The Chemical Composition
of Living Things

Physical Properties




Describe physical
appearance
Color, texture, shape


Physical Changes
Change in
appearance only
 Reversible
 Melting, freezing,
breaking, etc.

Chemical Properties

Describe how
material reacts
Flammability,
reactive, & pH
Chemical Changes
Change in
composition
 Irreversible
 Burning, oxidizing,
digesting, etc.



Chemical rxns require
energy (activation
energy)
Enzymes lower the
activation energy
needed to start a
chemical rxn.
Catalyst = speed
things up
 Allows biological
processes to happen
faster


Shape determines
function


Specific enzyme for
each different
chemical rxn
Ex: Lactase enzyme
speeds up the
metabolism of lactose

Denature


If an enzyme’s shape
changes, it won’t
work as effectively
Caused by:
 Change in temp
 Toxins (acids, bases)
 Radiation

# protons =
+ charge
Atomic Number
# neutrons =
C




6
No charge
# electrons =

- charge
Symbol
12.01
Atomic Mass

Nucleus –


protons + neutrons
Electron clouds
Surround nucleus
 1st –
 2nd –
 3rd –
 4th –
 5th –
 6th –
 7th 

Valence Electrons –


Electrons in the outer
most energy level
Octet Rule

Must fill 1st level
before move onto the
next

Protons - ___________

Neutrons - _________

Electrons - _________

Valence - __________

Protons - ___________

Neutrons - _________

Electrons - _________

Valence - __________

Protons - ___________

Neutrons - _________

Electrons - _________

Valence - __________

Protons - ___________

Neutrons - _________

Electrons - _________

Valence - __________

2/more atoms join to become more stable
Atoms become stable when they have a full outer
energy level
 Most organic elements need 8 electrons
 Hydrogen is the exception – it only needs 2


Atoms gain/lose
electrons to increase
stability



Gains  (-) ion
Loses  (+) ion
Opposing charges
attract  forming a
bond

Formulas




1st – (+) ion
2nd - (-) ion
# indicates how many
of each element are
needed
NaCl

Sodium & Oxygen



2/more atoms share
electrons to increase
their stability
Occurs when neither
element can “give
away” electrons
Atoms joined by
covalent bonds are
called molecules

Carbon & Sulfur
Nitrogen & Oxygen
Bond ____________
Formula ___________

Most dense in liquid form


Allows ice to float
Importance to living things?
 Aquatics
 Terrestrial

Water has a high surface tension
Cohesion – molecules “stick” to themselves
 Adhesion – molecules “stick” to another substance
 Capillary Action – molecules drawn up a tube
 Importance to living things?

 Blood
 Plants

High Specific Heat



Resists changes in temperature
Requires increased energy to raise temp
Importance for Living Things?
 Aquatic Organisms
 Mammals
 Climate

Versatile Solvent
Water is “polar” or charged
 Any polar substance will dissolve in water
 “Like dissolves Like”
 Gives water the ability to form mixtures, acids &
bases
 Importance to living things?

 Structure
 Nutrient/waste exchange
 Buffer

pH Scale

Solutions:


Homogeneous  1
substance equally
dissolved in another
Examples:

Suspensions:


Heterogeneous 
2/more layers form;
particles “hanging”
Examples:

COLLOID



Gel-like substance
w/clusters large
molecules spread
throughout
Properties both liquid
& solid depending
upon pressure
applied
Examples: