22.E: Prokaryotes - Bacteria and Archaea (Exercises)
22.1: Prokaryotic Diversity
Prokaryotes are ubiquitous. They cover every imaginable surface where there is sufficient moisture, and they live on and inside of other living things. In the typical human body, prokaryotic cells outnumber human body cells by about ten to one. They comprise the majority of living things in all ecosystems. Some prokaryotes thrive in environments that are inhospitable for most living things.
Review Questions
The first forms of life on Earth were thought to be_________.
- single-celled plants
- prokaryotes
- insects
- large animals such as dinosaurs
- Answer
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A
Microbial mats __________.
- are the earliest forms of life on Earth
- obtained their energy and food from hydrothermal vents
- are multi-layered sheet of prokaryotes including mostly bacteria but also archaea
- all of the above
- Answer
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D
The first organisms that oxygenated the atmosphere were
- cyanobacteria
- phototrophic organisms
- anaerobic organisms
- all of the above
- Answer
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A
Halophiles are organisms that require________.
- a salt concentration of at least 0.2 M
- high sugar concentration
- the addition of halogens
- all of the above
- Answer
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A
Free Response
Describe briefly how you would detect the presence of a non-culturable prokaryote in an environmental sample.
- Answer
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As the organisms are non-culturable, the presence could be detected through molecular techniques, such as PCR.
Why do scientists believe that the first organisms on Earth were extremophiles?
- Answer
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Because the environmental conditions on Earth were extreme: high temperatures, lack of oxygen, high radiation, and the like.
22.2: Structure of Prokaryotes
There are many differences between prokaryotic and eukaryotic cells. However, all cells have four common structures: the plasma membrane, which functions as a barrier for the cell and separates the cell from its environment; the cytoplasm, a jelly-like substance inside the cell; nucleic acids, the genetic material of the cell; and ribosomes, where protein synthesis takes place.
Review Questions
The presence of a membrane-enclosed nucleus is a characteristic of ________.
- prokaryotic cells
- eukaryotic cells
- all cells
- viruses
- Answer
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B
Which of the following consist of prokaryotic cells?
- bacteria and fungi
- archaea and fungi
- protists and animals
- bacteria and archaea
- Answer
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D
The cell wall is ________.
- interior to the cell membrane
- exterior to the cell membrane
- a part of the cell membrane
- interior or exterior, depending on the particular cell
- Answer
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B
Organisms most likely to be found in extreme environments are ________.
- fungi
- bacteria
- viruses
- archaea
- Answer
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B
Prokaryotes stain as Gram-positive or Gram-negative because of differences in the cell _______.
- wall
- cytoplasm
- nucleus
- chromosome
- Answer
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A
Pseudopeptidoglycan is a characteristic of the walls of ________.
- eukaryotic cells
- bacterial prokaryotic cells
- archaean prokaryotic cells
- bacterial and archaean prokaryotic cells
- Answer
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C
The lipopolysaccharide layer (LPS) is a characteristic of the wall of ________.
- archaean cells
- Gram-negative bacteria
- bacterial prokaryotic cells
- eukaryotic cells
- Answer
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B
Free Response
Mention three differences between bacteria and archaea.
- Answer
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Responses will vary. A possible answer is: Bacteria contain peptidoglycan in the cell wall; archaea do not. The cell membrane in bacteria is a lipid bilayer; in archaea, it can be a lipid bilayer or a monolayer. Bacteria contain fatty acids on the cell membrane, whereas archaea contain phytanyl.
Explain the statement that both types, bacteria and archaea, have the same basic structures, but built from different chemical components.
- Answer
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Both bacteria and archaea have cell membranes and they both contain a hydrophobic portion. In the case of bacteria, it is a fatty acid; in the case of archaea, it is a hydrocarbon (phytanyl). Both bacteria and archaea have a cell wall that protects them. In the case of bacteria, it is composed of peptidoglycan, whereas in the case of archaea, it is pseudopeptidoglycan, polysaccharides, glycoproteins, or pure protein. Bacterial and archaeal flagella also differ in their chemical structure.
22.3: Prokaryotic Metabolism
Prokaryotes are metabolically diverse organisms. There are many different environments on Earth with various energy and carbon sources, and variable conditions. Prokaryotes have been able to live in every environment by using whatever energy and carbon sources are available. Prokaryotes fill many niches on Earth, including being involved in nutrient cycles such as nitrogen and carbon cycles, decomposing dead organisms, and thriving inside living organisms, including humans.
Review Questions
Which of the following elements is not a micronutrient?
