Robert Hooke's studies in 1665 on a plant material would make it possible to determine a regular structure similar to a pore surrounded by a wall which he called "cells", which in itself, without his knowledge , was the discovery of the fundamental unity of all living beings. In 1838, a botanist called Schleiden derived the theory "The basic unit of structure and function of all living organisms is the cell." More than 150 years later, this can be considered one of the best known and most important facts in biological fields. Drawing of cork cells published by Robert Hooke 1665. The cell itself and the use of cytology: The cell may be thought of as a bag in which the chemistry of life is allowed to occur, partially separated from the he environment outside the cell, it exists in all living organisms as a basic structure. The study of cells is made possible through the use of “cytology,” the preparation of materials for examination under a microscope. because an average animal cell exists on a scale of 10 microns, or about a hundredth of a millimeter. Originally, optical microscopy was used in this field, but with the advancement of knowledge, scientists limited themselves to a magnification of 200 nm, or 2 tenths of a micron. Become aware of the existence of cellular organelles within the cellular structure, allowing the functioning of the cell itself to occur; It was necessary to increase the magnification using an alternative radiation source (alternative to light). The result was the electron microscope, whereby the short wavelength and negative charge of electrons when energized allowed greater focusing with electromagnetism. This method bends the path of the beam like a lens towards the light. Cellular organelles and variation between plant and animal cells: We have already determined that the cell is the basis of all organisms, but the term cell is associative and categorizes a great deal of variation. Every animal cell has a specified function, whether it is producing hair, mucus, or processing other chemicals (multiple reactions occur within a cell for other purposes, e.g. the creation of ATP, the production of proteins, etc.). we need to look at the cell in more detail and determine what it contains that creates its specialized function and separates it as an individual type. Plant cells vary from one animal cell to another by the existence of certain organelles. Organelles are the substances that provide a cell with the ability to produce (a production line) and exist within the confines of the cells.