INSS Biology Module I: Carbon, Life, and Cycling
Modeling Activity I
Introduction:
Although approximately 100 types of atoms exist in the universe, living
organisms are composed primarily of carbon, hydrogen, oxygen, nitrogen, phosphorus,
and sulfur. (C,H,N,O,P,S) These 6 elements comprise approximately 96% of the matter
of any organism.
All the hydrogen (H) atoms of the human body, in bacteria, or in the atmosphere
are as old as the universe itself, approximately 12 billion years old. All the other atoms
in your body were synthesized long ago in a star that went supernova approximately
10 billion years ago. Thus, you, your family, your pets, your germs, and the ground
beneath your feet are quite literally made of “stardust”.
As you learned in geology, the Earth itself formed from this stardust
approximately 4.5 billion year ago. Life, in the form of prokaryotic cells, formed from
this stardust approximately 3.5 billion years ago. Again, the proportions of atoms in
living organisms differ dramatically from those of their surroundings. For example,
silicon (Si) makes up 28% of the Earth by weight, but is only present as a trace element
in humans. Likewise, carbon, which accounts for approximately 20% of the weight of
any organism, makes up less than 1% of the Earth.
The appearance of life on this planet was an extraordinary event, which at this
time is undocumented by humans anywhere else in the universe. Life has profoundly
affected this planet. The appearance of the first living cells started a chain of events; one
result is the appearance of the reader of this text! Life has changed the very chemical
nature of Earth; early cells created an oxygen atmosphere where none had existed.
Today, humans, progeny of those first simple cells, are also dramatically changing the
chemistry of the Earth’s atmosphere.
For 3.5 billion years, organisms have been exchanging the atoms of life with each
other, and with their abiotic (non-living) environments. Thus the carbon atoms in your
pinky have cycled, cycled, and recycled for billions and billions of years.
The purpose of these exercises are to
1) illustrate where carbon atoms “fit into” living organisms
2) provide clues for how carbon atoms are continually cycled within the living and
non-living components of our planet
Activity I: Constructing Molecules of an Ecosystem
Draw an atom of Oxygen
Pre-Activity Questions
Draw Oxygen covalently bonded with
Hydrogen Atoms
1. How many valence (outer shell) electrons did oxygen have before bonding?
2. How many electrons occupy oxygen’s outer shell after covalently bonding with
hydrogen? (Count the shared electrons too!)
3. How many covalent bonds did oxygen form?
Draw an atom of Nitrogen
Draw Nitrogen covalently bonded with hydrogen
atoms
1. How many covalent bonds did nitrogen form?
2. How many covalent bonds does a single hydrogen atom form?
Draw a carbon atom
Draw carbon bonded with hydrogen atoms
Questions:
1. What is a covalent bond?
2. What is a double covalent bond?
3. How many covalent bonds must each of the following atoms form to achieve
stability? (Have a full outer shell)
Element
Number of covalent bonds needed for stability
H (Hydrogen)
O (Oxygen)
N (Nitrogen)
C (Carbon)