2. AP Biology Adapted from: Kim Foglia at Explore Biology for Northeast Kings Biology The Chemistry of Life

3. AP Biology Why are we studying chemistry? Chemistry is the foundation of Biology

4. AP Biology ProtonNeutronElectron Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons +0–  Everything is made of matter  Matter is made of atoms

5. AP Biology The World of Elements Different kinds of atoms = elements

6. AP Biology 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)

7. AP Biology Bonding properties  Effect of electrons  electrons determine chemical behavior of atom  depends number of electrons in atom’s outermost shell, the valence shell How does this atom behave?

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

9. AP Biology Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

10. AP Biology Elements & their valence shells Elements in the same column have the same valence & similar chemical properties

11. AP Biology – – – Chemical reactivity  Atoms tend to  complete a partially filled valence shell or  empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

12. AP Biology Bonds in Biology  Weak bonds  hydrogen bonds  hydrophobic & hydrophilic interactions  van derWaals forces  (ionic)  Strong bonds  covalent bonds – – H 2 (hydrogen gas) Covalent bond

13. AP Biology Covalent bonds  Why is this a strong bond?  two atoms share a pair of electrons  both atoms holding onto the electrons  Forms molecules – – H 2 (hydrogen gas) H — H H 2 O (water) H H Oxygen H H O

14. AP Biology Multiple covalent bonds  2 atoms can share >1 pair of electrons  double bonds  2 pairs of electrons  triple bonds  3 pairs of electrons  Very strong bonds More is better! H H–C–H H – –

15. AP Biology H H Oxygen Polar covalent bonds  Pair of electrons shared unequally by 2 atoms  Water = O + H  oxygen has stronger “attraction” for the electrons than hydrogen  oxygen has higher electronegativity  water is a polar molecule  + vs. – poles  leads to many interesting properties of water… + + – – – –

16. AP Biology Hydrogen bonding  Polar water creates molecular attractions  positive H atom in one H 2 O molecule attracted to negative O in another H 2 O  can occur wherever an -OH exists in a larger molecule  Weak bond

17. AP Biology More about Water Why are we studying water? All life occurs in water  inside & outside the cell All life occurs in water  inside & outside the cell

18. AP Biology Chemistry of water  H 2 O molecules form H-bonds with each other  + attracted to –  creates a sticky molecule

19. AP Biology Elixir of Life  Special properties of water  cohesion & adhesion  surface tension, capillary action  good solvent  many molecules dissolve in H 2 O  hydrophilic vs. hydrophobic  lower density as a solid  ice floats!  high specific heat  water stores heat  high heat of vaporization  heats & cools slowly I like the part about the ice!

20. AP Biology Cohesion & Adhesion  H bonding between H 2 O is cohesion  water is “sticky”  surface tension  drinking straw  H bonding between H 2 O & other substances is adhesion  capillary action  meniscus  water climbs up paper towel or cloth Can you suck sugar up a straw?

21. AP Biology How does H 2 O get to top of tree? Transpiration built on cohesion & adhesion Let’s go to the videotape!

22. AP Biology Water is the solvent of life  Polarity makes H 2 O a good solvent  polar H 2 O molecules surround + & – ions  solvents dissolve solutes creating solutions

23. AP Biology Do you dissolve in water?  Hydrophilic  substances have attraction to H 2 O  polar or non-polar?

24. AP Biology Or don’t you?  Hydrophobic  substances that don’t have an attraction to H 2 O  polar or non-polar? fat (triglycerol)

25. AP Biology 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 And this has made all the difference!

26. AP Biology Ice floats

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

28. AP Biology Specific heat  H 2 O resists changes in temperature  high specific heat  takes a lot to heat it up  takes a lot to cool it down  H 2 O moderates temperatures on Earth

29. AP Biology Specific heat & climate

30. AP Biology Heat of vaporization

31. AP Biology Evaporative cooling  Organisms rely on heat of vaporization to remove heat

32. AP Biology Ionization of water & pH  Water ionizes  H + splits off from H 2 O, leaving OH –  if [H + ] = [ - OH], water is neutral  if [H + ] > [ - OH], water is acidic  if [H + ] < [ - OH], water is basic  pH scale  how acid or basic solution is  1  7  14 H 2 O  H + + OH –

33. AP Biology pH Scale 10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 10 –2 2 10 –3 Vinegar, cola, beer 3 10 –4 Tomatoes 4 10 –5 Black coffee, Rainwater 5 10 –6 Urine, Saliva 6 10 –7 Pure water, Blood 7 10 –8 Seawater 8 10 –9 Baking soda 9 10 –10 Great Salt Lake 10 10 –11 Household ammonia 11 10 –12 Household bleach 12 10 –13 Oven cleaner 13 10 –14 Sodium hydroxide14

34. AP Biology 10 0 1 2 3 4 5 6 7 8 9 3 Amount of base added Buffering range 452 pH Buffers & cellular regulation  pH of cells must be kept ~7  pH affects shape of molecules  shape of molecules affect function  pH affects cellular function  Control pH by buffers  reservoir of H +  donate H+ when [H + ] falls  absorb H+ when [H + ] rises