Intro to Microscopes and Onion Cell Plasmolysis
Purpose:
The objectives of this lab are to:
●​ Introduce you to using a microscope
●​ Give you a sense of the size of cells
●​ Help you estimate the size of real
cells, AND
●​ Identify particular structures in
eukaryotic cells
For Reference:
1 m = 1000 mm (millimeters)
1 mm = 1000 µm (micrometers)
1 µm = 1000 nm (nanometers)
Label: eyepiece, objective lens, coarse & fine
focus, light source, stage, & diaphragm
Red onion cell plasmolysis
Prepare one red onion skin slides as demonstrated. Remember to peel off the red epidermal
layer and place flat on the slide.
Put two drops of distilled water on the onion epidermal cells, and then place the coverslip over
it.
Focus on the cells starting at 40x, then 100x, and finally at 400x. In your notebook, make a
sketch of one cell at the final magnification. Label the cell wall and cell membrane, and
title your drawing.
Taking care not to move the coverslip too much, place a small paper towel at one edge of the
cover slip, and add NaCl water to the other edge. This should flush the cell with NaCl water.
Wait a minute, and then make a sketch of the onion cell. Label the cell wall and cell
membrane, and title your drawing.
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Part A: A Sense of Scale
1. Place the mm side of your ruler on the stage of the microscope (above the light) and on the
lowest setting (40x), focus in on the mm divisions.
a. Estimate how many mm fit across the field of view. ______
b. Determine how many µm this is. ______
2. Change the objective to (100x), focus in on the mm divisions.
a. Estimate how many mm fit across the field of view. ______
b. Determine how many µm this is (is it = 40% the diameter of the 40x f.o.v?). ______
3. INFER – if you were to change the objective to (400x) - (you will not be able to see this…so
you have to infer with a calculation)
a. Estimate how many mm would fit across the field of view. ______
b. Determine how many µm this is (is it = 25% the diameter of the 100x f.o.v?). ______
Part B: Cell size problems
1. If 10 cells fit across the diameter of the field of view at 40x – how large is each cell in µm?
2. If 10 cells fit across the diameter of the field of view at 100x – how large is each cell in µm?
3. If 10 cells fit across the diameter of the field of view at 400x – how large is each cell in µm?
What if it is 8 cells?​ ​
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12 cells?
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