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Unformatted text preview: Biology 101 Notes Chapter 3 Water and the Fitness of the Environment I. The Molecule That Supports All of Life a. Water is the basis of life 1. Cells are made of 70-95% water. 2. of earth is water. 3. Water is the only substance to exist in all three states of matter. 4. The structure of a water molecule allows it to form weak chem. bonds w/ other molecules, including water molecules. II. The polarity of water molecules results in hydrogen bonding a. The water molecule is simple. 1. Its 2 hydrogen atoms are joined to oxygen atom by single covalent bonds. 2. Oxygen is more electronegative than hydrogen, so electrons of polar bonds spend more time closer to oxygen atom. 3. Bonds are polar covalent bonds. 4. Polar Molecule- Opposite ends of the molecule have opposite charges: Oxygen is and hydrogen is +. 5. Anomalous properties aa. Electrical attraction hydrogen is attracted to oxygen of other molecule and theyre held together by hydrogen bonds. III. Four emergent properties of water contribute to Earths fitness for life a. Cohesion 1. Water molecules stay close b/c of hydrogen bonding. 2. In liquid, hydrogen bonds are fragile. 3. Cohesion- Hydrogen bonds hold the substance together. aa. Hydrogen bonds are constantly breaking and re-forming. bb. Helps transport water and nutrients against gravity in plants. 4. Adhesion- The clinging of one substance to another. aa. In a plant, adhesion to walls of the cells helps counter downward pull of gravity. 5. Surface Tension- A measure of how difficult it is to stretch or break the surface of a liquid. aa. Water is coated with an invisible film. bb. Ex. Overfilling a drinking glass cc. Animals can walk on water b. Moderation of Temperature 1. Water moderates air temp by absorbing warm air and releasing stored heat to cooler air. c. Heat and Temperature 1. Kinetic Energy- The energy of motion. aa. Atoms have KE b/c always moving. bb. The faster a molecule moves, the greater kinetic energy....
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- Fall '07