Cells

Cells are the most basic structural and functional unit of all the living organisms on earth. In 1665, the English natural philosopher Robert Hooke discovered the cell—and this discovery preceded the cell theory by almost two hundred years. Cells are commonly known as the “building blocks of life.” The term “cell” comes from the Latin word “cellula,” which means “a small room” and was coined by Hooke in a book he published in the same year of his momentous discovery. Cell count can be used as a classification for organisms. Unicellular organisms have a single cell (most bacteria are included in this category), while multicellular organisms are made up of up to trillions of cells. In fact, human bodies contain around ten trillion cells—each and every component of a person’s body is made up of more cells than one could possibly hope to count. As he was looking at plant tissue through a microscope in 1835, the Czech anatomist and physiologist Jan Evangelista Purkyne observed tiny “granules” in the specimen. This observation was made before the final cell theory was developed in 1839. The German scientists Matthias Jakob Schleiden and Theodor Schwann developed the cell theory, which states: “all organisms are composed of one or more cells.” This theory also continues to describe cells as to have originated from pre-existing cells; that the vital functions that an organism requires in order to live occur within these cells; and that all the cells in the organism’s body contain hereditary information required to regulate cell functions, as well as for passing information on to the next generation of cells within the body. There are two basic kinds of cells: eukaryotic (found in multicellular organisms) and prokaryotic (usually independent) cells. There are different components to a single cell, including the membrane, the cytoplasm, DNA, RNA, and other biomolecules. Despite the minuscule size of most cells, they are of a very complicated and impressive design. This section contains information on cells, which are the basic structural and functional unit of all living organisms.