Micrometry - A1Biology-EL

Linear measurement of cells
Units of measurement in cell study
• Millimeter (mm)
– 1mm=0.001m
• Micrometer (μm)
– 1μm=0.001mm=0.000 001m
• Nanometer (nm)
– 1nm=0.001μm=0.000 000 001m
The micrometer eyepiece
How to use it
• 1. Calibrate
– Calibration slide (0.01mm)
• 2. Set the microscope to low power and focus
on the lines engraved on the surface of the
calibration slide.
• 3. count the number of lines
– The total number of eyepiece lines (X)
– The total number of calibration slide lines (Y)
X=38 lines
Y=10 lines
note that the little lines mark
off half spaces and that the
first line is not counted
because is shows the zero
• 4. Calculate how much each line of the
eyepiece measures.
In step 3, 10/38x10μm=2.63μm
• How big is this cell?
• 5. under medium power
• X=95 lines
• Y=10 lines
• 10/95x10μm=1.05μm
How big are the cells?
• 6. Do the same for the high power. (0.26μm)
• 7. Now you can use the microscope to observe
and measure things.
Note that if you change microscopes, the calibration process
must be done again for each of the objective lenses that you
are using. Why? Because the magnification is different on
different microscopes. To save time, only calibrate the
eyepiece for the objective lenses that you will be using.
More examples:
• A tomato cell's nucleus seen at high power.
How big is the nucleus?
• An onion skin at high power. How big is a
typical nucleus?
• A banana cell at high power. How big are the
starch grains?