Seeing Organelles
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    Now that you have begun to learn about organelles, it is time to make sure that you understand how we see these things!  Because, if you are like me, it is hard to understand what something is or does without knowing what it looks like.   Or how big it is.  Or how to see it.

    People really didn't know anything about most of the organelles until the 1950s.  And they didn't really make much sense out of it all until the 1960s.  So, the study of cell biology didn't really blossom until recently.  The specific thing that brought about the explosion our understanding of cells was the electron microscope.  You see, most of the organelles that you are learning about are invisible using even the nicest light microscopes.  And you will certainly not see these items in your microscopes at home (or in a $100,000 light microscope in a government lab).

    Your book describes electron microscopes a little bit for you.   Go ahead and read about them.  I'll also tell you a little bit about them here.  Please keep in mind that the information on this page is only here to help you... I will NOT be testing you on how light or microscopes specifically work, but I want to show you.  It really helps to understand things that are so tiny.

    Regular light microscopes, like the ones you have purchased, use light to help you see an item.  seeitems.jpg (8774 bytes)That should make sense, because our eyes only see when there is light around.  If light does not go through something or bounce off of something, we don't see anything.  In this drawing I made, I have tried to show this to you... when you look at another person, light is reflected off of them and then you see it when that reflected light reaches your eye.  When you look in your microscope, the light passes through the material of interest on your slide and then up through the ocular to your eye.  Either way, the light carries some of the information about what you are seeing, and then your eye can recognize that information.

    This alone is pretty impressive.  And to understand it a little better, it helps to know that light travels in waves.

    Light seems so small to us.  We can't see the little light waves.  But then again, cells are too small for us to see, too.  At some point, as we try to see things that are smaller and smaller and smaller, we will have to get so small that we reach the size of light.

    Light waves are really small.  They are around 1 - 2 micrometers in size.  That is 1 - 2 thousandths of a millimeter.  And the eukaryotic cells we are studying are around 10 - 30 micrometers in diameter.  So light is small enough to show us these eukaryotic cells.  But, the parts that make up the cell have to be much smaller than the cell itself.  It is most of these parts that we cannot see with the microscope.  Here's why.

light.jpg (28295 bytes)     At the top of this picture I have drawn light reflecting off a person.   This is to show you that a person is big enough to reflect and change light.

    In the middle, I have drawn a picture of light going through a eukaryotic cell... This is like the situation that you create when you look at cells under your microscope.  The light comes from below the stage as normal white light, and then runs through your specimen, and changes (in this case, it changed color) as a result.   You can see the cell because it was at least as large as the light wave.

    At the bottom, I have drawn a small organelle.  This is something like a ribosome or lysosome, which are typically less than 1 micrometer in size.  It could be the ER, which is less than 1 micrometer in diameter, even if it is extensive.  Note that this item is smaller than the light wave.  The light wave doesn't even notice it and runs right past it without changing.

    So, if an organelle is around 1 micrometer in size or larger, the light will change from it and you will see it.  If it is smaller than that, the light will not be affected by it and you will not see it.

Electron microscopes do not use light

    Electron microscopes run an electron beam through the tissue you are interested in.  Electron waves are much smaller than light waves.  They can pick up things in the nanometer range (1000 nm = 1 micrometer).  Of course, we can't see the electron beam, so we need special equipment to help us see our images.  Electron microscopes are quite finicky and expensive and difficult to use-- that's why most schools (including STCC) do not own one.

    I hope you can understand, though, after this little tirade of mine, why we learned so much after the electron microscope was developed.  We had never seen the rER or the Golgi complex or the lysosome before the electron microscope.   Once we could see them, then we could figure out what they did and why they were important.  As you look around the WWW at images of cellular organelles, you will encounter many that were taken with the electron microscope.  Most of these appear in grayscale, although some people like to colorize them to make them prettier.


2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.

Last changed: January 21, 2007