Question 1

Which of the following best describes a chemically defined medium used in microbiology laboratories?

Accepted Answer

A medium in which the exact amounts of all organic and inorganic compounds are known.

Question 2

A microbiologist wants to determine the specific nutritional requirements of a newly discovered bacterium. Which type of medium should they use for this experiment?

Accepted Answer

Chemically defined medium

Question 3

Which of the following statements about fastidious bacteria is correct?

Accepted Answer

They require enrichment with plant and animal tissue extracts to grow.

Question 4

A student measures the optical density (O.D.) of a bacterial culture at 600 nm and finds a high O.D. value. What does this indicate about the culture?

Accepted Answer

The culture is highly turbid, indicating heavy bacterial growth.

Question 5

Which of the following media would be most appropriate for growing a fastidious organism?

Accepted Answer

Yeast Extract Broth

Question 6

If a culture tube shows a %T (transmittance) reading of 10% at 600 nm, what can you infer about the bacterial growth in the tube?

Accepted Answer

The tube is highly turbid, indicating heavy bacterial growth.

Question 7

Which of the following best explains why complex media are often used for routine cultivation of bacteria in the laboratory?

Accepted Answer

They contain a variety of nutrients that support the growth of many different bacteria, including those with unknown requirements.

Question 8

A culture of Escherichia coli is grown in Glucose Salts Broth. After incubation, the culture is turbid. What does this indicate about E. coli's nutritional requirements?

Accepted Answer

E. coli can synthesize all essential nutrients from glucose and inorganic salts.

Question 9

Which of the following equations correctly relates optical density (O.D.) and percent transmittance (%T) in spectrophotometry?

Accepted Answer

$$O.D. = -\log_{10}(\%T/100)$$

Question 10

A student is comparing the growth of Alcaligenes faecalis in Inorganic Salts Broth and Nutrient Broth. The O.D. in Nutrient Broth is significantly higher. What is the most likely explanation?

Accepted Answer

Alcaligenes faecalis is unable to utilize inorganic salts as a sole nutrient source.

Question 11

Which of the following best describes the function of a spectrophotometer in a microbiology laboratory?

Accepted Answer

It measures the amount of light absorbed or transmitted by a bacterial culture to estimate cell density.

Question 12

Enterococcus faecalis is incubated in Yeast Extract Broth and Inorganic Salts Broth. After 24 hours, only the Yeast Extract Broth shows turbidity. What does this suggest about E. faecalis?

Accepted Answer

It requires complex nutrients found in yeast extract for growth.

Question 13

Which of the following is NOT a component of the Inorganic Salts Broth described in the experiment?

Accepted Answer

Beef extract

Question 14

A culture medium contains beef extract and peptone. How would you classify this medium?

Accepted Answer

Complex medium

Question 15

A student accidentally labels the glass tube instead of the cap with tape. What is the most likely problem this could cause in a microbiology experiment?

Accepted Answer

The label may fall off during incubation, leading to misidentification of samples.

Question 16

Which of the following best explains why the wavelength of 600 nm is commonly used for measuring bacterial growth in a spectrophotometer?

Accepted Answer

600 nm is not absorbed by the culture medium but is scattered by bacterial cells, allowing for accurate measurement of turbidity.

Question 17

A microbiologist observes that a bacterium grows well in Nutrient Broth but not in Glucose Salts Broth. What is the most likely explanation?

Accepted Answer

The bacterium requires complex nutrients present in Nutrient Broth.

Question 18

Which of the following is a correct step when preparing to inoculate culture tubes in the described experiment?

Accepted Answer

Label the side of the cap with tape.

Question 19

If a culture has an O.D. of 0.8 at 600 nm, and another has an O.D. of 0.2, what can you conclude about the relative cell densities?

Accepted Answer

The culture with O.D. 0.8 has a higher cell density.

Question 20

Which of the following best describes the relationship between turbidity and bacterial growth in a liquid culture?

Accepted Answer

Turbidity increases as bacterial growth increases.

Nutritional Requirements of Bacteria and Media Types: Laboratory Study Notes

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