Question 1

DNA sequences can change at different rates for the same gene in different microorganisms, falsely grouping Bacteria based on the amount of sequence divergence rather than common ancestry.

Accepted Answer

This statement is true. DNA sequences can change at different rates in different microorganisms due to factors such as mutation rates, genetic drift, and natural selection. Depending on the rate of change, organisms with a relatively high amount of sequence divergence may not necessarily share a more recent common ancestor than those with less divergence. Therefore, grouping organisms solely based on sequence divergence can lead to false interpretations of evolutionary relationships.

Question 2

Which of the following organisms can DIRECTLY utilize inorganic sulfur?

Accepted Answer

Primary producers such as sulfur bacteria and some algae have the ability to use inorganic sulfur, such as sulfate or sulfur dioxide, in their metabolic processes through a process called chemosynthesis. Decomposers, secondary consumers, and tertiary consumers cannot directly use inorganic sulfur.

Question 3

A veterinarian wants to determine what types of bacteria colonize the mouths of cats. She takes a cheek swab from her pet cat. How can the veterinarian determine which bacteria are present in this sample?

Accepted Answer

The veterinarian can use culturing to determine which bacteria are present in the sample by looking for different morphological characteristics. She can also assess how many different rRNA sequences are in her sample, or amplify whole genomes within her sample.

Question 4

Photosynthetic bacteria are all found on one branch of the bacterial phylogenetic tree.

Accepted Answer

Photosynthetic bacteria are found in several different branches of the bacterial phylogenetic tree, indicating that photosynthesis has evolved more than once among bacteria.

Question 5

Like carbon, copious amounts of nitrogen are stored in (and released from) geological reservoirs such as sedimentary rocks.

Accepted Answer

Nitrogen is not stored in significant amounts in geological reservoirs like sedimentary rocks; it primarily cycles through the atmosphere, biosphere, and hydrosphere.

Question 6

_____ is an element that is abundant in Earth's atmosphere; however, usable forms of this element (such as ammonia) are comparatively rare in certain soils. To circumvent this problem, soybean plants form symbiotic relationships with bacteria.

Accepted Answer

The answer of _____ is an element that is abundant...

Question 7

Scientists generate phylogenetic trees for a group of organisms using molecular data such as gene sequences. The 16S rRNA gene is used for this type of analysis because the gene phylogeny accurately reproduces the evolutionary history of the organisms from which the sequences were derived. Assume that the phylogeny below, which was produced based on analysis of the 16S rRNA gene, represents the evolutionary history of bacteria.  You are interested in determining other genes that may be used to recover the same phylogeny. For each microbe in the tree, you sequence two other genes. The first is rpoB, which encodes one of the subunits in RNA polymerase holoenzyme and is located on the bacterial chromosome. The second is cat, a gene that confers resistance to the antibiotic chloramphenicol (a drug that targets the ribosome) and is located on a plasmid. Examine the two trees below. On the left is the phylogeny recovered using cat sequences and on the right is the phylogeny recovered using rpoB sequences.  One of the two trees supports the hypothesis presented in the 16S rRNA gene phylogeny for this group of bacteria. Which of the following helps to explain why only one of the two trees matches the 16S rRNA gene phylogeny?

Accepted Answer

The answer of Scientists generate phylogenetic trees for a group...

Question 8

Nitrogen gas (N₂) in the atmosphere can be DIRECTLY utilized by which of the following organisms?

Accepted Answer

Nitrogen gas in the atmosphere can only be directly utilized by nitrogen-fixing bacteria and archaeons, which convert it into a usable form of nitrogen for other organisms. Algae and other eukaryotes do not have the ability to directly utilize nitrogen gas from the atmosphere.

Question 9

Why are scientists unable to grow the majority of Bacteria and Archaea in pure culture in a laboratory setting?

Accepted Answer

Many species of bacteria and archaea have specific metabolic requirements that are difficult to replicate in a laboratory setting. This makes it challenging to grow them in pure cultures.

