Food is the most vital product of the agriculture sector. But there other non-food products critical to the economy generated in this multi-billion dollar industry, including cotton, wool and tobacco. Prior to the Great Depression, government subsidies to the agriculture sector were relatively limited.
Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, that all cells come from preexisting cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.
Cells have many reasons to excrete materials. One reason is to dispose of wastes. Another reason is tied to the function of the cell. Within a larger organism, some cells are specialized to produce certain chemicals.