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Ch. 6 - Microbial Growth
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 6 - Microbial GrowthProblem 4
Chapter 6, Problem 4

Which of the lines best depicts the log phase of Listeria monocytogenes growing in a human?
Graph showing three lines labeled a, b, and c depicting different bacterial growth rates over time on a log scale.

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Understand that the log phase (also called the exponential phase) in bacterial growth is characterized by a period of rapid, exponential increase in the number of cells.
Look at the graph where the y-axis represents the logarithm (base 10) of the number of cells and the x-axis represents time. During the log phase, the number of cells increases exponentially, so the graph should show a straight line with a positive slope on this log scale.
Analyze each line: Line 'a' shows the steepest positive slope, indicating the fastest increase in cell number; line 'b' shows a positive slope but less steep than 'a'; line 'c' is flat, indicating no increase in cell number.
Since the log phase is the period of rapid growth, the line that best depicts this phase is the one with the steepest positive slope, which is line 'a'.
Therefore, line 'a' best represents the log phase of Listeria monocytogenes growing in a human.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bacterial Growth Phases

Bacterial growth occurs in distinct phases: lag, log (exponential), stationary, and death. The log phase is characterized by rapid, exponential cell division, where the population size increases logarithmically over time. Understanding these phases helps interpret growth curves and bacterial behavior in different environments.
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Logarithmic (Log) Phase Characteristics

During the log phase, bacteria multiply at their maximum rate under optimal conditions, leading to a straight, upward-sloping line on a logarithmic growth graph. This phase reflects active metabolism and cell division, making it critical for studying bacterial growth dynamics and antibiotic susceptibility.
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Interpreting Growth Curves on a Log Scale

A logarithmic scale on the y-axis means equal distances represent tenfold changes in cell number. Lines with positive slopes indicate growth, with steeper slopes showing faster growth rates. A flat line indicates no growth, helping distinguish between lag, log, and stationary phases in bacterial populations.
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Related Practice
Textbook Question

Define and explain the importance of each of the following:

a. Catalase

b. Hydrogen peroxide

c. Peroxidase

d. Superoxide radical

e. Superoxide dismutase

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Textbook Question

Seven methods of measuring microbial growth were explained in this chapter. Categorize each as either a direct or an indirect method.

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Textbook Question

By deep-freezing, bacteria can be stored without harm for extended periods. Why do refrigeration and freezing preserve foods?

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Textbook Question

Which of the lines best depicts the log phase of a thermophile incubated at room temperature?

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Textbook Question

Assume you inoculated 100 facultatively anaerobic cells onto nutrient agar and incubated the plate aerobically. You then inoculated 100 cells of the same species onto nutrient agar and incubated the second plate anaerobically. After incubation for 24 hours, you should have

a. more colonies on the aerobic plate.

b. more colonies on the anaerobic plate.

c. the same number of colonies on both plates.

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Textbook Question

Macronutrients (needed in relatively large amounts) are often listed as CHONPS. What does each of these letters indicate, and why are they needed by the cell?

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