Levels of Organization Image Map

Studying Cells

In 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)
  • Oxygen (bubbled into the fluid)
  • Removal of waste gas
    (chemical reaction neutralizes it
  • Warm temperature (outer box is temperature controlled)



Cell Culture System Image









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.

Organizing Structures
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 organization.



Dog Image


Have you dissected a frog yet? If not, you can do 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 called organelles.
We can see with unaided eyes organ systems, organs, and tissues. The structure of cells can be observed with ordinary microscopes (on the right). 
Organelles are 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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