Question 1

Which of the following best describes a psychrophile?

Accepted Answer

An organism with an optimum growth temperature below 20°C

Question 2

A culture of Geobacillus stearothermophilus is incubated at 4°C, 22°C, 37°C, and 60°C. After 48 hours, which tube would you expect to show the highest turbidity, and why?

Accepted Answer

The 60°C tube, because Geobacillus stearothermophilus is a thermophile with an optimum growth temperature above 50°C

Question 3

Which of the following is the most likely reason that Serratia marcescens produces a red pigment at 22°C but not at 37°C?

Accepted Answer

Pigment production is regulated by temperature and may provide protection against environmental stresses at lower temperatures

Question 4

Which of the following best explains why most human pathogens are classified as mesophiles?

Accepted Answer

They are adapted to the human body temperature, which is approximately 37°C

Question 5

A student observes that Escherichia coli grows well at 37°C and 22°C, but poorly at 4°C and 60°C. What category does E. coli belong to?

Accepted Answer

Mesophile

Question 6

Which of the following factors is LEAST likely to determine the ability of a bacterium to grow at a particular temperature?

Accepted Answer

The color of the bacterial colony

Question 7

If you wanted to culture a psychrophile in the laboratory, which incubation temperature would be most appropriate?

Accepted Answer

$$4^\circ\mathrm{C}$$

Question 8

Which of the following best describes the expected growth of Enterococcus faecalis after 48 hours at 60°C?

Accepted Answer

Little or no growth, because it is a mesophile and 60°C is above its optimum range

Question 9

A researcher finds bacteria thriving in a geothermal hot spring at 65°C. Which category do these bacteria most likely belong to?

Accepted Answer

Thermophiles

Question 10

Which of the following statements about the effect of temperature on bacterial enzymes is correct?

Accepted Answer

Enzyme activity generally increases with temperature up to an optimum point, after which activity declines due to denaturation

Question 11

A sample of Serratia marcescens is streaked on two TSA plates, one incubated at 22°C and the other at 37°C. Both plates show similar amounts of growth, but only the 22°C plate has red colonies. What is the most likely explanation?

Accepted Answer

Pigment production is temperature-dependent and occurs optimally at 22°C

Question 12

Which of the following best explains why mesophiles show little growth at 4°C?

Accepted Answer

Enzyme activity and membrane fluidity are too low at this temperature

Question 13

Which of the following is a likely benefit of temperature-regulated pigment production in bacteria?

Accepted Answer

Protection from oxidative stress or UV damage at certain temperatures

Question 14

A bacterium is classified as a mesophile. Which of the following temperature ranges would you expect to be optimal for its growth?

Accepted Answer

$$20^\circ\mathrm{C} to$$ $$50^\circ\mathrm{C}$$

Question 15

Which of the following best describes the growth pattern of a thermophile when incubated at 37°C compared to 60°C?

Accepted Answer

It will show much less growth at 37°C than at 60°C

Question 16

Which of the following is the most likely habitat for psychrophilic bacteria?

Accepted Answer

Polar oceans and alpine environments

Question 17

A student wants to culture a mesophile and a thermophile in the lab. Which incubation temperatures should they use for each, respectively?

Accepted Answer

$$37^\circ\mathrm{C}$$	ext{ for the mesophile, }60^\circ\mathrm{C}$$ for the thermophile

Question 18

Which of the following best explains why a thermophile's proteins remain stable at high temperatures?

Accepted Answer

Their proteins have structural adaptations that prevent denaturation at elevated temperatures

Question 19

If a bacterium shows strong growth at 4°C and little to no growth at 37°C and 60°C, which category does it most likely belong to?

Accepted Answer

Psychrophile

Question 20

Which of the following is a correct prediction about the growth of Serratia marcescens at 22°C and 37°C?

Accepted Answer

It will grow at both temperatures, but produce more red pigment at 22°C

lab 12 - Temperature and pH Effects on Bacterial Growth

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