MODULE #1: Biology: The Study of Life
Biological Keys
If a discussion of all groups in our classification system is prohibitively long, how will we ever be able to classify organisms? In order to classify organisms, biologists often refer to biological keys. These keys help you to classify organisms without having to memorize the characteristics of all groups within the classification scheme. A simple biological key is given below. It also is given in Appendix A in the “Back o' the Book“ section at the end of this course.
Now don't get overwhelmed by this key. It is actually quite simple to use once you are led through it. You see, a biological key is just a series of questions that you can answer by looking at the major features of the organism you are studying. Based on the answer to a question, you are led to other questions until you eventually run out of questions. At that point, you have classified the organism as well as the biological key allows. For example, consider the elephants shown below.
Click to hear Dr. Jay use the biological key
To classify any organism (including an elephant), you would just start at the top of the key. When you answer the question, you proceed to the number that follows that characteristic. You continue to do this until you reach a classification that is not followed by a number.
So, we start at the top of the key. Key 1 asks about size. Since we don't need to magnify an elephant in order to see it, the elephant is macroscopic. This means that we move to key 3, because a “3” follows the term macroscopic. In key 3, we are asked whether or not the elephant is autotrophic (uses photosynthesis to make food) or heterotrophic (eats other organisms). Clearly, the elephant is heterotrophic; it eats plants in order to live. This means we move to key 5, where we need to determine whether it is a decomposer or a consumer. Since the elephant eats plants, it is a consumer. That tells us that our first classification is kingdom Animalia.
Now of course, this should be no surprise. An elephant is an animal. The key also tells us to move on to key 6 for a more detailed classification. Here, we determine whether or not it has a backbone. Now from the picture, you might not be able to tell, but all you have to do is think. Have you seen pictures or movies of people riding on elephants' backs or elephants carrying heavy loads on their backs? They must have a backbone to do that, so we learn that the elephant is in phylum Chordata
(kor dah' tuh), and we move on to key 22.
Key 22 asks if the animal has a jaw or beak. Since the elephant's mouth opens and closes up and down, it has a jaw. Thus, we move to key 23, which asks if there are scales on the skin. There are not, so we move to key 26. This key asks about hair or feathers. The picture on the right shows hair on the head. Thus, we move to key 28, which distinguishes between hair and feathers. Based on that distinction, we learn that the elephant is in class Mammalia, and we move to key 29.
In key 29, we must decide whether or not the elephant has hooves. Looking at the picture on the left, the feet have skin all the way to the bottom, so there are no hooves. This means we go to key 31, which asks whether the elephant is a herbivore or carnivore. Although not readily apparent from the picture, you should probably already know that elephants eat plants, making them herbivores. That means we move to key 33, which asks about teeth. There are certainly no enlarged teeth apparent in the picture on the right, so we move to key 35. In this key, we are asked whether there is an enlarged trunk. Yes, there is. Thus, we know that the elephant is in order Proboscidea (pro' boh sid' ee uh). This is as detailed a classification as we can make with this key. As far as this key is concerned, then, the elephant classification is:
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Proboscidea
Note that in the case of the elephant, we went all the way to the end of the key. This will rarely be the case. You continue on in the key until you run out of numbers. At that point, you have as detailed a classification as is possible with that key. Take your own turn at classification by performing Experiment 1.1.