Test 2 October 2019, questions PDF

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Practice Questions for BLG 151 Midterm 1 1. After Christian Gram developed the Gram stain in 1884, it soon became evident that most bacteria could be divided into two major groups based on their response to the Gramstaining procedure: Gram-positive bacteria stained purple, whereas Gram-negative bacteria were pink or red. This difference in staining has a lot to do with their cell walls. Which of the following statements about Gram-negative and Gram-positive cells is/are true? 1. The periplasmic space present in both Gram-negative and Gram-positive cells is usually 30 to 70 nm wide. 2. Gram-negative cell walls have larger pores than Gram-positive cell walls. 3. When bacteria are treated with ethanol in the decolorization step, the alcohol is thought to shrink the pores of the peptidoglycan found in the cell walls of typical Gram-negative bacteria, preventing the loss of crystal violet. 4. When typical Gram-negative bacteria are exposed to lysozyme or penicillin, the peptidoglycan sacculus is destroyed, but the outer membrane remains. These cells are called protoplasts. A. 1, 2, and 4 only. B. 2, 3, and 4 only. C. 2 and 3 only. D. 2 only. E. 4 only.

2. Which of the following statements accurately describes the difference between capsules and slime layers? A. Slime layers are layers that are well organized and not easily washed off, whereas a capsule layer is a zone of diffuse, unorganized material that is removed easily. B. The term glycocalyx encompasses capsules but not slime layers because capsules are composed of polysaccharides and slime layers are composed of glycoproteins. C. Capsules are clearly visible in the light microscope, slime layers are not. D. Capsules are only present in gram-positive bacteria, slime layers are only present in gram-negative bacteria. E. Capsules help bacteria resist phagocytosis; slime layers help bacteria survive under harsh environmental conditions.

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3. Bacterial ribosomes are called 70S ribosomes and are constructed of a 50S and a 30S subunit. The S in 70S and similar values stands for Svedberg unit. Which of the following statements about the Svedberg unit is true? A. The slower a particle travels when centrifuged, the lower its Svedberg value. B. Heavier and more compact particles normally have larger Svedberg numbers and sediment slower. C. The faster a particle travels when centrifuged, the lower its Svedberg value. D. Heavier and more compact particles normally have smaller Svedberg numbers and sediment faster. E. It is a measurement a measure of sedimentation acceleration in a centrifuge.

4. Which of the following statements about the surface area-to volume ratio (S/V ratio) is correct? 1. Being small decreases the surface area-to volume ratio (SA/V ratio). 2. As the SA/V ratio increases, the uptake of nutrients and the diffusion of these and other molecules within the cell become less efficient. 3. A coccus with the same volume as a rod has a higher SA/V ratio than does the rod. 4. Having a highly convoluted plasma membrane increases the SA/V ratio. A. 1, 2, and 3 only. B. 2 and 4 only. C. 4 only. D. 3 only. E. All of 1, 2, 3, and 4.

5. Each species has a definite pH growth range and pH growth optimum. Recall that pH is a measure of the relative acidity of a solution and is defined as the negative logarithm of the hydrogen ion concentration (expressed in terms of molarity). Which of the following statements about pH is correct? A. A solution of pH 1 has 2 times more hydrogen ions than a solution of pH 2. B. A solution of pH 1 has 1,000 times more hydrogen ions than a solution of pH 3. C. A solution of pH 3 has 3 times more hydrogen ions than a solution of pH 1. D. A solution of pH 1 has 100 times more hydrogen ions than a solution of pH 3. E. A solution with pH 2 has 10 times more hydrogen ions than a solution of pH 1.

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6. Microorganisms are placed in different classes based on their temperature ranges for growth. They are ranked in order of increasing growth temperature range as psychrophiles, psychrotolerants, mesophiles, thermophiles, and hyperthermophiles. Representative ranges and optima for these five types are illustrated below.

Using the graph provided above, which of the following statements are true? 1. Compared to the others, thermophiles and hyperthermophiles have the largest quantity of the amino acid proline. 2. Compared to the others, psychrophiles have the highest concentration of Nucleoid-associated proteins (NAPs). 3. Many psychrophiles will begin to leak cellular constituents at temperatures higher than 20oC. 4. Thermophiles use compatible solutes increase the freezing point of the cytosol. 5. DNA gyrase is present in mesophiles and psychrotolerants, but none of the others. A. 1 and 2 only. B. 1, 2, and 3 only. C. 1 and 3 only. D. 3 and 4 only. E. 2, 3, and 5 only.

