THE STUDY OF CELLS: DO NOT WRITE ON THIS
Purpose:
1. To examine cells and become familiar with their common structures
2. Compare and contrast the features of animal and plant cells
3. Proficiency in the use of the compound microscope
Introduction:
The cell is the basic unit of life and the individual part of which the whole organism is composed. Many
of the substances in a cell are organized into specific organelles. In this investigation you will be able to see
some of these organelles as they exist in animal and plant cells.
When Robert Hooke first observed cells almost 400 years ago, he saw only the cell walls of what were
once living cells that came from cork tissue. You may not know it, but the cork that is used in bottles and to
make bulletin boards does come from a species of tree. However, what you see are the compressed remains of
cells, which is a good example of how strong cell walls are. Even in a “dead” state, they remain for years before
they decompose. Refer to the upper corner of page 12 in the LIFE books to see what Hooke saw.
PART 1: CELLS OF THE ELODEA LEAF
Since plants are stationary and lack a skeletal system, it makes sense that their cells should have rigid
cell walls for support. The Elodea plant is an ideal specimen for observing the cell wall in plants and the
chloroplasts which contain chlorophyll, the pigment that
makes photosynthesis possible. It’s also a good example for
demonstrating basic microscope technique because of the
relative ease in finding cells.
Procedure and Observations:
Remove a fresh leaf from and Elodea plant. Hold the
leaf in your hand for a minute to warm it (this will get the
chloroplasts to swirl around within the cytoplasm which is
pretty cool). Prepare a wet mount of the whole leaf by placing
it in the center of a glass slide. Add one or two drops of water
and a coverslip according to the procedure discussed in class.
Find a good section of cells with the LOW power lens, (the red 4X one). Use your eye to do this first,
NO CAMERA. Move up to the mid power lens, and refocus. Finally, move up the highest power (the blue lens)
and refocus.
Now, place the camera on the eyepiece and take a picture of a group of cells under HIGH power (the
yellow 40X lens). This gives you a total magnification of 400X. Calibrate the software according to step 4 on
your Motic camera handout.
Measure the length and width of the smallest and largest cell you see in the field of vision. Label the
cell wall, and chloroplasts. Include what magnification the cells were pictured at. Put the picture, labeled
structures and total magnification in a Word document.
PART 2: ONION EPIDERMAL CELLS
The epidermis or “skin” of an onion is an ideal subject for the study of cells because it is composed of a
single layer of cells and you can distinguish several individual organelles. Remember, you are looking into
functioning units of living material!
Procedure and Observations
Obtain a section of an onion from me. This specimen is interesting because it is only one cell layer
thick, and is transparent. Apply a single drop of IODINE to the specimen and apply a coverslip according to the
procedure discussed in class. The iodine is absorbed by the cell to make certain structures more visible.
(CAUTION: Avoid wrinkling the tissue. Doing so will cause the cell layers to “accordion” on top of one
another). The iodine should make the cell wall and cell membrane visible. The nucleus is the auburn
structure and the nucleolus is visible inside the nucleus.
Find a good section of cells with the LOW power lens (the
red 4X one). Use your eye to do this first, NO CAMERA. Move
up to the mid power lens, and refocus. Now, place the camera on
the eyepiece and take a picture of a group of cells under MIDDLE
power (the yellow10X lens). This gives you a total magnification
of 100X. Calibrate the software according to step 4 on your Motic
camera handout.
Measure the length and width of the smallest and largest
cell you see in the field of vision. Label the cell wall, and
nucleus. Include what magnification the cells were pictured at.
Put the picture, labeled structures and total magnification in a
Word document.
For Your Information… The small dark spots in the cytoplasm are vacuoles, containing compounds
that gives the onion its odor. When an onion is peeled and the cell membranes are broken, these compounds
spread into the air and are picked up by cells in your nose. These cells communicate with the olfactory lobes in
the brain and you “smell” it. These potent compounds also initiate a reaction from the lacrimal glands in the
corner of your eyes and tears are produced as a response to an irritation of the cornea (the surface of the eye) by
these compounds.
PART 3: CELLS OF TOMATO PULP
In this part, you will examine the cells of a tomato from a
pulp mixture. These cells are characteristically thin walled, very
large and mostly circular as opposed to the rectangular shape of the
Elodea cells and the diamond shaped cells of the onion. In addition
these cells contain structures called chromoplasts. Chromoplasts
are similar to chloroplasts but they can contain a variety of
different pigments other than green.
Procedure and Observations:
Place one or two drops of tomato pulp on the center of a
glass slide and apply a coverslip according to the procedure discussed in class. Position the specimen over the
center of the lighted portion of the stage. You may have to move the slide around with your fingers a little.
Position the specimen so it is in the center of the field of vision. Examine the cells under low power (4X). Set
the diaphragm to #1. Too much light coming through the stage will make these cells invisible to the eye.
Find a good section of cells with the LOW power lens (the red 4X one). Use your eye to do this first, NO
CAMERA. Now, place the camera on the eyepiece and take a picture of a group of cells under LOW power.
This gives you a total magnification of 40X. Calibrate the software according to step 4 on your Motic camera
handout. Measure the length and width of the smallest and largest cell you see in the field of vision). Label the
cell wall. Include what magnification the cells were pictured at. Put the picture, labeled structures and total
magnification in a Word document.
PART 4: STUDY OF HUMAN CHEEK CELLS
In this observation, you will see a typical animal cell (yes, you are an animal!) and how it is different from a
plant cell.
Procedure and Observations:
Gently scrape the inside of your cheek with a
toothpick. Smear the material on the center of a glass slide
in a circular motion about the size of a dime. Add one small
drop of METHYLENE BLUE. Apply a coverslip according
to the procedure discussed in class. The methylene blue is
used to make the cell membrane and nucleus stand out and
be more visible. BE CAREFUL. THIS WILL STAIN YOUR
CLOTHES!
Note the irregular shape of the cells; not quite square and not
quite circular. The cells may appear in clumps or individually.
This was the purpose of spreading out the specimen. Just this
tiny scraping contains hundreds of cells. Ideally, you want to find a single cell.
Find a good section of cells with the LOW power lens (the red 4X one). Use your eye to do this first, NO
CAMERA. Move up to the mid power lens, and refocus. Finally, move up the highest power (the blue lens) and
refocus.
Now, place the camera on the eyepiece and take a picture of a group of cells under HIGH power (the
yellow 40X lens). This gives you a total magnification of 400X. Calibrate the software according to step 4 on
your Motic camera handout.
Measure the length and width of the smallest and largest cell you see in the field of vision). Label the
cell membrane, and nucleus. Include what magnification the cells were pictured at. Put the picture, labeled
structures and total magnification in a Word document.
CONCLUSION:
This lab demonstrated, through direct observation, that living things are composed of smaller units not
visible to the naked eye. It also allowed you to see how the compound microscope is used to see the detail of
these smaller units called cells.
You learned how to apply the micron as a unit of measurement, and how to measure the size of cells
using a digital camera; noting that not all cells are the same size. In addition, cell shape varies greatly and these
four specimens only show a fraction of this variety.
Finally, you should be aware that although the compound microscope can offer a glimpse into the
microworld, we have much more powerful, electron microscopes that provide scientists with much more detail.
These details provide an in depth study of structure and function of living things as well as non living things
which may affect your life in ways you are completely unaware of.