1. Why are the unique properties of water so essential to life?
The Biology of water…
Why are the unique properties of water so essential to life?
How does the molecular structure of water drive its special properties?

2. What makes water special?
75% of the earth’s surface, 70% of all living things
70% of earth’s surface is covered with water
96.5% of water is in the ocean
Water cycle 0 water is constantly moving from one form to another….

3. Water is the only common substance that exists in the natural world in all three physical states of matter: solid ice, liquid water, and water vapour.
This is the Trift Glacier, which you can see from the Susten Pass…
Can you think of any other substances that exist naturally as solid, liquid and gas?
Which is more dense? – ice or water?
What do you think would happen if ice didn’t float?

4. 1. How does water rise from the roots of a redwood tree to the very top?
2. How do insects walk on water?
3. Why does ice float rather than sink?
4. Why do people become seriously ill, or die, if they go without liquid for a week or so?
5. How would life in a lake be affected if ice sank and lakes froze from the bottom up?

5. Water Important biological properties
Cohesion, Adhesion, Surface Tension
High specific heat
Heat of vaporization
Solvent of life
Insulation of bodies of water (floating ice) in winter

6. How does water do this

7. Concept 1 Water is a polar molecule The polarity of water molecules results in hydrogen bonding between molecules

8. Molecular structure of water

9. Concept 1 The polarity of water molecules results in hydrogen bonding
The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond
Each water molecule can form hydrogen bonds with up to four neighbors

10. Cohesion, Adhesion and Surface tension are phenomena which reflect the polarity of the water molecules, and hydrogen bonds between water molecules adhesion

11. Cohesion
The attraction of like molecules to be attracted to each other, as occurs with polar water molecules Such molecules form a highly dynamic structure with many breaking and forming bonds Plays a key role in life processes, including transport of water and dissolved nutrients against gravity in plants Play from 35s
Due to cohesion, water can act like a skin….the water molecules cling to each other rather than to the air molecules around them.
Drip water onto the penny. How does the water stick to the leaf and grow larger?

12. Adhesion
Attraction process between polar molecules of different substances (e.g. water/glass)
Again, due to the polarity of water and hydrogen bonding

13. Capillary Action is Due to Adhesion
Adhesion – like to unlike: menuscus in glassware; capillary action of water moving up xylem in a plant (also involves cohesion between water molecules).

14. How does the crown get water?

15. Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force
It is a measure of the force necessary to stretch or break the surface of a liquid
Related to cohesion
Several effects of surface tension are evident with water
Water has a relatively high surface tension
How can small animals walk on water? The very light feet of the spider/inset don’t puncture the water

16. Let’s watch cohesion, adhesion and surface tension in action!

17. 1. Filling up a penny!
You have a penny, a beaker of water and a dropper pipette.
How many drops of water can fit on to the top of the penny?
Now repeat the test using ethyl alcohol…

18. Why does water bead?
The water molecules beneath the surface are pulled in all directions. The molecules at the surface are pulled together and in. This creates a tighter arrangement of molecules at the surface and the round shape of a drop of water.

19. Alcohol has one O–H bond which is polar but a large portion of the molecule is made up of C–H bonds which are non-polar.
Alcohol molecules do not attract each other as strongly as water molecules and have a weaker surface tension.

20. 2. The Magic pepper plate…

21. The Magic pepper plate
The charged end of a detergent molecule attracts water molecules at the surface in an outward direction. This disrupts the way the molecules normally attract at the surface and weakens the surface tension, causing the drop to collapse.

22. Why can these animals walk on water?

23. Water moderates temperatures on Earth because it has a high heat capacity

24. Water has a high heat capacity since its polar molecules are connected by hydrogen bonds

25. Let’s have a demonstration!
The magic balloon

26. Heat and Temperature All atoms and molecules have kinetic energy
energy of motion
What is heat?
Heat is a measure of the total quantity of kinetic energy due to molecular motion in a body of matter.
Temperature measures the intensity of heat due to the average kinetic energy of molecules.

27. How does the polarity of water help in temperature moderation?
In order for water to change from a liquid to a gas, it has to absorb a lot of energy to first break the hydrogen bonds and allow its molecules to speed up.
So water absorbs a lot of energy before increasing temperature
Large bodies of water can absorb a lot of heat energy without chancing temperature

29. Specific Heat
The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C
Water has a specific heat of 1 cal/g/oC.
Important because water does not change temperature quickly & large bodies of water can store much heat to warm the air.

