p. 1 of 6
MICROSCOPES AND CELLS
Bring a living (or previously living) specimen with you to this lab!
Goals:
• View microscopic features of living organisms and associate those features with the properties of life.
• Understand the size ranges of objects viewed with the microscope.
• Distinguish between the cells of animals, plants, and protists.
Review before you begin:
• The seven properties shared by all living organisms.
• Differences between cells of prokaryotes and eukaryotes.
• Differences between cells of plants and animals.
• The metric scale and the size ranges of different types of cells.
Introduction
Due to their small size, cells must be viewed with a microscope. You are probably familiar with objects
the size of a meter (m), centimeter (cm), or millimeter (mm). A tall man that is 2 m is also 200 cm or
2000 mm, because 1 m has 100 cm or 1000 mm. Although 1 mm appears small to our eyes, it is still
much larger than a cell. Most animal and plant cells are between 0.01 – 0.1 mm. That means that
etween XXXXXXXXXXanimal or plant cells could line up end-to-end within a single millimeter. Bacterial cells
are even smaller- about a thousand typical bacterial cells could fit within 1 mm.*
Light microscopes, such as those you will use in lab today, can be used to see objects as small as animal,
plant, or even bacterial cells. Light microscopes pass light though magnifying lenses in order to make
specimens appear larger. To see objects smaller than bacterial cells, like viruses or small cellular
components such as ribosomes, scientists use an electron microscope. Viruses and ribosomes are so small
that 10,000-100,000 could fit within 1 mm! Electron microscopes bounce electrons off of objects to
produce an image of much more detail than is possible to visualize with light.
You will view several types of cells with the light microscope today. Animals, plants, fungi, and protists
have eukaryotic cells. Eukaryotic cells organize their components within compartments called organelles.
For example, DNA is held within the nucleus organelle. In plant cells, photosynthesis is conducted
within the chloroplast organelle. Bacteria and archaea have prokaryotic cells. Prokaryotic cells lack
organelles and are usually much smaller than eukaryotic cells.
*Objects smaller than 1 mm are measured in micrometers (µm) or nanometers (nm).
1 mm = 1000 µm = 1,000,000 nm
The microscopes are very expensive and must be cared for properly! Some important rules:
1. Use the microscope co
esponding to the number on your desk and be sure to return it to the co
ectly
numbered cu
y.
2. Ca
y the microscope with one hand on the arm and your other hand under the base of the
microscope.
3. Only special lens paper can be used to clean the eyepiece or any microscope lens. NEVER use a
tissue, your shirt, or anything else. If your scope or a lens seems dirty, ask your instructor for help.
4. Always cover a specimen with a cover slip before placing the slide onto the microscope stage.
5. Do not tilt or slide the microscope once you have plugged it in and turned it on.
6. Do not force knobs past their stopping points or try to remove any microscope part.
7. Report any malfunctions or missing pieces immediately.
Microscope p. 2 of 6
COMPOUND LIGHT MICROSCOPE
Getting started:
1. Use the coarse focus (outer knob) to lower the stage as much as possible.
2. Prepare your slide and place it on the stage, secured by the stage clip.
3. Use the stage control knobs to center the specimen over the light source.
4. Adjust the distance between the eyepiece lenses to fit your eyes (the lenses are adjusted co
ectly
when you see one circle of light through the microscope and not two).
Focusing an image:
1. Begin with the 4x (lowest power and shortest) objective lens clicked into place.
2. Turn the coarse focus (outer knob) to minimize the distance between the stage and objective lenses.
3. While looking through the eyepieces, slowly turn the coarse focus knob until your specimen comes
into view.
4. Further adjust the focus with the fine focus (inner knob).
5. Switch to the 10x objective and further adjust the focus with the fine focus knob.
6. To see further detail, switch to the 45x (may be 40x on some scopes) objective and fine-tune the focus
with the fine focus knob. When the 40x or 45x objective lens is clicked into place, use ONLY the
fine focus knob to adjust focus.
7. Do not use the 100x objective- it requires oil, which is too advanced for today’s activity.
8. As you increase magnification, you will need to use the light control knob to increase light.
9. You may also need to adjust the contrast. Open and close the diaphragm level that is underneath the
stage to practice adjusting the contrast.
Putting scope away:
1. Click the 4x objective (shortest objective) back into place.
2. Turn the coarse focus (outer knob) to maximize the distance between the stage and objective lenses.
3. Remove your slide and dispose of it in the used slide disposal beaker.
4. ASK YOUR INSTRUCTOR TO CHECK THAT YOUR SCOPE IS READY TO PUT AWAY.
5. Put the dust cover on the scope (if available) and return to the appropriately numbered cu
y.
Eyepiece lenses
(usually magnify 10x)
Arm (to ca
y
microscope)
Coarse focus- outer,
larger knob (use to
adjust focus with 4x
or 10x obj.)
Fine focus- inner,
smaller knob (use to
adjust focus with 40x
or 100x obj.)
Diaphragm lever (open or
close to adjust contrast)
Stage (where slide
is placed)
Stage Clip (holds slide in place)
Objective lenses
(magnify 4x, 10x,
45x, or 100x)
Nosepiece (rotate to click
objective lenses into place)
Stage control knobs
(use to move position
of slide)
Light control knob
(adjust amount of
light)
Microscope p. 3 of 6
DISSECTING LIGHT MICROSCOPE (STEREOMICROSCOPE)
Use to view larger, whole organisms in three dimensions.
Instructions for use:
1. Obtain the appropriately numbered stereomicroscope and a light source.
2. Position the light so that it shines upon the center portion of the microscope staging area.
3. Place your specimen onto the microscope staging area. (If necessary, place into a plastic dish to keep
the staging area clean.)
4. Adjust the distance between the eyepiece lenses to fit your eyes (the lenses are adjusted co
ectly
when you see one circle of light through the microscope and not two).
5. Start by turning the magnification knob to its lowest setting, at 1.
6. Use the focusing knob to
ing the object into focus.
7. While observing your object, turn the magnification knob to slowly increase magnification.
When finished, return the microscope and light source into the co
ectly numbered cu
y.
EXERCISE 1: MAGNIFICATION AND RELATIVE CELL SIZE.
Total magnification is calculated by multiplying the magnification of eyepiece lenses x the magnification
of the objective lenses. The eyepiece lenses on your scope magnify 10x. The objective lenses magnify
4x, 10x, 40x (or 45x), and 100x.
You will mostly use the 4x and 10x objectives today. If the 4x objective is clicked into place, the total
magnification is 40 times (40x). What is the total magnification when using the 10x obj.? .........................
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If 10 cells fit end-to-end across 1 mm, what is the length of each cell? Show your work or explain how
you determined the answer. .............................................................................................................................
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