Chapter 3 Chemical and Physical Features of Seawater

1. Chapter 3 Chemical and Physical Features of Seawater

2. Water for life…

3. Water facts… • Most cells are 70-95% water • Three-quarters of the earth’s surface is covered by water. • Water is the only common substances that can be found in all 3 physical states (solid, liquid or gas) within earth’s temperature range. • Less than 1% of the earth’s water is freshwater. • Water makes life possible, as we know it, on earth.

4. What is it about water that makes it a suitable medium for life? Most of the properties that make water suitable for life are related to water’s ability to form hydrogen bonds

5. Hydrogen bonding Water is polar because of the unequal sharing of electrons in the bond between H and O in a water molecule. dipoles The attraction between opposite dipoles of separate water molecules is a hydrogen bond.

6. Recap important features… • Polar covalent bonds • Hydrogen bonds • electronegativity

7. Water cycle

8. Discovery education- cycles • http://www.etap.org/demo/biology_files/lesson6/instruction4tutor.html

9. What role does water play in the carbon cycle??

10. Ocean is called a carbon sink • Carbon dioxide is dissolved in large amounts in the ocean • Source is primarily cellular respiration and burning fossil fuels

11. Phases of water • Solid- ice (molecules not moving around) • Liquid- water (molecules moving around with some speed) • Gas- water vapor (molecules moving around very fast, too fast to form H bonds)

12. Organisms depend on the cohesion and adhesion of water molecules Surface tension!

13. Cohesion- H bonds attract water molecules to each other • Adhesion- water “sticks” to other materials

14. Surface tension • “skin like” surface of water. • Due to H-bonds- HIGH surface tension • Water’s resistance to objects attempting to penetrate its surface • Individual H bonds are weak compared to covalent bonds but the bonds have cumulative strength in numbers

15. Viscosity- the tendency for a fluid to resist flow (colder, the “thicker” it is because more molecules in a space). This allows plankton to use less energy to stay afloat

16. The cohesive nature of water molecules allows water to resist temperature change… Specific heat is the amount of heat needed to change the temperature of a substance by 1 degree Celsius. Specific heat of H2O = 1 calorie (cal) to raise 1 g by 1 degree C

17. Specific heat of water • HIGH due to hydrogen bonds • Water will change its temperature less when it absorbs or loses a given amount of heat • WHY? Much of the heat is used to break the H bonds before molecules can begin moving faster

18. High specific heat relevance to life • 1. A large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while warming only a few degrees. At night and during the winter, the gradually cooling water can warm the air

19. 2. stabilizes ocean temperatures creating favorable environment for marine life • 3. since organisms are made primarily of water, they are better able to resist changes in their own temperature than if they were made of a liquid with a lower specific heat

20. Sssooooo……. • Water that covers the earth keeps temperature fluctuations on land and in water within limits that permit life

21. Heat Capacity • Water has the highest latent heats of melting and evaporation and one of the highest heat capacities of any natural substance. • Latent Heat of Melting and Evaporation Fastest molecules (with most energy) break free of bonds. Slower ones left behind = lower temp.

22. How does H-bonding affect temperature change? Water molecules tend to “stick together” through H-bonding. Much of the energy that goes into a body of water must first go into breaking these bonds before temperature (i.e. “molecular movement”) can increase.

25. What implications does water’s high specific heat have for living systems? Large bodies of water can absorb lots of heat from the sun and change temp. very slowly! Living organisms are made mostly of water which stabilizes body temperature.

26. Water has a high heat of vaporization… …it takes a great deal of heat to get water to boil (go from liquid to gas phase). Water’s heat of vaporization = 580 cal/g/0C Evaporative cooling!