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7. __________________ grow equally well whether O2 is present or not; they can tolerate O2, but they do not make use of it. A. Microaerophiles B. Facultative anaerobes C. Obligate anaerobes D. Aerotolerant anaerobes E. Both B and D. 8. Traditionally, five types of relationships to oxygen have been described. There are obligate aerobes, microaerophiles, facultative anaerobes, aerotolerant anaerobes, and obligate anaerobes. Which of the following statements about the five types of relationships to oxygen is false? A. Obligate anaerobes are usually killed by prolonged exposure to O2. B. In order to grow, microaerophiles require the atmospheric level of O2 to be within the range of 2 to 10% C. Obligate anaerobes may be recovered from habitats that are oxic. D. Almost all multicellular organisms are obligate aerobes. E. None of the above are false. 9. Bacteria and archaea live in the deep sea (ocean depths of 1,000 m or more), where the hydrostatic pressure can reach 600 to 1,100 atm. For example, a piezophile recovered from the Mariana trench near the Philippines (depth about 10,500 m) grows only at pressures between about 400 to 500 How does this microbe survive under such conditions? A. As the pressure increases, bacterial piezophiles increase the amount of unsaturated fatty acids in their membrane lipids. B. As the pressure increases, bacterial piezophiles increase the amount of saturated fatty acids in their membrane lipids. C. As the pressure increases shorten the length of their fatty acids. D. Both A and C are true. E. Both B and C are true.

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10. In the image below, each dot represents an individual bacterial colony within the agar or on its surface. The surface, which is directly exposed to atmospheric oxygen, is oxic. The oxygen content of the medium decreases with depth until the medium becomes anoxic toward the bottom of the tube. What are you able to conclude from the image below?

1. Tube B is an aerotolerant anaerobe and Tube C is facultative anaerobe. 2. The enzyme superoxide dismutase (SOD) is absent in Tube D. 3. The bacterial population present in tube D is better at protecting itself from reactive oxygen species (ROS) than the population present in tube A. 4. Tube A contains both superoxide dismutase (SOD) and catalase. A. 1 and 3 only. B. 2 and 4 only. C. 1, 2, and 4 only. D. 1, 2, and 3 only. E. All of 1, 2, 3, and 4 can be concluded.

11. Our world is bombarded with electromagnetic radiation of various types. Sunlight is the major source of radiation on Earth. It includes visible light, ultraviolet (UV) radiation, infrared rays, and radio waves. Which of the following statements about radiation is false? A. Low levels of ionizing radiation will produce mutations that indirectly result in death. B. Longer wavelengths of UV light induce the breakdown of the amino acid tryptophan to toxic photoproducts. These toxic photoproducts plus the near-UV radiation itself produce breaks in DNA strands. C. The only source of radiation on Earth that does not damage or kill microbial cells when present in sufficient intensity is visible light. D. At sea level, there is very little UV radiation at wavelengths below 290 nm because wavelengths shorter than this are absorbed by O2 in Earth’s atmosphere. E. None of the above are false. 5

12. When a few bacteria are inoculated into an environment such as the large intestine or a liquid growth medium and the population is counted at intervals, it is possible to plot a bacterial growth curve that shows the growth of cells over time. The figure below shows the five phases of the growth curve. Which of the following statements about the figure below is/are true?

1. A represents a period of inactivity called the lag phase, D represents a period where the number of viable cells declines exponentially, called the death phase. 2. C shows that the total number of viable microorganisms remains constant. 3. Growth arrest is illustrated in phase D. 4. During phase B, each microorganism is dividing at constant intervals. A. 1, 2, and 3 only. B. 1, 2, and 4 only. C. 2 and 4 only. D. 1 and 4 only. E. 1 only. 13. A protoplast is A. A long thin protein appendage that is used to transfer genetic material between two bacteria B. The sticky layer of polysaccharide slime that surrounds some bacteria C. A membrane bound organelle found only in eukaryotes D. The cytoplasmic membrane and everything surrounded by it E. An archaean that is capable of oxidizing H2 gas for energy and electrons and can grow at unusually high temperatures

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14. You inoculate a culture vessel with 500 cells of a bacterium that has a generation time of 40 minutes. If the cells lag for 1 hour before entering the exponential phase, how many cells will there be after 9 hours? A. 6.0 x 103 B. 2.0 x 106 C. 2.6 x 106 D. 1.6 x 107 E. 5.8 x 107 15. The cell cycles of several bacteria—Escherichia coli, Bacillus subtilis, and the aquatic bacterium Caulobacter crescentus— have been examined extensively, and our understanding of the bacterial cell cycle is based largely on these studies. Which of the following statements about bacterial cell cycle is correct? 1. Like eukaryotes, some bacteria are able to initiate new rounds of replication before the first round of replication and cytokinesis is finished. 2. Each linear chromosome of bacteria has a single site at which replication starts called the origin of replication. 3. To date, binary fission is the only reproductive strategy that has been identified in bacterial cells. 4. Bacterial chromosome replication and partitioning occur simultaneously. A. 1 and 4 only. B. 2 and 3 only. C. 4 only. D. 3 and 4 only. E. 1, 2, and 4 only.

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