order for us to study how cells work, it helps to be able to grow
them as a culture.
The picture on the right shows a modern system for culturing
cells. This machine has many hollow tubes in parallel (pink
area). Cells attach to the tube lining, and are bathed in a
fluid that is slowly pumped through the tubes.
A culture system needs several things
to keep cells alive:
- Fresh nutrient supply (chemicals
put in the fluid)
(bubbled into the fluid)
- Removal of waste gas
reaction neutralizes it
- Warm temperature (outer box is
Translucent door of this indubator is raised to show the
"plumbing." Tube on the left carries nutrient fluid into a
chamber filled with many hollow core cylinders (like straws)
where the cells cling. Tube on the right returns the fluid
to an oxygenator.
|When you first look at an animal,
you see the whole animal. But it has parts that make it up.
What you don't see is that it is made up of many parts and levels of
|Have you dissected a frog yet? If not, you can
a dissection on the Web. Such dissections show that there
are different levels of structure: whole animal, organ system,
organ, and tissue levels. You see different organs: brain,
lungs, stomach, intestines, muscles, and so on.
If you take any organ from its
system, cut into thin slices, stain it, and look at it through
a microscope, you can view different types of tissues.
For example, if you cut through the lungs, you would see thin
layers of cells lining the airspaces (epithelium), small muscle
cells surrounding air ducts (smooth muscle tissue), blood
(blood is a tissue), flat sheets that hold things together
(connective tissue), and nerve fibers (nervous tissue).
|With still more magnification, you see that every
tissue has multiple small parts that look alike. These are the
cells. Cells are intact units that are surrounded by membranes.
A given organ may have several kinds of cells, as mentioned above
for lungs. Inside each cell, there are other, even smaller structures
|We can see with unaided eyes organ
and tissues. The
structure of cells can be observed with ordinary microscopes (on
best seen with more powerful scopes, such as electron
microscopes. On the left, U.S. Department of Agriculture
scientists operate a "scanning" electron microscope, which
produces a 3-D view of very small structures.
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