rain More basic Threats to Water Quality on Earth uman acvies such as burning fossil fuels threaten water quality C 2 is released by fossil fuel combuson and contributes to: A warming of earth called the greenhouse effect Acidificaon of the oceans leads to a decrease in the ability of corals to form calcified reefs 2 (l) C 2 (g) <==> 2 C 3 (aq) 2 C 3 (C 3 C 2 3 ) Shils toward C 3 Not enough C 3 2 You should now be able to: 1. List and explain the four properes of water that emerge as a result of its ability to form hydrogen bonds 2. Disnguish between the following sets of terms: hydrophobic and hydrophilic substances; a solute, a solvent, and a soluon 3. Define acid, base, and p 4. Explain how buffers work