Question 1

A fastidious organism might be grown on which of the following types of media?

Accepted Answer

Enriched media contain nutrients and growth factors that support the growth of fastidious organisms, which have complex nutritional requirements.

Question 2

At temperatures higher than the maximum growth temperature for an organism,

Accepted Answer

At temperatures higher than the maximum growth temperature, hydrogen bonds can break, leading to protein denaturation, and membranes can become too fluid, disrupting cellular function.

Question 3

A microbe recovered from an environmental sample grows on a medium composed of agar and a mix of salts. The agar is not digested during incubation. The growth rate increases in high CO 2 conditions. The organism is likely a(n)

Accepted Answer

The organism's growth rate increases in high CO2 conditions, suggesting it uses CO2 as a carbon source, which is characteristic of autotrophs.

Question 4

An organism that requires chemical nutrients which serve as final electron acceptors is a(n)

Accepted Answer

Chemotrophs obtain energy by oxidizing chemical compounds, using them as electron acceptors.

Question 5

An organism that produces catalase enzyme is protected from the harmful effects of

Accepted Answer

Catalase breaks down hydrogen peroxide (H2O2) into water and oxygen, protecting the organism from the harmful effects of peroxide anion.

Question 6

Prokaryotes living in the ocean around volcanic vents use the volcanic gasses carbon dioxide (CO2) and hydrogen sulfide (H2S) to fuel their metabolism. They are therefore

Accepted Answer

Prokaryotes that use inorganic molecules as an energy source are called lithotrophs. Those that use CO2 as a carbon source are called autotrophs. Therefore, the correct answer is D: lithoautotrophs.

Question 7

Which of the following oxidizing agents is sometimes produced during aerobic respiration?

Accepted Answer

Superoxide radicals are produced as a byproduct of aerobic respiration when oxygen is reduced incompletely in the electron transport chain.

Question 8

A microbiologist inoculates a growth medium with 100 bacterial cells/ml. If the generation time of the species is 1 hour, and there is no lag phase, how long will it be before the culture contains more than 10,000 cells/ml?

Accepted Answer

The bacterial population doubles every hour. Starting with 100 cells/ml, it will take 7 hours to exceed 10,000 cells/ml: 100 -> 200 -> 400 -> 800 -> 1600 -> 3200 -> 6400 -> 12800.

Question 9

Obligate anaerobes may be cultured in the laboratory

Accepted Answer

Obligate anaerobes require environments devoid of oxygen to grow, and a reducing medium helps create such an environment by removing oxygen.

Question 10

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)

Accepted Answer

Thioglycollate medium is used to test the oxygen requirements of microorganisms. A microbe that grows only at the bottom of the tube is likely an obligate anaerobe, as this area has the least amount of oxygen.

Question 11

The are an important source of nitrogen compounds that can be metabolized by most other organisms.

Accepted Answer

Cyanobacteria are capable of nitrogen fixation, converting atmospheric nitrogen into compounds that can be used by other organisms.

Question 12

Joan wants to discover a microbe capable of degrading an environmental contaminant. Which of the following is the process she should use?

Accepted Answer

Enrichment culture is a technique used to isolate microbes with specific capabilities, such as degrading environmental contaminants, by providing conditions that favor their growth over others.

Question 13

A food product is labeled as having antioxidants. It may therefore contain

Accepted Answer

Vitamin C and E are both antioxidants.

Question 14

Microbial growth rates are controlled in a chemostat by

Accepted Answer

In a chemostat, microbial growth rates are controlled by the continuous addition of a limiting nutrient, which regulates the growth rate and population density.

Question 15

Bacteria living in communities of microbes change the genes they are expressing in response to

Accepted Answer

Quorum-sensing molecules are chemical signals that bacteria use to communicate with each other. When the concentration of quorum-sensing molecules reaches a certain threshold, it triggers a change in gene expression in the bacteria. This allows the bacteria to coordinate their behavior and respond to changes in their environment.

Question 16

An aquatic microbe that can grow only near the surface of the water is probably which of the following?

Accepted Answer

A phototroph requires light for energy, so it would grow near the surface of the water where light is available.

Question 17

A cell that uses an organic carbon source and obtains energy from light would be called a

Accepted Answer

A photoheterotroph uses light as its energy source and organic compounds as its carbon source.

Question 18

You open a jar that has been in the refrigerator for a couple of weeks and find the contents do not look or smell right. What type of microbe has been growing in your refrigerator?

Accepted Answer

Psychrophiles are microbes that thrive in cold environments, such as those found in refrigerators.

Question 19

Organisms that can grow with or without oxygen present are

Accepted Answer

Organisms that can grow with or without oxygen present are either facultative anaerobes or aerotolerant anaerobes. Facultative anaerobes can grow in the presence or absence of oxygen, while aerotolerant anaerobes can grow in the presence of oxygen but do not require it.

Question 20

An epidemiologist is investigating a new disease and observes what appear to be bacteria inside tissue cells in clinical samples from victims. The scientist wants to try to isolate the bacteria in the lab. What culture conditions are most likely to be successful?

Accepted Answer

The bacteria are observed inside tissue cells, suggesting they are intracellular bacteria. Therefore, inoculation of cell cultures, which can provide the necessary environment for intracellular growth, is most likely to be successful.

Quiz 6: Microbial Nutrition and Growth