Mini-Exam Chapters 6-7 - Chase M Morgan Microbiology...

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Chase M. Morgan 10/6/13 Microbiology & Immunology Mini Exam 2 (Chapters 6 and 7) 1A) See Graph 1B) Lag Phase (0-1 hours) Exponential (log) Phase (2-10 hours) Stationary Phase (10-12 hours) Death Phase (12-15 hours) 1C) During the lag phase, bacteria have just been introduced into a fresh culture medium, causing no immediate increase in cell number counts. In this phase, new enzymes and other compounds are synthesized so that the bacteria can obtain nutrients from the medium. Transitioning to the exponential phase, cells replicate DNA material, increase in size and begin to divide. In the exponential, or log, phase, the cells are growing and dividing at the maximum rate at which they are capable. To achieve this rate, environmental factors more than likely are not negatively influencing the growth of the bacteria. In fact, the culture may possibly be growing at its optimal temperature, or the temperature where the growth is fastest. The growth rate during exponential phase is constant, causing the population as a whole to be uniform. However, this rate of growth can be decreased due to changes in the same environmental factors or the nutritional value of the medium in which the culture is being grown. In stationary phase, population growth plateaus causing the graphical growth curve to level off and become horizontal. The number of viable cells remains constant, due to the balance between cell division and death. Because some cells are beginning to
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