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Chapter 22: Problem 29

Which statement best explains which organisms need nitrogen fixation and why? a. Prokaryotes cannot use gaseous nitrogen to synthesize macromolecules, so it must be converted into ammonia. b. Prokaryotes cannot use ammonia to synthesize macromolecules, so it must be converted into gaseous nitrogen. c. Eukaryotes cannot use ammonia to synthesize macromolecules, so it must be converted into gaseous nitrogen. d. Eukaryotes cannot use gaseous nitrogen to synthesize macromolecules, so it must be converted into ammonia.

Short Answer

Expert verified
d: Eukaryotes cannot use gaseous nitrogen to synthesize macromolecules, so it must be converted into ammonia.

Step by step solution

01

Understand Nitrogen Fixation

Nitrogen fixation is the process by which nitrogen in the atmosphere is converted into ammonia (NH鈧�) or related nitrogenous compounds. This process is crucial because most organisms cannot use atmospheric nitrogen (N鈧�) directly.
02

Identify Organisms That Perform Nitrogen Fixation

Primarily, certain prokaryotes, including bacteria and archaea, are capable of performing nitrogen fixation. These organisms convert N鈧� into a usable form like ammonia (NH鈧�).
03

Determine Why Nitrogen Fixation Is Necessary

Both prokaryotes and eukaryotes need nitrogen to synthesize macromolecules such as amino acids and nucleotides. However, atmospheric nitrogen (N鈧�) is not directly usable by most organisms.
04

Analyze Provided Statements

a) Prokaryotes cannot use gaseous nitrogen to synthesize macromolecules, so it must be converted into ammonia. b) Prokaryotes cannot use ammonia to synthesize macromolecules, so it must be converted into gaseous nitrogen. c) Eukaryotes cannot use ammonia to synthesize macromolecules, so it must be converted into gaseous nitrogen. d) Eukaryotes cannot use gaseous nitrogen to synthesize macromolecules, so it must be converted into ammonia.
05

Eliminate Incorrect Statements

Prokaryotes convert N鈧� into NH鈧�, so statement b is incorrect. Eukaryotes rely on fixed nitrogen (NH鈧�) rather than performing nitrogen fixation, so statement c is wrong. Eukaryotes use ammonia, not gaseous nitrogen, so statement d is correct. Thus, d is the best explanation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

prokaryotes
Prokaryotes are simple, single-celled organisms that lack a nucleus and other membrane-bound organelles. These include bacteria and archaea. Prokaryotes play a critical role in nitrogen fixation, a process that converts atmospheric nitrogen (N鈧�) into a form (ammonia, NH鈧�) that can be used by living organisms.
  • Different types of prokaryotes, such as free-living bacteria (e.g., Azotobacter) and symbiotic bacteria (e.g., Rhizobium), are involved in nitrogen fixation.
  • These organisms possess a special enzyme called nitrogenase, which helps them carry out the conversion of N鈧� to NH鈧�.
  • These microorganisms often live in the soil or in plant roots, particularly in leguminous plants like peas and beans.
By providing ammonia and other nitrogenous compounds, prokaryotes support both themselves and plants, which subsequently support the entire food web.
eukaryotes
Eukaryotes are more complex organisms that consist of one or more cells. Their cells contain a nucleus and other organelles enclosed within membranes. This group includes animals, plants, fungi, and protists. Unlike prokaryotes, eukaryotes do not perform nitrogen fixation.
  • Eukaryotes rely on fixed nitrogen, such as ammonia and nitrates, which is often provided by prokaryotes through the process of nitrogen fixation.
  • Plants, specifically, absorb these nitrogenous compounds from the soil through their roots.
  • Animals obtain nitrogen by consuming plants or other organisms.
It's important to highlight that while eukaryotes require nitrogen to build macromolecules like proteins and nucleic acids, they cannot directly utilize atmospheric nitrogen (N鈧�) and must instead depend on the forms of nitrogen altered by prokaryotes.
ammonia
Ammonia (NH鈧�) is a key nitrogenous compound that is vital for various biological processes. It is the product of nitrogen fixation, making nitrogen accessible to most living organisms.
  • Ammonia can be absorbed by plants and used to build essential macromolecules such as amino acids and nucleotides.
  • Most organisms, including animals, depend on the nitrogen found in plants or other food sources to meet their nutritional needs.
  • Excess ammonia in soil is typically converted into other nitrogenous compounds like nitrates through a process called nitrification, carried out by different types of bacteria.
This cycle ensures that nitrogen is continuously made available in a form usable by eukaryotes, which cannot directly use atmospheric nitrogen. Ammonia thus serves as a crucial bridge in the nitrogen cycle, linking biological systems and facilitating the flow of nitrogen through ecosystems.

