WHAT ARE LIGHT AND ELECTRON MICROSCOPES? - HOW DO THEY WORK?

Light and electron microscopes

The beauty of biology and all that we know today is due to the invention of microscopes. The light microscope uses light as a source of radiation and has shown us inside cells. It shows us simple structures like the nucleus, the cell wall and the cell membrane. Light microscope is still used in basic studies in schools today.

Light microscopy

Microscopes had been available since the beginning of the 17th century but a lot of improvements made in the quality of glass lenses in the early 19 century. The branch of biology dealing with microscope design, slide preparation and examination is called cytology. The general structure of animal and plant cell is also due to the light microscope.

Electron microscopy

Then came the electron microscopes, which made our microscopic world more detailed. Due to the electron microscopes we not only saw the cell wall, the nucleus and the cytoplasm but we also saw the more minute organelles like the mitochondria, endoplasmic reticulum and the Golgi apparatus.

The light microscopes were doing great, but no matter how much their designs improved, there was extent to which the light microscopes could show. Anything smaller than 200 nm could not be seen. In an electromagnetic spectrum, there are radiations smaller than light, these are ultraviolet radiations and x-rays.

Microscopes with both ultraviolet and x-ray radiation were built, but alas, x-rays could not be focused and so these designs were discarded.

Electrons are negatively charged particles which orbit the nucleus of an atom. When a metal becomes very hot some of its electrons gains so much energy that they escape from their orbits, like shooting stars.

Free electrons behave like electromagnetic radiation they have a very short wavelength the greater the energy the shorter the wavelength. Electrons are very suitable form of radiation for microscope for two major reasons. Firstly wavelength is extremely short and secondly because they are negatively charged they can be focused easily using electromagnets. The magnet can be made to alter the path of the being the equivalent of a glass lens bending light.

There are two types of electron microscopes in use today. In the transmission electron microscope, the beam of electrons is passed through the specimen before being viewed. Only those electrons that are transmitted are seen. This allows us to see thin sections of specimens and thus to see inside cells.

In scanning electron microscope, the electron beam is used to scan the surfaces of structures and only the reflected beam is observed. The advantage of this is that surface structure, for example,like the chitinous outer body of insects can be seen in great detail.

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Timestamp:

00:00 The use of the microscope
00:30 Light microscope
00:47 Electron microscope
01:20 How does an electron microscope work?
02:04 Types of electron microscope
02:12 Transmission Electron Microscope (TEM)
02:24 Scanning Electron Microscope (SEM)