30. How do we measure temperature?
In most biological settings, temperature is measured on the Celsius scale (oC).
At sea level, water freezes at O oC and boils at 100oC.
Human body temperature averages 37 oC.
The Blog provides details of other commonly used temperature scales, namely the Kelvin Scale and the Farhenheit Scale

32. How does water’s high specific heat impact living things?
Since the temperature of water rises and falls slowly, it is easier for organisms to regulate and maintain a stable internal temperature

33. How does water’s high specific heat impact living things?
Large bodies of water absorb heat during the day, release heat at night Coastal temperatures remain relatively constant

34. Oceans/ lakes and atmospheric temperature regulation
Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature

35. A lot of energy is required to convert water into water vapour

36. Water has a high heat of vaporization

37. Latent Heat
Latent Heat is the heat given up or absorbed by a substance as it changes state. It is called latent because it is not associated with a change in temperature

38. Vaporization/evaporation
The transformation of a molecule from a liquid to a gas, occurs when the molecule moves fast enough to overcome the attraction of other molecules
Even in a low temperature liquid (low average kinetic energy), some molecules are moving fast enough to evaporate.
Heating a liquid increases the average kinetic energy and increases the rate of evaporation.
Heat of vaporization is the quantity of heat that a liquid must absorb for 1 g of it to be converted from liquid to gas.

39. Water has a high heat of vaporization
Water has a relatively high heat of vaporization, requiring about 580 cal of heat to evaporate 1 g of water at room temperature.
This is double the heat required to vaporize the same quantity of alcohol or ammonia.
This is because hydrogen bonds must be broken before a water molecule can evaporate from the liquid.
up to 42s then 1.08 to end

40. Alcohol has one O–H bond which is polar but a large portion of the molecule is made up of C–H bonds which are nonpolar. Alcohol molecules do not attract each other as strongly as water molecules and boil at a lower temperature.

41. Evaporative Cooling
The high heat of vapourisation provides animals with an efficent cooling mechanism
As we sweat, body heat vapourises water and cools the body surface.
Evaporation of water from the leaves of plants cools their surfaces

42. Evaporative cooling and atmospheric temperature regulation
Evaporative cooling moderates temperature in lakes and ponds and prevents terrestrial organisms from overheating.

43. Ice is less dense than water

44. Ice Floats… Water is less dense as a solid than a liquid
Usually substances shrink as they cool
Hydrogen bonding in ice causes water molecules to form a lattice,
making it less dense than
Water
Canada Nature animation

46. How do living things benefit from water expanding as it freezes?
If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid.
During the summer, only the upper few centimeters of the ocean would thaw.
Instead, the surface layer of ice insulates liquid water below, preventing it from freezing and allowing life to exist under the frozen surface.

47. Water is the solvent of life

48. Mixtures Solutions Suspensions
Note – water is NOT the universal solvent…it cannot dissolve non polar substances such as oils and fats

49. Mixture
‘A material composed of two or more elements or compounds that are physically mixed but not chemically combined’
Other mixtures:
Salt and pepper
Sugar and sand
The air in the atmosphere

50. Solution
A liquid that is a completely homogeneous mixture of two or more substances
The dissolving agent is the solvent, and the substance that is dissolved is the solute.
In an aqueous solution, water is the solvent.
Water is not a universal solvent, but it is very versatile because of the polarity of water molecules.

51. Solution

52. Suspension
‘Materials do not dissolve, but separate into pieces so small that they do not settle out,, rather are kept suspended by the movement of water molecules around them’

53. Let’s take a look at the behaviour of solutions and suspensions!

54. Water can dissolve other polar compounds, ionic compounds and charged compounds

55. Water is an excellent solvent for ionic compounds

56. Example: Sucrose dissolves easily in water
The ball-and-stick and first space-filling model show that sucrose is a large molecule made up of carbon, oxygen, and hydrogen.
Sucrose has many O–H bonds which are polar.These polar areas are shown with a + near the hydrogen atom and a − near the oxygen atom.
The second space-filling model shows two sucrose molecules held together by their opposite polar areas.
These molecules will separate from each other when sucrose dissolves.