- boron
- calcium
- chromium
- manganese
- Answer
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B
Prokaryotes that obtain their energy from chemical compounds are called _____.
- phototrophs
- auxotrophs
- chemotrophs
- lithotrophs
- Answer
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C
Ammonification is the process by which _____.
- ammonia is released during the decomposition of nitrogen-containing organic compounds
- ammonium is converted to nitrite and nitrate in soils
- nitrate from soil is transformed to gaseous nitrogen compounds such as NO, N 2 O, and N 2
- gaseous nitrogen is fixed to yield ammonia
- Answer
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A
Plants use carbon dioxide from the air and are therefore called _____.
- consumers
- producers
- decomposer
- carbon fixers
- Answer
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B
Free Response
Think about the conditions (temperature, light, pressure, and organic and inorganic materials) that you may find in a deep-sea hydrothermal vent. What type of prokaryotes, in terms of their metabolic needs (autotrophs, phototrophs, chemotrophs, etc.), would you expect to find there?
- Answer
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Responses will vary. In a deep-sea hydrothermal vent, there is no light, so prokaryotes would be chemotrophs instead of phototrophs. The source of carbon would be carbon dioxide dissolved in the ocean, so they would be autotrophs. There is not a lot of organic material in the ocean, so prokaryotes would probably use inorganic sources, thus they would be chemolitotrophs. The temperatures are very high in the hydrothermal vent, so the prokaryotes would be thermophilic.
22.4: Bacterial Diseases in Humans
Devastating pathogen-borne diseases and plagues, both viral and bacterial in nature, have affected humans since the beginning of human history. The true cause of these diseases was not understood at the time, and some people thought that diseases were a spiritual punishment. Over time, people came to realize that staying apart from afflicted persons, and disposing of the corpses and personal belongings of victims of illness, reduced their own chances of getting sick.
Review Questions
A disease that is constantly present in a population is called _____.
- pandemic
- epidemic
- endemic
- re-emerging
- Answer
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C
Which of the statements about biofilms is incorrect?
- Biofilms are considered responsible for diseases such as cystic fibrosis.
- Biofilms produce dental plaque, and colonize catheters and prostheses.
- Biofilms colonize open wounds and burned tissue.
- All statements are incorrect.
- Answer
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D
Which of these statements is true?
- An antibiotic is any substance produced by a organism that is antagonistic to the growth of prokaryotes.
- An antibiotic is any substance produced by a prokaryote that is antagonistic to the growth of other viruses.
- An antibiotic is any substance produced by a prokaryote that is antagonistic to the growth of eukaryotic cells.
- An antibiotic is any substance produced by a prokaryote that prevents growth of the same prokaryote.
- Answer
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A
Free Response
Explain the reason why the imprudent and excessive use of antibiotics has resulted in a major global problem.
- Answer
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Antibiotics kill bacteria that are sensitive to them; thus, only the resistant ones will survive. These resistant bacteria will reproduce, and therefore, after a while, there will be only resistant bacteria.
Researchers have discovered that washing spinach with water several times does not prevent foodborne diseases due to E. coli . How can you explain this fact?
- Answer
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E. coli colonizes the surface of the leaf, forming a biofilm that is more difficult to remove than free (planktonic) cells. Additionally, bacteria can be taken up in the water that plants are grown in, thereby entering the plant tissues rather than simply residing on the leaf surface.
22.5: Beneficial Prokaryotes
Not all prokaryotes are pathogenic. On the contrary, pathogens represent only a very small percentage of the diversity of the microbial world. In fact, our life would not be possible without prokaryotes. Just think about the role of prokaryotes in biogeochemical cycles.
Review Questions
Which of these occurs through symbiotic nitrogen fixation?
- The plant benefits from using an endless source of nitrogen.
- The soil benefits from being naturally fertilized.
- Bacteria benefit from using photosynthates from the plant.
- All of the above occur.
- Answer
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D
Synthetic compounds found in an organism but not normally produced or expected to be present in that organism are called _____.
- pesticides
- bioremediators
- recalcitrant compounds
- xenobiotics
- Answer
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D
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
- Answer
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B
Free Response
Your friend believes that prokaryotes are always detrimental and pathogenic. How would you explain to them that they are wrong?
- Answer
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Remind them of the important roles prokaryotes play in decomposition and freeing up nutrients in biogeochemical cycles; remind them of the many prokaryotes that are not human pathogens and that fill very specialized niches. Furthermore, our normal bacterial symbionts are crucial for our digestion and in protecting us from pathogens.