Exam 27: Bacteria and Archaea

Use the following information to answer the question. Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free oxygen (O₂)reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocysts are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." Given that the enzymes that catalyze nitrogen fixation are inhibited by oxygen, what mechanism might nitrogen-fixing prokaryotes use to protect these enzymes from oxygen?

Use the information in the following paragraph to answer the question. A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. Adherence to the intestinal lining by this bacterium is due to its possession of ________.

Use the following information and graph to answer the question. The figure below depicts changes to the amount of DNA present in a recipient cell that is engaged in conjugation with an Hfr cell. Hfr cell DNA begins entering the recipient cell at Time A. Assume that reciprocal crossing over occurs (in other words, a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA). During which two times can the recipient accurately be described as "recombinant" due to the sequence of events portrayed in the figure?

Mitochondria are thought to be the descendants of certain alpha proteobacteria. They are, however, no longer able to lead independent lives because most genes originally present on their chromosomes have moved to the nuclear genome. Which phenomenon accounts for the movement of these genes?

In a hypothetical situation, the genes for sex pilus construction and for tetracycline resistance are located on the same plasmid within a particular bacterium. If this bacterium readily performs conjugation involving a copy of this plasmid, then the result should be the ________.

Compared to eukaryotes, prokaryotes are ________.

The pathogenic prokaryotes that cause cholera are ________.

Which of the following statements is not true?

Which of the following observations about flagella is accurate and is consistent with the scientific conclusion that the flagella from archaea and bacteria evolved independently?

The following question refers to the figure. In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor)E. coli population. Which term best describes what has occurred among the experimental populations of cells over this eight-year period?

Assuming that each of these possesses a cell wall, which prokaryotes should be expected to be most strongly resistant to plasmolysis in hypertonic environments?

The predatory bacterium Bdellovibrio bacteriophorus drills into a prey bacterium and, once inside, digests it. In an attack upon a gram-negative bacterium that has a slimy cell covering, what is the correct sequence of structures penetrated by B. bacteriophorus on its way to the prey's cytoplasm?

A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. The cell also lacks F factors and F plasmids. Which of the following statements about the bacteria is most probably accurate?

Bacteria perform each of the following ecological roles. Which role typically does not involve symbiosis?

Use the following information and figure to answer the question. The sea slug Pteraeolidia ianthina (P. ianthina)can harbor living dinoflagellates (photosynthetic protists)in its skin. These endosymbiotic dinoflagellates reproduce quickly enough to maintain their populations. Low populations of the dinoflagellates do not affect the sea slugs very much, but high populations (> 5 x 10⁵ cells/mg of sea slug protein)can promote sea slug survival. Percent of sea slug respiratory carbon demand provided by indwelling dinoflagellates. If we assume that carbon is the sole nutrient needed by sea slugs to drive their cellular respiration, then based on the graph, during which season(s)is it least necessary for P. ianthina to act as a chemoheterotroph?