26. Prokaryotes

Prokaryote Metabolism and Ecology

Streptococcus mutans obtains energy by oxidizing sucrose. This bacterium is abundant in the mouths of Western European and North American children and is a prominent cause of cavities. The organism is virtually absent in children from East Africa, where tooth decay is rare. Propose a hypothesis to explain this observation. Outline the design of a study that would test your hypothesis.

Biologists often use the term “energy source” as a synonym for “electron donor.” Why?

 Oxygen, sulfur, light, water, and some minerals 

 No. Oxygen can be acquired from the splitting of water molecules. Sulfur is not required. Nitrogen is another essential substance. 

 Carbon dioxide, sulfur, light, water, and some minerals 

 No. Nitrogen is also required. Sulfur is not. 

 Nitrogen, light, water, and some minerals 

 No. How can photosynthesis occur without carbon dioxide? 

 Carbon dioxide, ammonium, water, light, and some minerals 

 No. Nitrogen-fixing bacteria require nitrogen to convert it to ammonium. 

 Carbon dioxide, nitrogen, water, light, and some minerals 

Cyanobacteria are considered some of the most self-sufficient organisms on Earth.

Choose the list below that contains the substances required by typical nitrogen-fixing cyanobacteria.

Bacteria perform the following ecological roles. Which role typically does not involve symbiosis?
a. skin commensalist
b. decomposer
c. gut mutualist
d. pathogen

 It is the most widespread pest-carried disease in the United States. 

The symptoms begin when Vibrio cholerae die and endotoxins are released from the cell walls.

No. Cholera is caused by an exotoxin released by Vibrio cholerae.

 People are apt to come down with cholera after eating improperly canned foods. 

 The disease is caused by typically harmless enteric bacteria. 

No. Vibrio cholerae is not a usual resident of the human intestines. E. coli, on the other hand, are typically harmless residents of the human digestive system that have some pathogenic strains.

 Its symptoms are caused by an exotoxin that stimulates intestinal cells to release chloride ions into the gut. 

How does cholera make people sick?

Which statement is true regarding cholera?

 No. Heterotrophs obtain their carbon from organic compounds. 

 No. Chemoautotrophs use inorganic chemicals for their energy source. 

These bacteria have the same energy source and carbon source as plants.

Organisms that use light for their energy source and CO2 for their carbon source are called __________.

Suppose that you’ve been hired by a firm interested in using bacteria to clean up organic solvents found in toxic waste dumps. Your new employer is particularly interested in finding cells that are capable of breaking a molecule called benzene into less-toxic compounds. Where would you go to look for bacteria that can metabolize benzene as an energy or carbon source? How would you design an enrichment culture capable of isolating benzene-metabolizing species?

 No. Just kidding. Not that kind of film. 

 No. Biofilms are colonies rather than multicellular prokaryotic organisms. 

 pure cultures representing a single prokaryotic species 

 No. Biofilms are colonies of prokaryotes from multiple species. 

 sites of intense nitrogen fixation by prokaryotes 

 No. Nitrogen fixation occurs in many bacterial communities. Depending on the community in a particular biofilm, there may be no nitrogen fixation occurring at all. 

 metabolic cooperation among prokaryotic species 

Biofilms contain many different types of prokaryotes.

Biofilms are an example of __________.

Prokaryote Ecology

 No. There are many photosynthetic organisms that are not bacteria. 

 No. Phosphate can be absorbed by plants. 

 No. The water cycle does not depend on prokaryotes. 

 No. The sulfur cycle does not depend on prokaryotes. 

Both bacteria and archaea are involved in this cycle.

Prokaryotes are completely indispensable to which chemical cycle?

Photoautotrophs use
a. light as an energy source and CO2 as a carbon source.
b. light as an energy source and methane as a carbon source.
c. N2 as an energy source and CO2 as a carbon source. 
d. CO2 as both an energy source and a carbon source.

 They carry out photosynthesis and nitrogen fixation. 

 No. Filaments are colonies of prokaryotic cells. In some cases, photosynthesis and nitrogen fixation cannot occur in a single cell because oxygen inactivates enzymes needed for nitrogen fixation. Heterocysts are specialized cells that carry out only nitrogen fixation. 

 They oxidize inorganic substances to obtain energy. 

Recall that heterocysts are surrounded by a thickened cell wall that restricts the entry of oxygen.

What is the role of heterocysts in a cyanobacterial filament?

Which of the following involves metabolic cooperation among prokaryotic cells?
a. binary fission
b. endospore formation
c. biofilms
d. photoautotrophy

 The bacteria have a parasitic relationship with the human body. 

 No. Humans also benefit from this relationship. 

 The bacteria have a commensal relationship with the human body. 

 No. Both the bacteria and humans benefit from this relationship. 

