Fund of Microbiology (BIOL 107 606)

Correct Answer B: Natural active immunity

Explanation:

Natural active immunity occurs when a person is exposed to a pathogen (like the chicken pox virus) and the immune system responds by producing antibodies and memory cells. This type of immunity is long-lasting and often lifelong, because the body "remembers" how to fight the infection in the future.

Why the other options are incorrect:

A) Artificial active immunity:

This occurs through vaccination, where a person is given a weakened or inactivated form of a pathogen to stimulate antibody production—not from natural infection.

C) Natural passive immunity:

This occurs when antibodies are passed naturally from one person to another, such as from mother to baby through the placenta or breast milk—no immune response is triggered in the recipient.

D) Artificial passive immunity:

This involves the injection of antibodies (e.g., antiserum or immunoglobulin therapy), providing temporary protection without the body generating its own immune response.

Correct Answer B: Archaea look more like Bacteria, but are more closely related to Eukarya

Explanation:

Archaea and bacteria are both prokaryotic, meaning they lack a nucleus and membrane-bound organelles, which makes them appear similar under a microscope. However, molecular and genetic evidence shows that Archaea are more closely related to Eukarya than to Bacteria. This includes similarities in DNA replication, RNA transcription, and protein synthesis.

Why the other options are incorrect:

A) Eukarya look more like Archaea, but are more closely related to Bacteria:

This is incorrect because while Eukarya are genetically more similar to Archaea, they do not "look" more like them. Eukaryotic cells are structurally more complex than both Archaea and Bacteria.

C) Bacteria look more like Archaea, but are more closely related to Eukarya:

While Bacteria and Archaea may appear similar as prokaryotes, Bacteria are not more closely related to Eukarya. In fact, it is Archaea that share a closer evolutionary relationship with Eukarya.

Correct Answer E: All of the answers listed are required for a pathogen to be successful.

Explanation:

A successful pathogen must perform all of the listed actions to cause disease and continue spreading. It must first attach to or penetrate host tissues to begin infection, evade the immune system to avoid destruction, survive transmission to reach a new host, and cause damage to host tissues to produce symptoms and ensure continued spread. Missing any one of these capabilities would limit its effectiveness as a pathogen.

Why the other options are incorrect:

A) It must be able to attach and/or penetrate host tissues:

While essential, this alone is not sufficient for success. A pathogen must also evade immunity, transmit, and cause damage.

B) It must be able to evade the host immune system:

Important for persistence, but not enough without tissue entry, transmission, and damage.

C) It must be able to survive passage from one host to the next:

Necessary for spreading, but not the only requirement.

D) It must be able to cause damage or malfunction in the host tissues:

Key to causing symptoms, but not enough to define a successful pathogen without the other steps.

Correct Answer D: Aerobic respiration

Detailed Explanation of the Correct Answer:

D. Aerobic respiration is correct because it is the most efficient method of converting glucose into usable ATP in the human body. In the presence of oxygen, glucose undergoes complete oxidation through a series of steps: glycolysis, the Krebs cycle, and the electron transport chain. This process can yield up to 36–38 ATP molecules per glucose molecule, making it far more efficient than any anaerobic process.

Explanation of Why the Other Options Are Incorrect:

A. Lactic acidosis – This is not a method of glucose conversion but rather a dangerous condition where lactic acid accumulates in the body, usually due to prolonged anaerobic metabolism. It can lead to muscle fatigue and other health issues.

B. Anaerobic respiration – This occurs when oxygen is not available. It includes glycolysis followed by lactic acid fermentation, producing only 2 ATP molecules per glucose, which is much less efficient than aerobic respiration.

C. Fermentation conversion – Like anaerobic respiration, fermentation produces minimal ATP. It helps regenerate NAD⁺ for glycolysis but results in very low energy yield (only 2 ATP per glucose).

Summary:

Aerobic respiration is the most efficient and productive method of glucose conversion for generating ATP in the human body. The correct answer is D. Aerobic respiration.

Correct Answer B: They serve as high-energy electron carriers that transport electrons throughout the cell

Detailed Explanation of the Correct Answer:

B. They serve as high-energy electron carriers that transport electrons throughout the cell is correct because NAD⁺ and FAD are coenzymes that become NADH and FADH₂ when they accept electrons during glycolysis, the citric acid (Krebs) cycle, and pyruvate oxidation. These reduced forms carry high-energy electrons and hydrogen atoms to the electron transport chain (ETC) in the mitochondria. There, the electrons are used to generate a proton gradient, which ultimately drives the synthesis of ATP through oxidative phosphorylation.

Explanation of Why the Other Options Are Incorrect:

A. They serve to help produce co-enzyme A – This is incorrect. Coenzyme A is involved in the conversion of pyruvate to acetyl-CoA, but NAD⁺/FAD are not involved in its production.

C. They serve as the final electron acceptor for the electron transport chain – This is incorrect. The final electron acceptor in the ETC is oxygen, not NAD⁺ or FAD.

