Chapter 2. DIVERSITY I—BACTERIA, ARCHAEA, PROTISTA

Learning Objectives

Pre-Lab—Microbes 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.

Procedural

  • Be able to describe and recognize bacterial shapes.

General Purpose

This laboratory is designed to introduce you to three major groups of organisms that are extant today. The three groups are Bacteria, Archaea and Protista. Two of these groups Bacteria and Archaea are domain level groupings and the third Protista is currently a kingdom level category. These three groups have many differences that set them apart. There is, however, one similarity that is the main reason they are covered together. They are all organisms that are single-celled organisms (though some Protists live in colonies), which is why these organisms are sometimes referred to as microorganisms or microbes. Because single cells in general are very small, many of the observations for these organisms require the use of a microscope.

BE SURE TO READ AND VIEW THE INFORMATION IN THE MICROSCOPY PRE-LAB BEFORE USING THE MICROSCOPE IN LAB.

For each of the different groups you should focus on the major trends and characteristics of the organisms within the group.

The organisms that comprise the domains Bacteria and Archaea were once classified in a single kingdom known as Monera. Organisms in both domains have prokaryotic (also spelled procaryotic) cell types. Comparisons of the molecular components of these organisms (including the arrangement of the genes in their DNA) had revealed that the Archaea are more similar to organisms within the domain Eukarya than they are organisms in the domain Bacteria (Figure 9-2).

Figure 9-2. The three domains showing their phylogenetic relationship.

Even though members of the Bacteria and Archaea are classified in different domains there are many similarities between them in terms of basic cell structure and morphology. The members of these domains are largely unicellular and feature prokaryotic cell structure. These cells lack most membrane-bound structures such as a nucleus, mitochondria, and chloroplasts. Since prokaryotic organisms lack a true nucleus, they do not undergo cell division using mitosis or meiosis. Cell division in prokaryotes occurs through a mechanism known as binary fission.

Although the prokaryotes are often thought of as primitive or simple organisms, the Bacteria and Archaea display a tremendous diversity in metabolic and nutritional pathways.

Many of the organisms of the domain Archaea inhabit some of the most extreme environments on Earth. Some of these extremophile species, as they are sometimes termed, can be found in hot springs, high salt environments, and in habitats with no oxygen (Figure 9-3).

Figure 9-3. Photo of a hot spring where thermophilic Archaeans are growing in large numbers.

There are also many Archaea species that are now frequently being discovered in less extreme environments. These species may have been overlooked because Archaea and Bacteria species are often indistinguishable from one another when using simple morphology.

Molecular biology techniques are able to discern Bacteria from Archaea and have shown that Archaea are more closely related to Eukarya (Figure 9-2). As the techniques of molecular biology have become more widely used, the discovery of more species of Archaeans has occurred and will likely continue.

Unlike Bacteria and Archaea, Protists are eukaryotic and therefore are members of Domain Eukarya. Protists are unicellular but they may also live as filamentous and colonial organisms. Historically the arrangement and placement of organisms that are members of Kingdom Protista has changed a number of times. One way this group can be organized is based on their mode of nutrition. The heterotrophic protists ingest their food primarily by phagocytosis (the uptake of large particles or whole organisms by the pinching inward of the plasma membrane). The photosynthetic protists include all algae, except the green algae (these are now included with the plants). The third category of nutrition includes the fungus-like slime molds that obtain their nutrition by absorbing nutrients from decomposing organic matter.

Because of time and availability the number and types of organisms from each group you will examine in the laboratory will vary.

Please view the following video for more information about the Bacteria, Archaea, and Protista:

Pre-Lab Quiz

Proceed to the Pre-Lab Quiz