Chapter 13 Glossary, Summary, and Practice Questions

KEY TERMS

Amoebozoa the eukaryotic supergroup that contains the amoebas and slime molds

anaerobic refers to organisms that grow without oxygen

anoxic without oxygen

Archaeplastida the eukaryotic supergroup that contains land plants, green algae, and red algae

Ascomycota (sac fungi) a division of fungi that store spores in a sac called ascus

basidiomycota (club fungi) a division of fungi that produce club shaped structures, basidia, which contain spores

biofilm a microbial community that is held together by a gummy-textured matrix

bioremediation the use of microbial metabolism to remove pollutants

Black Death a devastating pandemic that is believed to have been an outbreak of bubonic plague caused by the bacterium

Yersinia pestis

botulism a disease produce by the toxin of the anaerobic bacterium Clostridium botulinum

capsule an external structure that enables a prokaryote to attach to surfaces and protects it from dehydration

Chromalveolata the eukaryotic supergroup that contains the dinoflagellates, ciliates, the brown algae, diatoms, and water molds

Chytridiomycota (chytrids) a primitive division of fungi that live in water and produce gametes with flagella commensalism a symbiotic relationship in which one member benefits while the other member is not affected conjugation the process by which prokaryotes move DNA from one individual to another using a pilus

cyanobacteria bacteria that evolved from early phototrophs and oxygenated the atmosphere; also known as blue-green algae

Deuteromycota a division of fungi that do not have a known sexual reproductive cycle (presently members of two phyla: Ascomycota and Basidiomycota)

endosymbiosis the engulfment of one cell by another such that the engulfed cell survives and both cells benefit; the process responsible for the evolution of mitochondria and chloroplasts in eukaryotes

epidemic a disease that occurs in an unusually high number of individuals in a population at the same time Excavata the eukaryotic supergroup that contains flagellated single-celled organisms with a feeding groove extremophile an organism that grows under extreme or harsh conditions

foodborne disease any illness resulting from the consumption of contaminated food, or of the pathogenic bacteria, viruses, or other parasites that contaminate food

Glomeromycota a group of fungi that form symbiotic relationships with the roots of trees

Gram-negative describes a bacterium whose cell wall contains little peptidoglycan but has an outer membrane

Gram-positive describes a bacterium that contains mainly peptidoglycan in its cell walls hydrothermal vent a fissure in Earth’s surface that releases geothermally heated water hypha a fungal filament composed of one or more cells

lichen the close association of a fungus with a photosynthetic alga or bacterium that benefits both partners

microbial mat a multi-layered sheet of prokaryotes that may include bacteria and archaea

mold a tangle of visible mycelia with a fuzzy appearance

MRSA (methicillin-resistant Staphylococcus aureus) a very dangerous Staphylococcus aureus strain resistant to antibiotics

mycelium a mass of fungal hyphae

mycorrhiza a mutualistic association between fungi and vascular plant roots

mycosis a fungal infection

Opisthokonta the eukaryotic supergroup that contains the fungi, animals, and choanoflagellates

pandemic a widespread, usually worldwide, epidemic disease

parasite an organism that lives on or in another organism and feeds on it, often without killing it

pathogen an organism, or infectious agent, that causes a disease

pellicle an outer cell covering composed of interlocking protein strips that function like a flexible coat of armor, preventing cells from being torn or pierced without compromising their range of motion

peptidoglycan a material composed of polysaccharide chains cross-linked to unusual peptides

phototroph an organism that uses energy from sunlight

plastid one of a group of related organelles in plant cells that are involved in the storage of starches, fats, proteins, and pigments

pseudopeptidoglycan a component of some cell walls of Archaea

Rhizaria the eukaryotic supergroup that contains organisms that move by amoeboid movement

saprobe an organism that feeds on dead organic material

septum the cell wall division between hyphae

stromatolite a layered sedimentary structure formed by precipitation of minerals by prokaryotes in microbial mats

thallus a vegetative body of a fungus

transduction the process by which a bacteriophage moves DNA from one prokaryote to another

transformation a mechanism of genetic change in prokaryotes in which DNA present in the environment is taken into the cell and incorporated into the genome

yeast a general term used to describe unicellular fungi

Zygomycota (conjugated fungi) the division of fungi that form a zygote contained in a zygospore

