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Microscopy and the Metric System – Estimating Sizes of Specimens
To complete this activity, you will need a ruler with metric units (which is sometimes on the opposite side of inches in many rulers) AND you will either need to print out this worksheet to take measurements on standard 8.5 inch x 11 inch paper -or- adjust the ‘zoom’ of the Word document on your computer screen so that the width of the worksheet ‘paper’ on your screen equals 8.5 inches wide on your screen. If you do the latter to complete this without printing, you will need your ruler held on your screen to help accomplish this and to take measurements for this lab. Image retrieved from https://www.scientistcindy.com/the-metric-system.html When using a microscope, it is often important to obtain an estimate of the size of the specimen you are viewing. Metric units of length are typically used to note the size of specimens. Although micrometers (μm) are the most frequently used units in light microscopy, larger specimens may be noted in millimeters (mm), especially when using a dissecting microscope, and much smaller specimens may be noted in nanometers (nm), particularly when an electron microscope is used to view such small specimens.
Example on metric conversions:
As shown in the table above, for example, if a specimen were found to be 1 mm in length, this would be equal to 1,000 μm or even 1,000,000 nm! This is because for every 1 mm in length there are 1,000 μm or 1,000,000 nm. Similarly, if we noted a specimen was approximately 1 μm in length instead, that specimen would also be the same as being 0.001 mm or 1,000 nm.
In this activity, you will need to approximate the sizes (lengths) of specimens in the METRIC UNITS asked of you. How you can estimate lengths of specimens is based upon the knowledge of the magnification or enlargement used to view the specimen.
Example on how to convert to actual size from a micrograph enlargement:
For example, if a specimen in a photograph taken under a microscope – called a micrograph – that is enlarged by 1,000X when printed out on standard printer paper is found to be 5 mm long, we would know that the actual size is equal to 5 mm divided by 1,000. This equals 0.005 mm. More appropriately, we may want to convert the units to μm instead. Therefore, the approximate size would be noted as 5 μm.
Length of Specimen = length of specimen in photo measured in mm ÷ enlargement factor
How to convert to actual size when viewing specimens directly under a microscope:
Estimating sizes of specimens viewed directly under a microscope is simplified and accomplished differently. Let’s say, for example, we were looking at a specimen at high power and its length spans approximately ¼ of the diamater of the field of view (the ‘circle’ area in which you are viewing when you look in a microscope). We know that high power in a light microscope has a 400X total magnification. That said, we typically also already know the diameter of the field of view at a particular magnification being used (shown below), thus simplifying the process of estimating the sizes of specimens directly viewed under a microscope. In our example, if we were using the high power objective lens, and we know the diameter at high power = 0.4 mm, we would estimate the size of specimen occupying a length of approximately ¼ of the field of view as 0.4 mm ÷ 4, which = 0.1 mm as the approximate size of the specimen. This could also be noted as 100 μm. In this example, the size (length) of the specimen is therefore 0. mm or 100 μm. The field of view diameters of the objective lenses of the light microscopes at GCC are as follows: Diameter of Field of View at High Power 0.4 mm ‘specimen’ ‘Specimen’ in this example occupies ¼ of the field of view
Use the choices from #2 above to respond to the following: Specimen A is _8.9____ and Specimen B is _1.88______. Magnification : 850* FOV NOT GIVEN FOV 100* 1.6MM FOV 850* : 1.6 * 100/850 = .18832MM FIT #. FOV .188M SIZE .188/21 =.0089 ,, * 1000=8.9UM FOV /FIT # .188/100 =.00188MM * 1000+1.88UM
- The micrograph below is 12,000X enlargement. Based on this, determine the actual size (length) of the dark oval specimen. 4cm = 40mm Enlargement= 4cm/12000=40mm/12000=. .00333 mm. Use the choices from #2 above to respond to the following: This specimen is _____
- Shown below is a micrograph of numerous specimens. The magnification is 55X. Based on this, determine the actual size of the circular specimens labeled A and B.
B
72.72 μm A
.254mm
Use the choices from #2 above to respond to the following: Specimen A is _____ and Specimen B is _______. A B 1.4 CM = 14mm , Enlargement : 55 4mm = 4000 um 14/55 =. Enlargement : 55 4000/55 = 72.72 mm
- The micrograph to the left is 69,000X enlargement. Based on this, determine the actual size of one of the circular specimens (like the one at the tip of the arrow). ___.362_________________ μm Use the choices from #2 above to respond to the following: This specimen is _____ 2.5cm= 25000um Enlargement = 25000/69000=.
- The micrograph to the right is 64,000X enlargement. Based on this, determine the actual size of one of the hexagonal viruses shown (like the one at the tip of the arrow). .39 nm Use the choices from #2 above to respond to the following: This specimen is _____ 2.5=.25mm=2500um Enlargement = 25000/64000=.
Eukarya and Animalia kingdom
- Imagine you are viewing a specimen directly under a microscope. Shown below are unicellular organisms called Paramecium caudatum at low power (100X total magnification). Approximately six of these organisms, such as the one at the ‘arrow’, can fit across the field. The approximate length of this cell is ____300____ μm. Show your work. 1010 = 100 (total magnification) Cac field of view of 104.5mm4.54/10* =1.8mm 1.8mm/6=.3mm*1000=300um This organism belongs to which domain and kingdom? Eukaryote and chomista kingdom
