Campbell Biology: Chapter 16 Study Notes

Chapter 16: Microbial Life: Prokaryotes and Protists

Introduction

  • Microorganisms residing in and on the human body outnumber individual human cells.
  • Scientists hypothesize that disrupting microbial communities can:
    • Increase susceptibility to infectious diseases.
    • Contribute to conditions such as:
    • Asthma
    • Other allergies
    • Irritable bowel syndrome
    • Crohn’s disease
    • Autism

16.1 Prokaryotes Are Diverse and Widespread

  • Prokaryotic cells are generally smaller than eukaryotic cells.
  • The total biological mass (biomass) of prokaryotes is at least 10 times that of all eukaryotes combined.
  • Prokaryotes have a significant impact on environmental and human health.
  • Two primary classifications of prokaryotes:
    1. Domain Archaea
    2. Domain Bacteria
  • Research is ongoing into the vast diversity of prokaryotic life.

16.2 External Features Contribute to the Success of Prokaryotes (1 of 2)

  • The shape of prokaryotic cells is crucial for identification; three common shapes include:
    1. Cocci: Spherical prokaryotic cells.
    2. Bacilli: Rod-shaped prokaryotes.
    3. Spirilla: Spiral-shaped prokaryotes, which can be further classified into:
    • Spirilla: Short and rigid cells.
    • Spirochetes: Longer and flexible cells.

16.2 External Features Contribute to the Success of Prokaryotes (2 of 2)

  • Nearly all prokaryotes possess a cell wall.
  • Prokaryotes can be differentiated by:
    • Cell shape
    • Response to Gram staining:
    • Gram-positive bacteria:
      • Have simpler cell walls with a thick layer of peptidoglycan.
    • Gram-negative bacteria:
      • Stain differently and have more complex cell wall structures.
  • Additional features may include:
    • Sticky capsules
    • Flagella (for movement)
    • Fimbriae (for attachment)

16.3 Populations of Prokaryotes Can Adapt Rapidly to Changes in the Environment

  • Prokaryotic populations can grow rapidly, leading to significant genetic variation.
  • This genetic variation increases the likelihood of survival in changing environments.
  • Some prokaryotes form endospores that can remain dormant under harsh conditions.

16.4 Prokaryotes Have Unparalleled Nutritional Diversity

  • Prokaryotes show greater nutritional diversity compared to eukaryotes, enabling them to inhabit diverse environments on Earth.
  • Prokaryotes can utilize two primary energy sources:
    1. Phototrophs: Capture energy from sunlight.
    2. Chemotrophs: Obtain energy from chemical compounds.
  • Nutritional types include:
    • Photoautotrophs: Use sunlight and carbon dioxide (CO₂).
    • Photoheterotrophs: Use sunlight and organic compounds.
    • Chemoautotrophs: Use inorganic chemicals and CO₂.
    • Chemoheterotrophs: Use organic compounds.

16.5 Connection: Biofilms Are Complex Associations of Microbes

  • Prokaryotes can attach to surfaces and form biofilm communities.
  • Biofilms are organized and often difficult to eradicate, presenting medical and environmental challenges.

16.6 Connection: Prokaryotes Help Clean Up the Environment

  • Bioremediation: Utilizes organisms to remove pollutants from soil, air, and water.
  • Prokaryotes play a significant role in bioremediation, particularly in sewage treatment facilities.

16.7 Bacteria and Archaea Are the Two Main Branches of Prokaryotic Evolution

(1 of 2)

  • Advances in molecular genetics suggest many prokaryotes have closer affinities with eukaryotes than other prokaryotes.
  • It is hypothesized that:
    • The first significant divergence in the history of life was between bacteria and later, separation of Archaea and Eukarya.

16.7 Bacteria and Archaea Are the Two Main Branches of Prokaryotic Evolution

(2 of 2)

  • Key differences among the three domains relate to cellular machinery for gene expression.

16.8 Archaea Thrive in Extreme Environments—and in Other Habitats

  • Domain Archaea includes:
    • Extreme halophiles (salt lovers)
    • Extreme thermophiles (heat lovers)
    • Methanogens, which thrive in anaerobic environments.

16.9 Bacteria Include a Diverse Assemblage of Prokaryotes

  • Domain Bacteria is subdivided into five groups based on genetic comparisons:
    1. Proteobacteria: Gram-negative, share specific rRNA sequences.
    2. Gram-positive bacteria
    3. Cyanobacteria: Capable of plant-like oxygen-generating photosynthesis.
    4. Chlamydias: Live inside eukaryotic cells.
    5. Spirochetes: Include notable pathogens.

16.10 Connection: Some Bacteria Cause Disease (1 of 2)

  • Pathogenic bacteria cause disease through:
    • Exotoxins: Proteins secreted by bacteria into their environment.
    • Endotoxins: Lipid components of the outer membrane of gram-negative bacteria released upon cell lysis.
  • Certain pathogenic bacteria (e.g., ** anthrax**) and toxins (e.g., *botulinum*) can be utilized as biological weapons.

16.10 Connection: Some Bacteria Cause Disease (2 of 2)

  • Checkpoint question: Contrast exotoxins vs. endotoxins.

