Atoms are the building blocks of all matter. It is through the reactions of atoms that organisms come into existence. The human body, for example, consists of the products of numerous complex, chemical reactions and is held together by natural, physical forces. Developing an understanding of the atom and its components is a foundational concept for understanding life.
Atomic Particles
Atoms contain three particles that are of great importance to the identification and behavior of an atom.
- Protons – particles with a positive electrical charge
- Neutrons – particles with a neutral or no charge
- Electrons – particles with a negative charge.
The number of protons dictates the identity of an atom, which is called an element. For example, one proton is a hydrogen atom. Oxygen has eight protons. This never changes. If the number of protons changes, the element changes.
Atomic Structure
The atom is the most basic functional structure. It consists of a nucleus at the center, and orbitals around the nucleus. The nucleus is the center of the atom where the protons and neutrons are found. Orbitals are areas where electrons reside. There can only be two electrons in any given orbital, so atoms with more electrons have more orbitals.
Isotopes
Generally, atoms contain the same number of protons and neutrons. For example, carbon most often contains six protons and six neutrons. This is denoted by adding the protons and neutrons together and placing the sum as a subscript to the left of the carbon symbol: 12C.
The number of neutrons can vary. For example, a carbon atom, which always has six protons, may have eight neutrons. This would give us carbon-14: 14C. Carbon-12 and carbon-14 are isotopes – the same atom, but a different number of neutrons.
Carbon-14 is used for dating fossils. The living body maintains a certain ratio of carbon-12 to carbon-14. When an organism dies, carbon-14 is no longer maintained, and the level of carbon-14 in the body decreases. For this reason, the ratio of carbon-12 to carbon-14 can give an approximate age.
Elements of Living Organisms
While many elements can be found in living organisms, only four are present in great amounts, including hydrogen and oxygen, which form water. According to Biology, by Brooker et al., "These elements [account for] about 95% of the mass of living organisms. Water accounts for approximately 60% of the mass of most animals and up to 95% or more in some plants. Nitrogen is a vital element in all proteins, and carbon is a major building block of all living matter."
Having a basic understanding of the structure of atoms is important to understanding the processes of life. Atoms come together to form molecules. Atomic reactions involve protons, neutrons, and electrons. It is at the molecular level where the complexities of life can be observed.
Reference
Brooker, Robert J., Widmaier, Eric P., Graham, Linda E., and Stiling, Peter D. Biology. New York: McGraw-Hill, 2008.
 |
