MIcroscope usage: Analysis of cell types – prokaryotes, eukaryotes and early animal development.

Estimating Viewing Field with a Ruler

Step 1:  Use a clear ruler with a cm/mm scale to measure the diameter of your viewing field at scanning (40x).  On our scopes, we estimated the viewing field to be about 4 mm across.

Step 2:  Repeat the process on low power (100x).  We estimate our low power viewing field to be about 2 mm across.

Convert mm to microns for both the scanning and low power.  There are 1000 microns in a millimeter.  So…     Scanning =  4000 microns;   Low Power = 2000 microns.

You can at this point use that measurement to measure anything in your viewing field that you can see with low or scanning power.  The measurement is an estimation though, and probably not very accurate.    For instance, if you have a slide with the word “are”  across it, use your measurement of the viewing field to estimate the distance of each of the letters.   In the drawing below, I have superimposed the slide over the millimeters of the ruler so you can make your estimation. Based on the ruler marks, the letter “r” is about 1100 microns, and the entire word, which takes up most of the viewing field is about 4000 microns across.  In reality, you cannot place your slide over the ruler, so you have to make a guess based on how large your microscope’s viewing field is.

Calculating High Power Field of View

Measurements on High Power can be a little more complicated.  If you try to use the clear ruler technique, you’ll find that you cannot see the individual ruler marks.  This is where math comes in, the values you estimated above can be used to solve a ratio problem and determine the size of your viewing field on high power.

Solving for “High Power Field of View” ….

X / 2000  =  100/400

X  (high power field of view)  = 500 microns

Now that you have 500 microns as an estimate of your viewing field, any object you are viewing under high power can be estimated based on that. I tell my students to look at a paramecium and guess how many paramecia can fit end to end on their slide.   They guess they can fit two, then the length of their paramecium is about 250 microns.

Task 1:

  1. Identify and observe a few prokaryotic and eukaryotic cells using the slide sets, set out for you. Using excel create a table to record your calculated size of 5 of each cell type. Find the average and std deviation and apply a t-test to determine if they are statistically different in size. You need to which dimensions to use.
  2. Secondly, observe the starfish development [blastula/gastrula] and use the above calculation process to determine the average size of: [for comparison use this website: http://www.discoverdevelopment.com/PhP/SlidesStarfish.php or http://faculty.baruch.cuny.edu/jwahlert/bio1003/development.html
      • the entire embryo [at similar stages
      • the individual cells

3. How do the animal cell sizes during development compare to the unicellular organisms?

From: http://www.biologycorner.com/2010/09/14/how-to-measure-with-the-microscope/

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