|MadSci Network: Physics|
As strange as it may seem, the atoms that you find in a piece of living tissue are exactly the same atoms as those that are found in plants or even rocks. The only difference between the various materials are the specific atoms used, meaning which ones of the many listed on the periodic table, and the spacial arrangement of these atoms in a particular molecule.
Let's give an example. Carbon dioxide is a colorless, odorless gas which makes up part of our atmostphere. This gas is absorbed by plant cells, such as those found in leaves, and converted to various sugars. This means that the carbon atoms that make up the complex sugars in the plants that we eat are exactly the same atoms that exist in the atmosphere. Upon eating the sugars, our bodies are able to extract energy and eventually release the carbon into the atomsphere in form of carbon dioxide. What we see is that a single carbon atom undergoes a cycle as it moves from the atmosphere, to plants, and eventually to animals. In spite of this complex cycle, the atom itself remains unchanged. If you analyzed a carbon atom in a plant and in your skin, they would be absolutely identical.
What makes up a living being, therefore, is not the atoms, but the complex ways in which the atoms are arranged. To illustrate the extreme importance of the atom arrangement let's consider two common substances; pasta and grass. Pasta is primarily composed of complex sugars containing the atoms carbon, hydrogen, and oxygen. Our body is able to digest these sugars to extract energy. However, when one makes one slight spacial adjustment to the sugar molecule, a startling result occurs. Athough the new molecule is composed of the same atoms, at looks almost identical, the human body is unable to digest it. This means that if a human eats grass, no matter how long he chews it, he will be unable to digest it. The difference in materials such at these is not the specific atom or even molecule, but rather that arrangment.
When humans grow, atoms are simply added on to preexisting molecules. Bone growth occurs because various minerals are deposited at the edge of already formed bone. Once again, the atoms themselves are not changed, but simply placed in different arrangments and different locations throughout the body. Likewise, when a person dies, the complex molecular structure breaks down, and the more simplified atoms enter the ground to continue the never-ending cycle.
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