Question 1

Which of the following genera does NOT undergo differentiation?

Accepted Answer

Escherichia is a unicellular bacterium that does not undergo differentiation. The other genera listed are capable of differentiation, which is a process that allows bacteria to form specialized cell types, such as spores or heterocysts, in response to environmental cues.

Question 2

Explain the difference between electrogenic and electroneutral coupled transport and give an example of each.

Accepted Answer

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Question 3

You are measuring growth in a bacterial culture. The number of viable cells remains constant, and when you check the medium, you find that the carbon source has been used up. What phase of growth is the culture in?

Accepted Answer

The culture is in stationary phase, because the number of viable cells is not increasing and the carbon source has been used up, indicating that the cells have exhausted their ability to divide and are in a period of stasis.

Question 4

What type of medium and conditions would you need to have in order to select for photoautotrophs?

Accepted Answer

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Question 5

If an organism produces seven offspring per generation, which of the following would express the rate of increase in population, where n corresponds to the number of generations?

Accepted Answer

The correct expression for the rate of increase in population when an organism produces seven offspring per generation is $7^n$, which matches choice C. This formula indicates that the population size multiplies by 7 with each generation (n).

Question 6

During biofilm formation, as more and more cells bind to the surface, they begin sending signals to each other in a process called:

Accepted Answer

During biofilm formation, bacteria communicate with each other through a process called quorum sensing. As more and more bacteria bind to the surface and multiply, they release signaling molecules that allow them to coordinate the expression of genes involved in biofilm formation. This enables the bacteria to act as a cohesive unit and form a protective community structure that is highly resistant to antibiotics and the immune system.

Question 7

Compare and contrast complex media, synthetic media, and enriched media.

Accepted Answer

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Question 8

Define the terms "viable" and "viable but nonculturable." Why are so many environmental organisms believed to be viable but nonculturable?

Accepted Answer

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Question 9

A cafeteria worker who fails to wash his hands thoroughly and fails to wear gloves inoculates a quiche with four E. coli cells when he uses his finger to test whether it is done. By the time you purchase the quiche, there are 128 E. coli cells in it. How many generations did the cells go through?

Accepted Answer

Each generation doubles the number of cells, so the number of generations can be found by dividing the final number of cells by the initial number of cells: 128/4 = 32. Therefore, the cells went through 32 generations before the quiche was sold. The closest choice to 32 is B, 5 generations, so that is the best choice.

Question 10

How do some cyanobacteria fix nitrogen while growing aerobically?

Accepted Answer

Some cyanobacteria have specialized cells called heterocysts that can fix nitrogen in anaerobic conditions. Heterocysts have a thick cell wall that limits the diffusion of oxygen from the atmosphere, creating an anaerobic environment that allows nitrogenase to function. However, because heterocysts lack photosystem II, they cannot perform photosynthesis, so the rest of the colony continues to carry out oxygen-producing photosynthesis in aerobic conditions.

Question 11

Mannitol salt agar (MSA) contains 7.5% NaCl, the carbohydrate mannitol, and the pH indicator phenol red. Some organisms can ferment mannitol, producing acids as a by-product. Is this medium likely to be selective and/or differential? Explain.

Accepted Answer

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Question 12

Which of the following is true of all biofilms?

Accepted Answer

All biofilms are characterized by the production of an extracellular polymeric substance (EPS), which is secreted by the bacteria and acts as a protective matrix for the community of cells. This EPS can be composed of various materials, including polysaccharides, proteins, lipids, and nucleic acids. Biofilms can contain multiple species of bacteria and are often highly structured, with different layers or zones of activity. The cells in a biofilm are typically not dormant, but are actively engaged in metabolic activity and communication with other cells in the community. A biofilm is not necessarily a continuous monolayer, as it can exist as discrete colonies or clusters of cells.

Question 13

Compare and contrast the ABC transporters and group translocation in terms of energy requirements and concentration gradients.

Accepted Answer

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Question 14

In which case would the shortest lag period most likely be observed?

Accepted Answer

Transferring microorganisms from a complex medium to fresh complex medium would most likely result in the shortest lag period because the organisms are already adapted to the nutrients and conditions of the complex medium, requiring minimal adjustment to resume growth.

Question 15

E. coli adjusts to the stationary phase by doing all of the following EXCEPT:

Accepted Answer

E. coli is a non-spore forming bacterium, so it cannot form spores. Therefore, forming spores is not a way for it to adjust to the stationary phase. Instead, it adjusts to the stationary phase by decreasing its size, synthesizing enzymes to handle oxygen radicals, synthesizing proteins to protect DNA and proteins, and increasing peptidoglycan cross-linking.

Question 16

When studying the metabolism of an organism, why is it better to grow organisms in a defined synthetic medium instead of a complex medium?

Accepted Answer

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Question 17

Why is iron so often a limiting nutrient, when it seems to be so abundant in the environment, and how can organisms overcome this problem?

Accepted Answer

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Question 18

Some bacteria form environmentally resistant forms called:

Accepted Answer

Endospores are a type of environmentally resistant structure formed by some bacteria. They allow the bacteria to survive harsh conditions, including heat, cold, and lack of nutrients. Heterocysts are a specialized type of cell found in some cyanobacteria, colonies refer to a group of individual bacteria living together, hyphae are long, branching filaments found in fungi, and actinomycetes are a type of bacteria that often forms filamentous structures.

Question 19

How do scientists know of the existence of "unculturable" organisms?

Accepted Answer

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Question 20

Why can't most organisms use the nitrogen gas that is so prevalent in the atmosphere? How do these organisms acquire a usable form of nitrogen?

Accepted Answer

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Quiz 4: Bacterial Culture, Growth, and Development