Cell Theory and Microscopy: History and Fundamentals

Posted on Dec 10, 2024 in Physics

Findings that Preceded the Cell Theory

In 1661, the Italian physician and physiologist Marcello Malpighi (1628-1694), the first researcher to use the microscope in medicine, discovered capillaries, arterioles connecting with small veins, so was able to complete the scheme of blood circulation. He was also the first to discover the red corpuscles that give color to the blood.
In 1665, a noted English scientist named Robert Hooke (1635-1703) published the results of his microscopic observations in plant tissues. He used the word “cell” to describe the small cells that structured small pieces of cork taken from the bark of cork oak. He noted that this was composed of hundreds of small chambers like a honeycomb, and called them cells because they reminded him of the small rooms of the monasteries, called cells. For all this, Hooke is considered the discoverer of the cell.
In 1677, another Dutchman, Anton van Leeuwenhoek (1632-1723), using a magnifying glass polished by himself, first observed in the history of humanity living cells: red cells, protozoa, muscle fibers, etc. Leeuwenhoek was the first man to examine drops of stagnant water and to describe different types of bacteria in plaque from the teeth.
In 1831 the Scottish botanist Robert Brown (1773-1858) discovered a particle that was constant in all the examined plant cells, which gave the name of the cell nucleus.
In 1838, the Czech physiologist Johannes Purkinje (1787-1809) discovered through microscopic techniques the presence of a mucilaginous substance in the cell’s internal environment in which certain movements are watched, and called it protoplasm.

Development of the Cell Theory

In 1838 the German botanist Matthias Schleiden (1804-1881) concluded that all plants were made of cells.
In 1839, a year later, another German zoologist Theodor Schwann (1810-1882) came to the same conclusion regarding the structure of animals: they were also made of cells.

These two findings and existing knowledge formed the basis for the constitution of the cell theory.

Postulates of the Cell Theory

All organisms are composed of one or more cells, from the smallest bacterium to the largest multicellular organism.
The cell is the basic unit of organization of life, i.e., the cell is what gives anatomical and physiological unity of living beings, is the structure in which they occur all the chemical reactions necessary for life, such as nutrition and respiration.

Later, in 1885, the German pathologist Rudolf Virchow (1821-1902), after studying cell reproduction and how disease affected agencies, established what is the third postulate of the cell theory:

All cells must be considered as metabolic units and are generated only from preexisting cells.

The Cell as a Unit of Living Things

It is considered that the unit cell is vital, anatomical, physiological and genetic of all living things.

It is a vital unity, as the living cell is smaller and simpler existence. It is an anatomical unit because it can be considered as an anatomical unit of living things and there is no living being that is not composed of at least one cell. It is a physiological unit because the cells have all the physiological and biochemical mechanisms necessary to stay alive. It is a genetic unit, as any other cell necessarily comes from preexisting cells.

Because of its great importance in the world of living beings, the cell is under study in virtually all branches of biology. These branches are:

Cytology: The study is based primarily on the organization and functioning of cells.
Biochemistry: The branch of biology that deals with the study of the vast number of chemical reactions that occur in cells, which are all necessary for these to be kept alive.
Physiology: The study of the functions performed by the cells, not only to stay alive, but also to fulfill their pledges.
Biophysics: Studies a range of physical phenomena that occur both in the cell, as its components.
Genetics: The study of the basic characteristics of the cells: their capacity to transmit hereditary characteristics.

History of the Microscope

By 1580, in European capitals began to use power lenses quite high. At first, they were used to determine the quality and accuracy of tissue fabrics for entertainment, etc. Later came the first microscopes.

A Dutch spectacle maker Zacharias Jansen (1580-1638), appears to have been the first who, in 1591, coupled a concave lens with a convex lens in a tube. Thus, if one looked on one side of the tube, the objects were increased, while the other side were reduced. He had made the first microscope. This consisted of a single lens system, so it is called a simple microscope.
Later, thanks to the contribution of outstanding treasuries as Kepler, building design was improved microscopes, so the compound microscope was created, which has two sets of lenses: one close to the sample in the study, called target, which extends the object in focus and one on which rests the eye for observation, known as ocular zoom in again.
More recently, the development of new instruments allowed observations with much greater detail and sharpness. In 1931, Ruska and colleagues built the first transmission electron microscope, and Von Ardenne in 1934 built the first scanning electron microscope.

