BIO 101 1st Edition Lecture 3 Outline of Last Lecture I Matter a Element b Compound II Structure and Behavior of Atoms a Atomic number b Atomic mass c Isotopes III Electrons and Energy IV Chemical bonds a Strong Bonds i Covalent bonds ii Ionic bonds V Chemical Reactions a Weak bonds Outline of Current Lecture I Life Begins in Water II Examples of Unusual Properties of H2O a High specific heat b H2O expands when H freezes c Water is the Biological Solvent i Aqueous solutions III Solute Concentration IV Acids Bases and pH a Mathematical definition of pH Chapter 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 behaviors The abundance and unusual behavior of H2O is the major reason the earth is habitable The 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 O H2O molecules are attracted to one another and to other polar or charged molecules due to charge attraction BIO 101 1st Edition Unusual properties of H2O are an example of emergent properties due to an increased level of structural organization caused by H bonding Some examples of Unusual Properties of H2O 1 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 temperature b If take out heat H bonds form releases heat again there is little change in temperature Biological significance of specific heat 1 living organisms are made up mostly of H2O and can therefore RESIST dramatic changes in temperature 2 this tends to stabilize ocean temperature protect marine organisms 2 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 forms b due to H bonding between H2O molecules c in liquid H2O H bonds form and break often as the molecules move around d at 0 oC the molecules are no longer moving fast enough to break Hbonds the H2O molecules become locked into a crystal lattice where each H2O is bonded to the maximum number of partners held farther apart from each other less dense 3 Water is the Biological Solvent solution liquid which is a homogeneous mix of 2 or more substances solute substance that is dissolved solvent the dissolving agent a H2O is the solvent in living organisms b The cell is like a tiny drop of H2O with many molecules solutes dissolved in it c The characteristic properties of H2O as a solvent are due to H bonding d H2O is a good solvent for charged or polar substances Ex NaCl table salt easily dissolves in H2O the polar H2O molecules pull the 2 ions apart and surround hem e Nonpolar substances do NOT dissolve in H2O polar and nonpolar substances do not mix oil and water oils nonpolar and water is polar Properties of Aqueous Solutions solutions where H2O is the solvent Cells are aqueous solutions so it is important to understand the properties of aqueous solutions BIO 101 1st Edition I We will discuss two properties of H2O solutions Solute Concentration number of molecules in a given amount of solution Terms 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 concentration o The concentration of substance in living cells is usually given in terms of molarity o 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 pH a 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 function d In pure H2O the H OH they are in balance e When acids or bases dissolve in water it shifts the balance of H and OHf In pure H2O H OH 10 7 M g An acid adds H to the solution h A base reduces H by holding H or donating OH i In aqueous solution H OH 10 14 M i If one goes down the other must go up to maintain the constant product j thus is you know the concentration of one you can figure out the concentration of the other k pH scale to measure the degree of acidity ranges from 1 14 mathematical definition of pH pH log H if the pH is 7 like in pure H2O that is called neutral if pH is greater than 7 basic if pH is less than 7 acidic each unit of pH represents a 10 fold change in H most biological fluids maintain a pH of 6 8 BIO 101 1st Edition
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