Question 1

Chloroplasts and mitochondria have relatively small circular chromosomes which supports the endosymbiotic theory that they arose from which of the following?

Accepted Answer

Chloroplasts and mitochondria have small circular chromosomes that resemble those found in bacteria. This supports the theory that they were originally free-living bacterial cells that were engulfed by larger eukaryotic cells and formed a symbiotic relationship, eventually evolving into organelles.

Question 2

A microbiologist gram stains a bacterium and finds the bacterium to be blue to purple in color,this identifies:

Accepted Answer

The blue to purple staining indicates that the bacterium has a thick peptidoglycan layer in its cell wall which is characteristic of gram positive bacteria. Gram negative bacteria on the other hand have a thinner peptidoglycan layer and would appear pink to red in color after a gram staining procedure. The species of the bacterium or whether it causes human disease cannot be determined solely from the gram staining result.

Question 3

A microbiologist gram stains a bacterium and finds the bacterium to be pink to red in color,this identifies:

Accepted Answer

Pink to red color in Gram staining indicates the presence of a thin peptidoglycan layer and an outer membrane, which is typical of Gram-negative bacteria. Therefore, the best choice is D, identifying the bacterium as Gram-negative. The other options cannot be determined from the Gram staining alone.

Question 4

As a budding basic scientist you work in a research laboratory and discover a chemical that removes the cell wall from bacteria but leaves the organism undamaged otherwise.Things that the bacteria will lose because of this include:

Accepted Answer

The cell wall is crucial for maintaining the structure necessary for a gram stain result. Without the cell wall, the bacteria cannot retain the stain, losing the ability to have a gram stain result.

Question 5

Which of the following is true of gram-positive bacteria,and not of gram-negative bacteria?

Accepted Answer

Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which is not found in gram-negative bacteria.

Question 6

Botox is a toxin produced by the bacterium Clostridium botulinum.When ingested with tainted food,Botox can cause distress by paralyzing the intestines,and in high doses can kill by paralyzing muscles needed for breathing and heartbeat.Why would Clostridium botulinum express botox?

Accepted Answer

Clostridium botulinum produces botox to paralyze the intestines, which can prevent the removal of the bacteria, allowing it to persist and potentially thrive in the host environment.

Question 7

Mycobacterium tuberculosis is an obligate aerobe.In which organ would you expect to find these bacteria?

Accepted Answer

Mycobacterium tuberculosis is a bacterium that causes tuberculosis, primarily affecting the lungs. Therefore, the best choice is the lung (E). The other options listed are not typically associated with tuberculosis infections.

Question 8

Escherichia coli and Salmonella can remain in one location in our intestines.They would most likely contain which of the following?

Accepted Answer

Pili are used by bacterial cells to attach to surfaces and host tissues, and both Escherichia coli and Salmonella use pili to attach to the lining of the intestine. Flagella are used by bacterial cells for movement, but they may not be necessary for these bacteria to colonize and remain in the intestine. Cilia are structures found on eukaryotic cells, not bacteria. Glycocalyx is a type of sugar coating that some bacterial cells have, but it is not particularly important for attachment or colonization within the intestine. Spirochetes are a type of bacteria with a coiled shape, but they are not typically found in large numbers in the intestine.

Question 9

Vibrio cholera is the cause of cholera,and has a single flagellum stretching off from one end looking very much like a tail.A characteristic of this organism should be:

Accepted Answer

The answer of Vibrio cholera is the cause of cholera,and...

Question 10

Streptomyces are aerobic soil bacteria that produce over two-thirds of our antibiotics of natural origin.Why might a bacterium produce antibiotics?

Accepted Answer

Bacteria produce antibiotics to kill competing bacteria of different species, as a mechanism of competition for resources in their environment. Antibiotics can prevent the growth and survival of other bacterial competitors, giving the producing bacteria a competitive advantage.

Question 11

Many drugs are produced by placing human genes into bacteria.The bacteria then transcribe and translate these genes into functional human proteins that can then be purified and given as drugs.The fact that this process works is consistent with which statement?

Accepted Answer

The fact that human genes can be expressed and translated into functional proteins by bacteria suggests that humans and bacteria share a common ancestor and use similar genetic machinery. This is because the genetic code used by all organisms is essentially the same, and the fundamental processes of transcription and translation are nearly identical across all domains of life.

Question 12

In a tetanus shot,patients are injected with small amounts of tetanospasmin,a toxin produced by the Clostridium tetani,the bacterium that causes tetanus.The gene for this protein is carried on a plasmid in the bacterium.Which of the following is true of this gene?

Accepted Answer

The gene for tetanospasmin is carried on a plasmid in the Clostridium tetani bacterium. Plasmids are able to undergo the process of horizontal gene transfer, by which genetic material can be transferred between bacterial cells. This can occur through mechanisms such as transformation, in which free DNA is taken up by a bacterial cell. Therefore, choice C is the correct answer.

Question 13

Polymyxins are antibiotics that bind to lipopolysaccharide (LPS)in the outer membrane of Gram-negative bacteria,disrupting both the outer and inner membranes.The hydrophobic tail is important in causing membrane damage,suggesting a detergent-like mode of action.Why doesn't polymyxin also damage human membranes?

Accepted Answer

Human membranes do not contain LPS, which is the specific target of polymyxins. Therefore, polymyxins do not damage human membranes.

Question 14

Clostridium tetani,the bacterium that causes tetanus,can survive in soil for up to 40 years.It is most likely in which of the following structures?

Accepted Answer

Clostridium tetani is a spore-forming bacterium, meaning it can produce endospores that are resistant to harsh environmental conditions. These endospores can survive in soil for many years, allowing the bacteria to persist and potentially infect individuals who are exposed to contaminated soil or objects.

Question 15

Cyanobacteria are phototrophic.Which of the following would they also be considered?

Accepted Answer

Cyanobacteria are able to use energy from sunlight to convert carbon dioxide into organic compounds via photosynthesis, making them autotrophic.

Question 16

Clostridium tetani,the bacterium that causes tetanus,can only survive in soil away from oxygen.It is considered which of the following?

Accepted Answer

Clostridium tetani can only survive in an environment without oxygen (anaerobic condition), making it an obligate anaerobe.

Question 17

The three most common shapes of bacteria are:

Accepted Answer

The three most common shapes of bacteria are spherical (round), rod-shaped, and spiral (curved). These shapes can affect how bacteria move, interact with other cells, and cause infections. Cubical or star-shaped bacteria are much less common.

Question 18

Escherichia coli and Salmonella can live in our intestines in the presence or absence of oxygen.They are considered which of the following?

Accepted Answer

Escherichia coli and Salmonella are facultative anaerobes, which means they can survive and grow in the presence or absence of oxygen.

Question 19

Prokaryotes lack which of the following?

Accepted Answer

Prokaryotes, including bacteria and archaea, lack a true nucleus with a membrane-bound structure surrounding their genetic material. Instead, their DNA is typically found in a single, circular chromosome located in the cytoplasm.

Question 20

Infections by Heliobacter pylori cause 90% of peptic ulcers in the U.S.These bacteria have pili that are expressed in acidic conditions.A characteristic of this organism should be:

Accepted Answer

The ability to attach to cells in the stomach is necessary for H. pylori to initiate infection and cause peptic ulcers. The expression of pili in acidic conditions allows the bacteria to adhere to the stomach lining, which is also acidic. None of the other answer choices provide characteristics specific to H. pylori.

Quiz 16: Bacteria and Archaea