16.11 Scientific Thinking: Stomach Microbiota Affect Health and Disease

(1 of 2)

  • Barry Marshall utilized Koch’s postulates to demonstrate that peptic ulcers are commonly caused by Helicobacter pylori.
  • Ongoing research indicates H. pylori may also have beneficial roles in stomach microbiota.

16.11 Scientific Thinking: Stomach Microbiota Affect Health and Disease

(2 of 2)

  • Checkpoint question: Research indicates infants treated with antibiotics prior to 6 months are more likely to be overweight at age 3. Does this support the hypothesis regarding the absence of H. pylori contributing to obesity?

16.12 Protists Are an Extremely Diverse Assortment of Eukaryotes

  • Protists are primarily unicellular eukaryotes found in various aquatic or moist environments.
  • Nutritional modes of protists include:
    • Autotrophic: Algae
    • Heterotrophic: Protozoans
    • Mixotrophic: Capable of both photosynthesis and heterotrophy.

16.13 Protist Diversity Is Organized in Supergroups

(1 of 2)

  • Protist phylogeny is provisional; some protist groups are more closely related to plants, fungi, or animals than to others.
  • Current hypotheses identify four monophyletic supergroups:
    1. SAR
    2. Excavata
    3. Unikonta
    4. Archaeplastida

16.13 Protist Diversity Is Organized in Supergroups

(2 of 2)

  • Checkpoint question: Identify which protist clade is most closely related to animals and which is related to land plants.

16.14 The SAR Supergroup Represents the Range of Protist Diversity

  • The SAR supergroup includes three clades:
    1. Stramenopila: Includes diatoms, brown algae, and water molds.
    2. Alveolata: Includes dinoflagellates, ciliates, and certain parasites.
    3. Rhizaria: Includes foraminiferans and radiolarians.

16.16 Some Excavates Have Modified Mitochondria (1 of 2)

  • The Excavata supergroup is characterized by an “excavated” feeding groove noted in some members.
  • Several excavates are anaerobic protists with modified mitochondria, such as:
    • Giardia: A parasitic protist.
    • Trichomonas vaginalis.
    • Trypanosoma.
  • Other excavates include Euglena, a mixotrophic organism, and endosymbionts of termites.

16.16 Some Excavates Have Modified Mitochondria (2 of 2)

  • Checkpoint question: Compare the nutritional modes of Euglena and Trichomonas.

16.17 Unikonts Include Protists That Are Closely Related to Fungi and Animals

  • The Unikonta supergroup includes:
    1. Amoebozoans: Including lobe-shaped pseudopodia amoebas, plasmodial slime molds, and cellular slime molds.
    2. Fungi and Animals: Also classified as unikonts.
  • Checkpoint question: Distinguish between the plasmodium of a plasmodial slime mold and the slug-like stage of a cellular slime mold.

16.18 Archaeplastids Include Red Algae, Green Algae, and Land Plants

(1 of 3)

  • Archaeplastida members are primarily autotrophic.
  • Red Algae: Mostly multicellular species contributing to coral reef structures and are commercially significant.

16.18 Archaeplastids Include Red Algae, Green Algae, and Land Plants

(2 of 3)

  • Green Algae: Can be unicellular, colonial, or multicellular. Many reproduce through alternation of generations involving:
    1. Haploid gametophyte generation
    2. Diploid sporophyte generation.
  • Includes land plants closely related to charophytes, a type of green algae.

16.18 Archaeplastids Include Red Algae, Green Algae, and Land Plants

(3 of 3)

  • Checkpoint question: Describe chromosome number differences between gametophyte and sporophyte generations in the alternation of generations life cycle.

16.19 Evolution Connection: Multicellularity Evolved Several Times in Eukaryotes

(1 of 2)

  • Increased complexity allows for greater variation and evolution of new forms of life.
  • Multicellular organisms possess specialized cells for different functions.
  • Multicellularity likely evolved in:
    • Stramenopiles (brown algae)
    • Unikonts (fungi and animals)
    • Archaeplastids (red and green algae, and plants).

16.19 Evolution Connection: Multicellularity Evolved Several Times in Eukaryotes

(2 of 2)

  • Checkpoint question: Identify fundamental differences between multicellular organisms and unicellular ones.

Conclusion: Learning Objectives

By the end of this chapter, you should be able to:

  1. Describe the structures and functions of the diverse features of prokaryotes and explain how these features contribute to their success.
  2. Explain how populations of prokaryotes can adapt rapidly to environmental changes.
  3. Describe the nutritional diversity of prokaryotes and the significance of biofilms.
  4. Explain how prokaryotes contribute to environmental cleanup.
  5. Compare the characteristics of the domains of life.
  6. Describe the diverse types of Archae living in extreme and moderate environments.
  7. Distinguish between the subgroups of domain Bacteria, noting their structure and habitats.
  8. Distinguish between bacterial exotoxins and endotoxins, providing examples.
  9. Describe the diverse assortment of protists.
  10. Describe major protist clades, highlighting characteristics and examples of each.
  11. Explain how multicellular life has evolved in eukaryotes.