Microscope

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Light Microscopes

It is not possible to see cells as seperate objects using the naked eye

The ability to see two or more objects as seperate objects is called resolution

The light miscrosope was developed in the late 16th century and gave a greater resolution than the human eye 

It allowed scientists to see plant, animal and bacterial cells

Some sub-cellular structures are even smaller than the resolution achived by the light microscope and cannot be seen using this method 

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Electron Microscopes

In 1933, scienties first used an electron microscope 

An electron microscope passes electrons, rather than light, through the specimen and can give much better resolution 

Cells can be seen in much finer detail, e.g. 

  • the structures inside the mitochondria and chloroplasts can be studied and this has helped scientists to fiind out how they work
  • ribosomes can be seen and their role in making proteins can be studied 
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Calculating Magnification

When a microscope is used to look at cells, scientists will often take photographs or produce drawings

These images are many times larger than the real cell or structure 

The magnification is how many times larger the image is than the real object

magnification = size of image / size of real object 

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The Size of Cells

A typical plant cell may be about 0.1mm in diameter and an animal cell 0.02mm in diameter

Prokaryotic cells are smaller - often about 0.002mm long

To describe the size of cells and suub-cellular structures, scientists use units that have different prefixes

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Key Points

The size of cells is often given in micrometers, e.g. a plant cell may be μma plant cell may be 100μm, an animal cell 20μm and a bacterium 2μm in size 

Magnification is not the same as resolution. Light can be built to magnify more and more, but after a certain point the images do not get any clearer 

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Key Words

  • Resolution
  • Electron Microscope 
  • Magnification
  • Light Microscope 
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