Exam 27: Bacteria and Archaea

Only certain prokaryotes can perform nitrogen fixation, but nitrogen-fixing prokaryotes are not known to live inside animals. Thus, how do animals gain access to fixed nitrogen?

Figure 27.2 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 (i.e., a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA). Use Figure 27.2 to answer the following questions. Figure 27.2 -Which two processes are responsible for the shape of the curve at Time B? 1) transduction 2) entry of single-stranded Hfr DNA 3) rolling circle replication of single-stranded Hfr DNA 4) activation of DNA pumps in plasma membrane 5) "toilet paper" replication of recipient cell's plasmids

Which of the following statements is not True?

The following questions refer to Figure 27.1 below, which is the same as Figure 27.10 in the textbook. In this 8-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. Figure 27.1 -Among the six statements below, which two best account for the results obtained by the researchers (see Figure 27.1)? 1) Low-glucose conditions caused mutations that made individual E. coli cells better suited to these conditions. 2) Daughter cells acquired the ability to tolerate low-glucose conditions as they received the enzymes and membrane components that had been modified by their mother cell. 3) The initial E. coli population may have included some cells whose genes favored their survival in low-glucose conditions-OR-such genetic variants arose by chance early in the experiment. 4) The first few generations of E. coli in low-glucose conditions responded to the challenge by increasing the use of certain enzymes and ion pumps, while decreasing the use of others. This behavior was recorded in their gene sequences, which were later transmitted to daughter cells. 5) From generation to generation, there was an increase in the proportion of the experimental populations adapted to low-glucose conditions, because such bacteria produced relatively more offspring than did ancestral bacteria under low-glucose conditions. 6) During each generation, individual cells evolved to increase their survival in low-glucose conditions.

The following questions refer to structures found in a gram-positive prokaryotic cell. -Which of the following contains a copy of the chromosome, along with a small amount of dehydrated cytoplasm, within a tough wall?

Broad-spectrum antibiotics inhibit the growth of most intestinal bacteria. Consequently, assuming that nothing is done to counter the reduction of intestinal bacteria, a hospital patient who is receiving broad-spectrum antibiotics is most likely to become

The following questions refer to structures found in a gram-positive prokaryotic cell. -Which of the following is a structure that permits conjugation to occur?

Which of these is the most common compound in the cell walls of gram-positive bacteria?

Match the numbered terms to the descriptions that follow. For each item, choose all appropriate terms, but only appropriate terms. 1. autotroph 2. heterotroph 3. phototroph 4. chemotroph -an organism that obtains both carbon and energy by ingesting prey

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 which can inhibit phagocytosis, what is the correct sequence of structures penetrated by B. bacteriophorus on its way to the prey's cytoplasm? 1) membrane composed mostly of lipopolysaccharide 2) membrane composed mostly of phospholipids 3) peptidoglycan 4) capsule

Photoautotrophs use

Which of the following use light energy to generate ATP, but do not release oxygen?

The following questions refer to Figure 27.1 below, which is the same as Figure 27.10 in the textbook. In this 8-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. Figure 27.1 -If new genetic variation in the experimental populations arose solely by spontaneous mutations, then the most effective process for subsequently increasing the prevalence of the beneficial mutations in the population over the course of generations is

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 chromosome 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 together 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 termite gut protist, Mixotricha paradoxa, has at least two kinds of bacteria attached to its outer surface. One kind is a spirochete that propels its host through the termite gut. A second type of bacteria synthesizes ATP, some of which is used by the spirochetes. The locomotion provided by the spirochetes introduces the ATP-producing bacteria to new food sources. Which term(s)is (are)applicable to the relationship between the two kinds of bacteria? 1) mutualism 2) parasitism 3) symbiosis 4) metabolic cooperation

The following questions refer to Figure 27.1 below, which is the same as Figure 27.10 in the textbook. In this 8-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. Figure 27.1 -Which term best describes what has occurred among the experimental populations of cells over this 8-year period?

Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free O₂ reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocytes are described as having "…a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intracellular connections allow heterocytes to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." Which two questions below arise from a careful reading of this quotation, and are most important for understanding how N₂ enters heterocytes, and how O₂ is kept out of heterocytes? 1) If carbohydrates can enter the heterocytes from neighboring cells via the "intracellular connections," how is it that O₂ doesn't also enter via this route? 2) If the cell walls of Anabaena's photosynthetic cells are permeable to O₂ and CO₂, are they also permeable to N₂? 3) If the nuclei of the photosynthetic cells contain the genes that code for nitrogen fixation, how can these cells fail to perform nitrogen fixation? 4) If the nuclei of the heterocytes contain the genes that code for photosynthesis, how can these cells fail to perform photosynthesis? 5) If the cell walls of Anabaena's heterocytes are permeable to N₂, how is it that N₂ doesn't diffuse out of the heterocytes before it can be fixed? 6) If the thick cell walls of the heterocytes exclude entry of oxygen gas, how is it that they don't also exclude the entry of nitrogen gas?