During this course you will be learning about all levels of the human body. To understand how our bodies work, you have to not only know about large things, like organ systems and organs, but also the tiniest things, like small molecules and atoms.  As you learn about each system, you will find yourself jumping around in the levels of living things. For example, from learning about cells of that system to the organs of that system, back to tissues of that system, and then large molecules of that system.  As you jump around the levels, it is impossible to really understand each system if you can’t picture in your mind how large each item is. For example, as you learn about actin in the muscular system, you will also learn about myosin– because those interact with each other.  Their interaction can happen because they are at the same level. Actin and myosin are both proteins, which puts them in the [1] level of organization. Calcium ions are also important in the muscular system, because the presence of calcium ions triggers the actin and myosin interaction that leads to a contraction. Calcium ions are at the smallest level of organization, which is this level: [2].

You will be learning about what happens when cells come together to create a function that they cannot create alone. An example of this can be imagined when thinking about the lining of a blood vessel. One cell alone cannot create the lining of a blood vessel.  But many cells together, linking with one another through adhesion points, can create an entire inner tube that is the lining of a blood vessel. Such a group of cells would be at the [3] level of organization. The blood vessel itself, which is more than just an interior lining but also has muscle in it to help it vasoconstrict or vasodilate, is at the [4] level of organization.

Typically, students find it difficult to understand the smallest levels of organization, mainly because these are things that we can’t see but can only imagine. There are plenty of models of these items, but you can’t really view them.  Pretty much, the smallest level of organization that can be seen under the light microscope is the [5] level of organization. But in humans, that is really only ever the nucleus. Other examples of this level, like the endoplasmic reticulum or the lysosome, are still too small for viewing. You will learn more about this in lab. As for the smaller levels, the chemical levels, you will need to keep working on understanding what fits into which level as you learn more this term.  It is true that big molecules are made up by combining smaller molecules, and small molecules are built from atoms.  However, our bodies don’t tend to put individual atoms together, but to rearrange existing chemicals. One chemical that is essential in this process in our bodies is water, and water is at the [6] level of organization.

In the nervous system you will learn about astrocytes, oligodendrocytes, neurons, microglia, and other items at the [7] level of organization. Each system has many items at this level of organization.  For example, in bone you will learn about osteocytes, osteoblasts, and osteoclasts. Don’t worry that there are so many types.  You will come to understand why it is necessary to have more than one type in each system. Remember, you have to build the entire human body, which is at the [8] level of organization.  It takes a lot of components to do that and make it work properly!

In future chapters you will find some assignment questions that force you to think back to these levels of organization and apply them to specific systems. Also, there will be questions relating to this on the final. So be sure to think about each new item you learn about and figure out where to place it on this scale of items.

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