Water and the Fitness of the Environment

1. Water and the Fitness of the Environment

2. H2O (water): The Molecule That Enables Life • The biological medium • All living organisms require water • Cells are about 70-95% water • Abundance of water is the main reason Earth is habitable

3. Polarity hydrogen bonds • Water is polar molecule • Polarity allows formation of hydrogen bonds – – O H H + + http://www.youtube.com/watch?v=VhWQ-r1LYXY

4. LE 3-2 Properties of Water • MW H2O = 18; MW cluster = 90

5. Properties of water contribute to Earth’s fitness for life • Thermal Properties of Water • Solvent Properties of Water • Cohesion and Adhesion of Water

6. Thermal Properties of Water • Most important --water is liquid over the temperature range for life

7. Other Thermal Properties • Absorption and Dissipation of Heat • Specific heat – amount of energy absorbed for given temperature rise (measured in J/g/°C) • Hydrogen bonds

8. Other Thermal Properties • Absorption and Dissipation of Heat • High Thermal Conductivity • 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

9. Other Thermal Properties • Absorption and Dissipation of Heat • High Thermal Conductivity • Density of Ice

11. Other Thermal Properties • Absorption and Dissipation of Heat • High Thermal Conductivity • Density of Ice • Melting and Vaporizing • Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water • Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor

12. Other Thermal Properties • Melting and Vaporizing • Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water (J/g) • Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor (J/g) • Evaporative cooling

13. Other Thermal Properties Melting and Vaporizing Heat of fusion -- melting Heat of vaporization 13

14. Other Thermal Properties • Absorption and Dissipation of Heat • Specific heat – amount of energy absorbed for given temperature rise • High Thermal Conductivity • Density of Ice • Melting and Vaporizing • Heat of fusion – amount of energy to convert 1 gram ice to 1 gram liquid water • Heat of vaporization – amount of energy to convert one mole of liquid to one mole of water vapor

15. Properties of water contribute to Earth’s fitness for life • Thermal Properties of Water • Solvent Properties of Water • Cohesion and Adhesion of Water

16. Solvent Properties of Water • Solution – homogeneous liquid mixture of substances • Solvent -- dissolving agent • Solute -- substance dissolved • Aqueous solution -- water is the solvent

17. – – – – O O H H H H + + + + Solvent Properties of Water • Excellent Solvent

18. – – – – O O H H H H + + + + Solvent Properties of Water • Excellent Solvent • Hydration shell

19. – Na+ + – + – + – – Na+ – + + Cl– Cl– + – – + – + – – LE 3-6

20. Solvent Properties of Water • Ionic Compounds • Polar Compounds • Very large non-polar molecules if they have ionic and polar regions

21. LE 3-7a Lysozyme molecule in a nonaqueous environment.

22. Lysozyme molecule in a aqueous environment. LE 3-7b

23. WATER Hydrophilic head Hydrophobic tails WATER Hydrophilic and Hydrophobic Substances • Hydrophilic – attracts water • Hydrophobic – “repels” water

24. Solute Concentration in Aqueous Solutions • Most biochemical reactions occur in water • Chemical reactions depend on concentration of solutes in an aqueous solution -- Moles • One mole being 6.02 x 1023 molecules – Avogadro’s Number • Molarity -- moles of solute per liter of solution

25. Properties of water contribute to Earth’s fitness for life • Thermal Properties of Water • Solvent Properties of Water • Cohesion and Adhesion of Water

26. Cohesion/ Adhesion • Hydrogen bonds hold water molecules together • High Surface Tension

27. Cohesion/ Adhesion • Cohesion -- holds water molecules together • High Surface Tension • High Tensile Strength • Water 30 MPa; Copper Wire 70 MPa (yield strength)

28. Cohesion/ Adhesion • Cohesion -- holds water molecules together • Adhesion – attraction of water to solid surfaces Water-conducting cells 100 µm

29. Hydronium ion (H3O+) Hydroxide ion (OH–) 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: • The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+)

30. Hydronium ion (H3O+) Hydroxide ion (OH–) 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: • Hydronium ion (H3O+) -- molecule with the extra proton; • Hydroxide ion (OH-) -- molecule that lost the proton

31. Hydronium ion (H3O+) Hydroxide ion (OH–) Dissociation of water molecules leads to acidic and basic conditions that affect living organisms • H2O + H2O <___> H3O+ + OH-

32. Effects of changes in pH • H2O + H2O < __ > H+ + H2O + OH- < __ > H3O+ + OH- • H+ and OH- concentrations equal in pure water • pH – negative log of the concentration of hydrogen ions • pH -- range 0-14 • Neutral – pH = 7; Acid – pH < 7; Base pH > 7 • Most biologicals pH 6-8 • Acids – increase H+ concentration • Bases -- increase OH- concentration

33. Table 2-2, p. 40

34. LE 3-8

35. Buffers • Buffers -- minimizes changes in pH • Most buffers consist of an acid-base pair that reversibly combines with H+ • Donate H+ in the presence of bases • Accept H+ in the presence of acids

36. The Threat of Acid Precipitation • Acid precipitation -- rain, snow, or fog with a pH lower than 5.6 • Caused mainly by the mixing of different pollutants (SO2, NO2, CO2) with water in the air

37. 0 More acidic 1 2 Acid rain 3 4 5 Normal rain 6 7 8 9 10 11 12 13 More basic 14 LE 3-9