Chemical Context of Life: Ants & the Duroia Trees

1. 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. 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.

5. Matter 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 I. Matter vs. Energy

6. Element “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 • 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:

10. Mass # (protons + neutrons) 4 2 He 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

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

13. 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.

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

16. 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

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

18. 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

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

22. 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.

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 • Eg. 6CO2 + 6H2O  C6H12O6 + O2 • Some reactions are reversible: • Eg. 3H2 + N2 2NH3 • Chemical equilibrium: point at which forward and reverse reactions offset one another exactly • Reactions still occurring, but no net changein concentrations of reactants/products

25. 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

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.

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. 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.

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 • “like dissolves like”

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.

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 Acidic Basic 7 14 0 pH Scale • Acid= increases H+ concentration (HCl) • Base= reduces H+ concentration (NaOH) • Most biological fluids are pH 6-8

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

45. Calculating pH [H+][OH-] = 10-14 • 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. 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