1. August 29, 2005 Biology 107 Water

2. Water Student Objectives:As a result of this lecture and the assigned reading, you should understand the following: 1.For all living organisms, life depends upon water, and living things are made up mostly of water molecules (H 2 O) 2.The dipoles produced by the polar covalent chemical bonds between the hydrogens and oxygen of the water molecule allow for hydrogen bonding between water molecules, and the properties of water are related to these intermolecular bonds. Water molecules "stick" to each other, cohesion, and to charged substances, adhesion. The cohesive and adhesive properties of water allow it to rise against the force of gravity through capillarity.

3. Water Related to cohesion is the property of surface tension - a measure of how difficult it is to stretch or break the surface of a liquid. Water’s hydrogen bonds moderate temperature and decrease water evaporation and vaporization. Ice is less dense than liquid water. Water's versatility as a solvent results from the polarity of its molecules; substances that dissolve in water are called hydrophilic (i.e., water-liking), while those that do not dissolve in water are hydrophobic (i.e., water-hating).

4. Water 3.A certain proportion of the water molecules dissociate into ions because of their polarity. The two ions formed in the chemical reaction that dissociates water are the hydrogen cation (H + ), which is simply a proton, and the hydroxide anion (OH - ) 4.Some substances when dissolved in water dissociate and release H + ions. By definition, these substances that release H + ions when dissolved in water are called acids. Acids increase the H + concentration of the solution. That is, the more acidic a solution, the higher its concentration of H + ions, and the lower its pH. 5.A base is any substance that accepts H + ions when dissolved in water.

5. Inventory of Water at the Earth's Surface. ReservoirVolume (cubic km x 1,000,000)Percent of Total Oceans137097.25 Ice Caps and Glaciers292.05 Groundwater9.50.68 Lakes0.1250.01 Soil Moisture0.0650.005 Atmosphere0.0130.001 Streams and Rivers0.00170.0001 Biosphere (Animals & Plants)0.00060.00004

6. Water Molecule Dipoles

7. Hydrogen Bonding of Water Molecules

8. Water Adhesion and Cohesion

9. Cohesion and Adhesion Cohesion and adhesion of water produces: 1) surface tension and 2) capillary action. Mechanism by which plants draw water upward from roots to leaves through small vessels. Mechanism by which water moves through groundwater reservoirs between the particles of rock.

10. Water Movement in Plants Cucumber stem in cross section showing vascular bundles that convey water by capillary action.

11. Hydrogen Bonding Helps Water Move Through Plants Some trees can move water from their roots to their leaves at a rate of 25 mm (1 inch) per second.

12. Hydrogen Bonding Holds Waters Molecules Together and Produces Surface Tension High tea in space

13. High Heat Holding Capacity 1.Water has a high boiling point, so water is a liquid over a wide temperature range. 2.Water has the ability to absorb much heat, so large bodies of water can minimize temperature changes. 3.Water produces evaporative cooling. The heat loss associated with evaporation makes evaporation an effective way for organisms to shed excess heat.

14. High Specific Heat of Water

15. Evaporative Cooling

16. Hydrogen Bonding of Water Molecules to Other Molecules

17. Water as a Polar Solvent

21. Why Ice Floats

22. Ice Floats Frozen water and frozen benzene

23. Ionization of Water In pure water only 10 -7 moles/liter of water are in dissociated, ionized form

24. pH Scale pH measures the hydrogen ion concentration of a solution The higher the H + concentration the lower the pH number Acids donate H +, while bases accept H +