1. AP Biology 2005-2006 Chapter 2. The Chemical Context of Life

2. AP Biology 2005-2006 Why are we studying chemistry?  Biology has chemistry at its foundation

3. AP Biology 2005-2006  Everything is made of matter  Matter is made of atoms  Atoms are made of:  protons+mass of 1 nucleus  neutrons0mass of 1 nucleus  electrons- mass <<1 orbits  Different kinds of atoms = elements The Basics

4. AP Biology 2005-2006 The World of Elements

5. AP Biology 2005-2006 Models of atoms (c)

6. AP Biology 2005-2006 Atomic structure determines behavior  The number of protons in an atom determines the element  # of protons = atomic number  this also tells you # of electrons  All atoms of an element have same chemical properties  all behave the same  properties don’t change

7. AP Biology 2005-2006 Life requires ~25 chemical elements  About 25 elements are essential for life  Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N)  Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K)

8. AP Biology 2005-2006

9. AP Biology 2005-2006 Isotopes  Different number of neutrons (heavier)  Some are unstable  nuclear reactions / decay  Split off neutrons &/or protons  radioactivity  Biological tool  Biological hazard

10. AP Biology 2005-2006 Bonding properties  Effect of electrons  chemical behavior of an atom depends on its electron arrangement  depends on the number of electrons in its outermost shell, the valence shell How does this atom behave?

11. AP Biology 2005-2006 Bonding properties  Effect of electrons  chemical behavior of an atom depends on number of electrons in its outermost shell How does this atom behave?

12. AP Biology 2005-2006 Elements & their valence shells  Elements in the same row have the same number of shells

13. AP Biology 2005-2006 Elements & their valence shells  Elements in the same column have the same valence & similar chemical properties

14. AP Biology 2005-2006 Elements & their valence shells  Moving from left to right, each element has a sequential addition of electrons (and protons)

15. AP Biology 2005-2006 Chemical reactivity  Atoms tend to  Complete a partially filled outer (valence) electron shell or  Empty a partially filled outer (valence) electron shell  This tendency drives chemical reactions

16. AP Biology 2005-2006 Ionic bonds

17. AP Biology 2005-2006 Ionic bonds  Transfer of an electron  Forms + & - ions  + = cation  – = anion  Weak bond  example:  salt = dissolves easily in water “Let’s go to the video tape!” (play movie here)

18. AP Biology 2005-2006 Covalent bonds  Two atoms need an electron  Share a pair of electrons  Strong bond  both atoms holding onto the electrons  Forms molecules  example:  water = takes energy to separate

19. AP Biology 2005-2006 Double covalent bonds  Two atoms can share more than one pair of electrons  double bonds (2 pairs of electrons)  triple bonds (3 pairs of electrons)  Very strong bonds

20. AP Biology 2005-2006 Multiple covalent bonds  1 atom can form covalent bonds with two or more other atoms  forms larger molecules  ex. carbon

21. AP Biology 2005-2006 Polar covalent bonds  Pair of electrons not shared equally by 2 atoms  Water = O + H  oxygen has stronger “attraction” for the shared electrons than hydrogen  oxygen has higher electronegativity

22. AP Biology 2005-2006 Polar covalent bonds  2 hydrogens in the water molecule form an angle  Water molecule is polar  oxygen end is –  hydrogen end is +  Leads to many interesting properties of water…. “Let’s go to the video tape!” (play movie here)

23. AP Biology 2005-2006 Hydrogen bonds  Positive H atom in 1 water molecule is attracted to negative O in another  Can occur wherever an -OH exists in a larger molecule  Weak bonds

24. AP Biology 2005-2006 Reductionist view of biology  Matter is made of atoms  Life requires ~25 chemical elements  Atomic structure determines behavior of an element  Atoms combine by chemical bonding to form molecules  Weak chemical bonds play important roles in chemistry of life  A molecule’s biological function is related to its shape  Chemical reactions make & break chemical bonds