D. They serve to directly help catalyze the reaction of ADP to ATP – Incorrect. While NADH and FADH₂ contribute to the process that leads to ATP production, they do not directly catalyze the conversion of ADP to ATP. That function is performed by ATP synthase.

Summary:

NAD⁺/NADH and FAD/FADH₂ function as electron carriers, shuttling high-energy electrons to the electron transport chain, where most of the cell's ATP is ultimately generated. Therefore, the correct answer is B.

Correct Answer D: All of these are ways in which a virus is categorized

Detailed Explanation of the Correct Answer:

D. All of these are ways in which a virus is categorized is correct because virologists use multiple characteristics to classify viruses. The structure, genetic material, and external components all influence how a virus functions and spreads, and they are considered together in viral taxonomy. Now let’s look at each individual option in detail to explain why all are valid criteria.

Explanation of Why the Other Options Are Correct But Incomplete on Their Own:

A. Presence or absence of an outer envelope

Viruses are classified based on whether they are enveloped or non-enveloped. Enveloped viruses have a lipid bilayer surrounding their capsid, which they acquire from the host cell membrane (e.g., HIV, Influenza). Non-enveloped viruses (e.g., Norovirus, Adenovirus) lack this envelope and are generally more resistant to harsh environmental conditions. This feature affects their transmission and stability but isn’t the sole basis for classification.

B. Size and shape

Viruses are also categorized by their capsid shape and overall structure. The capsid can be helical, icosahedral, complex, or spherical. For example, bacteriophages have complex structures with tails, while poliovirus is icosahedral. Size varies widely among viruses and is an important morphological feature used in microscopy and diagnostics, but again, it is only one part of the classification process.

C. Type of nucleic acid

Viruses are fundamentally divided by the kind of genetic material they contain—either DNA or RNA, which can be single-stranded (ss) or double-stranded (ds), linear or circular, and segmented or non-segmented. For instance, coronaviruses have single-stranded RNA, while herpesviruses have double-stranded DNA. This is a core part of the Baltimore classification system, making it a critical factor in viral categorization, but still not the only one.

Summary:

While the presence of an envelope, morphological features, and type of nucleic acid are each important in viral classification, no single factor is sufficient alone. Virologists use all of these features together to categorize viruses accurately. Therefore, the correct answer is D. All of these are ways in which a virus is categorized.

Correct Answer B: Stage

Detailed Explanation of the Correct Answer:

B. Stage is correct because the stage is the flat platform on a light microscope where the microscope slide is placed for observation. The stage typically includes stage clips or a mechanical stage to hold the slide securely in place. It may also have knobs that allow for precise movement of the slide to bring different areas into view.

Explanation of Why the Other Options Are Incorrect:

A. Lens – The lenses (objective and ocular) are used for magnifying the image, not for holding the slide. The slide must be placed in the focal path beneath the lens, but not on the lens itself.

C. Arm – The arm is the structural part of the microscope that connects the base to the head. It is used to carry or support the microscope but not to hold the slide.

D. Base – The base is the bottom support structure of the microscope. It keeps the microscope stable on a surface but has no role in slide placement.

Summary:

The correct place to position a slide on a light microscope is the stage, which holds the specimen for viewing. The correct answer is B. Stage.

Correct Answer B: Hydrolysis

Explanation:

Hydrolysis is a chemical reaction in which water is added to break the bonds between monomers in a polymer. This process splits large molecules into smaller subunits, and it’s essential in digestion and cellular metabolism.

Why the other options are incorrect:

A) Dehydration synthesis:

This is the opposite of hydrolysis. It joins monomers by removing water to form polymers.

C) Oxygenation:

This involves adding oxygen to a molecule, commonly in metabolic or combustion processes, not polymer breakdown.

D) Hydrogenation:

This involves the addition of hydrogen, typically to unsaturated fats, and is not related to breaking polymers.

Correct Answer D: Net movement of particles from areas of high concentration to areas of low concentration

Simple diffusion is the process where molecules move passively down their concentration gradient, meaning they move from a region where they are more concentrated to where they are less concentrated. This process does not require cellular energy or assistance from transport proteins, and it occurs until equilibrium is reached.

Why Other Options are Incorrect

A)Net movement of particles between cells:  Movement between cells describes transport across cell junctions or extracellular spaces, not diffusion across a plasma membrane.

B) Net movement of particles from areas of low concentration to areas of high concentration:  Movement from low to high concentration requires energy input and is characteristic of active transport, not simple diffusion.

C) Net movement of particles into and out of the cell using vacuoles for bulk transport:  Movement involving vacuoles refers to bulk transport mechanisms such as endocytosis or exocytosis, which are energy-dependent and different from diffusion.

Summary:

Simple diffusion is the passive movement of particles directly through the plasma membrane from an area of higher concentration to lower concentration, without energy or specialized transport mechanisms.