BIOL 107 606 Fundamentals of Microbiology

Correct Answers

C: P. aeruginosa,

D: E. coli

Explanation:

A Gram-negative rod must have:

A negative Gram reaction (-)

A bacillus (rod-shaped) cell morphology

From the table:

E. coli: Gram-negative (–), bacillus → matches

P. aeruginosa: Gram-negative (–), bacillus → matches

B. subtilis: Gram-positive (+), bacillus → incorrect Gram reaction

S. aureus: Gram-positive (+), coccus (spherical) → incorrect Gram reaction and morphology

Why the other options are incorrect:

A) B. subtilis:

It is a Gram-positive bacillus — does not meet the Gram-negative requirement.

B) S. aureus:

It is a Gram-positive coccus — incorrect for both Gram stain and cell shape.

Therefore, the unknown could only be E. coli or P. aeruginosa.

Correct Answer B: ATP

Detailed Explanation of the Correct Answer:

B. ATP is correct because the mitochondrion produces adenosine triphosphate (ATP), which is the primary energy currency of the cell. During a process called cellular respiration, mitochondria break down glucose and other fuel molecules in the presence of oxygen to generate ATP. This energy is then used to power vital cellular activities such as muscle contraction, nerve signaling, active transport, and biosynthesis. Because of this critical role in energy production, the mitochondrion is often referred to as the "powerhouse of the cell."

Explanation of Why the Other Options Are Incorrect:

A. Proteins – While mitochondria have their own DNA and ribosomes, they are not the main site of protein production; that happens mostly in the cytoplasm on ribosomes or in the rough endoplasmic reticulum.

C. Enzymes – Mitochondria use enzymes to drive reactions, but they do not primarily produce enzymes as their main function.

D. DNA – Mitochondria have a small circular DNA molecule, but this is not what makes them the powerhouse. Their ability to produce ATP is what earns them that nickname.

Summary:

Mitochondria generate ATP, the energy molecule that powers most cellular functions, which is why they are known as the powerhouse of the cell. The correct answer is B. ATP.

Correct Answer B: 15

Explanation:

The atomic number of an atom is determined by the number of protons in its nucleus. In this case, the atom has 15 protons, so its atomic number is 15. The atomic number defines the element and its position on the periodic table (in this case, phosphorus).

Why the other options are incorrect:

A) 31:

This is the mass number, which is the sum of protons and neutrons (15 + 16 = 31), not the atomic number.

C) 17:

This is the number of electrons, which does not determine the atomic number.

D) 16:

This is the number of neutrons, which affects the isotope, not the atomic number.

E) 33, F) 48, G) 32:

These values do not correspond to the number of protons in the atom and are unrelated to the atomic number in this case.

Correct Answer A: Energy from the chemical bonds of food molecules is captured by an organism and converted to ATP.

Explanation:

Cellular respiration is the metabolic process in which cells break down glucose and other food molecules in the presence of oxygen to produce ATP, the energy currency of the cell. This process occurs in several stages: glycolysis, the Krebs cycle, and the electron transport chain.

It captures the energy stored in the chemical bonds of nutrients (like glucose) and converts it into ATP, which powers cellular activities.

Why the other options are incorrect:

B) ATP molecules are converted into water and sugar:

Incorrect—ATP is used for energy, not converted into water and sugar.

C) Oxygen is produced during metabolic activity:

Incorrect—oxygen is consumed in cellular respiration, not produced. (Oxygen is produced during photosynthesis, not cellular respiration.)

D) Light energy is converted into heat:

Incorrect—this is not a definition of cellular respiration; this could describe a non-biological process like radiation absorption.

Correct Answer E: Multiple alleles and codominance

Detailed Explanation of the Correct Answer:

E. Multiple alleles and codominance is correct because the ABO blood group system is governed by a single gene (I) that has three different alleles: Iᴬ, Iᴮ, and i. This makes it an example of multiple alleles. Additionally, Iᴬ and Iᴮ are codominant, meaning that if a person inherits both (genotype IᴬIᴮ), both A and B antigens are expressed on the surface of red blood cells. This results in blood type AB, where both alleles are fully and simultaneously expressed, rather than blending.

Explanation of Why the Other Options Are Incorrect:

A. Balanced polymorphism and codominance – While codominance is correct, "balanced polymorphism" refers to a situation where multiple alleles are maintained in a population due to evolutionary advantages. That concept does not fully define the ABO system.

B. Balanced polymorphism but not codominance – This is incorrect because codominance is a key feature of the ABO system.

C. Multiple alleles but not codominance – This is partially true (multiple alleles), but codominance is an essential part of the ABO blood group, so this answer is incomplete.

