Free Practice Quiz Question List

4 Microbial Growth and Control Online Quiz Questions

Use this free practice quiz with 20 questions to review 4 Microbial Growth and Control, test your knowledge, and prepare for your next test or exam.

20 questions

True or false

1 point

True or false: Refrigerating an item reliably sterilizes it by killing all microbes.

A
True
B
False

True or false

1 point

True or false: Pasteurization makes food sterile by destroying every form of microbial life, including endospores.

A
True
B
False

Choose one

1 point

A microorganism grows in both an oxygen-rich culture and a culture without oxygen. Which oxygen-requirement category best fits it?

A
Obligate aerobe
B
Facultative anaerobe
C
Obligate anaerobe
D
Microaerophile

Fill in the blank

1 point

A medium with a known chemical composition is , whereas a medium containing ingredients such as extracts with variable exact composition is .

Written response

1 point

A microorganism requires oxygen, but grows best when its oxygen level is lower than that of the atmosphere. What oxygen-requirement category describes it?

Choose one

1 point

A mixed bacterial sample is plated on MacConkey agar. Which result is consistent with the medium's described functions?

A
It enriches all bacteria equally, and lactose nonfermenters form pink colonies.
B
It selects for many Gram-negative bacteria, and lactose fermenters form pink colonies.
C
It sterilizes the sample, and all surviving bacteria form pink colonies.
D
It selects for many Gram-positive bacteria, and lactose fermenters form colorless colonies.

Choose all

1 point

Which statements correctly describe roles of major elements in microbial cells? Select all that apply.

A
Nitrogen is needed for proteins and nucleic acids.
B
Potassium forms the backbone of cellular molecules.
C
Phosphorus is part of DNA, RNA, and phospholipids.
D
Oxygen is the element found in some amino acids and coenzymes.
E
Sulfur occurs in some amino acids and coenzymes.

True or false

1 point

True or false: A turbidity reading by itself can distinguish living microbial cells from dead ones.

A
True
B
False

Fill in the blank

1 point

In the phase of a batch culture, new cells form at roughly the rate cells die. In the phase, cell death exceeds cell formation and viable-cell numbers fall.

Choose one

1 point

A population begins with 100 cells and doubles once per generation. Using $N = N_0 \times 2^n$ , how many cells are present after three generations?

A
300 cells
B
600 cells
C
800 cells
D
1,000 cells

Choose all

1 point

A laboratory needs to sterilize heat-stable equipment and a separate heat-sensitive liquid. Which choices match the material to an appropriate sterilization method? Select all that apply.

A
Use pressurized steam for heat-stable equipment.
B
Filter a heat-sensitive liquid to remove microbes.
C
Use refrigeration as a reliable way to sterilize equipment.
D
Rely on pasteurization to make the liquid sterile.
E
Use disinfection on an inanimate surface when complete endospore destruction is required.

Written response

1 point

A plate has 120 colonies after a dilution with a dilution factor of 100. If 1 mL was plated, calculate the original sample concentration using $\text{CFU/mL} = \frac{\text{colonies counted} \times \text{dilution factor}}{\text{volume plated (mL)}}$ . Enter the numerical value in CFU/mL.

Open ended

1 point

Explain how a continuous culture differs from a closed batch culture in how it manages fresh medium and culture removal, and how this affects growth conditions over time.

Choose one

1 point

A water sample is expected to contain microbes at such a low concentration that they cannot be counted reliably on plates. Which method is commonly used to estimate their number?

A
Turbidity, because it counts only living cells.
B
Direct microscopic counts, because they exclude dead cells and debris.
C
Most probable number, because it estimates sparse populations statistically.
D
Viable plate counts, because each colony always arises from one cell.

Choose one

1 point

A bacterium forms pink colonies on MacConkey agar. Which interpretation best fits this result?

A
The organism is a lactose nonfermenter; the medium selects for many Gram-negative bacteria.
B
The organism is a lactose fermenter; the medium selects for many Gram-negative bacteria.
C
The organism is a lactose fermenter; the medium selects only for Gram-positive bacteria.
D
The organism is a lactose nonfermenter; the medium permits all microbes equally.

Choose one

1 point

A microorganism grows both when oxygen is present and when it is absent. Which oxygen-requirement category describes it?

A
An obligate aerobe
B
An obligate anaerobe
C
A facultative anaerobe
D
A microaerophile

Written response

1 point

In a batch culture, nutrients are becoming limited and waste is accumulating. Which growth phase has roughly equal rates of new cell formation and cell death?

Choose one

1 point

A researcher measures the optical density of a cloudy culture to estimate its cell density. What important limitation should the researcher keep in mind?

A
It directly counts only viable cells that can form colonies.
B
It counts individual cells and excludes debris and dead cells.
C
It estimates culture density indirectly but does not distinguish living from dead cells.
D
It statistically estimates microbes that are too sparse to count on plates.

Choose one

1 point

A heat-sensitive liquid must be cleared of microbes without being heated. Which method is most suitable?

A
Pressurized steam, because it sterilizes heat-sensitive liquids without heating them
B
Filtration, because it physically removes microbes without heating the liquid
C
Pasteurization, because it guarantees the liquid is sterile
D
Refrigeration, because cold reliably destroys all microbial life

Written response

1 point

A plate has 36 colonies from 0.2 mL of a sample diluted to $10^{-3}$ (dilution factor 1000). Calculate the original sample concentration using $\text{CFU/mL} = \frac{\text{colonies counted} \times \text{dilution factor}}{\text{volume plated (mL)}}$ .