57. Example: Sucrose dissolves easily in water
Sucrose animation

58. What types of substances dissolve in water? What substances don’t?
Even large molecules, like proteins, can dissolve in water if they have ionic or polar regions

59. Definitions Hydrophilic Hydrophobic
Any substance that has an affinity for water: ‘water loving’
Contain many ionic or polar bonds
includes substances that do not dissolve because their molecules are too large
Hydrophobic
Substances that have no affinity for water: water fearing
Contain many non-ionic and nonpolar covalent bonds
Hydrophobic molecules are major ingredients of cell membranes.

60. Acids, bases and pH

61. Why do we care about pH? Organisms are sensitive to changes in pH
Acid rain
Rain is typically acidic because it combines with CO2
Normal rain pH 5.6
Acid rain pH <5.6
Result of pollution
Burning of fossil fuels

62. Dissociation of water molecules leads to acidic and basic conditions that affect living organisms

63. Sometimes, an H2O molecule loses a H+ ion that is in turn accepted by another H2O

64. Ionization of Water . . . . . . . . H H H . . . . . . . .
Occasionally, in water, a H+ is transferred between H2O molecules
H:O: :O:H H:O:H :O:H-
H H H
water molecules hydronium hydroxide ion (+) ion (-)
LecturePLUS Timberlake

65. H+ leaves its electron behind and is transferred as a single proton - a hydrogen ion (H+)
The water molecule that lost a proton is now a hydroxide ion (OH-)
The water molecule with the extra proton is a hydronium ion (H3O+)

66. H2O <=> H+ + OH- This reaction is reversible.
At equilibrium the concentration of water molecules greatly exceeds that of H+ and OH-
At equilibrium the concentration of H+ or OH- is 10-7M (25°C)
Adding solutes (acids or bases) changes the concentration of H+ and OH-
Solutions with more OH- than H+ are basic solutions.
Solutions with more H+ than OH- are acidic solutions.
Solutions in which concentrations of OH- and H+ are equal are neutral solutions.

67. Pure Water is Neutral H2O + H2O H3O+ + OH- H3O+ OH-
Pure water contains small, but equal amounts of ions: H3O+ and OH-
H2O + H2O H3O OH-
hydronium hydroxide ion ion
1 x 10-7 M 1 x 10-7 M
H3O+
OH-
LecturePLUS Timberlake

68. Acids & Bases Acids are formed by hydrogen cations
Bases are formed by hydroxide anions

69. Acids H3O+ OH- Increase H+ HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)
More [H3O+] than water > 1 x 10-7M
As H3O+ increases, OH- decreases
[H3O+] > [OH-]
H3O+
OH-
LecturePLUS Timberlake

70. Acids Donate protons (Hydrogen Ions) to water to form hydronium ionspH
Taste Sour
Turn litmus paper red
Strong acids completely dissociate to form ions

71. Bases OH- H3O+ Increase the hydroxide ions (OH-) H2O
NaOH (s) Na+(aq) OH- (aq)
More [OH-] than water, [OH-] > 1 x 10-7M
When OH- increases, H3O+ decreases
[OH] > [H3O+]
OH-
H3O+
LecturePLUS Timberlake

72. Bases Donate hydroxide pH 7.01-14 Accept protons Taste bitter
Feel slimy
Turn litmus paper blue
Strong bases completely dissociate to form ions

73. Bases Base  increases [OH- ]
Some bases reduce the H+ concentration directly by accepting hydrogen ions
For example, NH3 + H+ <=> NH4+
Other bases reduce H+ indirectly by dissociating to OH-, which then combines with H+ to form water.
For example, NaOH -> Na+ + OH- OH- + H+ -> H2O

74. pH In a neutral solution [H+] = 10-7 M, and the pH = 7.
Values for pH decline as [H+] increase.
Most biological fluids???
Each pH unit represents a tenfold difference in H+ and OH- concentrations.
A small change in pH actually indicates a substantial change in H+ and OH- concentrations
Fig. 3.9

75. pH Demonstration

76. Reading Quiz tomorrow! On page 39 – 43
You can use any notes you have made today or this evening…
Quiz mark will count towards your interim grade.