D. Multiple alleles and incomplete dominance – This is incorrect because the ABO system does not involve incomplete dominance. In incomplete dominance, heterozygous individuals show a blended phenotype, which is not the case here.

Summary:

The ABO blood group is determined by three alleles (Iᴬ, Iᴮ, i) and features codominance between Iᴬ and Iᴮ, making the correct answer E. Multiple alleles and codominance.

Correct Answer B: Ionic

Explanation:

An ionic bond forms when one atom transfers one or more electrons to another atom. This usually occurs between a metal and a non-metal, resulting in the formation of oppositely charged ions that are held together by electrostatic attraction.

Why the other options are incorrect:

A) Hydrogen:

A hydrogen bond is a weak attraction between a hydrogen atom in one molecule and an electronegative atom in another. It is not formed by electron transfer.

C) Covalent:

A covalent bond forms when atoms share electrons, not transfer them. Covalent bonds typically occur between non-metal atoms.

Correct Answer A: Pyruvate

Detailed Explanation of the Correct Answer:

Pyruvate is not a product of the Krebs cycle; it is actually a reactant that enters the mitochondrial matrix before the cycle begins. Specifically, pyruvate is produced during glycolysis, which occurs in the cytoplasm. Once formed, pyruvate is transported into the mitochondrion, where it is converted into acetyl-CoA during a process called pyruvate oxidation. Acetyl-CoA then enters the Krebs cycle to be further broken down.

The actual products of the Krebs cycle (per one glucose molecule, which generates two turns of the cycle) include:

– 6 NADH (3 per cycle)

– 2 FADH₂ (1 per cycle)

– 4 CO₂ (2 per cycle)

– 2 ATP (or GTP) (1 per cycle)

Explanation of Why the Other Options Are Correct Products:

NADH is a key product of the Krebs cycle and serves as an electron carrier that delivers high-energy electrons to the electron transport chain.

Carbon dioxide (CO₂) is released as a waste product during the decarboxylation steps in the cycle, when carbon atoms are removed from intermediates.

ATP (or in some cells, GTP) is produced directly through substrate-level phosphorylation during one of the steps of the Krebs cycle.

Summary:

Pyruvate is not produced by the Krebs cycle—it is converted before the cycle begins

Correct answer B: flagellum

Detailed explanation:

The flagellum is a long, whip-like appendage that extends from the surface of many bacteria and is primarily responsible for motility — allowing bacteria to move toward or away from stimuli, a phenomenon known as taxis. The movement of the flagellum is powered by a rotary motor embedded in the bacterial cell membrane, and it enables bacteria to swim through liquids, such as in water or bodily fluids. Flagella are essential for the motility of many bacteria, and they allow bacteria to move in response to various environmental cues like nutrients (chemotaxis) or light (phototaxis).

Flagella can be located in various positions on the bacterial cell: they can be monotrichous (one flagellum), lophotrichous (multiple flagella at one end), amphitrichous (flagella at both ends), or peritrichous (flagella distributed all over the surface of the cell).

Why the other options are incorrect:

A. pilus

A pilus (or pili in plural) is a hair-like appendage found on the surface of many bacteria, but it is not involved in motility. Pili are mainly used for attachment to surfaces or for genetic exchange (such as in conjugation), not for movement.

C. glycocalyx

The glycocalyx is a gel-like outer layer composed of polysaccharides (or occasionally proteins) that surrounds the cell. It is involved in adhesion, protection, and biofilm formation, but it does not contribute to bacterial motility. The glycocalyx can help bacteria stick to surfaces, but it does not enable movement.

D. fimbriae

Fimbriae are short, bristle-like appendages on the bacterial surface that allow the bacterium to adhere to surfaces or host tissues. Like pili, they are primarily involved in attachment rather than motility.

Summary:

The flagellum is the cellular appendage that allows bacteria to be motile. It enables bacteria to swim and move in response to environmental stimuli. The other options (pilus, glycocalyx, and fimbriae) are not involved in motility. Thus, the correct answer is B flagellum.

Correct Answer B: Genotype

Detailed Explanation of the Correct Answer:

B. Genotype is the correct answer because it refers to the genetic makeup of an organism, specifically the sequence of nucleotides (DNA bases: A, T, C, G) in a gene that determines a particular trait. The genotype provides the instructions for building proteins that contribute to the organism’s characteristics.

Explanation of Why the Other Option Is Incorrect:

A. Phenotype – This refers to the observable traits or characteristics of an organism, such as eye color or height, which result from the interaction of the genotype with the environment. It is the expression, not the genetic code itself.

Summary:

The genetic code or nucleotide sequence that determines a trait is called the genotype. Therefore, the correct answer is B. Genotype.