Tst 102 Sraw Homework Answers

ECON102 Instructor: Dr. Dave Brown Homework 2 Due: IN CLASS , Monday, February 4 th . Must be turned in by the end of class. Graphing Supply and Demand This is the instruction sheet and problem list for homework 2. Please read all instructions and problems carefully! Instructions: 1. For each problem, only draw the curve(s) specified. If you are only asked to draw a demand curve, just draw a demand curve and DO NOT put a supply curve in the graph. If you are asked to draw both a supply and demand curve, you will need to draw both curves. Since this is a graphing assignment, you can draw your graphs and write your labels. Typing your answers is not required. 2. For correct labeling and graphing, refer to the file posted on ANGEL titled "Supply and Demand Graphing" in the “Supplements” folder. In addition, refer to your notes for some helpful examples. 3. Draw your graphs neatly! Take your time to make your graphs clear and your writing legible. As such, you may want to practice or do a "first-draft" of your graphs on another sheet of paper

Unformatted text preview: HOMEWORK 1 Name Answer Key ID # -­‐1 if Name or ID missing Due Monday, June 27 BEFORE class begins. -­‐2 if turned in once lecture started (10% per day late) This homework is worth 20 points. Only legible writing within the boxes will be graded. Ignore all text outside of boxes You may work in groups. (5 pts) Problem 1. Mycobacteria are acid-­‐fast bacilli that are slow-­‐growing obligate aerobes. Mycobacterium smegmatis has a doubling time of 6 hours. A. (2 pts) Would you be able to detect a M. smegmatis colony on solid media after 4 days? Assume bacterial colonies are not visible until it contains at least 1 million cells, that individual CFU were spread on the plate, and that they form clusters of 5 cells (on average). Show your work. (1 pt) NO Yes/No (0.5 pt for some version of this) n (# generations) = 4 days / 0.25 days/gen = 16 gen. (0.5 pt for this calculation) N = No x 2n = 5 x 216 = 3.3 x 105 cells B. (1 pt) Describe the appearance of the cells (morphology, color) under brightfield microscopy after performing a typical Gram staining procedure on M. smegmatis. (0.5 pt) Colorless (0.5 pt) Bacilli C. (1 pt) A closely related species, Mycobacterium leprae, causes leprosy. This organism is primarily localized to the extremities of the human body, including the nose, toes, and fingers, where it targets nerves and leads to loss of protective sensation. Which one factor is most likely to explain its preference for this body site: salinity, temperature, oxygen concentration, or pH? Briefly explain your answer. (0.5 pt) Temperature. (0.5 pt) The extremities are cooler than other parts of the body [but the pH, oxygen concentration, and salinity are not significantly different from other surface sites]. (Okay to accept other answers with reasonable explanations.) D. (1 pt) Mycobacterium tuberculosis causes an infection of the respiratory tract. Which one factor is most likely to explain its preference for this body site? Briefly explain. (0.5 pt) Oxygen concentration. (0.5 pt) This organism is an obligate aerobe, meaning that it must have oxygen to grow, and the concentration of oxygen is highest in the lungs. (Okay to accept other reasonable, informed answers.) MIC 102 001 SS1 Page 1 of 4 Last updated: 6/27/16 HOMEWORK 1 Name Answer Key (4 pts) Problem 2. You have isolated a new species of bacterium, Microbium caffeinum, from a compost heap that was enriched with coffee grinds. You discover that it can grow using caffeine as its only carbon source, but it seems to grow slowly. You decide to compare its growth rate in defined minimal media (MM) that contains glucose as the sole carbon source with its growth rate in MM containing caffeine. You inoculate M. caffeinum into both caffeine MM and glucose MM at 8 AM and measure the turbidity at regular intervals throughout the day. You graph the turbidity (reported as optical density units, O.D.) over