Question 1

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

Accepted Answer

Lactic acid bacteria are important for the initial fermentation of cheese, producing lactic acid which lowers the pH and helps to form the cheese curds. Propionibacterium are important in some types of cheese, such as Swiss cheese, for their production of carbon dioxide gas which creates characteristic holes in the cheese. Therefore, both lactic acid bacteria and Propionibacterium are important in cheese-making. The other two options, Clostridium acetylbutylicum and Desuflovibrio, are not commonly used in cheese-making.

Question 2

Cyanobacteria

Accepted Answer

Cyanobacteria are prokaryotes, which means that they lack a nucleus and membrane-bound organelles. They are classified as bacteria and not algae, although they are sometimes referred to as blue-green algae due to their photosynthetic pigments. Cyanobacteria use water as an electron source in photosynthesis.

Question 3

Methanogens often grow in association with

Accepted Answer

Methanogens are anaerobic microorganisms that produce methane as a byproduct of their metabolism. They often grow in association with fermentative bacteria, which provide them with organic compounds necessary for their growth and metabolism. This symbiotic relationship is commonly observed in anaerobic environments such as the rumen of ruminant animals or anaerobic digesters used for wastewater treatment. Methanogens do not typically grow in association with nitrifying, lithotrophic, or photosynthetic bacteria.

Question 4

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 5

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.

Question 6

The earliest oxygenic phototrophs are thought to be

Accepted Answer

Cyanobacteria are believed to be the earliest oxygenic phototrophs, as they were first to evolve the photosynthetic pigments that allowed them to carry out oxygenic photosynthesis.

Question 7

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 8

The purple sulfur and green sulfur bacteria

Accepted Answer

Both purple sulfur bacteria and green sulfur bacteria use hydrogen sulfide as a source of electrons. They are both anaerobic and photosynthetic, but they differ in their pigments and the types of electron donors they use.

Question 9

Clostridium, Lactobacillus, and Propionibacterium all

Accepted Answer

The answer of Clostridium, Lactobacillus, and Propionibacterium all
...

Question 10

Anoxygenic phototrophs

Accepted Answer

Anoxygenic phototrophs do not produce oxygen, do not use water as a source of electrons, and do not use the same form of chlorophyll found in terrestrial plants. Instead, they use hydrogen sulfide or organic compounds as a source of electrons, allowing them to carry out photosynthesis without producing oxygen.

Question 11

Propionibacterium

Accepted Answer

Propionibacterium is responsible for the holes in Swiss cheese due to its production of CO2 gas as a byproduct of propionic acid fermentation, which creates the characteristic holes. Therefore, the best choice is E, which states that Propionibacterium produces propionic acid and is responsible for the holes in Swiss cheese. Options A, B, C, and D are incorrect because Propionibacterium produces propionic acid (not lactic acid), is responsible for the holes in Swiss cheese (not just producing acids), and is a facultative anaerobe (does not require aerobic conditions).

Question 12

Comparatively greater energy is released when

Accepted Answer

Oxygen is one of the strongest electron acceptors in the process of cellular respiration, and therefore releases the greatest amount of energy when it serves as the final electron acceptor in the electron transport chain. This is because it has a higher electronegativity than other possible electron acceptors, allowing it to hold onto electrons more tightly and release more energy.

Question 13

Which of the following colonize the vagina during childbearing years?

Accepted Answer

Lactobacilli are the dominant bacterial group that colonizes the vagina during childbearing years. Streptococci and Enterobacter may also be present, but they are not the dominant group. Clostridium may be present in rare cases, but it is not a normal resident of the vaginal microbiota, so choice E is incorrect.

Question 14

Streptococcus pyogenes

Accepted Answer

Streptococcus pyogenes is beta-hemolytic, meaning it completely lyses red blood cells and causes a clear zone around the colonies on blood agar plates. It does not form endospores.

Question 15

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

Accepted Answer

Intestinal bacteria live in an anaerobic environment, where there is little to no oxygen present. This means that they are primarily obligate anaerobes, which cannot survive in the presence of oxygen. Only a small percentage of intestinal bacteria are facultative anaerobes, which can survive in both anaerobic and aerobic environments. Therefore, choice D is the best answer.

Question 16

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

Accepted Answer

Anabaena is one of the few genera of bacteria known to form heterocysts, which are specialized cells for nitrogen fixation.

Question 17

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

Accepted Answer

Lactobacilli help maintain the acidity of the vagina by producing lactic acid, which creates an environment that is hostile to many pathogenic bacteria.

Question 18

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 instead rely on fermentation to produce energy. They also do not produce catalase, which is an enzyme that breaks down hydrogen peroxide into water and oxygen. While they can survive in anaerobic environments, they can also grow in the presence of small amounts of oxygen.

Question 19

The methanogens

Accepted Answer

Methanogens are part of the Archaea domain and they oxidize hydrogen gas to produce methane. They are anaerobic organisms and do not utilize oxygen as a terminal electron acceptor.

Question 20

Hydrogen sulfide

Accepted Answer

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

Quiz 11: The Diversity of Prokaryotic Organisms