Cracking the AP Biology Exam

9

Diversity of Organisms

HOW CLASSIFICATION WORKS

The order of classification from fewest to most characteristics in common is:

Notice that as we move down the list, we find that organisms have more and more in common. Consequently, each step down the scale includes fewer and fewer members. The domain is the biggest group, and includes the greatest number of members, while the species is the smallest group, and counts the fewest members. Moreover, organisms in the same phylum have more in common than those in the same kingdom. Those in the same class have more in common than those in the same phylum, and so on. This means that as we move from top to bottom, we go from “less in common” to “more in common.”

NAMING NAMES

The binomial classification system was developed by Carolus Linnaeus. By binomial, we simply mean that all organisms are given scientific names consisting of a genus name and a species name, often in Latin. For example, we humans are called Homo sapiens. Homo is our genus name, and sapiens is our species name. Homo means “man” and sapiens means “wise.”

For the AP Biology Exam, you should memorize the order of classification. Do you remember the mnemonic we saw in Chapter 1?

King Philip of Germany decided to walk to America. What do you think happened?

Dumb

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Domain

King

-

Kingdom

Philip

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Phylum

Came

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Class

Over

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Order

From

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Family

Germany

-

Genus

Soaked

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Species

THE NITTY GRITTY OF CLASSIFICATION

Now that we’ve discussed the classification scheme, let’s take a closer look at how organisms are actually ordered into various levels. We’ll start with the kingdoms. All organisms belong to one of six kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

You should know, however, that many biologists now use a new level of classification above the kingdom—the domain. There are three domains: Archaea (which corresponds to Archaeabacteria), Bacteria (which corresponds to Eubacteria) and Eukarya (the remaining four kingdoms, or all of the eukaryotes). Archaebacteria are considered among the most primitive types of organisms known. Archaebacteria are placed into a separate domain because they have significant molecular and biochemical differences when compared to Eubacteria. Furthermore, gene sequencing has led scientists to believe that Archaebacteria are more closely related to Eukaryotes, hinting they are descendants from a common ancestor. Eukarya later split from the Archaeabacteria.

Here’s a quick summary of the kingdoms along with some of the principal characteristics you’ll need to know for the AP Test.