Exam 24: Early Life and the Diversification of Prokaryotes

Prokaryotic ribosomes differ from those present in eukaryotic cytosol. Because of this, which of the following is correct?

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 heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." -Which two of the following questions arise from a careful reading of this quotation, and are most important for understanding how N2 enters heterocysts, and how O2 is kept out of heterocysts? 1. If carbohydrates can enter the heterocysts 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 heterocysts contain the genes that code for photosynthesis, how can these cells fail to perform photosynthesis? 5) If the cell walls of Anabaena's heterocysts are permeable to N2, how is it that N2 doesn't diffuse out of the heterocysts before it can be fixed? 6) If the thick cell walls of the heterocysts exclude entry of oxygen gas, how is it that they don't also exclude the entry of nitrogen gas?

Which two structures play direct roles in permitting bacteria to adhere to each other, or to other surfaces? 1. capsules 2) endospores 3) fimbriae 4) plasmids 5) flagella

Use the information in the following paragraph to answer the next few questions. 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

Which of these statements about prokaryotes is correct?

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

If all prokaryotes on Earth suddenly vanished, which of the following would be the most likely and most direct result?

Genetic variation in bacterial populations cannot result from

During which two times can the recipient accurately be described as "recombinant" due to the sequence of events portrayed in Figure 24.2?

Which of the following statements is not true?

Which species is most self-sustaining in terms of obtaining nutrition in environments containing little fixed nitrogen or carbon?

Which question, arising from the results depicted in Figure 24.2, is most interesting from a genetic perspective, and has the greatest potential to increase our knowledge base?

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?

Which of the following statements provides the strongest evidence that prokaryotes evolved before eukaryotes?

Several scientific laboratories across the globe are involved in research concerning the origin of life on Earth. Which of these questions is currently the most problematic and would have the greatest impact on our understanding if we were able to answer it?

Table 24.1 depicts characteristics of five prokaryotic species (A-E). Use the information in the table to answer the following questions. Table 24.1 -Which species should be able to respond most readily to taxes (plural of taxis)?

Fossilized stromatolites

Several scientific laboratories across the globe are performing research concerning the origin of life on Earth. Given our current understanding of Earth's first genetic systems, which of the following results would you predict would be obtained in abiotic experiments testing the potential for hydrogen bonding between various nucleic acids and amino acids?

Match the numbered terms to the description that follows. Choose all appropriate terms. 1. autotroph 2) heterotroph 3) phototroph 4) chemotroph A prokaryote that obtains both energy and carbon as it decomposes dead organisms

How many of these species probably have a cell wall that partly consists of an outer membrane of lipopolysaccharide?