1. The Chemical Context of Life
Chapter 2
The Chemical Context of Life

2. Ants & the Duroia Trees
Ants use formic acid to prevent other plants from growing so that the Duroia trees can serve as their home.

3. You Must Know The three subatomic particles and their significance.
The types of bonds, how they form, and their relative strengths.

4. A patient is diagnosed with anemia resulting from iron deficiency
A patient is diagnosed with anemia resulting from iron deficiency. What is the best way to supplement the patient’s diet with iron?
The patient should add fine metallic iron filings to his morning cereal.
The patient should periodically suck on rusty nails.
The patient should cook with a cast-iron skillet and eat vegetables with high iron content, such as spinach.
The patient should eat more red meat.
Answer c should increase the uptake of iron into the patient’s body and red blood cells. Answer d may also help, but may have other undesirable effects such as increased fat and cholesterol intake. Choice a will be ineffective, as the reduced (metallic) form of iron is not available to cells; choice b is only marginally better, and unpleasant. This question could lead to a discussion about biologically active forms (ionization states) of the elements.
Based on Concept 2.1 on essential elements and Concept 2.3 on ionization. 4

5. I. Matter vs. Energy Matter Energy Has mass & takes up space
Affected by gravity
Consists of elements and compounds
Energy
Moves matter
Potential, kinetic
Ability to do work
Conversions
Sound, light, heat

6. Element Compound “pure” substance
Can’t be broken down by “ordinary” means to another substance
Ex. hydrogen (H), nitrogen (N)
Compound
2 or more different elements combined in a fixed ratio
Ex. H2O, CO2

7. Elements of Life 25 elements Hint: Remember CHNOPS 96% : O, C, H, N
~ 4% : P, S, Ca, K & trace elements (ex: Fe, I)
Hint: Remember CHNOPS

9. II. Atomic Structure
Atom = smallest unit of matter that retains properties of an element
Subatomic particles:
Mass
(dalton or AMU)
Location
Charge
neutron 1
nucleus
proton +1
electron
negligible
shell -1

10. He 4 2 Mass # (protons + neutrons) symbol
Atomic # (protons or electrons)

11. What do elements with atomic numbers 6, 14, and 22 have in common?
A) same number of electrons
B) same atomic mass
C) same valence and will form the same number of covalent bonds
D) all of the above
E) none of the above
Answer: c
This question focuses on Concept 2.2. It highlights the fact that these elements have the same basic structures and therefore the same basic properties. 12

12. Isotopes # neutrons varies, but same # of protons
Radioactive isotopes used as tracers (follow molecules, medical diagnosis)
Uncontrolled exposure causes harm

13. More than one of the above options is correct.
Water is a polar molecule because of the presence of ___________ bonds.
ionic
covalent
polar covalent
hydrogen
More than one of the above options is correct.
Answer: c
This question focuses on the properties that result from different bonding patterns in molecules. 14

14. III. Chemical Bonds Strongest Bonds: Covalent: sharing of e-
Polar: covalent bond between atoms that differ in electronegativity
Nonpolar: e- shared equally; eg. O2 or H2

15. Based on the periodic table shown here, which elements will most likely form a covalent bond?
Na and Cl
C and O
N and O
Si and Cl
H and H
Answer: e is the best choice
This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. One way to change this question would be to add C and H as a choice. This could be used to lead into a more detailed discussion. 16

16. Na and Cl C and O, and N and O Si and Cl, and H and H all of the above
Based on the periodic table shown here, which elements will most likely form a polar covalent bond?
Na and Cl
C and O, and N and O
Si and Cl, and H and H
all of the above
none of the above
Answer: b is the best choice
This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. 17

17. III. Chemical Bonds Strongest Bonds:
Ionic: 2 ions (+/-) bond (givers/takers)
Na+Cl-
Affected by environment (eg. water)

