3. Water and the Fitness of the Environment

3. Water and the Fitness of the Environment - Chapter 3:...

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Unformatted text preview: Chapter 3: Water and the Fitness of the Environment 12/02/2008 10:29:00 Table of Contents Overview 3.1- The Polarity of Water Molecules Results in Hydrogen Bonding 3.2- Four Emergent Properties of Water Contribute to Earth’s Fitness for Life 3.3- Dissociation of Water Molecules leads to Acidic and Basic Conditions that Affect Living Organisms Overview 12/02/2008 10:29:00 • Water is the biological medium on Earth • Life on Earth began in water and evolved for 3bllion years before spreading onto land • ¾ of the Earth’s surface is submerged in water o most is in liquid form • Water is the only common substance to exist in the natural environment in all 3 physical states of matter o Solid o Liquid o Gas • The abundance of water is a major reason Earth is habitable 3.1- The Polarity of Water Molecules Results in Hydrogen Bonding 12/02/2008 10:29:00 Overview • Water o 2 Hs & 1 O Bonded by covalent bonds o Oxygen is more EN than H The electrons of the polar bonds spend more time closer to the O o The bonds that hold together the atoms in a water molecule Polar covalent o Bent shape o A polar molecule Opposite ends of the molecule have opposite charges O is partial negative Hs are partial positive o 3.2- Four Emergent Properties of Water Contribute to Earth’s Fitness for Life 12/02/2008 10:29:00 Cohesion • Waster molecules stay close together as a result of H-bonds • In liquid form o H-bonds are very fragile 1/20 as strong as covalent bonds o They form/break/re-form frequently o Each bond lasts only a few trillionths of a second o At any instant, a substantial percentage of all the water molecules are bonded to their neighbors Water is one of the more structured fluids • Cohesion o Sticks to self o Hydrogen bonds holding the substance together o Cohesion due to hydrogen bonding Contributes to transport of water (and nutrients) against gravity (in plants) As water leaves from the leaves, they pull the farther down molecules up • Adhesion o Clinging of one substance to another o Helps water stick to the walls of cells against gravity • Surface Tension o A measure of how difficult it is to stretch or break the surface of a liquid o Water has a greater surface tension than most other liquids Moderation of Temperature • Water moderates air temperature o Absorbs heat from air that is warmer o Releases stored heat to cooler air • Water is effective as a heat bank o Can absorb/release relatively large amounts of heat with a slight ∆T Heat & Temperature o Kinetic energy The energy of motion The faster something moves, the greater its KE...
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This note was uploaded on 04/29/2008 for the course BISC 220L taught by Professor Herrera,mcclure during the Spring '07 term at USC.

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3. Water and the Fitness of the Environment - Chapter 3:...

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