Question 10

Two graduate students are trying to identify new species of bacteria based on the criteria of Ernst Mayr. They are having a lot of trouble with this method, and then suddenly realize that they can't use Mayr's definition of a species for identifying bacteria species. Why not?

Accepted Answer

Ernst Mayr's biological species concept is based on reproductive isolation and sexual reproduction, which bacteria do not undergo. Additionally, horizontal gene transfer allows DNA exchange between different bacterial species, complicating species identification.

Question 11

Cyanobacteria are the most diverse group of bacteria, containing gram-positive bacteria, purple sulfur bacteria, and firmicutes.

Accepted Answer

Cyanobacteria are a group of photosynthetic bacteria that are classified as gram-negative bacteria, not gram-positive. Purple sulfur bacteria and firmicutes are not cyanobacteria, but belong to different groups of bacteria.

Question 12

There are bacteria that live on single-celled eukaryotes.

Accepted Answer

Yes, there are bacteria that can live as symbionts on single-celled eukaryotes such as protozoa. For example, some bacteria live inside the digestive system of protozoa and help them break down cellulose.

Question 13

Why is genomic information often more useful than phenotypic information in the bacterial phylogenetic tree?

Accepted Answer

Most bacteria cannot be cultured, so genomic information is often the only way to study them.

Question 14

Whereas the gene encoding the small subunit of ribosomes was used to generate the tree of life, many genes are inappropriate choices for this type of analysis because these genes have been subject to horizontal gene transfer for billions of years.

Accepted Answer

This is true. Many genes, particularly those involved in more recent cellular functions such as metabolism and motility, have been subject to extensive horizontal gene transfer over billions of years, making them inappropriate for generating a tree of life based on vertical descent.

Question 15

Why are genes associated with nitrogen fixation NOT typically used to identify bacteria species?

Accepted Answer

These genes are often exchanged between bacteria by horizontal gene transfer, making them unreliable for species identification due to their variability across different species.

Question 16

H₂S is absorbed from the environment by bacteria, algae, and plants; however, this molecule is quickly reduced by organisms to form SO₄^-.

Accepted Answer

H₂S represents the chemical formula for hydrogen sulfide (H2S), which is indeed absorbed by bacteria, algae, and plants, but it is not directly reduced to form SO₄^-, which represents the chemical formula for sulfur dioxide (SO2). The reduction and oxidation processes in biological systems involving sulfur compounds are more complex and do not directly convert H2S to SO2.

Question 17

Which of the following is NOT a characteristic that differentiates Bacteria from Archaea?

Accepted Answer

Bacteria and Archaea both can be chemoautotrophic, meaning they can produce their own food by chemical reactions. The other options (A, C, D) are characteristics that differentiate Bacteria from Archaea.

Question 18

Molecular features that distinguish major groups of Bacteria evolved billions of years ago. The DNA sequences continued to change within each group, potentially masking inherited sequence similarities from a common ancestor that otherwise would have defined the group.

Accepted Answer

The statement is true as molecular features that distinguish major groups of Bacteria evolved billions of years ago, and over time, the DNA sequences continued to change within each group, potentially masking inherited sequence similarities from a common ancestor that otherwise would have defined the group.

Question 19

Even without the nitrogen cycle, life on Earth would continue with minimal interruption due to compensation by the carbon and sulfur cycles.

Accepted Answer

While the carbon and sulfur cycles play important roles in Earth's ecosystems, without the nitrogen cycle, there would be a significant decrease in the availability of necessary nutrients for plant growth and food webs, leading to a cascade of ecological impacts.

Question 20

Why does Ernst Mayr's biological species concept NOT apply to Archaea and Bacteria?

Accepted Answer

Ernst Mayr's biological species concept defines a species as a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. However, bacteria and archaea do not have a typical sexual reproduction process involving meiosis and fertilization, making it difficult to apply this concept to them. Therefore, the biological species concept does not apply to prokaryotic organisms.

Quiz 26: Bacteria and Archaea