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Biology Chapter 3 Notes

by: Alina Hasan

Biology Chapter 3 Notes BSC 1010C

Marketplace > Valencia College > Science > BSC 1010C > Biology Chapter 3 Notes
Alina Hasan

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General Biology - BSC 1010C Water and Life: Molecules and Bonds
General Biology
Professor Bouyahyaoui
Class Notes
Molecules, MCAT, Science, MCAT Biology, Biology, basic
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This 3 page Class Notes was uploaded by Alina Hasan on Monday October 10, 2016. The Class Notes belongs to BSC 1010C at Valencia College taught by Professor Bouyahyaoui in Fall 2016. Since its upload, it has received 5 views. For similar materials see General Biology in Science at Valencia College.


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Date Created: 10/10/16
Biology Chapter 3: Water and Life The Molecule That Supports All Life  Water is the biological medium on Earth. Water is the only common substance to exist in the natural environment in all three physical states.  The structure of the water molecule allows it to interact with other molecules.  Properties of Water: Cohesive, Moderates Temperature, Versatility as a solvent,  Expansion upon Freezing. Polar covalent bonds in water molecules result in hydrogen bonding  In the water molecule, the electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen. The water molecule is thus a polar molecule: the overall  charge is unevenly distributed. Polarity allows water molecules to form hydrogen bonds with each other. Cohesion of Water Molecules  Collectively, hydrogen bonds hold water molecules together, a phenomenon called  cohesion.  Cohesion helps the transport of water against gravity in plants  Adhesion is an attraction between different substances, for example, between water and  plant cell walls.  Surface Tension is the measure of how hard it is to break the surface of a liquid. Water  has an unusually high surface tension due to hydrogen bonding between molecules at the  air­water interface and to the water below. Moderation of Temperature by Water  Water absorbs heat from warmer air and releases stored heat to cooler air. Water can  absorb or release a large amount of heat with only a slight change in its own temperature.  Kinetic energy is the energy of motion.  The kinetic energy associated with random motion of atoms or molecules is called  thermal energy.  Temperature is a measure of energy that represents the average kinetic energy of the  molecules in a body of matter.  Thermal energy in transfer from one body of matter to another is defined as heat.  A calorie (cal) is the amount of heat required to raise the temperature of 1 g of water by  1°C  Kilocalories (kcal) 1 kcal = 1000 cal  Joule (j) 1 j = 0.239 cal, or 1 cal = 4.184 j  The specific heat of a substance is the amount of heat that must be absorbed or lost for 1  g of that substance to change its temperature by 1°C  The specific heat of water is 1 cal/g/°C  Water resists changing its temperature because of its high specific heat. 1 Biology Chapter 3: Water and Life  Water’s high specific heat can be traced to hydrogen bonding  Heat is absorbed when hydrogen bonds break  Heat is released when hydrogen bonds form  Evaporation is transformation of a substance from liquid to gas.  Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas.  As a liquid evaporates, its remaining surface cools, a process called evaporative cooling.  Evaporative cooling of water helps stabilizes temperatures in organisms and bodies of  water.  Floating of Ice on Liquid Water  Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice  less dense than water.  Water reaches its greatest density at 4°C  If ice sank, all bodies of water would eventually freeze solid, making life impossible on  Earth. Water: The Solvent of Life   A solution is a liquid that is a completely homogeneous mixture of substances.  A solvent is the dissolving agent of a solution.  The solute is the substance that is dissolved.  An aqueous solution is one in which water is the solvent.  Water is a versatile solvent due to its polarity.  When an ionic compound is dissolved in water, each ion is surrounded by a sphere of  water molecules called a hydration shell.  A hydrophilic substance is one that has an affinity for water.  A hydrophobic substance is one that does not have an affinity for water.  Oil molecules are hydrophobic because they have relatively nonpolar bonds Acidic and Basic   A hydrogen atom in a hydrogen bond between two water molecules can shift from one to  the other.  The hydrogen atom leaves its electron behind and is transferred as a proton, or  hydrogen ion (H+)  The molecule that lost the proton is now a hydroxide ion (OH−)  The molecule with the extra proton is now a hydronium ion (H O+),3though it is  often represented as H+.  Changes in concentrations of H+ and OH− can drastically affect the chemistry of a cell.  Biologists use something called the pH scale to describe whether a solution is acidic or  basic(the opposite of acidic).  An acid is any substance that increases the H+ concentration of a solution. 2 Biology Chapter 3: Water and Life  A base is any substance that reduces the H+ concentration of a solution.  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 of H+ and OH− away from neutrality.  Acidic solutions have pH values less than 7.  Basic solutions have pH values greater than 7.  Most biological fluids have pH values in the range of 6 to 8.  Buffers are substances that minimize changes in concentrations of H+ and OH− in a  solution. 3


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