25. AP Biology 2005-2006 Any Questions??

26. AP Biology 2004-2005 Chapter 3. Water— The Elixir of Life!

27. AP Biology 2004-2005 Why are we studying water?  All life occurs in water  inside & outside the cell

28. AP Biology 2004-2005 Chemistry of water  Water is polar molecule  remember polar covalent bonds  + & – poles

29. AP Biology 2004-2005 Chemistry of water  H 2 O molecules form H bonds with each other  + attracted to –  creates a sticky molecule “Let’s go to the video tape!” (play movie here)play movie here

30. AP Biology 2004-2005 Cohesion  H bonding between H 2 O creates cohesion  water is “sticky”  surface tension  drinking straw  can you suck sugar up a straw?

31. AP Biology 2004-2005 How does H 2 O get to top of tree?  Transpiration “Let’s go to the video tape!” (play movie here)play movie here

32. AP Biology 2004-2005 Adhesion  H 2 O molecules form H bonds with other substances  capillary action  meniscus  water climbs up fiber  ex. paper towel

33. AP Biology 2004-2005 Water is the solvent of life  H 2 O is a good solvent due to its polarity  polar H 2 O molecules surround + & – ions  solvents dissolve solutes creating aqueous solutions

34. AP Biology 2004-2005 Hydrophilic  Hydrophilic  substances have affinity for H 2 O  polar or non-polar?  ionic

35. AP Biology 2004-2005 Hydrophobic  Hydrophobic  substances do not have affinity for H 2 O  polar or non-polar?  non-ionic fat (triglycerol)

36. AP Biology 2004-2005 The special case of ice  Most (all?) substances are more dense when they are solid  But not water…  Ice floats!  H bonds form a crystal with loose structure

37. AP Biology 2004-2005 Ice floats

38. AP Biology 2004-2005 Why is “ice floats” important?  Oceans & lakes don’t freeze solid  if ice sank…  eventually all ponds, lakes & even ocean would freeze solid  during summer, only upper few inches would thaw  surface ice insulates water below  allowing life to survive the winter  seasonal turnover of lakes  cycling nutrients

39. AP Biology 2004-2005 Specific heat  H 2 O has high specific heat  due to H bonding  H 2 O resists changes in temperature  takes a lot to heat it up  takes a lot to cool it down  H 2 O moderates temperatures on Earth

40. AP Biology 2004-2005

41. AP Biology 2004-2005 Evaporative cooling  Organisms rely on heat of vaporization to remove heat

42. AP Biology 2004-2005 Water forms ions  Hydrogen ion (H + ) splits off from water to leave a hydroxide ion ( - OH) H 2 0 ----> H + + - OH  If concentration of 2 ions is equal, water is neutral  If [H + ] > [ - OH], water is acidic  If [ - OH] > [H + ], water is basic  pH scale = how acidic or basic a solution is

43. AP Biology 2004-2005 pH Scale  In pure water only 1 water molecule in every 554 million is dissociated.  very small amount of ions  [H + ] or [OH - ] is 10 -7 M [H + ] [OH - ] = 10 -14  pH scale is based on this equation

44. AP Biology 2004-2005 pH Scale  In neutral solution [H + ] = 10 -7  pH = 7  Values for pH decline as [H + ] increase  Acids  adding acid increases [H +]  Bases  adding base increases [OH - ]

45. AP Biology 2004-2005 pH & Biology  pH of a neutral solution = 7  Acidic solutions =pH 7  Most biological fluids have pH 6 – 8  pH values in human stomach can reach 2  Each pH unit represents a 10-fold difference in H + & OH - concentrations.  small change in pH actually indicates a substantial change in [H + ] & [OH - ]

46. AP Biology 2004-2005  Water is a polar molecule  The special properties of water make life on Earth possible  The chemical behavior of water governs how organisms function Punchline

47. AP Biology 2004-2005 Any Questions??