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Chemistry of Life
There are four basic elements found in all living things. More than 96% of your body is made up of these four
elements: carbon, hydrogen, oxygen, and nitrogen. Sulfur and phosphorus are inorganic compounds that are found
in your body in small amounts. Those six elements make up most of the Earth’s living matter and flow through the
environment in cycles.
The Carbon Cycle
The carbon cycle shows how carbon
and oxygen cycle through an ecosystem.
Plants obtain carbon in the form of carbon
dioxide to make carbon-based sugar
molecules. When animals eat plants, they
obtain the carbon they need for their bodies.
As they digest their food, they breather out
carbon dioxide as a waste product. So,
carbon compounds are passed from animal
to animals when one animal eats another.
Carbon is stored in fossil fuels deep
underground. Carbon cycles when fossil fuels
(coal and gas) are burned to form carbon
dioxide and water vapor. The carbon dioxide
is released into the atmosphere and
absorbed by plants.
The Nitrogen Cycle
Nitrogen cycles through living and nonliving parts of the environment as well. The atmosphere is
78% nitrogen but most plants cannot use that source of nitrogen. Certain nitrogen-fixing bacteria can
convert nitrogen in the air into nitrogen compounds that plants can use. Plants then absorb those
nitrogen compounds
from the soil and use it
to form plant cells.
Those nitrogen
compounds are passed
through the food web
when animals eat the
plants or each other.
Decomposers (worms
and fungi) break down
nitrogen compounds
found in dead organisms
and plants, to return the
nitrogen compounds to
the soil.
Carbon compounds
Most compounds in living cells are organic compounds. An organic compound is a compound that
contains the element carbon. All organic compounds contain carbon atoms. However, not all compounds
with carbon are organic. For example, carbon dioxide is not an organic compound.
Carbon Bonds
Carbon is a unique element because of the types of bonds it forms. Carbon can form four covalent bonds
with other elements and other carbon atoms. Carbon can form short chains, long chains, rings, and
branched chains. Carbon can also form double and triple bonds. Carbon is the basis of life because it
forms many different organic molecules or various sizes, shapes, and chemical properties.
Compounds of Life
Reminder: A polymer is a large molecule formed from smaller molecules called monomers. A monomer is
a small molecule that forms a link in a polymer.
The human body contains 60-75 percent water. The rest of the body is carbon and non-carbon
compounds. A large organic molecule found in living organisms is called a macromolecule. Some
macromolecules are lipids, proteins, carbohydrates, and nucleic acids. Amino acids are monomers that
make up proteins. Sugars are monomers that make up carbohydrates. Nucleotides are the monomers
that make up nucleic acids. Lipids are fats and oils that are not polymers.
Nucleic Acid
A nucleic acid is a biomolecule that is found in all plant and animal cells. RNA and DNA are examples of
nucleic acids that store cellular information in cells. DNA, or deoxyribonucleic acid, is the genetic material
of living organisms. The DNA in your cells determines your hair color, eye color, height, and every other
feature of your body. RNA, or ribonucleic acid, is the blueprint to make proteins.
DNA and RNA are composed of monomers called nucleotides.
Lipids
Lipids are oils and fats. They are not soluble in water, meaning they do not mix with water, and contain
carbon, hydrogen, oxygen, and phosphorous. Some examples or lipids are olive oil, bacon fat, and
vegetable oil.
Carbohydrates
A carbohydrate is an organic compound used by cells to store and release energy. Carbohydrates contain
carbon, hydrogen, and oxygen. Glucose, sucrose, starch, and cellulose are examples of carbohydrates.
Three main types of complex carbohydrates are starch, cellulose, and glycogen.
Proteins
A protein is an organic polymer made of amino acid monomers. Proteins are not random arrangements of
amino acid monomers. The amino acids that make up proteins have specific arrangements and the
instructions for building proteins is stored in DNA. RNA are copies of the DNA that proteins are made
from.
1. What are the four compounds of life?
2. What is DNA made of?
3. What are the 6 elements that make up all living matter?
4. How do humans figure in to the carbon cycle?
5. Describe the steps of the nitrogen cycle.
6. Why is carbon special?