Types of Microscopes

The optical microscope uses white light to illuminate the elements to observe; it can enlarge a thousand times and uses optical lenses.

The electron microscope uses a beam of electrons instead of light to increase the observed image and uses electromagnetic fields, electronic devices that perform a function similar to that of optical lenses (focusing the electron beam). The transmission electron microscope studies the surfaces of objects, and the scanning electron microscope allows observing cell ultrastructure. If the maximum magnification of an optical microscope is 2000 times, the electron microscope can increase some 150,000.

The Optical Microscope

Also called a compound microscope, powered by a beam of light incident on the sample being analyzed.

Its power of resolution comes to 100 nanometers (0.1 micron = 10^-7 meters) and enlarges a sample up to 1500 times (1500x). Its operation depends on 3 systems: mechanical system, lens system, and lighting system.

Mechanical System

Main tube: a metal tube that is at the top of the microscope which eyepiece and adjust the gun
Revolver: a rotating circular piece, adapted to the bottom of the main tube. The objectives are coupled to stir
Focus System: consists of macro and micrometric screws. These screws allow you to move up or down the main tube to focus.
Arm: a metal portion in an arc, united at the top to the main tube and the bottom to the base. Allows tilt graduated instrument.
Plate: a round or square sheet which is set perpendicular to the arm. In the center is an opening that allows passage of light.
Car: A system consisting of 2 plates that support the preparation and slide a device that allows
Base: is the support arm attached to the microscope, and generally has a U shape

Lens System

Eye: the lens is placed on top of the tube and increases several times the image provided by the lens. For example 6x, 6 times the image increases, 10x increases it 10 times.
Objectives: are the lenses that are attached to the revolver, which when rotated, can be changed. In the gun are several objectives.

Each of these different lenses provides increased image 5x 10x 50x etc. The total increase is due to the increase goal. So is 6x eyepiece and the objective using is 10x total magnification is 60 times.

Lighting System

Condenser: is located below the deck. Its function is to focus the light rays and thus allow more light.
Diaphragm: is below the condenser and regulates the amount of light entering the
Mirror: is attached to the arm below the diaphragm and allows you to direct light rays to the condenser.

Magnification is the magnification of an object observed under the microscope. It refers to the bigger picture is under the microscope in relation to its actual size. The maximum magnification of the microscope is 1500 times (1500x) the actual size of the sample.

Resolving power: A measure of clarity with which an image under the microscope. Refers to the minimum distance between two points the microscope. Refers to the minimum distance between two points that the microscope can separate and make visible as two different points. The resolving power of the microscope is 0.2 micrometers, i.e., 2×10^-4 mm, the electron microscope is 0.0002 micrometers, i.e., 2×10^-7 millimeters

Using Dry Objectives

Steps:

Turn the stir and place the lowest power objective
Lower the condenser, turn the light source and move the mirror until you see through the eyepiece, the field is illuminated. Regulate the aperture to obtain a homogeneous illumination of the entire field.
Place the slide containing the preparation covered with the cover glass of the microscope in the car, set the slide with forceps. Move the car until the mixture is in the center of the opening of the platen.
Looking directly at the preparation, outside the main gate beam moving down the coarse adjustment knob until the target is very close without touching operational preparedness.
Look through the eyepiece and begin to slowly climb the main tube, moving the coarse adjustment knob until you see the image of the preparation. Use the coarse adjustment knob to sharpen the image.
Once the image focus can change the target of a smaller increase in growth medium. To do this, looking out and not move the coarse adjustment knob, turn the gun and placed the new target. Look through the eyepiece and make adjusting the image with the micrometer screw.
By movement of the screws that are part of the car, preparing to watch her move in their different fields.

Using Immersion Objective