Due to the limitations of light microscopes, electron microscopes were developed. In the 1930s, biologists found that light microscopes had theoretical limits, and the scientific desires to see fine details of the interior structures of organic cells were increasing. The first type of electron microscope to be developed was the transmission electron microscope and includes a focused beam of electrons to see through the specimen. This type of electron microscope was developed by Max Knoll and Ernst Ruska in 1931. Around 1942, the first scanning electron microscope was used, and its development came from the electronics involved in scanning the beam of electrons across the specimen.
Electron microscopes are sophisticated types of magnification devices used mostly in archaeology, medicine and geology to look at surfaces as well as layers of objects such as organs and rocks. Electron microscopes don’t use light. Instead, they point a stream of electrons at the specimen and a computer attached to the microscope analyses how the electrons are scattered by the material. The specimen, however, must be suspended inside a vacuum chamber. When scientists use electron microscopes, they get views of the slices of the object in two dimensional form, but in different depths. As these instruments are very powerful, both the resolution and the degree of magnification are very high.
Light microscopes are entirely operated by hand and use a light bulb to illuminate the specimen which is mounted between two glass slides and clipped onto the stage just under the main lens, on top of the light source. A dial is used to focus the image. These tools use a simple series of magnifying lenses and mirrors to bring the image up to an eyepiece. Light microscopes are mostly used in biology. They give a two dimensional slice of the specimen, and at the same time, it can attain a high enough magnification to see parts of cells or even hair strands. However, light microscopes do not have high resolution, often causing a blurry image.
An electron microscope includes an electron gun emitting electrons onto the specimen to create a magnified image. Magnetic lenses creating the magnetic fields are used to direct as well as focus the electrons onto the specimen. Electron microscopes use a vacuum system due to the fact that electrons are easily scattered by air molecules. Light microscopes consist of two lens systems, including the objective and the ocular which are at opposite ends of a closed tube. The objective consists of several lens elements making up an enlarged image of the examined object. The lenses are set up so that the image which has been formed by the objective lies at a certain focal point of the ocular.
Electron microscopes have a greater resolution and magnification compared to light microscopes. Electron microscopes are able to produce micrographs, which are photographs of the image being viewed, but for light microscopes, you have to draw the image yourself. Using a light microscope enables you to view specimens in colour, and living specimens can also be observed, hence their movement can be studied. Contrasting to light microscopes, electron microscopes are unable to view live specimens, as they have to be prepared using various techniques including staining, dehydration and placement in a vacuum. Images coming from the electron microscope are monochrome, and therefore no colour can be seen on the images. Electron microscopes have a smaller field of view than light microscopes. Electron microscopes come with a very high price tag compared to light microscopes, but the greater the magnification of a light microscope, the higher the price as well. Light microscopes also cause health related problems, for example, eye fatigue. Light microscopes also lower efficiency, speed and its accuracy as images have to be hand drawn, and therefore the image is difficult to share. For beginners and students, light microscopes are used in classes as they are easier to use than electron microscopes, which are more complex.
Here's what a star student thought of this essay
Quality of writing
Spelling and grammar are fine throughout. However, despite the fact that the candidate accurately describes both microscopes they use very few technical terms, I would expect an A-level candidate to include terms such as photomicrograph which is the image produced on screen from an electron microscope. In addition to this, the candidate consistently uses the term ‘light microscope’ and it is more accurate to say ‘optical microscope’ which is the scientific name.
Level of analysis
The candidate could have developed this essay further by going on to discuss the ways in which specimens are prepared, perhaps even describing ultracentrifugation which is an A-level topic. This would have shown a greater depth of understanding and it is very useful to be able to link together topics in biology. Furthermore the candidate fails to conclude their work, you should always write a conclusion even for a short essay like this. It allows you to draw the essay to a close and leave the reader with a good impression. A good conclusion consists of a summary of your key points, you should include reasons for why these points are important, this helps the reader to see that your essay is important and is worth reading.
Response to question
The candidate starts with a good opening sentence, they define the terms linked with the word microscope, which is good way to engage the reader. However their introduction is just one sentence. A good introduction should include what you plan to discuss, so that you introduce your essay. However the candidates overall response to this topic is good, they describe how both types of microscopes work and have compared the basic proprieties of each, such as resolution and magnification.