The
Chemistry of Life
AP Biology
2009-2010
Why are we studying chemistry?
Chemistry is the foundation of Biology
AP Biology
The World of Elements
H
C N O
Na Mg
K Ca
AP Biology
P S
Elements & their valence shells
Elements in the same column
have the same valence &
similar chemical properties
Remember
some food chains
are built on
reducing O to H2O
& some on
reducing S to H2S
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
–
–
–
AP Biology
Hydrogen bond
Bonds in Biology
H2O
H2O
Covalent bond
–
–
AP Biology
H2 (hydrogen gas)
Nonpolar covalent bond
 _____________________________________

example: hydrocarbons = CxHx
 methane (CH4 )
AP Biology
Lots of
energy stored…
& released
balanced, stable,
good building block
Polar covalent bonds
 _______________________
_______________________

AP Biology
______________________
_
+
 oxygen has stronger
–
“attraction” for the
electrons than hydrogen
 oxygen has higher
electronegativity
 water is a polar molecule
H
 + vs – poles
 leads to many interesting
H
properties of water…
–
Oxygen
+
–
–
Hydrogen bonding
 Polar water creates
H bonds
molecular attractions
________________________
________________________
________________________
________________________
____
 also can occur wherever
an -OH exists in a larger
molecule

 Weak bond
AP Biology
H
H
O
Chemistry of Life
Properties of Water
AP Biology
2010-2011
More about Water
Why are we studying water?
All life occurs in water

AP Biology
inside & outside the cell
Chemistry of water
 H2O molecules form H-bonds
with each other
+H attracted to –O
 creates a
sticky molecule

AP Biology
Elixir of Life
Ice!
I could use
more ice!
AP Biology
1. Cohesion & Adhesion
 ______________________


H bonding between H2O molecules
water is “sticky”
 _______________________
 drinking straw
 ______________________

H bonding between H2O & other substances
 _______________________
 _______________________
 water climbs up
paper towel or cloth
AP Biology
Try that
with flour…
or sugar…
How does H2O get to top of trees?
Transpiration is built on cohesion & adhesion
AP Biology
2. Water is the solvent of life
 _____________________________________
polar H2O molecules surround + & – ions
 solvents dissolve solutes creating solutions

AP Biology
What dissolves in water?
 ________________________
substances have attraction to H2O
 polar or non-polar?

AP Biology
What doesn’t dissolve in water?
 ________________________
substances that don’t have
Oh, look
an attraction to H2O
hydrocarbons!
 polar or non-polar?

AP Biology
fat (triglycerol)
3. 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
Ice!
I could use
more ice!
And this has
made all the
difference!
AP Biology
Why is “ice floats” important?
 Oceans & lakes don’t freeze solid

_____________________________________
_
 allowing life to survive the winter

if ice sank…
 ponds, lakes & even oceans would freeze solid
 in summer, only upper few inches would thaw

_____________________________________
_
 __________________________________________
AP Biology
4. Specific heat
 ______________________________________
high specific heat
 takes a lot to heat it up
 takes a lot to cool it down

 _____________________________________
Specific heat
AP
& Biology
climate
5. Heat of vaporization
Evaporative cooling
Organisms rely on heat of
vaporization to remove body heat
AP Biology
Ionization of water & pH
 Water ionizes

H+ splits off from H2O, leaving OH–
 if [H+] = [-OH], water is ________
 if [H+] > [-OH], water is ________
 if [H+] < [-OH], water is ________
 pH scale
how acid or basic solution is
 _____________________

AP Biology
H2O  H+ + OH–
H+ Ion
Concentration
pH
Examples of Solutions
100
0
10–1
1
10–2
2
Stomach acid, Lemon juice
10–3
3
Vinegar, cola, beer
10–4
4
Tomatoes
pH1  pH2
10-1  10-2
10–5
5
Black coffee, Rainwater
10–6
6
Urine, Saliva
10 times less H+
10–7
7
Pure water, Blood
pH8  pH7
10-8  10-7
10–8
8
Seawater
10–9
9
Baking soda
10 times more H+
10–10
10
Great Salt Lake
pH10  pH8
10-10  10-8
10–11
11
Household ammonia
10–12
12
Household bleach
10–13
13
Oven cleaner
10–14
14
Sodium hydroxide
pH Scale
tenfold change
in H+ ions
100 times more H+
AP Biology
Hydrochloric acid
Buffers & cellular regulation
 pH of cells must be kept ~7
_____________________________________
 _____________________________________
 _____________________________________

 Control pH by _________
reservoir of H+
7
 donate H+ when [H+] falls
6
 absorb H+ when [H+] rises
5
4
pH

9
8
Buffering
range
3
2
1
0
AP Biology
0
1
2
3
4
5
Amount of base added
He’s gonna
earn a
Darwin Award!
Any
Questions?
Do one brave thing today…then run like hell!
AP Biology
2009-2010
Ice Fishing in Barrow, Alaska
Regents Biology