18. Na and Cl, and Li and F C and O N and O Si and Cl all of the above
Based on the periodic table shown here, which elements will most likely form an ionic bond?
Na and Cl, and Li and F
C and O
N and O
Si and Cl
all of the above
Answer: a is the best choice
This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. 19

19. Weaker Bonds:
Hydrogen: H of polar covalent molecule bonds to electronegative atom of other polar covalent molecules

20. Weaker Bonds:
Van der Waals Interactions: slight, fleeting attractions between atoms and molecules close together
Weakest bond
Eg. gecko toe hairs + wall surface

21. Bonds Covalent Ionic Hydrogen All important to life
Form cell’s molecules
Quick reactions/ responses
H bonds to other electronegative atoms
Strong bond
Weaker bond (esp. in H2O)
Even weaker
Made and broken by chemical reactions

22. is an electrical attraction. is a unique chemical attraction.
The force of the chemical bond (the attraction between the different elements)
is an electrical attraction.
is a unique chemical attraction.
results from the sharing of electrons.
results from atoms filling their outermost valence shell.
Answer: a
This question focuses on understanding the force that holds atoms together in molecules. Answers c and d are potentially correct but do not answer the question in terms of what creates the attraction. 23

23. All bonds affect molecule’s SHAPE  affect molecule’s FUNCTION
Similar shapes = mimic
morphine, heroin, opiates mimic endorphin (euphoria, relieve pain)

24. Chemical Reactions Reactants  Products Some reactions are reversible:
Eg. 6CO2 + 6H2O  C6H12O6 + O2
Some reactions are reversible:
Eg. 3H2 + N NH3
Chemical equilibrium: point at which forward and reverse reactions offset one another exactly
Reactions still occurring, but no net change in concentrations of reactants/products

25. Water and the Fitness of the Environment
Chapter 3
Water and the Fitness of the Environment

26. You Must Know
The importance of hydrogen bonding to the properties of water.
Four unique properties of water, and how each contributes to life on Earth.
How to interpret the pH scale.
The importance of buffers in biological systems.

27. The four emergent properties of water that are important for life are:
Cohesion, expansion upon freezing, high heat of evaporation, and capillarity
Cohesion, moderation of temperature, expansion upon freezing, and solvent properties
Moderation of temperature, solvent properties, high surface tension, and capillarity
Heat of vaporization, high specific heat, high surface tension, and capillarity
Polarity, hydrogen bonding, high specific heat, and high surface tension
Answer: b

28. 1. Polarity of H2O
O- will bond with H+ on a different molecule of H2O = hydrogen bond
H2O can form up to 4 bonds

29. 2. Properties of H2O Cohesion = H-bonding between like molecules
Surface Tension = measure of how difficult it is to break or stretch surface of liquid

30. Which one of the following hypothetical changes in a water molecule would tend to make it more polar?
It is a linear molecule, as in H-O-H.
Adjacent water molecules form covalent bonds with each other.
The electronegativity values for H is increased.
The electronegativity value for O is increased.
All of the above would make water more polar.
Answer: d

31. 2. Properties of H2O Adhesion = bonding between unlike molecules
Adhesion of H2O to vessel walls counters ↓ pull of gravity

32. 2. Properties of H2O C. Transpiration = movement of H2O up plants
H2O clings to each other by cohesion; cling to xylem tubes by adhesion

33. 3. Moderation of temperature
Heat = Total amount of KE in system Temperature = measure intensity of heat due to average KE of molecules Which has higher temp? More heat?

