Metric units of length
Unit
Kilometer (km)
Meter (m)
Decimeter (dm)
Centimeter (cm)
Millimeter (mm)
Micrometer (μm)
Nanometer (nm)
Relationship
1 km = 103 m
Base unit
101 dm = 1m
102 cm = 1m
103 mm = 1m
106 μm = 1m
109 nm = 1m
Example
Five city blocks
Height of door knob
Large orange
Shirt button
Thickness of a five-cent coin
Diameter of bacteria
Thickness of RNA
Calculating Magnification
Magnification =
Image size
Actual object size
Calculations in Microscopy
1. Calculate the magnification of these scale bars:
Measured length = 21mm = 21,000um
Magnification = 21,000um / 67um
= 313 x
Measured length = 29mm = 29,000,000nm
Magnification = 29,000,000nm / 100nm
= 290,000 x
2. Calculate the actual size of these images:
Measured length = 43mm
Actual size = 43mm / 1,000
= 0.043mm
= 43um
Measured length = 57mm
Actual size = 57mm / 5,000
= 0.0114mm
= 11.4um
3. What would you need to do if you were only given a scale bar and asked to calculate actual
size?
Demonstrate by finding the length of this stoma in µm. Show your working.
i. Calculate magnification of scale bar
Measured length = 18mm = 18,000um
Magnification = 18,000um / 20um
= 900x
ii. Calculate actual size
Measured length = 73mm = 73,000um
Actual size = 73,000um / 900
= 81.1 um
4. a. Calculate the length of this epithelial cell.
b. Calculate the diameter of the nucleus of this cell.
i. Calculate magnification of scale bar
Measured length = 23mm = 23,000um
Magnification = 23,000um / 10um
= 2,300x
a. Length of epithelial cell
Measured length = 89mm = 89,000um
Actual length = 89,000um / 2,300
= 38.7um
b. Diameter of nucleus
Measured length = 27mm = 27,000um
Actual length = 27,000um / 2,300
= 11.7um
5. a. Calculate the diameter of the main body of this
human egg cell AND the thickness of one section of
the zona pellucida.
i. Calculate magnification of scale bar
Measured length = 18mm = 18,000um
Magnification = 18,000um / 40um
= 450x
a. Diameter of main body
Measured length = 30mm = 30,000um
Actual length = 30,000um / 450 = 66.7um
a. Thickness of zona pellucida
Measured length = 6mm = 6,000um
Actual length = 6,000um / 450 = 13.3um
6. Calculate the length of this Elodea cell. [Answer: 47.8um]
Written questions:
1. A student views an image of a cell magnified 50000 times. The image is 60mm long.
a. What is the actual length of the sample in the image?
Answer: 12um
b. Is the cell more likely to be a plant cell, animal cell, bacterium or virus? Explain why.
2. A sperm cell has a tail 50µm long. A student draws it 50mm long. What is the magnification?
Answer: 1000x