 The bacteria directly create a network of intestinal blood vessels necessary to absorb food. 

 No. Signals from these bacteria activate human genes that build the network of vessels. 

Many pathogenic strains of B. thetaiotaomicron have emerged.

No. Many pathogenic strains of E. coli have emerged, however.

 The bacteria have a mutualistic relationship with the human body. 

What type of symbiotic relationship does this represent?

Which example below is a correct statement about Bacteroides thetaiotaomicron, a bacterium that lives in the human intestines?

What do some photosynthetic bacteria use as a source of electrons instead of water?
a. oxygen (O2)
b. hydrogen sulfide (H2S)
c. organic compounds (e.g., CH3COO−)
d. nitrate (NO3-)

 No. Prokaryotes are used in all sorts of industrial applications, from sewage treatment to extraction of gold ore. 

 The vast majority of prokaryotes are pathogenic. 

 No. Only 1 or 2% of known bacteria are pathogenic. 

 Prokaryotes are not useful in genetic engineering because their DNA is so different from that of eukaryotes. 

 No. Bacteria are used in many bioengineering applications because their DNA is structurally the same as eukaryotes, and they are easier to work with. 

 It is important to try and rid your body of all prokaryotes. 

 No. First of all, it would be nearly impossible to rid your body of all prokaryotes. In addition, many prokaryotes living in and on humans have mutualistic relationships with their hosts. 

 Prokaryotes are widely used for bioremediation. 

Think of some of the ways humans use prokaryotes.

Which statement about prokaryotes is true?

 No. In mutualism, both parties benefit. 

 No. A commensal organism does not cause harm to its host. 

 No. Although decomposition is an important role for prokaryotes, it is not an interaction between species. 

 No. Which type of symbiosis? Not all symbiotic relationships involve harm being inflicted on one member of the relationship. 

In this relationship, one organism is considerably larger than the other.

A type of ecological relationship called __________ involves one organism living at the expense of another organism.

Which of the following statements is true?
(A)Archaea and bacteria have identical membrane lipids.
(B)The cell walls of archaea lack peptidoglycan.
(C)Prokaryotes have low levels of genetic diversity.
(D)No archaea are capable of using CO2 to oxidize H2, releasing methane.

Which of the following describes a bacterium that lives in the human intestine and causes disease?
(A)commensalist
(B)decomposer
(C)gut mutualist
(D)symbiotic pathogen

What are organisms called that use inorganic compounds as electron donors in cellular respiration?
a. phototrophs
b. heterotrophs
c. organotrophs
d. lithotrophs

No. Vibrio cholerae causes cholera and is spread when someone consumes water containing infected copepods (tiny crustaceans that are typically the hosts of Vibrio cholerae).

No. Ticks do not transmit Salmonella.

Mycobacterium tuberculosis; tuberculosis

No. Ticks do not transmit Mycobacterium tuberculosis.

No. Ticks do not transmit Clostridium botulinum.

Borrelia burgdorferi; Lyme disease

This is one particularly nasty example of a pathogenic bacteria.

Ticks that live on deer and field mice are responsible for spreading the bacterium __________, which causes __________.

 No. Cyanobacteria require light for photosynthesis. 

 No. Photoheterotrophs require light as an energy source. 

 No. This term indicates that these bacteria like acidic and hot environments, but it does not give you information about their energy and carbon source. 

 No. Photoautotrophs require light for photosynthesis. 

Consider the source of energy and the source and formation of organic compounds.

In an experiment, a microbiologist put equal numbers of each of the following organisms into a flask of sterile broth, consisting mostly of sugar and a few amino acids. She then placed the flask in the dark. Which of the organisms would be most likely to survive?

Prokaryote Metabolism

No. Aerobic means "with oxygen."

 No. Chemoautotrophs can produce their own organic compounds. 

 No. Autotrophs do not require pre-made organic compounds. 

 There is insufficient information to answer this question. 

 No. You know that the organism requires organic compounds and is poisoned by oxygen. This is enough information to answer the question. 

The Desulfovibrio bacterium breaks down organic matter (which it must have) and uses sulfate (not oxygen) as an electron acceptor. As a result, it produces hydrogen sulfide (H2S), accounting for the "rotten egg" smell of swamp muck. Oxygen is a deadly poison to Desulfovibrio. We would call Desulfovibrio a(n) __________.

 Some are single cells, whereas others live in filamentous colonies. 

 No. This is a true statement, but there is a better answer. 

 They are the only prokaryotes that perform plantlike, oxygenic photosynthesis. 

 Some species may carry on nitrogen fixation. 

 It can be said that nitrogen-fixing cyanobacteria are the most self-sufficient of all organisms. 

 All of the listed responses are correct. 

Review the major groups of bacteria.

Which of the following statements about cyanobacteria is/are true?

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