Living organisms are not composed of special substances but of relatively few elements found on the earth. In addition to water molecules, organisms are composed of organic compounds containing carbon. Organic compounds were considered as compounds that do not exist in nature and that can only be produced by organisms. Although many types of organic compounds are available in nature, organisms are primarily composed of proteins, lipids, carbohydrates, and nucleic acids. Thus, organisms appear simple at the material level; however, an organism cannot be created by simply mixing the above mentioned components together. In this chapter, we examine the organic compounds that comprise living organisms, while in the next, we will explore how these organic compounds comprise structures and confer functions to organisms through the formation of systems.
