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Cells — If You Know
4
One, Do You Know
Them All?
Cross-section through human skin.
This and many other photos were made available
courtesy of Johannes Liefer.
sizes: from sperm, measuring only 2 microm-
eters, to large mucous membrane cells from the
mouth measuring 60 – 80 micrometers all the way
up to ova (egg cells) measuring a whopping 100 mi-
crometers (that's a tenth of a millimeter). If all of the cells
from your body were to be lined up in a row, they would
form a cell chain several kilometers long!
Animal Cell Design
Can you tell from looking at a cell where it came from? Indeed, because a liver cell
looks different than a skin cell or a cell from the intestinal wall. But that's not sur-
prising if you consider that every part of our body has very specialized tasks to per-
form. In fact, every part of the body generally has several tasks to perform at the
same time. For example, the skin has a number of duties to fulfill. It is our outer
wall and has to prevent undesired intruders such as pathogens or toxic substances
from penetrating onto our "grounds." After a 100 meter sprint, the skin has a
different function: It sweats and hence prevents our body from overheating. But
the skin is also one of our most important sense organs, since it tells us whether an
object is hot, cold, sharp, soft, or sticky. It's wrong, therefore, to simply say "skin
cell." As you can see in the image to the left, human skin is actually composed of
a number of different types of cells. Each cell type looks a little different than the
others, depending on what task the cell performs.
The Prototypical Animal Cell
It's very easy for you to observe cells from your own body under the micro-
scope. To do this, you will need:
a cotton swab, a slide, a cover slip, the pipette, water
First prepare a slide with a drop of water. To do this, and to learn the most
important steps when making a preparation, also read the tips in the follow-
ing box.
Use the cotton swab to rub along the inside of your cheek. When you do this,
14
It's mind-boggling when you try to
imagine that our body consists of
teensy weensy cells from our head
to our feet. After all, about 70 trillion
cells (that's a 7 with 13 zeros!) make up
our bodies along with their organs. And
there are cells in a wide variety of sizes
which are usually indicated in micrometers
(µm). A micrometer is a thousandth of a
millimeter. Human cells come in all different
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