The technical use of microscopes to view and observe objects and specimens which cannot be seen by the naked human eye is called microscopy. To study cells, their structure, composition and to understand the molecular nature of cells and life components, scientists faced a major problem that the cells were of very small dimensions and transparent. The human eye could not see them, magnify or distinguish the minute particles.
A microscope is an instrument that has high magnification and resolving power than the human eye, to look at smaller objects and produce an image that shows the object larger. These images produced by microscopes are called micrographs. Magnification is the method in which the image of the object is increased in size so the retina is stimulated to send an impulse allowing the object to be perceived.
Microscopes are of different types. The magnifying glasses or microscopes having only one lens are called simple microscopes. Microscopes that have an eyepiece and lens are called compound microscopes. In biological studies, two types of microscopes are used most extensively.
The optical microscope uses visible light and a system of lenses for illuminating and magnifying the images of small objects. These types of optical microscopes are the old designs of microscopes. Light microscopes are cheap and easy to purchase and simple to use. light microscopes show the natural colors of the specimen. Contrary to that, they have very restricted magnification only up to 1500X. They lack in-depth field.
Parts of light Microscope:
The light microscope consists of an eyepiece, objective lens, condenser lens, stage, fine focus, base, and table.
Light microscopes use transparent, relatively small, spare, and thin specimens. These are best to see mitochondria, most bacterial types, microvilli, etc as they have magnification up to 1200X.
The technique used to get high-resolution images of biological specimens and non-biological objects. The purpose of electron microscopy is to study, understand and research the structure, composition, shape, size of cells, tissues, or other non-living micro-entities.
Electron microscopy works with a much shorter wavelength to attain resolution as low as 3 Aᵒ with usually ranging from 5 to 12 Aᵒ.
Principle of Working:
An electron microscope uses an electron beam accelerated from heated metal wire by high voltages from 20,000 to 100,000 volts to generate an image of an object and magnification of an object is done by electromagnetic fields in which light waves are used to generate an image and magnification is get by optical lenses.
Electron microscope functions under vacuum that means samples and specimens are placed under vacuum system in the course of analysis.
Electron microscopes provide you with very high magnification and resolution power. It allows the greater depth field of study and material is rarely distorted by preparation. On the other hand, its size, cost, the expense of maintenance makes it difficult to use in small labs.
Transmission electron microscope (TEM)
The transmission electron microscope is used to see the interior of cells, protein structure, molecular arrangement and organization in living cells, cytoskeletal fragments, viruses, etc.
In this type of electron microscope, electrons pass through the specimen to generate the image. So, for this, the specimen should be ultra-thin.
Scanning electron microscope (SEM)
A scanning electron microscope produces an image by scanning the specimen with the help of a focused electron beam. These are used to generate images of objects which cannot be seen by TEM.