The science of microbiology has its roots in a very simple fact; All life is built on cells. This seemingly small detail is the main principle of cell theory, which has allowed scientists to study the base material that makes up our existence. This has led to life saving advancements in medicine and brought us farther down the path to discovering the origins of life on Earth.
The discovery of the cell is credited to Robert Hooke. In 1665, Hooke had been examining samples of cork when he noted that they seemed to be made up of very small porous structures, not unlike a honeycomb. The discovery of these pores, which he called cells, prompted scientists to decode their function. In 1839, two scientists named Theodor Schwann and Matthias Jakob Schleiden proposed that all living things are made of cells and that they are the basic building blocks of life. Continuing the work of Schwann and Schleiden, Rudolf Virchow postulated that all cells are generated by pre-existing cells. The classical cell theory was accepted by 1858.
Modern Concept of Cell Theory
Modern cell theory has added several points to what had been previously proposed by Schwann, Schleiden and Virchow. Modern cell theory states that in addition to being a unit of structure, cells are also units of reproduction, heredity and function. Further study also uncovered that some organisms are made up of no more than one cell. We now know that all cells have essentially the same chemical composition as well. This point is substantial as it tells us that the genetic material within the cell is what makes organisms different, not the cells themselves.
Types of Cells
Two distinct types of cells were discovered while modern cell theory was developed. This first type is known as prokaryotes. The defining trait of this group is that it lacks a nucleus. Archae and bacteria are classes of this type of cell. The other type of cell is eukaryotes, which include plants, animals (including humans) and fungi. These do have a nucleus, which houses genetic material in chromosomes. Chloroplasts, endoplasmic reticulum, lysosomes and mitochondria are all organelles in Eukaryote cells.
Cell theory has brought on a whole new chapter in scientific discovery. Stem cell research and the race to decode the human genome would not have been possible without the work of the scientists that developed cell theory. With a deeper understanding of the basic material with which all life is composed, large leaps forward have been made in the treatment of hereditary ailments such as heart disease and certain cancers.
Viruses and Cell Theory
There is a debate over whether viruses are in fact living things or not. This debate is a slippery slope in relation to cell theory. Viruses contain genetic information in the form of either DNA or RNA, but they do not contain cells or any material that behaves in a cellular manner. So despite exhibiting characteristics of life (e.g. reproduction), viruses, by definition of the cell theory, cannot be alive because they do not contain cellular material.