1.1.4 Microscopy

In this lesson, we will explore how microscopyThe use of microscopes to observe small structures. has developed over time and how improvements in technology have allowed scientists to study cells in increasing detail. We will compare light and electron microscopes in terms of magnificationThe number of times larger an image appears compared to the real object. and resolutionThe ability to distinguish two separate points as distinct., and practise calculations involving image sizeThe measured size of an object as seen under a microscope., real size and magnification, including expressing answers in standard formA way of writing very large or very small numbers as a number between 1 and 10 multiplied by a power of ten. where required.

Development of Microscopy Techniques

Microscopy has played a vital role in the development of biology. Cells are too small to be seen with the naked eye, so microscopes allow scientists to observe their structure and organisation. As microscopes have improved, our understanding of cells and sub-cellular structures has become much more detailed.

The first widely used microscopes were light microscopes. These use visible light and glass lenses to magnify specimens. For many years, light microscopes were the main tool for studying cells and tissues, and they are still widely used in schools and laboratories today.

In the 20th century, electron microscopes were developed. Instead of using light, they use a beam of electrons. Because electrons have a much shorter wavelength than visible light, electron microscopes can achieve much higher magnification and resolution. This has allowed scientists to observe much smaller structures inside cells.

Magnification and Resolution

Magnification and resolution are two different but related concepts. Magnification describes how many times larger an image appears compared to the real object (i.e. the ratio of an object’s image size to its real size).

Resolution, on the other hand, is the ability to distinguish two separate points as distinct from each other (i.e. a measure of the clarity of the image).

Light microscopes typically magnify up to about ×1000. Their maximum resolution is around 200 nanometres (nm). This means that if two structures are closer together than 200 nm, they will appear as one blurred structure. Very small structures such as ribosomes cannot be seen clearly using a light microscopeA microscope that uses visible light and glass lenses to magnify specimens..

In comparison, electron microscopes can magnify images hundreds of thousands to over a million times. More importantly, they have a much higher resolution, down to a few nanometres. This allows scientists to observe very small sub-cellular structures, including ribosomes and internal membrane details within mitochondriaAn organelle where aerobic respiration occurs and energy is released. and chloroplasts. Because of this increased resolution, electron microscopy has greatly improved our understanding of cell structure and function.

Magnification Calculations

When using microscopes, it is important to calculate magnification correctly so that the real size of structures can be determined. The formula for magnification is:

To calculate magnification, you divide the image size by the real size of the object. The image size is how large the specimen appears under the microscope, while the real size is its actual dimension, usually much, much smaller.