CHAPTER SUMMARY

Prokaryotic Diversity

Prokaryotes existed for billions of years before plants and animals appeared. Microbial mats are thought to represent the earliest forms of life on Earth, and there is fossil evidence, called stromatolites, of their presence about 3.5 billion years ago. During the first 2 billion years, the atmosphere was anoxic and only anaerobic organisms were able to live.

Cyanobacteria began the oxygenation of the atmosphere. The increase in oxygen concentration allowed the evolution of other life forms.

Prokaryotes (domains Archaea and Bacteria) are single-celled organisms lacking a nucleus. They have a single piece of circular DNA in the nucleoid area of the cell. Most prokaryotes have cell wall outside the plasma membrane. Bacteria and Archaea differ in the compositions of their cell membranes and the characteristics of their cell walls.

Bacterial cell walls contain peptidoglycan. Archaean cell walls do not have peptidoglycan. Bacteria can be divided into two major groups: Gram-positive and Gram-negative. Gram-positive organisms have a thick cell wall. Gram-negative organisms have a thin cell wall and an outer membrane. Prokaryotes use diverse sources of energy to assemble macromolecules from smaller molecules. Phototrophs obtain their energy from sunlight, whereas chemotrophs obtain it from chemical compounds.

Infectious diseases caused by bacteria remain among the leading causes of death worldwide. The excessive use of antibiotics to control bacterial infections has resulted in resistant forms of bacteria being selected. Foodborne diseases result from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food.

Prokaryotes are used in human food products. Microbial bioremediation is the use of microbial metabolism to remove pollutants. The human body contains a huge community of prokaryotes, many of which provide beneficial services such as the development and maintenance of the immune system, nutrition, and protection from pathogens.

Eukaryotic Origins

The first eukaryotes evolved from ancestral prokaryotes by a process that involved membrane proliferation, the loss of a cell wall, the evolution of a cytoskeleton, and the acquisition and evolution of organelles. Nuclear eukaryotic genes appear to have had an origin in the Archaea, whereas the energy machinery of eukaryotic cells appears to be bacterial in origin. The mitochondria and plastids originated from endosymbiotic events when ancestral cells engulfed an aerobic bacterium (in the case of mitochondria) and a photosynthetic bacterium (in the case of chloroplasts). The evolution of mitochondria likely preceded the evolution of chloroplasts. There is evidence of secondary endosymbiotic events in which plastids appear to be the result of endosymbiosis after a previous endosymbiotic event.

Protists

Protists are extremely diverse in terms of biological and ecological characteristics due in large part to the fact that they are an artificial assemblage of phylogenetically unrelated groups. Protists display highly varied cell structures, several types of reproductive strategies, virtually every possible type of nutrition, and varied habitats. Most single-celled protists are motile, but these organisms use diverse structures for transportation.

The process of classifying protists into meaningful groups is ongoing, but genetic data in the past 20 years have clarified many relationships that were previously unclear or mistaken. The majority view at present is to order all eukaryotes into six supergroups. The goal of this classification scheme is to create clusters of species that all are derived from a common ancestor.

Fungi

Fungi are eukaryotic organisms that appeared on land over 450 million years ago. They are heterotrophs and contain neither photosynthetic pigments such as chlorophylls nor organelles such as chloroplasts. Because they feed on decaying and dead matter, they are saprobes. Fungi are important decomposers and release essential elements into the environment. External enzymes digest nutrients that are absorbed by the body of the fungus called a thallus. A thick cell wall made of chitin surrounds the cell. Fungi can be unicellular as yeasts or develop a network of filaments called a mycelium, often described as mold. Most species multiply by asexual and sexual reproductive cycles, and display an alternation of generations.