time and determine that both cultures reached exponential phase by 9 AM. You use the following measurements to calculate the growth rates. Media O.D. at 10 AM O.D. at 7 PM Caffeine MM 0.109 0.794 Glucose MM 0.031 0.512 A. (3 pts)Which carbon source does M. caffeinum prefer? Show your work. (1 pt) Select the preferred C source with an X: X Glucose _______ Caffeine n= [log10(N) – log10(No)] / 0.301 Caffeine: (0.5 pt) n = [log10(0.794) – log10(0.109)] / 0.301 = 2.9 generations (0.5 pt) g = 9 hr/2.9 gen = 3.1 hrs/gen Glucose: (0.5 pt) n = [log10(0.512) – log10(0.031)] / 0.301 = 4.0 generations (0.5 pt) g = 9 hr/4 gen = 2.25 hrs/gen You may also compare the specific growth rate: k = 0.693/g Caffeine: k = 0.693/3.1 hrs/gen = 0.22 gen/hr Glucose: k = 0.693/2.25 hrs/gen = 0.308 gen/hr B. (1 pt) Why was it important to grow the cells in defined media for this experiment? In order to compare the dependence of growth rate on the carbon source, caffeine or glucose should be the only carbon source available to the bacteria. If you used non-­‐ defined media, such as nutrient broth, other sources of (organic) carbon would be present and may influence the growth rate. MIC 102 001 SS1 Page 2 of 4 Last updated: 6/27/16 HOMEWORK 1 Name Answer Key (4 points) Problem 3. A culture of Vibrio cholerae was subjected to autoclaving treatments (121oC, 15 psi with steam) of different durations. After each treatment, a specific volume of treated cells was plated onto nutrient agar. The plates were incubated for 24 hours before the number of colony forming units (CFU) were counted. This process was repeated with an oven treatment (200oC). The results are shown in the graph below. Autoclave*(wet*heat)* Oven*(dry*heat)* Comparison"of"dry"heat"v."wet"heat"killing"of"bacteria" 10,000,000" 1,000,000" 100,000" CFU/mL" 10,000" 1,000" 100" 10" 1" 1" 2" 3" 4" 5" 6" Time"(minutes)" A. (0.5 pt each) Determine the Decimal Reduction Time (DRT) for both treatments. To find the DRT (D-­‐value in text), identify two cell densities that are 1 log apart (example above: 100,000 and 10,000). Draw lines perpendicular to both points to determine the amount of time that elapsed during this 90% decrease in cell density. Autoclave DRT 0.25-­‐0.45 minutes Oven DRT ~5 minutes B. (1.5 pts) How long would it take to sterilize a culture of one billion cells/mL using the autoclave (wet heat)? (Sterile = no viable cells remain) Show your work. Decrease cell density by orders of magnitude until have 0.1 cells = 10 DRT (Note: in real world, allow extra DRTs to account for the possibility of uneven exposure to the treatment in the flask, no chance of cells surviving, etc.) >9 DRT x min/DRT or 10 DRT x min/DRT C. How long would it take to sterilize the same culture using the oven (dry heat)? (0.5 pt) >9 DRT x min/DRT = >~45 min or 10 DRT x min/DRT = ~50 minutes MIC 102 001 SS1 Page 3 of 4 Last updated: 6/27/16 HOMEWORK 1 Name Answer Key D. (0.5 pt) Which heat treatment is more effective? Autoclave, moist heat (3 points) Problem 4. In this phylogenetic tree of RNA genomes from HIV-­‐1 subtypes, identify the virus that is: (May be more than one) Source: Library.med.utah.edu A. (1 pt) Most distantly related to SIV Ant-­‐70, MVP-­‐5180 B. (1 pt) Has a viral genome most similar to U-­‐455 ZR-­‐V1191 Briefly explain your answer. (1 pt) They share the most recent common ancestor; share a node; are sister groups/taxa, etc. (4 points, 0.5 pts each) Problem 5: Write in the number of carbons in each of the following molecules: 6 Glucose-­‐6-­‐phosphate 4 Erythrose-­‐4-­‐phosphate 5 Pentose-­‐5-­‐phosphate 2 (acetyl)+ 21 (Co-­‐enzyme A; 2 or 23 accepted Acetyl coenzyme A 3 Glyceraldehyde-­‐3-­‐phosphate 3 Pyruvate 7 Sedoheptulose-­‐7-­‐phosphate 5 2-­‐Oxoglutarate (α-­‐ketoglutarate) (Links have been added to Session 4 of our Canvas site that will help you find the structure of these molecules.) MIC 102 001 SS1 Page 4 of 4 Last updated: 6/27/16 ...
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