34. 3. Moderation of temperature
Water’s high specific heat
Change temp less when absorbs/loses heat
Large bodies of water absorb and store more heat  warmer coastal areas
Create stable marine/land environment
Humans ~65% H2O  stable temp, resist temp. change

35. 3. Moderation of temperature
Evaporative Cooling
Water has high heat of vaporization
Molecules with greatest KE leave as gas
Stable temp in lakes & ponds
Cool plants
Human sweat

36. 3. Moderation of temperature
Insulation by ice – less dense, floating ice insulates liquid H2O below
Life exists under frozen surface (ponds, lakes, oceans)
Ice = solid habitat (polar bears)

37. Water has an unusually high specific heat
Water has an unusually high specific heat. This is directly related to which one of the following?
At its boiling point, water changes from liquid to vapor.
More heat is required to raise the temperature of water.
Ice floats in liquid water.
Salt water freezes at a lower temperature than pure water.
Floating ice can insulate bodies of water.
Answer: b

38. 4. Solvent of life
Solution = liquid, homogeneous mixture of 2+ substances
Solvent = dissolving agent (liquid)
Solute = dissolved substance
Water = versatile solvent

39. 4. Solvent of life Hydrophilic Hydrophobic “like dissolves like”
Affinity for H2O
Repel H2O
Polar, ions
Nonpolar
Cellulose, sugar, salt
Oils, lipids
Blood
Cell membrane

40. Figure 3.8 A water-soluble protein

41. Which of the following explains what is happening when sodium chloride dissolves in water?
More hydrogen bonds are forming between water molecules.
Sodium and chloride atoms are separating from one another.
Hydration shells are forming around the sodium and chloride ions.
Covalent bonds are breaking and re-forming.
Nonpolar substances are mixing with polar substances.
Answer: c

42. 5. Acids and Bases
H2O H+ + OH- (gains proton) H+ + H2O  H3O+ (hydronium ion) (loses proton) H2O – H+  OH- (hydroxide ion)

43. 5. Acids and Bases 7 14 Basic Acidic pH Scale
Acid = increases H+ concentration (HCl)
Base = reduces H+ concentration (NaOH)
Most biological fluids are pH 6-8 7 14
Basic
Acidic
pH Scale

44. Figure 3.10 The pH scale and pH values of some aqueous solutions

45. Calculating pH [H+][OH-] = 10-14 pH = -log [H+]
If [H+] = 10-6 M, then [OH-] = 10-8
pH = -log [H+]
If [H+] = 10-2
-log 10-2 = -(-2) = 2
Therefore, pH = 2
If [OH-] = 10-10
[H+] = 10-4
-log 10-4 = -(-4) = 4
Therefore, pH = 4

46. H2CO3 (carbonic acid)  HCO3- (bicarbonate) + H+
5. Acids and Bases
Buffers: minimize changes in concentration of H+ and OH- in a solution (weak acids and bases)
Buffers keep blood at pH ~7.4
If blood drops to 7 or up to 7.8, then death
Carbonic Acid – Bicarbonate System: important buffers in blood plasma
H2CO3 (carbonic acid)  HCO3- (bicarbonate) + H+

47. Ocean acidification threatens coral reef ecosystems
CO2 mixed with seawater  Carbonic acid (lowers ocean pH)

48. The effects of acid precipitation on a forest

49. Scientists are concerned about increased concentrations of atmospheric carbon dioxide due to increased fossil fuel combustion and deforestation. In addition to major effects on global temperatures, increased levels of CO2 can threaten aquatic organisms in which way?
forming more carbonic acid in a solution that raises the pH of seawater
forming more carbonic acid that decreases the concentration of carbonate ions in seawater
increasing photosynthesis rates in aquatic plants and algae
decreasing the oxygen available for cellular respiration in aquatic organisms
increasing the levels of harmful sulfur oxides and nitrous oxides
Answer: b

50. Examples of Benefits to Life
H2O Property
Chemical Explanation
Examples of Benefits to Life
Cohesion
polar
H-bond
like-like
↑gravity plants, trees
Adhesion
unlike-unlike
plants xylem
bloodveins
Surface Tension
diff. in stretch
break surface
bugswater
Specific Heat
Absorbs & retains E
oceanmod temp protect marine life
Evaporation
liquidgas KE
Cooling
Homeostasis
Universal Substance
Polarityionic
Good dissolver
solvent