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Cross-section through the stalk of a sunflower
This is how the onion skin is prepared.
TIP
When preparing slides, very sharp
cutting tools are important. But
in order to ensure that you just
cut the object of study and not
your finger, you should prepare
the razor blade appropriately with
insulating tape or a cork. Follow
the advice on page 11 and have an
adult help you.
Onion skin cells
at crime scenes (skin cells or blood residues of the culprit, for example, which also
contain DNA) with the DNA of possible perpetrators. To do this, the police obtain
DNA for comparison from the mucous membrane skin cells in the mouths of the
suspects.
Are your mucous membrane skin cells different from those of your parents? Are
the cells of older and, above all, larger organisms larger too, perhaps? Or does
your father simply have more cells? The prepared slide labeled "Mouth mucous
membrane skin cells" from your microscope set is the red-stained smear from an
adult's mouth. There, it is particularly easy to see the cell nuclei. So you can com-
pare your mouth mucous membrane skin cells with those of an adult and answer
the question yourself!
It Depends on the Function
Now you've become acquainted with a typical example of an animal cell. So do
plant cells look different, or what?
That brings us back to the elephant and the carrot from the introduction. What
differences are there between an elephant cell and a carrot cell? As you already
learned, there is actually no such thing as an "elephant cell." And there is of
course no such thing as a "plant cell," either. Just like the cells in our bodies, the
cells of a plant must also carry out a wide variety of tasks. With some practice that
you can acquire by using the objects presented in these instructions, it is often pos-
sible to determine the function of a plant cell just by its appearance.
In the figure, you can see a cross-section through the stalk of a sunflower. Even in
this small section, it becomes clear how many different kinds of cells a plant can be
made of. You'll encounter several of these cell types later on. In the next object,
you can see several examples of typical plant cells. By the way, the slide prepara-
tion, which you can easily prepare using the following description, is also included
as a stained prepared slide in your microscope set. You will find a description of
this permanent preparation in Chapter 16.
Onion Cells
Onion cells are good examples of typical plant cells that can be obtained very
easily for observation under the microscope. For this, you will need:
• a slide and a cover slip
• the pipette and water
• a quarter of a cooking onion
• a razor blade (see page 11)
• the tweezers
Peel the onion and take one of the outer layers. Using the razor blade, care-
fully cut a checkered pattern on the inside of this layer of onion. Now, us-
ing the tweezers, you can peel a square piece of tissue quite easily from the
sample. The little piece of tissue detaches from the tweezers almost on its own
if you dip it into the water drop on your slide. Now place a cover slip on it
so that there are no bubbles (cf. box on page 13). Now look at your prepara-
tion under the microscope, first under low magnification and then under the
higher magnifications. If you are unable to make out a clear cell pattern, your
piece of onion tissue may be too thick.
In addition to the fact that the cells of the onion skin, with a length of 400
micrometers, are larger than the cells of the mucous membrane skin from your
mouth, another important difference between plant and animal cells becomes
apparent: They are clearly shaped differently. While the cells of the mucous mem-
brane skin from your mouth are irregularly shaped blobs and covered with lots of
recesses and protrusions, the cells of the onion skin look like small, pointed bricks.
Is this a coincidence simply due to the two examples we have selected? You'll find
the answer to this and many other questions regarding the differences between
plant and animal cells in the next chapter.
16
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