3.4: Biological Diversity

Learning Objectives

• Recognize the characteristics of life
• Discuss the difference between a virus, viroid, prion, and a living cell.
• Describe the mechanisms of viral infection.
• Describe the distinguishing characteristics of organisms within Bacteria, Archaea, and Eukaryota
• Compare and contrast the variety of organisms within Protista
• Describe the characteristics of the Fungi, Plantae, and Animalia

In this section, the diversity of life is explored with a detailed study of various organisms and a discussion of emerging phylogenetic relationships. This unit moves from viruses to living organisms like bacteria, discusses the organisms formerly grouped as protists, and devotes multiple chapters to plant and animal life.

• 3.4.1: Acellular Entities - Viruses, Prions, and Viroids

  Viruses are acellular, parasitic entities that are not classified within any kingdom. Viruses are not cells and cannot divide. They infect a host cell and use the host’s replication processes to produce identical progeny virus particles. Viruses infect organisms as diverse as bacteria, plants, and animals and exist in a netherworld between a living organism and a nonliving entity. Living things grow, metabolize, and reproduce.

• 3.4.2: Kingdoms Bacteria and Archaea

  Prokaryotes were the first inhabitants on Earth, appearing 3.5 to 3.8 billion years ago. Prokaryotes are unicellular organisms that lack organelles or internal membrane-bound structures. Therefore, they do not have a nucleus. They generally have a single chromosome—a piece of circular, double-stranded DNA located in an area of the cell called the nucleoid. Most prokaryotes have a cell wall outside the plasma membrane.

• 3.4.3: Protists

  Most protists are microscopic, unicellular organisms that are abundant in soil, freshwater, brackish, and marine environments. They are also common in the digestive tracts of animals and in the vascular tissues of plants.

• 3.4.4: Kingdom Fungi

  The kingdom Fungi includes an enormous variety of living organisms collectively referred to as Eucomycota, or true Fungi. While scientists have identified about 100,000 species of fungi, this is only a fraction of the 1.5 million species of fungus likely present on Earth. Edible mushrooms, yeasts, black mold, and the producer of the antibiotic penicillin, Penicillium notatum, are all members of the kingdom Fungi, which belongs to the domain Eukarya.

• 3.4.5: Kingdom Animalia - Evolution and Phylogeny

  Animal evolution began in the ocean over 600 million years ago with tiny creatures that probably do not resemble any living organism today. Since then, animals have evolved into a diverse kingdom known as Animalia or Metazoa. Although over one million extant species of animals have been identified, scientists are continually discovering more species as they explore ecosystems around the world.

• 3.4.6: Kingdom Animalia - Adaptations

  Animals are primarily classified according to morphological and developmental characteristics, such as a body plan. One of the most prominent features of the body plan of true animals is that they are morphologically symmetrical. This means that their distribution of body parts is balanced along an axis. Additional characteristics include the number of tissue layers formed during development, the presence or absence of an internal body cavity, and other features of embryological development, suc

• 3.4.7: Kingdom Plantae - Evolution and Phylogeny

  The kingdom Plantae constitutes large and varied groups of organisms. There are more than 300,000 species of cataloged plants. Of these, more than 260,000 are seed plants. Mosses, ferns, conifers, and flowering plants are all members of the plant kingdom. Some biologists also consider green algae to be plants, although many others exclude all algae from the plant kingdom and place them in Protista.

• 3.4.8: Kingdom Plantae - Adaptations

  As plants adapted to life on land, they had to contend with several challenges in the terrestrial environment, the largest being a lack of easy access to water as compared to an aquatic environment. Four major adaptations are found in all terrestrial plants: the alternation of generations, a sporangium in which the spores are formed, a gametangium that produces haploid cells, and apical meristem tissue in roots and shoots.

Thumbnail: Phylogenetic-symbiogenetic tree of living organisms. (CC BY-SA 3.0; Maulucioni y Doridí).