Biochemistry Water and the Fitness of the Environment

1. Biochemistry Water and the Fitness of the Environment

2. Water: The molecule that supports life on this planet! • Living things are 96% C, H, O, N; 3% trace elements • Water is the biological medium for all life on Earth • All living organisms require water more than any other substance

3. Water: The molecule that supports life on this planet! • 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

4. Water: The BONDS are EVERYTHING!!! • Covalent bonds: Nonpolar vs Polar • Polar covalent bonds between H & O • Atoms vary in their electronegativity; O is MORE electronegative

5. Water: The BONDS are EVERYTHING!!! • Making the region around O slightly negative • Region around H slightly positive • This allows for the hydrogen bonding that gives water many of its unique properties

6. More about H-Bonds • Hydrogen bonds are relatively weak bonds known as intermolecular forces (IMFs) that form between H of one water molecule & O of another • Each water molecule can form up to 4 H-bonds at a time • Hydrogen bonding gives water many of its unique properties

7. Talk with a Partner!!! Describe the two types of bonds that water forms and where they are located.

8. FOUR Emergent Properties of water contribute to Earth’s suitability for life • Water’s cohesive & adhesive behavior • Water’s ability to moderate temperature • Water’s expansion upon freezing • Water’s versatility as a solvent.

9. Water’s cohesive & adhesive behavior • Cohesion is when water molecules stick to each other. • Adhesion is when water molecules stick to some other type of substance like plant cell walls.

10. What causes water molecules to both cohere and adhere? • Yep! Our good buddy the intermolecular force (IMF) named hydrogen bonding • Capillary action, the spontaneous movement or “pull” of water into a narrow tube or porous material is due to BOTH cohesion & adhesion

11. What causes water molecules to both cohere and adhere? • An example of Capillary action can be seen in transpiration, the movement of water through xylem tubes in plants and the evaporation of water from the stomata

12. Related to cohesion is surface tension • Surface tension is the tendency of fluid surfaces to shrink into the minimum surface area possible.  • Surface tension is a measure of how hard it is to break the surface of a liquid. • Surface tension is a consequence of cohesiondue to hydrogen bonding. • Surface tension allows insects denser than water, to float and slide on a water surface.

13. How does water moderate temperature? • Water has a high heat capacity. • Heat capacity is the amount of heat required to raise 1 gram of water by 1o Celsius (1 calorie = 4.184 J) • What does that mean? It means water can absorb large quantities of heat without much change in its own temperature, thus it’s a good thermo regulator. • Makes temperature of Earth’s oceans relatively stable

14. Water’s High Specific Heat • Water’s high specific heat can be traced to hydrogen bonding • Heat is absorbed when hydrogen bonds break • Heat is released when hydrogen bonds form • The high specific heat of water minimizes temperature fluctuations to within limits that permit life as most of the energy absorbed is used to BREAK the H-bonds instead of heating the water

15. Comparison of specific heat capacities of varying substances

16. How does water moderate temperature? • The fact that each water molecule can make FOURH-bonds each means they are really, really attracted to each other, thus more ENERGY must be added to the water sample to increase their molecular motion and raise the temperature of water. • Remember, temperature is a measure of the average kinetic energy of a sample of molecules!

17. How does water moderate temperature? • We should also discuss this effect as it relates to “air” with regard to the amount of water vapor in the air or humidity. • The more water vapor in the air, the more heat the air can absorb.

18. How does water moderate temperature? • Large bodies of water absorb heat from warmer air and release stored heat to cooler air. • This explains why temperature at the coast is a little cooler, but also more humid • Where land is cooler, like Michigan, land areas near the water are warmer and less humid

19. Care to examine some data? Formulate an explanation for the temperature data presented below. Your explanation should address the properties of water as they relate to thermoregulation. What do you notice about the temperature trends as we leave the coastline?

20. Evaporative Cooling • Water absorbs the heat from other surfaces, making those surfaces cooler • Evaporation is transformation of a substance from liquid to vapor • Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to vapor • As a liquid evaporates, its remaining surface cools, a process called evaporative cooling • Evaporative cooling of water helps stabilize temperatures in organisms (sweating, panting, etc.)and bodies of water

21. Evaporative Cooling Demo • Alcohol has a LOW heat of vaporization compared to water • Your body heat transfers more than enough energy to vaporize alcohol • As a liquid evaporates, its remaining surface cools, a process called evaporative cooling • Your body heat does NOT transfer enough energy to vaporize water

