MODULE #1: Biology: The Study of Life
Biological Classification
Now that we've spent considerable time on the limitations of science, it's time to turn our attention to some of the strengths of science. Classification is probably one of the greatest accomplishments of science. In the study of biology, we uncover many, many facts. For example, there are many, many organisms on the earth, and they have many, many properties and characteristics. Some of their characteristics they have in common with other organisms, and some of their characteristics are unique. All of these facts make up a huge volume of data that, by itself, would be hard to understand and virtually impossible to use. Much like we have split this book into modules and have further split the modules into sections, “On Your Own” questions, study guides, and tests, we need to take all of the data in biology and split them up into an organized system.
Now there are many different classification systems in biology. You have already seen that all organisms can be split into three groups: producers, consumers, and decomposers. You have also seen that we can split most consumers into herbivores, carnivores, and omnivores. Those classification systems were rather simple. They took many, many different organisms and lumped them into only a few groups. Now we need to get more detailed. We need to learn a classification system that takes all organisms and splits them into several groups. The number of groups that we split the organisms into must be large enough so that we are not grouping incredibly different organisms into the same group. At the same time, however, there cannot be too many groups, because the classification system must make the data easier to understand than they were originally. With too many groups, the classification system becomes almost as complex as the data themselves.
The classification system that we will use most frequently is multi-level. It starts by splitting up all organisms into five different groups known as kingdoms. The organisms within each kingdom can then be further divided into different groups called phyla
(fye' luh), the singular of which is phylum (fye' lum). Each phylum can be further divided into classes, which can be further divided into orders. Within an order, organisms can be divided into families, which can be further divided into genera (jon' ur uh), the singular of which is genus (jee' nus), which can finally be broken down into species. This multi-level (often called “hierarchical”) classification scheme is summarized in the figure below. The specific classification of a bald eagle is given in parentheses so that you can see how the classification scheme is used for a particular organism.
To make sure that you can remember the names and orders of this classification system, you can use the following mnemonic:
Since the first letter of each word in this sentence can stand for a group in our classification system, you can use it to remember the order in which we place these groups. It is important to note that the classification of organisms is so complicated that we often split these groups into subgroups. Thus, do not be confused if you run across a term like “subphylum.” A subphylum is simply used to split organisms in a phylum into smaller groups before they are split into classes. There are also subclasses, suborders, and subfamilies. Another issue to remember is that some classification schemes use “division” instead of “phylum” for certain kingdoms. Although we will not do that, you need to be aware that others might.
Now that we know the groups and their respective orders, it's time to see how we use this system to classify organisms in nature. As we mentioned before, we generally split all of the organisms in nature into five separate kingdoms. The names of these kingdoms are Monera (muh nihr' uh), Protista (pro tee' stuh), Fungi (fun' jye), Plantae, and Animalia. The proper names of all our classification groups are Latin, and when we use those names, we capitalize them to emphasize that these are proper classification names.
How do we know what organisms go into what kingdom? Well, we group organisms together based on similar characteristics. Since the first step in classification deals with placing organisms in kingdoms, the common characteristics that organisms in the same kingdom share are pretty basic. You will learn about that in the next section.