Question 1

The methanogens

Accepted Answer

The methanogens are a group of archaea that are known for their ability to produce methane (CH4) as a byproduct of their metabolism. They are part of the Domain Archaea and are anaerobic organisms that do not use oxygen as a terminal electron acceptor. Instead, they oxidize hydrogen gas (H2) to produce methane. Therefore, option E, which states that methanogens are part of the Domain Archaea and oxidize hydrogen gas to produce methane, is the correct choice.

Question 2

The genus of bacteria that is able to fix nitrogen and form heterocysts is

Accepted Answer

Anabaena is the genus of bacteria that is able to fix nitrogen and form heterocysts. Pseudomonas, Escherichia, and Vibrio do not have the ability to form heterocysts for nitrogen fixation.

Question 3

Lactic acid bacteria such as Lactococcus

Accepted Answer

Lactic acid bacteria are obligate fermenters, meaning that they do not use oxygen as a final electron acceptor and rely solely on fermentation to generate energy. They do not produce catalase and do not require anaerobic environments, although some species may be aerotolerant.

Question 4

Clostridium,Lactobacillus,and Propionibacterium all

Accepted Answer

Clostridium, Lactobacillus, and Propionibacterium are all bacteria that use organic compounds as terminal electron acceptors and oxidize organic compounds.

Question 5

A particular characteristic of disease-causing Streptococcus is

Accepted Answer

Beta-hemolysis is a characteristic of Streptococcus species that are pathogenic, meaning they have the potential to cause disease. Beta-hemolysis refers to the complete hemolysis (lysis or destruction) of red blood cells in the presence of the bacterium, resulting in a clear zone surrounding the bacterial colony on blood agar plates.

Question 6

It has been estimated that 99% of the intestinal bacteria are

Accepted Answer

Intestinal bacteria live in an environment that is largely devoid of oxygen, and most of them are unable to grow in the presence of oxygen, indicating that they are obligate anaerobes.

Question 7

Hydrogen sulfide

Accepted Answer

All of the choices are correct. Hydrogen sulfide is produced by certain microbes like Desulfovibrio when sulfur compounds are used as terminal electron acceptors. It can react with iron to produce a black precipitate and has a distinctive rotten egg smell.

Question 8

Which of the following microbes is(are)important to cheese-making?

Accepted Answer

Lactic acid bacteria (LAB) are crucial for the production of cheese, as they ferment lactose into lactic acid, which lowers the pH of the milk and coagulates the milk proteins. Propionibacterium is also important for certain types of cheese, such as Swiss cheese, as it produces carbon dioxide gas, creating the characteristic holes in the cheese. Clostridium acetylbutylicum and Desulfovibrio are not typically used in cheese-making.

Question 9

Cyanobacteria

Accepted Answer

Cyanobacteria are prokaryotes, which means they are single-celled organisms without a nucleus or other membrane-bound organelles.

Question 10

The lactobacilli,in their role as normal flora of the vagina,help the vagina resist infection by contributing to

Accepted Answer

Lactobacilli produce lactic acid which contributes to the acidic environment of the vagina (pH 3.5-4.5). This acidity helps to inhibit the growth of pathogenic bacteria and yeast, reducing the risk of infection.

Question 11

Anoxygenic phototrophs

Accepted Answer

Anoxygenic phototrophs do not produce oxygen, and do not use water as a source of electrons. Instead, they use hydrogen sulfide or organic compounds as a source of electrons. They also use a different form of chlorophyll than that found in terrestrial plants.

Question 12

Comparatively greater energy is released when

Accepted Answer

Oxygen has a higher electronegativity than nitrate, carbon dioxide, and hydrogen, making it a stronger final electron acceptor. This results in a greater release of energy through oxidative phosphorylation in aerobic respiration.

Question 13

Methanogens often grow in association with

Accepted Answer

Methanogens are a type of bacteria that produce methane through the process of fermentation. They often grow in association with fermentative bacteria, which provide the necessary substrates for methanogen metabolism.

Question 14

The purple sulfur and green sulfur bacteria

Accepted Answer

Both purple sulfur and green sulfur bacteria use hydrogen sulfide as a source of electrons in their photosynthetic processes.

Question 15

Phycobiliproteins are

Accepted Answer

Phycobiliproteins are found in cyanobacteria and are used to gather wavelengths of light that are not well absorbed by chlorophyll.

Question 16

Streptococcus pyogenes

Accepted Answer

Streptococcus pyogenes is beta-hemolytic, meaning it completely lyses red blood cells in a blood agar medium, resulting in a clear zone around the colony. It does not form endospores.

Question 17

Which of the following colonize the vagina during childbearing years?

Accepted Answer

Lactobacilli are the primary bacteria that colonize the vagina during childbearing years. Streptococci may also be present, but they are not the primary colonizers. Clostridium and Enterobacter are not typical vaginal microbiota during childbearing years. The option E is incorrect as Clostridium is not present in the vagina during childbearing years.

Question 18

The earliest oxygenic phototrophs are thought to be

Accepted Answer

Cyanobacteria are the earliest oxygenic phototrophs. They evolved the oxygenic photosynthesis process around 2.7 billion years ago, which led to the oxygenation of the Earth's atmosphere. The other options mentioned are also photosynthetic bacteria but are not known to be oxygenic phototrophs.

Question 19

Propionibacterium

Accepted Answer

Propionibacterium is responsible for the holes in Swiss cheese, which are created as a result of its production of propionic acid during fermentation. Therefore, it is correct to say that it produces propionic acid and is responsible for the holes in Swiss cheese. Additionally, Propionibacterium is a facultative anaerobe, which means it can grow under both aerobic and anaerobic conditions.

Question 20

Endospores

Accepted Answer

Endospores are a dormant form of a bacterium and are formed by members of medically relevant groups of bacteria such as Bacillus and Clostridium. They are not a form of reproduction but rather a survival mechanism that allows the bacterium to withstand harsh environmental conditions like heat, drought, and radiation. Endospores are not involved in anaerobic respiration, which is a process of generating energy without oxygen.

Quiz 11: The Diversity of Prokaryotic Organisms