BIOL 107 606 Fundamentals of Microbiology

Correct answer  A: allows the bacteria to be motile

Detailed explanation:

The flagella is a long, whip-like appendage that extends from the surface of many bacteria. The primary function of the flagella is to enable motility, which allows bacteria to move toward or away from stimuli in their environment (a behavior known as taxis).

Motility is important for bacteria because it allows them to navigate their environment in search of nutrients or to move away from harmful substances or unfavorable conditions.

The flagellum operates like a propeller, rotating to propel the bacterium forward or backward, allowing it to move in liquid environments, such as water, mucus, or bodily fluids.

Why the other options are incorrect:

B ability to transfer genetic information from one cell to another

This process is known as conjugation, and it involves the transfer of genetic material through a pilus (not a flagellum). Pili are specialized structures used for transferring DNA between bacteria, while flagella are used for motility, not for genetic exchange.

C ability to survive under very harsh conditions for a long time

This function is carried out by endospores, not flagella. Endospores are dormant, highly resistant structures produced by certain bacteria to survive extreme conditions like heat, desiccation, and chemicals. Flagella do not contribute to survival in harsh conditions; they are used for movement.

D protection of bacteria from phagocytosis by white blood cells

This function is typically associated with the capsule or glycocalyx of bacteria. The capsule helps bacteria evade the immune system, including preventing phagocytosis (the process where immune cells engulf and digest pathogens). Flagella are not involved in immune evasion.

Summary:

The flagella's main function is to provide motility for bacteria, allowing them to move in response to environmental cues. This mobility helps bacteria find nutrients or escape harmful environments. The other options are related to different bacterial structures or processes. Therefore, the correct answer is A allows the bacteria to be motile.

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 A: Hydrophilic

Explanation:

The molecule C₁₂H₂₄O₁₂ contains a high number of oxygen atoms, which typically appear in hydroxyl (–OH) groups. These groups can form hydrogen bonds with water, making the molecule water-attracting (hydrophilic).

This formula is similar to carbohydrates, which are polar and dissolve well in water.

Why the other option is incorrect:

B: Hydrophobic:

Hydrophobic molecules lack polar groups (like –OH) and tend to be composed mostly of carbon and hydrogen with few or no oxygen atoms. This molecule has many oxygen atoms, so it is not hydrophobic.

Correct Answer D: Cell wall

Detailed Explanation of the Correct Answer:

D. Cell wall is correct because the cell wall is a rigid outer layer found in plant cells (and some fungi and bacteria) that provides structural support and acts as a protective barrier. It is primarily made of cellulose, a complex carbohydrate that gives the wall its strength. The cell wall helps maintain the shape of the plant cell, prevents excessive water intake, and supports the overall structure of the plant.

Explanation of Why the Other Options Are Incorrect:

A. Xylem – Xylem is a type of vascular tissue in plants that transports water and minerals, but it is not a part of an individual plant cell’s structure.

B. Cell membrane – While the cell membrane is a selective barrier that controls what enters and exits the cell, it does not provide the rigid support that the cell wall does.

C. Chloroplast – Chloroplasts are the organelles where photosynthesis takes place. They help the plant make food but do not act as a barrier or support structure.

Summary:

The cell wall is the part of a plant cell that provides support and acts as a protective barrier, making the correct answer D. Cell wall.

Correct Answer B: Oxygen

Detailed Explanation of the Correct Answer:

B. Oxygen is correct because aerobic respiration is the process by which cells generate energy (ATP) by breaking down glucose in the presence of oxygen. Oxygen acts as the final electron acceptor in the electron transport chain, a critical step that allows for the efficient production of large amounts of ATP. Without oxygen, cells cannot complete the aerobic pathway and must switch to less efficient anaerobic processes like fermentation.

Explanation of Why the Other Options Are Incorrect:

A. Water – Water is a byproduct of aerobic respiration, not a required starting molecule.

C. Lactic acid – Lactic acid is produced during anaerobic respiration, particularly in muscle cells when oxygen is scarce, not during aerobic respiration.

D. Carbon dioxide – Carbon dioxide is also a waste product of aerobic respiration, released during the Krebs cycle, but it is not required for the process to occur.

Summary:

Oxygen is essential for aerobic respiration because it enables the complete breakdown of glucose and supports efficient ATP production. The correct answer is B. Oxygen.

Correct Answer A: Hydrophobic

Explanation:

Phospholipids have a unique structure with a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails. The tails are made of fatty acid chains, which do not mix well with water and therefore orient themselves away from aqueous environments.

