Question 1

If the GC content of two organisms is 45% in both,

Accepted Answer

While having the same GC content could be an indication of potential relatedness, it is not a definitive factor. Other genetic and environmental factors could contribute to differences between the two organisms. The AT content cannot be determined solely from the GC content information provided.

Question 2

Based on DNA hybridization, humans and chimpanzees are the same species.

Accepted Answer

The answer of Based on DNA hybridization, humans and chimpanzees...

Question 3

A sample must contain many microorganisms in order for them to be seen any using microscopy techniques. Why is this so?

Accepted Answer

The area on a microscope slide is very large compared to the relative size of microbes, and you take a very small amount of your sample to place on the slide surface. Therefore, you must have a large number of microbes initially in the culture to increase the chances that you'll be able to see bacteria on the slide.

Question 4

Why are molecular methods particularly useful for identification of microbes that are difficult to grow?

Accepted Answer

Molecular methods can identify microbial DNA even when the microbe is difficult to grow or cannot be grown at all. This is because even trace amounts of DNA can be detected and used for identification.

Question 5

rRNA sequence comparisons are useful for determining evolutionary relationships.

Accepted Answer

rRNA sequences are highly conserved and relatively slow to evolve, making them useful for comparing evolutionary relationships between different species or groups of organisms. By comparing the similarities and differences in rRNA sequences, scientists can construct phylogenetic trees that illustrate the evolutionary distances between different organisms.

Question 6

Phylogenetic relationships between prokaryotes are most accurately determined using

Accepted Answer

Prokaryotes have a limited fossil record and phenotypic characterizations can be misleading, therefore genotypic information, such as DNA sequencing, provides the most accurate and reliable method for determining phylogenetic relationships between prokaryotes.

Question 7

The three domain systems consist of Archaea, Bacteria, and Eukarya.

Accepted Answer

The three domain systems consist of Archaea, Bacteria, and Eukarya, which are based on differences in cellular structures, biochemical pathways, and genetic sequences.

Question 8

Streptococcus pyogenes can be easily distinguished microscopically from other Streptococcus species.

Accepted Answer

Microscopically, Streptococcus pyogenes looks very similar to other Streptococcus species, such as Streptococcus agalactiae and Streptococcus pneumoniae. Therefore, it cannot be easily distinguished microscopically from other Streptococcus species. Differentiation usually requires additional tests such as biochemical tests, serological tests, or DNA sequencing.

Question 9

Size and shape may allow one to differentiate between a bacterium, fungus, and protozoan.

Accepted Answer

Size and shape are important characteristics for identifying microorganisms. Bacteria commonly appear as small, single cells with distinct shapes such as rods, spheres, or spirals. Fungi may vary in size and shape, but typically develop long, branching hyphae and form distinct reproductive structures. Protozoa are typically larger and more complex than bacteria, with a variety of shapes, including spherical, elongated, or irregular shapes, and may also have appendages such as cilia or flagella.

Question 10

All known species of bacteria are described in Bergey's Manual of Systematic Bacteriology.

Accepted Answer

Bergey's Manual of Systematic Bacteriology is a comprehensive reference work that describes all known species of bacteria.

Question 11

Please select the False statement regarding taxonomic hierarchy.

Accepted Answer

The statement "A domain is a collection of similar kingdoms; there are three domains: Bacteria, Archaea, and Animalia" is false. A domain is the highest level of taxonomic hierarchy and includes multiple kingdoms. The three domains are Bacteria, Archaea, and Eukarya, which includes multiple kingdoms such as Animalia, Plantae, and Fungi.

Question 12

Explain the difference between a biotype and a serotype.

Accepted Answer

A biotype refers to the biochemical profile of a microorganism, while a serotype refers to the difference in surface structures/antigens that lead to separate immune responses (characterized by presence of different antibodies in the individual's serum). Therefore, D is the best choice.

Question 13

Serratia marcescens are red when incubated at 37°C.

Accepted Answer

Serratia marcescens produces a red pigment called prodigiosin at temperatures below 30°C; at 37°C, typically used for incubation in laboratories, the bacteria do not produce the pigment and thus do not appear red.

Question 14

Why might it be easier to identify the bacterium that caused pneumonia than one that caused a wound infection?

Accepted Answer

Bacteria that cause pneumonia can be identified with few tests because the lungs have no normal microbiota. Many bacteria are normally found on the skin however; these may be in the wound, complicating identification. This means that there are fewer potential causative agents in the lungs compared to those on the skin, making it easier to identify the bacterium that caused pneumonia.

Question 15

If each of two bacteria have a GC content of 50%, they are both definitely closely related.

Accepted Answer

While a similar GC content can indicate a degree of relatedness, it cannot be assumed that two bacteria with the same GC content are necessarily closely related. Other factors, such as gene content and morphology, also play a role in determining bacterial relatedness.

Question 16

Which statement regarding the Gram stain is False?

Accepted Answer

Gram staining does not typically differentiate between different species of bacteria within the same group, such as E. coli and Salmonella enterica, which are both Gram-negative rods. Further testing beyond Gram staining is required to distinguish between such closely related species.

Question 17

When DNA probes are used to identify bacterial DNA similarities by hybridization, the probe DNA is heated and the template DNA is treated to separate the two strands. Why would the probe DNA be heated?

Accepted Answer

The probe may contain parts that are double-stranded. Heating it up breaks the hydrogen bonds holding the strands together, creating single-stranded sequences that hybridize with their complementary targets.

Question 18

A DNA similarity of 75% between two organisms

Accepted Answer

A DNA similarity of 75% between two organisms suggests they are closely related at the species level, as such a high level of similarity typically indicates a close evolutionary relationship. DNA similarity is used to infer phylogenetic relationships, and a similarity of 75% is significantly high, suggesting a close genetic relationship.

Question 19

Horizontal DNA transfer may make it more difficult to construct phylogenetic trees.

Accepted Answer

Horizontal DNA transfer, also known as lateral gene transfer, involves the transfer of genetic material between non-parental organisms. This results in the mixing of genetic information and can make it difficult to construct accurate phylogenetic trees based on traditional methods of comparing genetic sequences.

Question 20

Disagreements between conclusions obtained from rRNA data and other techniques may be explained by

Accepted Answer

Horizontal DNA transfer, or the transfer of genetic material between organisms that are not parent and offspring, can introduce discrepancies between rRNA data and other evolutionary techniques. This is because rRNA is not typically subject to horizontal transfer, whereas other genes and genomic regions may be.

Quiz 10: Identifying and Classifying Microorganisms