The divisions of fungi are the Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota, Glomeromycota, and the Deuteromycota, a polyphyletic group.

Fungi establish parasitic relationships with plants and animals. Fungal diseases can decimate crops and spoil food during storage. Compounds produced by fungi can be toxic to humans and other animals. Mycoses are infections caused by fungi. Superficial mycoses affect the skin, whereas systemic mycoses spread through the body. Fungal infections are difficult to cure.

Fungi have colonized all environments on Earth but are most often found in cool, dark, moist places with a supply of decaying material. Fungi are important decomposers because they are saprobes. Many successful mutualistic relationships involve a fungus and another organism. They establish complex mycorrhizal associations with the roots of plants. Lichens are a symbiotic relationship between a fungus and a photosynthetic organism, usually an alga or cyanobacterium.

Fungi are important to everyday human life. Fungi are important decomposers in most ecosystems. Mycorrhizal fungi are essential for the growth of most plants. Fungi, as food, play a role in human nutrition in the form of mushrooms and as

agents of fermentation in the production of bread, cheeses, alcoholic beverages, and numerous other food preparations. Secondary metabolites of fungi are used in medicine as antibiotics and anticoagulants. Fungi are used in research as model organisms for the study of eukaryotic genetics and metabolism.

ART CONNECTION QUESTIONS

• Figure 13.6 Which of the following statements is true?

• Gram-positive bacteria have a single cell wall formed from peptidoglycan.
• Gram-positive bacteria have an outer membrane.

REVIEW QUESTIONS

• The first forms of life on Earth were thought to be.
• single-celled plants
• prokaryotes
• insects
• large animals such as dinosaurs
• The first organisms that oxygenated the atmosphere were .
• cyanobacteria
• phototrophic organisms
• anaerobic organisms
• all of the above
• Which of the following consist of prokaryotic cells?

• bacteria and fungi
• archaea and fungi
• protists and animals
• bacteria and archaea
• Prokaryotes stain as Gram-positive or Gram-negative because of differences in the .
• cell wall
• cytoplasm
• nucleus
• chromosome
• Prokaryotes that obtain their energy from chemical compounds are called .
• phototrophs
• auxotrophs
• chemotrophs
• lithotrophs
• Bioremediation includes .
• the use of prokaryotes that can fix nitrogen
• the use of prokaryotes to clean up pollutants
• the use of prokaryotes as natural fertilizers
• All of the above
• What event is thought to have contributed to the evolution of eukaryotes?

CRITICAL THINKING QUESTIONS

• 
  The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.
• Gram-negative bacteria have a cell wall made of peptidoglycan, while Gram-positive bacteria have a cell wall made of phospholipids.

• global warming
• glaciation
• volcanic activity
• oxygenation of the atmosphere
• Mitochondria most likely evolved from

.

• a photosynthetic cyanobacterium
• cytoskeletal elements
• aerobic bacteria
• membrane proliferation
• Protists with the capabilities to absorb nutrients from dead organisms are called.
• photoautotrophs
• autotrophs
• saprobes
• heterotrophs
• Which parasitic protist evades the host immune system by altering its surface proteins with each generation?
• Paramecium caudatum
• Trypanosoma brucei
• Plasmodium falciparum
• Phytophthora infestans
• Which polysaccharide is usually found in the cell walls of fungi?
• starch
• glycogen
• chitin
• cellulose
• What term describes the close association of a fungus with the root of a tree?
• a rhizoid
• a lichen
• a mycorrhiza
• an endophyte

• Explain the reason why the imprudent and excessive use of antibiotics has resulted in a major global problem.
• Your friend believes that prokaryotes are always detrimental and pathogenic. How would you explain to them that they are wrong?
• Describe the hypothesized steps in the origin of eukaryote cells.
• 
  How does killing Anopheles mosquitoes affect the

Plasmodium protists?

• Without treatment, why does African sleeping sickness invariably lead to death?
• Why can superficial mycoses in humans lead to bacterial infections?