Q: A bacterial suspension is added to a Petroff-Hausser cell counter. If 14 cells are counted in a large square and the volume over the square is $$\frac{1}{1,250,000} ml$$, how many cells are in 1 ml?

$$14 \times 1,250,000 = 17,500,000$$ cells/ml

Question 1

Which phase of bacterial growth is characterized by intense metabolic activity but no increase in cell number?

Accepted Answer

Lag phase

Question 2

A bacterial culture starts with 2 cells and undergoes 10 generations of binary fission. How many cells will be present at the end? Use the formula $$2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$2^{10} = 1024$ cells

Question 3

Which group of microorganisms would most likely be found growing in a refrigerator at 4°C?

Accepted Answer

Psychrophiles

Question 4

A bacterium that grows best at pH 9.0 is classified as which type?

Accepted Answer

Alkaliphile

Question 5

What happens to a bacterial cell placed in a hypertonic solution?

Accepted Answer

Plasmolysis occurs due to water loss

Question 6

Which of the following is NOT a chemical requirement for microbial growth?

Accepted Answer

Light

Question 7

Which type of culture medium allows only the growth of desired microbes by inhibiting unwanted organisms?

Accepted Answer

Selective medium

Question 8

Which of the following is a chemically defined medium for growing Escherichia coli?

Accepted Answer

Contains glucose, ammonium phosphate, sodium chloride, magnesium sulfate, potassium phosphate, and water

Question 9

Which enzyme is responsible for breaking down hydrogen peroxide into water and oxygen, as shown in the equation $$2\ H_2O_2 \xrightarrow{catalase} 2\ H_2O + O_2$?

Accepted Answer

Catalase

Question 10

A microbiologist wants to isolate a pure culture from a mixed sample. Which method should they use?

Accepted Answer

Streak plate method

Question 11

Which type of bacteria would grow only at the bottom of a tube of thioglycollate medium?

Accepted Answer

Obligate anaerobes

Question 12

Which method is best for counting bacteria in a water sample with very low bacterial concentration?

Accepted Answer

Filtration

Question 13

A spectrophotometer is used to estimate bacterial numbers by measuring which property?

Accepted Answer

Turbidity (optical density)

Question 14

Which of the following is a function of the extracellular polymeric substances (EPS) in biofilms?

Accepted Answer

Protects against environmental stress and holds colonies in place

Question 15

Which biosafety level requires sealed, negative pressure labs and double filtration of exhaust air?

Accepted Answer

BSL-4

Question 16

A bacterial suspension is added to a Petroff-Hausser cell counter. If 14 cells are counted in a large square and the volume over the square is $$\frac{1}{1,250,000} ml$$, how many cells are in 1 ml?

Accepted Answer

$$14 	imes 1,250,000 = 17,500,000$$ cells/ml

Question 17

Which of the following is a real-world consequence of biofilm formation on medical devices?

Accepted Answer

Increased risk of systemic infection

Question 18

Which type of medium is used to distinguish among different organisms based on their biochemical properties?

Accepted Answer

Differential medium

Question 19

A water sample is tested using the MPN method. If the combination of positives is 5-3-1, what is the MPN index per 100 ml?

Accepted Answer

110

Question 20

Which of the following is NOT a benefit of biofilms in environmental contexts?

Accepted Answer

They increase the risk of dental disease

Microbial Growth: Principles, Environmental Factors, and Laboratory Methods

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