BIO 101 1st EditionLecture 3Outline of Last LectureI. Mattera. Elementb. CompoundII. Structure and Behavior of Atomsa. Atomic number b. Atomic massc. IsotopesIII. Electrons and EnergyIV. Chemical bondsa. Strong Bondsi. Covalent bondsii. Ionic bondsV. Chemical Reactionsa. Weak bondsOutline of Current LectureI. Life Begins in WaterII. Examples of Unusual Properties of H2Oa. High specific heatb. H2O expands when H freezesc. Water is the Biological Solventi. Aqueous solutionsIII. Solute ConcentrationIV. Acids, Bases and pHa. Mathematical definition of pHChapter 3- Water (H2O)Life began in water, all organisms are made mostly of H2O (75-95%)We live on a planet where water dominates (3/4 of earth surface)H2O is a substance with many unusual behaviorsThe abundance and unusual behavior of H2O is the major reason the earth is habitableThe unusual behavior of H2O is due to hydrogen bonding:H2O is a polar molecule (due to polar covalent bonds between O and H)(-)charge on H(+) charge on OH2O molecules are attracted to one another (and to other polar or charged molecules) due to charge attractionBIO 101 1st EditionUnusual properties of H2O are an example of emergent properties (due to an increased level of structural organization caused by H-bondingSome examples of Unusual Properties of H2O1. High specific heat- amount of heat (in calories) required to increase the temperature of a substance by 1^(oC)a. With H2O, heat goes first to break H-bonds: little change in temperatureb. If take out heat, H-bonds form (releases heat) again, there is little change in temperatureBiological significance of specific heat1. living organisms are made up mostly of H2O and can therefore RESIST dramatic changes in temperature2. this tends to stabilize ocean temperature, protect marine organisms2. H2O expands when H freezes (ice floats on liquid water)a. H2O is one of only a few substances where the solid form is less dense than the liquid formsb. due to H-bonding between H2O moleculesc. in liquid H2O, H-bonds form and break often as the molecules move aroundd. at 0^oC, the molecules are no longer moving fast enough to break H-bonds, the H2O molecules become locked into a crystal lattice where eachH2O is bonded to the maximum number of partners held farther apart from each other: less dense 3. Water is the Biological Solventsolution= liquid which is a homogeneous mix of 2 or more substancessolute- substance that is dissolvedsolvent- the dissolving agenta. H2O is the solvent in living organismsb. The cell is like a tiny drop of H2O with many molecules (solutes) dissolved in itc. The characteristic properties of H2O as a solvent are due to H-bondingd. H2O is a good solvent for charged or polar substancesEx: NaCl (table salt)- easily dissolves in H2O, the polar H2O molecules pullthe 2 ions apart and surround heme. Nonpolar substances do NOT dissolve in H2O- polar and nonpolar substances do not mix (oil and water), oils nonpolar and water is polarProperties of Aqueous Solutions: solutions where H2O is the solvent- Cells are aqueous solutions, so it is important to understand the properties of aqueous solutionsBIO 101 1st Edition- We will discuss two properties of H2O solutionsI. Solute Concentration= number of molecules in a given amount of solutionTerms- Mole= number of grams of a substance equal to its molecular weight (in Daltons)- Molecular weight= sum of the atomic masses of each atom in the molecule- Molar (M)= number of moles of a solute in 1 liter of solution; the concentrationo The concentration of substance in living cells is usually given in terms of molarityo This is because molarity gives information about the number of molecules*One mole of any substance has the same number of molecules as ONE MOLE of any other substance = 6.02 *10^23 molecules*II. Acids, Bases, and pHa. The H2O molecules can dissociate H2O H(+) and OH(-)b. This happens rarely (approx. 1 in 555 million H2O molecules)c. Though rare, it is important because small changes in H(+) ad OH(-) can cause dramatic changes in the ability of biological molecules to functiond. In pure H2O, the [H+]=[OH-], they are in balancee. When acids or bases dissolve in water, it shifts the balance of H+ and OH-f. In pure H2O, [H+]=[OH-]= 10^(-7)Mg. An acid adds H+ to the solutionh. A base reduces H+ (by holding H+ or donating OH-)i. In aqueous solution [H+][OH-]=10^(-14)Mi. If one goes down, the other must go up to maintain the constant productj. thus is you know the concentration of one, you can figure out the concentration of the otherk. pH scale, to measure the degree of acidity, ranges from 1-14mathematical definition of pHpH=(-)log[H+]if the pH is 7 (like in pure H2O), that is called neutralif pH is greater than 7= basicif pH is less than 7= acidiceach unit of pH represents a 10-fold, change in [H+]most biological fluids maintain a pH of 6-8BIO 101 1st
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