Chapter 2. DIVERSITY I—BACTERIA, ARCHAEA, PROTISTA

Learning Objectives

Pre-Lab—Diversity Overview
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General Purpose

Conceptual

  • Be able to compare and contrast the diversity within the domains Bacteria, Archaea, and Eukarya.
  • Be able to describe the major evolutionary trends in each kingdom.
  • Be able to describe the important structures and lifestyle differences in each major group.

Background Information

The diversity of organisms studied in biology can be overwhelming. That’s why biologists use phylogenetics to organize their knowledge. Grouping organisms by evolutionary trends provides a framework to remember the domains, kingdoms, and phyla (or divisions) studied. Given the characteristics of a species, a scientist can place it in the correct domain, kingdom, and phylum (or division). The diversity that we see today is the outcome of the evolutionary process and therefore can be arranged in a phylogenetic classification.

The first characteristics used by scientists separate organisms into three domains reflecting fundamental differences at the cellular level.

Figure 9-1. The three domains showing their phylogenetic relationship.

Bacteria and Archaea are single-celled organisms that lack intracellular structures. In fact, until molecular biology techniques became common, it was not possible to differentiate between the two domains because microscopically they look alike. Domain Bacteria and Archaea have fundamental differences at the molecular level including how the DNA is organized. Eukarya have intracellular structures that are visible microscopically that distinguish them from both Bacteria and Archaea. Surprisingly, even though the Archaea look much more like Bacteria under the microscope, they are more closely related to Eukarya.

Each of the individual domains can be further subdivided into smaller more specific subgroups. These subdivisions utilize more characteristics to further classify and define the subgroupings. The major group right below the domain level in the hierarchy is a group referred to as kingdom.

To understand more of how the diversity of life is organized and for further description of the characteristics used to produce the subdivisions view the following video:

Pre-Lab Quiz

Proceed to the Pre-Lab Quiz