Microbiology, 2021

362 9 • Review Questions
processes.
• Psychrophiles grow best in the temperature
range of 0–15 °C whereas psychrotrophs thrive
between 4°C and 25 °C.
• Mesophiles grow best at moderate
temperatures in the range of 20 °C to about 45
°C. Pathogens are usually mesophiles.
• Thermophiles and hyperthemophiles are
adapted to life at temperatures above 50 °C.
• Adaptations to cold and hot temperatures
require changes in the composition of
membrane lipids and proteins.
9.5 Other Environmental Conditions
that Affect Growth
• Halophiles require high salt concentration in
the medium, whereas halotolerant organisms
can grow and multiply in the presence of high
salt but do not require it for growth.
REVIEW QUESTIONS
Multiple Choice
1. Which of the following methods would be used to
measure the concentration of bacterial
contamination in processed peanut butter?
A. turbidity measurement
B. total plate count
C. dry weight measurement
D. direct counting of bacteria on a calibrated
slide under the microscope
2. In which phase would you expect to observe the
most endospores in a Bacillus cell culture?
A. death phase
B. lag phase
C. log phase
D. log, lag, and death phases would all have
roughly the same number of endospores.
3. During which phase would penicillin, an
antibiotic that inhibits cell-wall synthesis, be
most effective?
A. death phase
B. lag phase
C. log phase
D. stationary phase
• Halotolerant pathogens are an important source
of foodborne illnesses because they
contaminate foods preserved in salt.
• Photosynthetic bacteria depend on visible light
for energy.
• Most bacteria, with few exceptions, require high
moisture to grow.
9.6 Media Used for Bacterial
Growth
• Chemically defined media contain only
chemically known components.
• Selective media favor the growth of some
microorganisms while inhibiting others.
• Enriched media contain added essential
nutrients a specific organism needs to grow
• Differential media help distinguish bacteria by
the color of the colonies or the change in the
medium.
4. Which of the following is the best definition of
generation time in a bacterium?
A. the length of time it takes to reach the log
phase
B. the length of time it takes for a population of
cells to double
C. the time it takes to reach stationary phase
D. the length of time of the exponential phase
5. What is the function of the Z ring in binary
fission?
A. It controls the replication of DNA.
B. It forms a contractile ring at the septum.
C. It separates the newly synthesized DNA
molecules.
D. It mediates the addition of new
peptidoglycan subunits.
6. If a culture starts with 50 cells, how many cells
will be present after five generations with no cell
death?
A. 200
B. 400
C. 1600
D. 3200
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