27. Ice is less dense then liquid water…

28. Why ice floats • Less dense as a solid than as a liquid • Water expands when freezing

29. Density • Density = mass / volume • Density is affected by • Temperature • Pressure • Salinity • Water is less dense as a solid

30. Lower density and LIFE… • If ice sank, then eventually all ponds, lakes, and oceans would freeze solid making life as we know it impossible • During summer, only the upper few inches of the ocean would thaw

31. INSTEAD…… • When a deep body of water cools, the floating ice insulates the liquid water below, preventing it from freezing and allowing life to exist under the frozen surface

32. Salinity and Density • Salinity varies with depth • Density differences cause water to layer • High density lies below low density

33. Water: the solvent of life • Solution- a liquid that is a completely homogeneous mixture of two or more substances • Solvent- dissolving agent • Solute- substance that is dissolved • Not “universal solvent”- if it were, it would dissolve any container in which it was stored. “versatile solvent” due to polarity

34. Water is a versatile solvent… table salt

35. Review- 4 Emergent Properties of water • Cohesive behavior • Ability to moderate temperature • Expansion upon freezing • Versatility as a solvent

36. BozemanBiology • Properties of Water • http://www.youtube.com/watch?v=DVCYlST6mYQ

37. Seawater • Nature of pure water • Materials dissolved in it • Seawater contains a little of almost everything • Solutes = dissolved materials (ex. ions in seawater) • Solvent = liquid doing the dissolving

38. Rule of Constant Proportions • The relative amounts of the various ions in seawater are always the same! • For seawater; no matter how much salinity varies, proportions of key inorganic elements stays the same • Only water amount and therefore salinity changes

39. Salt composition in seawater • Salinity- the total amount of salt dissolved in seawater • Salinity is expressed in the number of grams left behind when 1,000 g of seawater are evaporated • Ex. 35g left from evaporating 1,000g water (35ppt) 35%

40. Average salinity of the ocean is about 35 ppt • Open ocean varies at 33-37 ppt depending on the balance between evaporation and precipitation

41. Salinity of water greatly affects the organisms that live in it • Most marine organisms die in fresh water • Even slight changes in salinity harm them

42. Pg 72: salinity, osmosis and diffusion • Osmosis • Diffusion • Concentration gradient • Hypertonic • Hypotonic • Isotonic

43. WHY DO FISH DRINK SEAWATER??? • Answer in caption figure 4.14

44. Many marine organisms are highly affected by changes in salinity. This is because of a process called osmosis which is the ability of water to move in and out of living cells, in response to a concentration of a dissolved material, until an equilibrium is reached. In general the dissolved material does not easily cross the cell membrane so the water flows by osmosis to form an equilibrium. Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic).

45. Did you write this????? • Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic).

46. Page 74: regulation of salt and water balance • Osmoconformers- internal concentrations change as the salinity of the water changes • Osmotic conformers have no mechanism to control osmosisand their cells are the same salt content as the liquid environment in which they are found (in the ocean this would be 35 o/oo salt). If a marine osmotic conformer were put in fresh water (no salt), osmosis would cause water to enter its cells (to form an equilibrium), eventually causing the cells to pop (lysis). If a marine osmotic conformer were put in super salty water (greater than 35 o/oo salt) then osmosis would cause the water inside the cells to move out, eventually causing the cells to dehydrate (plasmolyze).

47. Hagfish- osmo conformers

48. Osmoregulate- control their internal concentrations to avoid osmotic problems. Adjust solute concentration in their body to match that of the environment

49. Osmotic regulators have a variety of mechanisms to control osmosis and the salt content of their cells varies. It does not matter what the salt content is of the water surrounding a marine osmotic regulator, their mechanisms will prevent any drastic changes to the living cells. Marine osmotic regulators include most of the fish, reptiles, birds and mammals. These are the organisms that are most likely to migrate long distances where they may encounter changes in salinity. An excellent example of this is the salmon fish. The fish is about 18 o/oo salt so in seawater it tends to dehydrate and constantly drinks the seawater. Special cells on the gills (called chloride cells) excrete the salt so the fish can replace its lost water. When a salmon migrates to fresh water its cells start to take on water so the salmon stops drinking and its kidneys start working to produce large amounts of urine to expell the water.

50. Do fish drink water??? • http://www.whfreeman.com/Catalog/static/whf/phelanpreview/doc/01_fish.pdf