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Most popular questions from this chapter

In a hypothetical research situation, scientists discover bacterial endospores in silt at the bottom of a marsh that has been contaminated with a pollutant for 25 years. The silt of the marsh was deposited in annual layers. The age of the endospores can be estimated, then, by identifying the layer of silt in which the endospores are found. In flask A, researchers place 20-year-old endospores along with growth medium and the pollutant. In flask B, researchers place 100-year-old endospores along with growth medium and the pollutant. Suppose the researchers observe the flasks for a while, continuing to replenish growth medium and pollutant as necessary. If the difference in the growth in each flask lessened after some time, which statement explains why? a. Because the endospores formed 100 years ago, before the marsh was polluted, they would evolve resistance to the pollutant fairly quickly. The bacteria in flask B would then grow more prolifically, and the difference in population size of each flask would lessen. b. Because the endospores formed 20 years ago would lose their resistance to the pollutant. The bacteria in flask A would die, and the difference in population size of each flask would lessen. c. Because the endospores formed 100 years ago, before the marsh was polluted, they would lose their resistance to the pollutant. The bacteria in flask B would then grow more prolifically, and the difference in population size of each flask would lessen. d. Because the endospores formed 20 years ago would evolve resistance to the pollutant fairly quickly. The bacteria in flask A would die, and the difference in population size of each flask would lessen.

Which statement about diseases is false? a. An epidemic is a disease that occurs in a high number of individuals in a population at a time. b. A pandemic is a widespread, usually worldwide, epidemic. c. An endemic disease is a disease that is constantly present, usually at high incidence, in a population. d. An emerging disease is a disease that has appeared in a population for the first time.

Extremophiles are considered an important area for research in the development of therapeutic drugs or industrial applications. Why do you think this is so? a. Extremophiles can be altered genetically in vitro to allow them to live in extreme conditions and this capability of alteration can be used to help humans. For example, some water-resistant prokaryotes have developed DNA repair mechanisms. Also, they could be developed and used in the treatment of human disease. b. Extremophiles have specialized adaptations that allow them to live in extreme conditions. These adaptations can be mobilized to help humans. For example, some water-resistant prokaryotes have developed DNA repair mechanisms. Also, they could be developed and used in the treatment of human disease. c. Extremophiles can be altered genetically in vitro to allow them to live in extreme conditions and this capability of alteration can be used to help humans. For example, some radiation-resistant prokaryotes have developed DNA repair mechanisms. Also, they could be developed and used in the treatment of human disease. d. Extremophiles have specialized adaptations that allow them to live in extreme conditions. These adaptations can be mobilized to help humans. For example, some radiation- resistant prokaryotes have developed DNA repair mechanisms. Also, they could be developed and used in the treatment of human disease.

Explain the statement that both Archaea and Bacteria have the same basic structures, but these structures are built from different chemical components. a. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region, ribosomes, and often a capsule, flagellum, and pili. However, these are sometimes made from different chemical compounds. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of Bacteria are fatty acids while those of Archaea are phytanyl groups. b. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Bacteria contain 70S ribosomes while Archaea contain 80S ribosomes. c. Typical cells in Archaea and Bacteria contain a cell wall, nuclear membranes, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of bacteria are fatty acids, while the plasma membrane lipids of Archaea are phytanyl groups. d. Typical cells in Archaea and Bacteria contain a cell wall, cell membrane, nucleoid region and often a capsule, flagellum, and pili but in some instances different chemical compounds make them. Cell walls of Bacteria contain peptidoglycan while Archaea do not. Plasma membrane lipids of Bacteria are phytanyl groups, while the plasma membrane lipids of Archaea are fatty acids.

Assuming that you could synthesize all of the nitrogen- containing compounds needed if you had nitrogen, what might you eat for a typical meal if you could fix nitrogen like some prokaryotes? a. My meal might be fruits or vegetables and water as nitrogen is present in the highest amount in water. b. My meal might be fruits or vegetables, water and air as atmospheric nitrogen could be simply absorbed. c. My meal might be fruits or vegetables, cheese, meat, water, and air as atmospheric nitrogen could be simply absorbed. d. My meal might be cheese or meat, water, and air as atmospheric nitrogen could be simply absorbed.
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