22. Evaporative Cooling Demo

23. Water’s expansion upon freezing Liquid water: transient hydrogen bonds as Molecules move randomly Ice: stable hydrogen bonds as kinetic energy decreases

24. Water’s expansion upon freezing

25. Ice is less dense than Liquid Water • Water’s MOST unique property; very FEW substances are less dense as solid than liquid • Ice floats in liquid water because hydrogen bonds in ice are more “ordered” forming a hexagonal shape with a hole in the middle, making ice lessdense. • Water reaches its greatest density at 4°C, which is excellent news if you’re a fish! • If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

26. Solid Water Floats Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Hydrogen bonds are stable

27. Water’s Versatility as a Solvent • A solution is a liquid that is a homogeneous mixture of substances • A solvent is the dissolving agent of a solution or “dissolver” • The solute is the substance that is dissolved or “disolvee” • An aqueous solution is one in which water is the solvent

28. Water’s Versatility as a Solvent • Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily. • The positive and negative regions of water molecules are attracted to oppositely charged ions or partially charged regions of polar molecules

29. Water’s Versatility as a Solvent • EX: When ionic compounds are placed in water, they completely dissociate • Each ion is surrounded by a sphere of water molecules called a hydration shell and dissolve into solution

30. Water’s Versatility as a Solvent • Water can also dissolve compounds made of nonionic polar molecules • Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

31. Hydrophilic vs. Hydrophobic • A hydrophilic substance is one that has an affinity for water due to electrical attraction; “likes water” • Examples: ionic & polar substances • A hydrophobic substance is one that does not have an affinity for water; “fears water” • Do not easily mix with or dissolve in water • Oil molecules are hydrophobic because they have relatively nonpolar bonds

32. Hydrophilic vs. Hydrophobic • A colloid is a stable suspension of fine particles in a liquid (like milk—fat suspended in water)

33. Dissociation of Water • A water molecule can dissociate into a hydrogen ion, (H+), an acid and an hydroxide ion (OH–), a base • Though the hydrogen ion immediately binds to another water molecule to form a hydronium ion (H3O+) • In pure water at 25°C, the concentrations of H+and OH– are the same 10-7M

34. Acids, Bases and Buffers • Though statistically rare, the dissociation of water molecules has a great effect on organisms • ONLY About 2 in every billion water molecules exist as H+ and OH– • Changes in concentrations of H+ and OH– can drastically affect the chemistry of a cell

35. Acids, Bases and Buffers • Concentrations of H+ and OH– are equal in pure water (referred to as neutral) • Adding certain solutes, called acids and bases, changes the concentrations of H+ and OH– • Biologists use the pH scale to describe whether a solution is acidic or basic (also known as alkaline)

36. The pH Scale – (potential of H+) • An acid is any substance that increases the H+ concentration of a solution • A base is any substance that reduces the H+ concentration of a solution • The scale was designed to compare WEAK acids and bases.

37. The pH Scale • Acidic solutions have pH values less than 7 • Basic solutions have pH values greater than 7 • Most biological fluids have pH values in the range of 6 to 8

38. The pH Scale • Because the pH scale is logarithmic, each numerical change represents a 10X change in ion concentration. • 1) How many times more acidic is a pH of 3 compared to a pH of 5? • 2) How many times more basic is a pH of 12 compared to a pH of 8?

40. Acids, Bases and Buffers Buffers • The internal pH of most living cells must remain close to pH 7 • Buffers are substances that RESIST changes in concentrations of H+ and OH– in a solution, therefore they RESIST a change in pH by neutralizing the added substance • Most buffers consist of an acid-base pair that reversibly combines with H+

41. Acids, Bases and Buffers Buffers help the cell maintain a stable pH by accepting excess H+ ions or donating H+ ions when H+ concentrations decrease

42. Acidification: A Threat to Water Quality • Human activities such as burning fossil fuels threaten water quality • CO2 is the main product of fossil fuel combustion • About 25% of human-generated CO2 is absorbed by the oceans • CO2 dissolved in sea water forms carbonic acid; this process is called ocean acidification

43. Buffers in Action • As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate • Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals • Corals are unable to produce calcium carbonate and grow as their carbonate is trapped as bicarbonate.

44. Acid Rain • The burning of fossil fuels is also a major source of sulfur oxides (SOx) and nitrogen oxides (NOx) • These “socks and knocks” compounds react with water in the air to form strong acids that fall within rain or snow • Acid precipitation- rain, fog, or snow with a pH lower than 5.2 • Acid precipitation damages life in lakes and streams and changes soil chemistry on land

45. Acid Rain: Before & After