The cell is the minimum and life-long component of an organism. In this way, all living things are made up of at least one cell, and each is derived from the other. The discipline devoted to the study of cells is called cytology.
The most widespread theories regarding the development of life are aimed at establishing that the appearance of this occurred when inorganic elements were transformed into organic elements thanks to the environment. In turn, these new elements were combined with each other, forming more complex structures and with the ability to replicate: this is how the first cell was born.
The structural features that a cell possesses are: individuality, insofar as it is separated and communicated with the outside by a kind of wall; the possession of a set of instructions that define its behavior in the genetic material that makes up DNA (deoxyribonucleic acid); and the containment of an aqueous medium called "cytosol", in which glucose is degraded.
At present, they are recognized two differentiated cell models. On the one hand, prokaryotic cells are identified, in which DNA is included in a single chromosome that is isolated in the cytosol. There are other accumulations of DNA in these cells that can be transmitted from one organism to another and which are called plasmids. It is this cell pattern that characterizes bacteria, some algae, and other primitive organisms. On the other hand, eukaryotic cells are identified, which make up fungi, plants and animals, including humans. In these cells, DNA is integrated into several pairs of chromosomes that are housed in a special structure known as the nucleus. These cells have some "organelles" with their own DNA, such as mitochondria and chloroplasts, whose characteristics are surprisingly similar to those of prokaryotic cells. Indeed, some experts presume that these organelles were autonomous organisms in ancient times, to later be integrated into a kind of symbiosis to give rise to the most complex living beings. As long as they constitute life-possessing units, cells have a series of characteristics that reflect this situation: they feed capturing elements from the environment, assimilating them, obtaining energy and eliminating waste; they grow, to the extent that they feed; are reproduced through division, forming other identical cells; and evolve, to the extent that they can undergo changes that will be inherited. The cell theory could only develop from the advancement of technical means, in particular, with the appearance and improvement of microscopes; For example, Robert Hooke's observations on cork, which were one of the first clues on the subject, were made thanks to one of those artifacts built by himself. Thus the information was accumulating and integrating, but only with Pasteur's research was a general consensus reached. Today it is undoubtedly admitted that all living organisms are made up of cells, which is why viruses are not part of the classification of living beings for the paradigms of current science. Moreover, insofar as it can subsist on its own in a suitable environment, a cell is itself a living organism, which has led to some philosophical friction among modern scientists. A single human cell, seeded in optimal culture media, can carry out its entire life cycle. Is this cell a new organism, or is the human being (as well as other forms of life) a sort of "colony" of multiple smaller organisms that could be considered partially autonomous? The debate, based on the progressive advances in cytology and genetics, seems to have only just begun within the framework of the theory of emergent properties in biology.
