Lesson 1: Biodiversity and Classification

Preview of Chapter

Biodiversity and classification are fundamental concepts in biology that provide insight into the vast array of life forms on Earth and their evolutionary relationships. Biodiversity itself refers to “a large collection of life of different forms.”

What We Will Study:

This chapter will help us understand the incredible diversity of life and the systematic ways biologists make sense of it.

1.1 – Three-Domain System of Classification

Five-Kingdom Classification System by Robert Whittaker (1969)

According to the five-kingdom classification system, proposed by American ecologist Robert Whittaker in 1969, all organisms were divided into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.

• The kingdom Monera included prokaryotes (organisms without a membrane-bound nucleus).
• The other four kingdoms (Protista, Fungi, Plantae, and Animalia) included eukaryotes (organisms with a membrane-bound nucleus).

The evolutionary relationship among organisms is called phylogeny. A diagram used to show phylogeny is called a phylogenetic or evolutionary tree.

Three-Domain System of Classification by Carl Woese (1990)

In 1990, American microbiologist Carl Woese suggested that there are two separate groups of prokaryotes: Archaea and Bacteria. Based on this, he classified living organisms into three domains:

1. Domain Archaea
2. Domain Bacteria
3. Domain Eukarya

According to his three-domain system:

• Domain Archaea and Domain Bacteria contain prokaryotes, but they differ in a number of features.
• Biologists now believe that Archaea and Bacteria evolved independently from some common ancestor.
• Molecular evidence suggests that Archaea are more closely related to Eukarya than to Bacteria. In other words, Eukarya evolved from Archaea, after Archaea split off from the Bacteria.

Interactive Tree of Life: Explore Classification Systems

Domain Archaea

In the five-kingdom system, Archaea were included within the kingdom Monera. However, they possess unique characteristics that differentiate them.

• The name Archaea comes from the Greek word archaios (“ancient”), reflecting their early divergence.
• They are prokaryotes that diverged from bacteria in very ancient times.
• Individual archaeans range from 0.1 μm to over 15 μm in diameter; some form aggregates or filaments up to 200 μm in length.
• They occur in various shapes, such as spherical, rod-shape, spiral, lobed, or rectangular.

Reproduction in Archaea:

• Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding.
• Mitosis and meiosis do not occur in Archaea, typical of prokaryotes.

How Are Archaea Unique? (Interactive Feature Comparison)

Archaea exhibit several unique features that distinguish them from Bacteria and Eukarya. Explore them below:

Significance of Archaea (Interactive Showcases)

Despite their small size, Archaea play crucial roles in various environments and have significant applications:

Major Groups of Archaea (Interactive Explorer)

Archaea are diverse and categorized into several major groups based on their characteristics and habitats: