2. Chapter 3 Water and the Fitness of the Environment

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

4. More about Water Why are we studying water? All life occurs in water inside & outside the cell All life occurs in water inside & outside the cell

5. 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

6. Chemistry of water H 2 O molecules form H-bonds with each other H 2 O molecules form H-bonds with each other –+ attracted to – –creates a sticky molecule

7. Elixir of Life Concept 3.2: Four emergent properties of water contribute to Earths fitness for life Special properties of water Special properties of water –cohesion & adhesion surface tension, capillary action surface tension, capillary action –good solvent many molecules dissolve in H 2 O many molecules dissolve in H 2 O hydrophilic vs. hydrophobic hydrophilic vs. hydrophobic –lower density as a solid ice floats! ice floats! –high specific heat water stores heat water stores heat –high heat of vaporization heats & cools slowly heats & cools slowly I like the part about the ice!

8. Cohesion & Adhesion H bonding between H 2 O molecules is cohesion H bonding between H 2 O molecules is cohesion –water is sticky surface tension surface tension drinking straw drinking straw H bonding between H 2 O & other substances is adhesion H bonding between H 2 O & other substances is adhesion –capillary action –meniscus –water climbs up paper towel or cloth Can you suck sugar up a straw?

9. How does H 2 O get to top of trees? Transpiration built on cohesion & adhesion

10. Water is the solvent of life Polarity makes H 2 O a good solvent Polarity makes H 2 O a good solvent –polar H 2 O molecules surround + & – ions –solvents dissolve solutes creating solutions

11. Do you dissolve in water? Hydrophilic Hydrophilic –substances have attraction to H 2 O –polar or non-polar?

12. Or dont you? Hydrophobic Hydrophobic –substances that dont have an attraction to H 2 O –polar or non-polar? fat (triglycerol)

13. The special case of ice Most (all?) substances are more dense when they are solid, but Most (all?) substances are more dense when they are solid, but Not water… Ice floats! Ice floats! –H bonds form a crystal And this has made all the difference!

14. Ice floats

15. Why is ice floats important? Oceans & lakes dont freeze solid Oceans & lakes dont freeze solid –surface ice insulates water below allowing life to survive the winter allowing life to survive the winter –if ice sank… ponds, lakes & even oceans would freeze solid ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw in summer, only upper few inches would thaw –seasonal turnover of lakes cycling nutrients in autumn cycling nutrients in autumn

16. Specific heat H 2 O resists changes in temperature H 2 O resists changes in temperature –high specific heat –takes a lot to heat it up –takes a lot to cool it down H 2 O moderates temperatures on Earth H 2 O moderates temperatures on Earth

17. Specific heat & climate

18. Heat of vaporization Evaporative cooling Organisms rely on heat of vaporization to remove body heat

19. Concept 3.3: Dissociation of water molecules leads to acidic and basic conditions that affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: 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 with the extra proton is now a hydronium ion (H 3 O + ) –The molecule that lost the proton is now a hydroxide ion (OH - )

20. Ionization of water & pH Water ionizes Water ionizes –H + splits off from H 2 O, leaving OH – if [H + ] = [ - OH], water is neutral if [H + ] = [ - OH], water is neutral if [H + ] > [ - OH], water is acidic if [H + ] > [ - OH], water is acidic if [H + ] < [ - OH], water is basic if [H + ] < [ - OH], water is basic pH scale pH scale –how acid or basic solution is –1 7 14 H 2 O H + + OH –

21. pH Scale 10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 10 –2 2 10 –3 Vinegar, cola, beer 3 10 –4 Tomatoes 4 10 –5 Black coffee, Rainwater 5 10 –6 Urine, Saliva 6 10 –7 Pure water, Blood 7 10 –8 Seawater 8 10 –9 Baking soda 9 10 –10 Great Salt Lake 10 10 –11 Household ammonia 11 10 –12 Household bleach 12 10 –13 Oven cleaner 13 10 –14 Sodium hydroxide14

22. 10 0 1 2 3 4 5 6 7 8 9 3 Amount of base added Buffering range 452 pH Buffers & cellular regulation pH of cells must be kept ~7 pH of cells must be kept ~7 –pH affects shape of molecules –shape of molecules affect function –pH affects cellular function Control pH by buffers Control pH by buffers –reservoir of H + donate H+ when [H + ] falls donate H+ when [H + ] falls absorb H+ when [H + ] rises absorb H+ when [H + ] rises

23. The Threat of Acid Precipitation Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6 Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6 Acid precipitation is caused mainly by the mixing of different pollutants with water in the air Acid precipitation is caused mainly by the mixing of different pollutants with water in the air Acid precipitation can damage life in lakes and streams Acid precipitation can damage life in lakes and streams Effects of acid precipitation on soil chemistry are contributing to the decline of some forests Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

24. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 More basic Normal rain More acidic Acid rain

25. Credits Pearson Publishing as Benjamin Cummings © 2005 Pearson Publishing as Benjamin Cummings © 2005 Kim Foglia – AP Bio Power Point 2007 Kim Foglia – AP Bio Power Point 2007