1. Essential Knowledge 2.A.3
Organisms must exchange matter with the environment to grow, reproduce, and maintain homeostasis

2. Three-quarters of the Earth’s surface is submerged in water
The abundance of water is the main reason the Earth is habitable

3. The first cells evolved in water

4. Living things are 70-90% water

5. Electronegativity
An atom’s attraction for the shared electrons of a covalent bond
The more electronegative an atom is, the more strongly the shared electrons are pulled toward it
Oxygen is more electronegative than hydrogen, so the electrons are pulled closer to oxygen and it becomes negatively charged, and hydrogen becomes positively charged

6. Polar covalent bonds occur when electrons are shared unequally

7. Water is a polar molecule (contains polar covalent bonds)
Water forms hydrogen bonds because it is a polar molecule

8. Hydrogen Bonds
Occur when charged regions of one molecule are attracted to oppositely charged regions of neighboring molecules forming weak chemical bonds

9. Water forms Hydrogen Bonds between the positive Hydrogen (electropositive) ends of one molecule and the negative Oxygen (electronegative) ends of another water molecule

10. Hydrogen bonding is not unique to water
Many biological molecules contain polar covalent bonds between electropositive hydrogen and electronegative oxygen or nitrogen
Hydrogen bonds can form between the positive hydrogen and the negative oxygen or nitrogen

11. Water’s Polarity and Hydrogen Bonds Give it Unique Properties

12. Water exists in all three states

13. Liquid Water
Hydrogen bonding in liquid water makes liquid water cohesive
Fewer bonds which are constantly breaking and reforming
This makes water fluid

14. Solid Water
Water molecules in ice have less energy, so they form maximum number of hydrogen bonds (4)
Water molecules become more evenly spaced out forming regular, crystalline structure

15. Maximum number of H-bonds causes molecules to be more evenly spaced out
Solid water (ice) is less dense than liquid water because of this

16. The hydrogen bonds in ice
Are more “ordered” than in liquid water, making ice less dense

18. Solid water is less dense and floats in liquid water

19. Life can exist under the frozen surfaces of lakes and polar seas
Since ice floats in water
Life can exist under the frozen surfaces of lakes and polar seas
Ice insulates water below, prevents freezing

20. Cohesion Water molecules exhibit cohesion
Cohesion is the ability of water molecules to cling to each other due to hydrogen bonding.
Water flows freely

21. Cohesion
Water molecules stick together because of their hydrogen bonding
This is apparent because water flows freely but does not separate from each other

22. Surface tension results from the property of cohesion
Surface of water molecules stick together
Is a measure of how hard it is to break the surface of a liquid

23. Copyright Pearson Prentice Hall
Surface Tension
The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
Copyright Pearson Prentice Hall

24. Adhesion
Water sticks to or adheres to polar surfaces as a result of hydrogen bonding

25. Cohesion and adhesion helps move water up through the microscopic vessels of plants

26. Water has property of capillarity

27. Capillarity The ability of water to move upwards in small tubes
Due to cohesion and adhesion

28. Cohesion/capillary action helps move water up plants from roots to leaves

29. Water is a good moderator of temperature-it resists temperature changes (coastal vs. inland)

30. Moderation of Temperature
Water moderates air temperature
By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler

31. Water’s High Heat Capacity
Water has a high heat capacity (specific heat), which allows it to absorb large amounts of heat without a great change in temperature, this minimizes temperature fluctuations to within limits that permit life
The temperature of water rises and falls slowly.

32. High Heat of vaporization
Hydrogen bonding prevents evaporation
Water must absorb large amounts of heat to vaporize (evaporate) because of hydrogen bonding between water molecules (0-100 C)

33. Heat of Vaporization High heat of vaporization
To raise water from 99 to 100 ºC; ~1 calorie
However, large numbers of hydrogen bonds must be broken to evaporate water
To raise water from 100 to 101 ºC; ~540 calories!

34. Evaporative cooling
Allows water to cool a surface, because calories (heat) to evaporate water comes from the surface of object water is evaporating from

35. Evaporative Cooling
Evaporating substances cools surface they evaporate from

36. Heat of Fusion Heat of fusion (melting)
To raise ice from -2 to -1 ºC; ~1 calorie
To raise water from -1 to 0 ºC; ~1 calorie
To raise water from 0 to 1 ºC; ~80 calories!
This is why ice at 0 ºC keeps stuff cold MUCH longer than water at 1 ºC
This is why ice is used for cooling
NOT because ice is cold

37. Water is a good solvent
Dissolves (surrounds and separates) ionic and or polar molecules
Water acts as solvent in cytoplasm, blood, sap
Water is a versatile solvent due to its polarity

38. Hydrophilic and Hydrophobic Substances
A hydrophilic substance
Has an affinity for water and dissolves easily
Polar and ionic compounds
A hydrophobic substance
Does not have an affinity for water, therefore does not dissolve in water

39. Water as a Solvent Solutions consist of:
A solvent (the most abundant part) and
A solute (less abundant part) that is dissolved in the solvent

40. The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them

41. Water can also interact with polar molecules such as proteins

42. Can have a great affect on living organisms
Water can dissociate or break apart to form hydronium (hydrogen) ions [H+] H3O+ and hydroxide ions [OH-]
Changes in the concentration of these ions
Can have a great affect on living organisms

43. 2.4 Acids and Bases

44. pH Scale
pH scale used to indicate acidity and alkalinity of a solution.
Values range from 0-14
0 to <7 = Acidic
7 = Neutral
>7 to 14 = Basic (or alkaline)
Logarithmic Scale
Each unit change in pH represents a change of 10X
pH of 4 is 10X as acidic as pH of 5
pH of 10 is 100X more basic than pH of 8

45. Buffers and pH Buffers are solutes in water that resist change in pH
When H+ is added, buffer may absorb, or counter by adding OH-

46. Buffers in Biology
Health of organisms requires maintaining pH of body fluids within narrow limits (homeostasis)
Human blood normally 7.4 (slightly alkaline) Bicarbonate ion (-HCO3) in blood buffers pH to 7.4
If blood pH drops below 7.0, acidosis results.
If blood pH rises above 7.8, alkalosis results.
Both are life-threatening situations.
Body has built-in mechanisms to prevent pH changes.
Example: carbonic acid buffer dissociates and re-forms to reduce changes in pH

47. Acid Precipitation Rain, snow, fog pH < 5.6
Destroys lakes, kills trees, ruins buildings, smog, kill amphibians
O2 combines with sulfur, nitrogen to form oxides-oxides react with H2O to form sulfuric, nitric acids
Sulfur, nitrogen come from burning fossil fuels (coal, oil, gas)