This causes phospholipids to form bilayers, where the hydrophobic tails face inward, shielded from water, and the hydrophilic heads face outward toward the watery environment inside and outside the cell.

Why the other option is incorrect:

B) Hydrophilic:

The head of the phospholipid is hydrophilic, not the tail. The tail’s nonpolar nature makes it hydrophobic.

Correct Answer C: He HAS a distinct pointing of his hair in the center of his forehead

Detailed Explanation of the Correct Answer:

C. He HAS a distinct pointing of his hair in the center of his forehead is correct because the man is heterozygous (Ww) for a dominant trait. Since widow’s peak is dominant, only one dominant allele (W) is needed for the trait to be expressed. Thus, regardless of the presence of the recessive allele (w), he will show the widow’s peak phenotype.

Explanation of Why the Other Options Are Incorrect:

A. ww (both lowercase) – This represents the genotype, not the phenotype, and it refers to someone who is homozygous recessive and would not show a widow’s peak.

B. He does NOT have a distinct pointing of his hair in the center of his forehead – This would only be true for someone with a ww genotype, which is not the case here.

D. WW (both uppercase) – This represents a homozygous dominant genotype, not the phenotype, and while it would also result in a widow's peak, it's not the man’s genotype.

E. Ww – This is the genotype, not the phenotype. It shows that the man is heterozygous, but the question asks for the phenotype (what is physically seen).

Summary:

A heterozygous individual (Ww) for a dominant trait like widow's peak will show the dominant phenotype, which is a distinct point in the hairline. Therefore, the correct answer is C. He HAS a distinct pointing of his hair in the center of his forehead.

Correct Answer A: Adenosine triphosphate (ATP)

Detailed Explanation of the Correct Answer:

A. Adenosine triphosphate (ATP) is the correct answer because ATP is known as the "molecular currency" of the cell. It provides the energy required for nearly all cellular processes, including muscle contraction, nerve impulse transmission, biosynthesis of macromolecules, and active transport across membranes. ATP stores energy in the high-energy bonds between its phosphate groups, and this energy is released when ATP is hydrolyzed to ADP and inorganic phosphate.

Explanation of Why the Other Options Are Incorrect:

B. Fatty acids – These are long-term energy storage molecules and components of cell membranes, but they are not used directly for immediate cellular work.

C. Glucose – This is a primary fuel source for cellular respiration, but it must first be broken down to generate ATP, which is the usable energy form.

D. Proteins – Proteins perform a wide range of functions (like enzymes and structural components), but they are not the primary molecules used directly as energy currency.

Summary:

ATP directly powers cellular processes, making it the immediate energy source for the cell. Therefore, the correct answer is A. Adenosine triphosphate (ATP).

Correct answer C: transcription then mRNA processing then translation

Explanation of the correct answer:

Option C is correct because it accurately reflects the sequence of steps in gene expression in a eukaryotic cell. In eukaryotic organisms, gene expression is a multi-step process that begins with transcription, continues with mRNA processing, and finishes with translation.

First, transcription occurs in the nucleus. During transcription, the DNA sequence of a gene is copied into messenger RNA. The enzyme RNA polymerase reads the DNA strand and synthesizes a complementary RNA molecule.

Next, the primary RNA transcript undergoes mRNA processing, which is unique to eukaryotes. This processing includes adding a 5’ cap to the beginning of the RNA, adding a poly-A tail to the end, and removing non-coding sequences called introns through a process called splicing. Only the coding regions, known as exons, remain in the final mature mRNA.

Finally, the processed mRNA exits the nucleus and enters the cytoplasm, where translation takes place. During translation, ribosomes read the mRNA sequence and use it to assemble a chain of amino acids in the correct order to form a protein. This chain folds into a functional protein that performs specific tasks in the cell.

Explanation of incorrect options:

A.mRNA processing -> transcription -> translation:

 is incorrect because it places mRNA processing before transcription. Processing cannot happen before transcription because RNA must first be produced in order to be processed.

B.translation -> mRNA processing -> transcription.

because it starts with translation and puts transcription last. Translation is the final step in the process, and it cannot happen until after transcription and processing have occurred. Additionally, mRNA cannot be processed before it is transcribed.

D.  transcription -> translation -> mRNA processingis

incorrect because it places translation before mRNA processing. In eukaryotes, translation only begins after the mRNA has been fully processed. Unprocessed RNA cannot be translated into a functional protein.

Summary:

In a eukaryotic cell, gene expression begins with transcription of DNA into RNA. The resulting RNA undergoes mRNA processing to become a mature messenger RNA. That mature mRNA is then translated into a protein. The correct order is transcription, mRNA processing, translation. Therefore, the correct answer is option C.