1. Water and the Fitness of the Environment Part I. Polarity and Emergent Properties

2. You Should Know Chap. 3 The importance of hydrogen bonding to the properties of water The importance of hydrogen bonding to the properties of water Four unique properties of water and how each contributes to life on Earth Four unique properties of water and how each contributes to life on Earth How to interpret the pH scale How to interpret the pH scale The importance of buffers in biological system The importance of buffers in biological system

3. Overview: The Molecule That Supports All of Life Water is the biological medium on Earth Water is the biological medium on Earth All living organisms require water more than any other substance All living organisms require water more than any other substance Most cells are surrounded by water, and cells themselves are about 70 – 95% water Most cells are surrounded by water, and cells themselves are about 70 – 95% water The abundance of water is the main reason the Earth is habitable The abundance of water is the main reason the Earth is habitable Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Concept 3.1: The polarity of water molecules results in hydrogen bonding The water molecule is a polar molecule: The opposite ends have opposite charges The water molecule is a polar molecule: The opposite ends have opposite charges Polarity allows water molecules to form hydrogen bonds with each other Polarity allows water molecules to form hydrogen bonds with each other Each water molecule can form a maximum of four hydrogen bonds at a time Each water molecule can form a maximum of four hydrogen bonds at a time Animation: Water Structure Animation: Water Structure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. Fig. 3-2 Hydrogen bond  – – H  + + H O — —  + +  + +  + +  – –  – –  – –

6. Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life Four of water ’ s properties that facilitate an environment for life are: Four of water ’ s properties that facilitate an environment for life are: –Cohesive behavior –Ability to moderate temperature –Expansion upon freezing –Versatility as a solvent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7. 3.2-Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion Cohesion helps the transport of water against gravity in plants Cohesion helps the transport of water against gravity in plants Adhesion is the clinging of one substance to another. Example, between water and plant cell walls Adhesion is the clinging of one substance to another. Example, between water and plant cell walls Animation: Water Transport Animation: Water Transport Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. Cohesion/Adhesion in Nature Transpiration- water molecules move up the very thin xylem tubes and their evaporation the stomates in the plant. Water molecules cling to each other because of cohesion and to the walls of the xylem tubes by adhesion. Transpiration- water molecules move up the very thin xylem tubes and their evaporation the stomates in the plant. Water molecules cling to each other because of cohesion and to the walls of the xylem tubes by adhesion.

9. Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

10. Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is related to cohesion Surface tension is related to cohesion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. Fig. 3-4

12. 3.2 Ability to Moderate Temperature Water absorbs heat from warmer air and releases stored heat to cooler air 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 Water can absorb or release a large amount of heat with only a slight change in its own temperature

13. 3.2 Ability to Moderate Temp.-Water’s High Specific Heat 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 º C 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 º C The specific heat of water is 1 cal/g/ º C The specific heat of water is 1 cal/g/ º C Water resists changing its temperature because of its high specific heat because: Water resists changing its temperature because of its high specific heat because: –Heat is released when hydrogen bonds form –Heat is absorbed when hydrogen bonds break The high specific heat of water minimizes temperature fluctuations to within limits that permit life The high specific heat of water minimizes temperature fluctuations to within limits that permit life Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. Fig. 3-5 San Diego 72° 40 miles Pacific Ocean 70s (°F ) 80s 90s 100s Santa Barbara 73° Los Angeles (Airport) 75° Burbank 90° San Bernardino 100° Riverside 96° Santa Ana 84° Palm Springs 106°