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BSC 114 Chapter 3

by: Alexis Elston

BSC 114 Chapter 3 BSC 114

Alexis Elston
GPA 4.0

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Complete Notes over Chapter 3
Principles Of Biology I
Daryl W. Lam
Class Notes
BSC114, Biology, notes, Water, Molecules, bonds
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This 4 page Class Notes was uploaded by Alexis Elston on Saturday September 17, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Daryl W. Lam in Fall 2016. Since its upload, it has received 26 views. For similar materials see Principles Of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 09/17/16
Chapter 3 Water and Life  Water supports ALL LIFE on Earth o Biological medium for life as we know it o Only common substance to exist in the natural environment in all three physical states of matter  Water is a Polar Molecule o Water molecules are highly polar because oxygen atoms have much higher electronegativity than  hydrogen atoms.  Hydrogen and Oxygen form covalent bonds, where the electrons spend more time near  the oxygen atom than the hydrogen, therefore making them Polar Covalent Bonds.   This makes water a Polar Molecule o Oxygen has partial negative charge o Hydrogens have partially positive charges  Polarity allows water molecules to form Hydrogen Bonds with each other and  with other polar compounds o Hydrogen bonds are weak, constantly being broken and reformed.  Four emergent properties of water contribute to Earth’s suitability for life o Cohesive and adhesive  Cohesion: chemical attraction between particles of the same substance  Hydrogen bonds hold water molecules together o One water molecule can form up to 4 hydrogen bonds with othercwater molecules and other polar compounds  One bond from each hydrogen, two from oxygen  Surface Tension: measure of how difficult it is to stretch or break the surface of  a liquid o Directly related to cohesion because of hydrogen bonds.   Water has greater surface tension than most other liquids  Examples:  Water­walking insects  Water globe above rim of a glass or on a coin  Adhesion: chemical attraction between different substances  Water will adhere to other polar or charged substances o Such as the cell walls of plants  Together, cohesion and adhesion make it possible for water to be transported against  gravity in plants o Ability to moderate temperature  Water is effective as a heat bank because it can absorb or release a relatively large  amount of heat with only a slight change in its own temperature  Temperature and Heat  Kinetic energy is the energy of motion o Temperature: measure of energy that represents the average kinetic  energy of the molecules in a body of matter, regardless of volume o Thermal Energy: the kinetic energy associated with random motion of  atoms or molecules, dependent in part by matter’s volume  Heat: thermal energy in transfer from one body of matter to  another  Specific heat of a substance is the amount of heat that must be absorbed or lost  for 1g of that substance to change its temperature by 1°C.  Calorie is the amount of heat it takes to raise the temperature  of 1g of water by 1°C.  Specific heat of water is 1 cal/gram times °C. o The greater the specific heat of a substance, the greater it resists  changing temperature when it absorbs or releases heat. Chapter 3  Compared to other substances, water has an unusually high  specific heat.  Can be traced to hydrogen bonding o Water absorbs heat when hydrogen bonds  are broken o Water releases heat when it forms hydrogen  bonds o The high specific heat of water minimizes temperature fluctuations to  within limits that permit life, and because organisms are made  primarily of water, they are better able to resist changes in their own  temperature  Evaporative Cooling: o Evaporation is transformation of a substance from liquid to gas  Heat of vaporization is the heat a liquid must absorb for 1g to  be converted to gas  Evaporative cooling: As liquid evaporates, its  remaining surface cools o Helps stabilize temperatures in organisms  and bodies of water  ie: sweating and panting allows  excess heat to escape the body  because water absorbs heat  High humidity increases discomfort from heat because high  concentration of water vapor in the  air inhibits the evaporation of sweat from the body o Expands upon freezing  In ice, each molecule of water is hydrogen­bonded to 4 other water molecules in a 3D  crystal shape  Each crystal is spacious, so ice has fewer molecules than an equal volume of  water in which hydrogen bonds are constantly breaking and reforming o Makes ice less dense than water  This is why bodies of water freeze from the top down  Ice insulates water below, allowing life to exist. o Versatility as a solvent for other polar and ionic compounds  A solution is a liquid that is a completely homogenous mixture of substances.  Solvent: the dissolving agent o Aqueous Solution: water is the solvent  Solute: substance dissolved in a solution o In sugar water, sugar is the solute and water is the solvent. The sugar  water is the solution.   Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds  easily  When an ionic compound (ie. NaCl) is dissolved in water, each ion is  surrounded by a sphere of water molecules called a hydration shell. o Example of a Solution: salt water  Solvent: water  Solute: sodium chloride  Solution: salt water  Water can dissolve ionic compounds and nonionic polar compounds Chapter 3 o Even large polar molecules such as proteins can dissolve in water if  they have sufficient polar and charged regions on their surface to form  hydrogen bonds  Hydrophobic and Hydrophilic Substances:  Only those substances that are ionic or polar will dissolve readily in water o Hydrophilic Substance: one that loves water (has an affinity for)  Can form hydrogen bonds with water due to polarity  o Hydrophobic Substance: one that hates water (does not have affinity  for)  Cannot form hydrogen bonds with water due to being nonionic and nonpolar  Molecular Mass and Solute Concentration in Aqueous Solutions  Molecular Mass: Sum of all atomic masses of all atoms in a molecule  Mole: molecular mass in gram units of mass  Molarity: number of moles of solute per liter of aqueous solution  Acidic and Basic conditions affect living organisms o Dissociation of Water molecules  A hydrogen atom in a hydrogen bond between two water molecules can shift from one to  the other.  Hydrogen atom leaves its electron behind and is transferred as a proton, or  hydrogen ion (H ) o The molecule with the extra proton is now a hydronium ion (H O3)+ +  Often represented by H ­ o Molecule that lost proton is now a hydroxide ion (OH )  Water is in a state of dynamic equilibrium when water molecules dissociate at  the same rate at which they are being reformed o Though statistically rare, the dissociation of water molecules has a  great effect on organisms  Changes in concentrations of OH and H  ions can drastically  affect the chemistry of a cell  Concentrations can be changed by adding acids and  bases to a solution o Acids and Bases +  Acid: any substance that increases the H  concentration of a solution  Adds hydrogen ions and removes hydroxide ions because of the tendency for H + ­ to combine with OH  and produc+ water  Base: any substance that reduces the H  to a solution  By either drawing H  out of the solution or adds OH to the solution o Because of the formation of water  Strong acids and bases dissociate completely in water  Weak acids and bases reversibly release and accept back hydrogen ions, but can  still shift the balance away from neutrality  pH scale: used to denote whether a solution is acidic or basic  Less than 7 is acidic  More than 7 is basic  7 is neutral o Most biological fluids have pH values of 6­8  Each whole number changes in pH represents a tenfold difference in hydroxide  and hydrogen ions o Buffers:   Internal pH of most living cells must be maintained close to pH 7 Chapter 3  Buffers: substances that minimize changes in concentrations of H and OH in a  solution o Most buffered solutions contain a weak acid and its corresponding  + base, which combine reversibly with H  ions


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