Typical gram-negative bacteria have an outer membrane containing lipopolysaccharide and a thin peptidoglycan layer. Typical gram-positive bacteria lack that outer membrane and have a thicker peptidoglycan layer. Both groups have a plasma membrane.

During lysogeny, the phage genome is maintained in the host and copied as the bacterium divides, without producing a lytic burst. Induction can initiate a lytic cycle, in which progeny phages are produced and the host cell lyses.

Peptidoglycan consists of sugar chains cross-linked by short peptides. Lipopolysaccharide is a component of the outer membrane of typical gram-negative bacteria. A capsid is a protein coat around a viral genome. Plasmids are extrachromosomal DNA molecules, usually circular; some can be transferred between bacteria.

Viruses and bacteria both have nucleic acid genomes. Viruses have a protein capsid and require host-cell machinery to produce progeny. Bacteria are cells with ribosomes and generally reproduce by binary fission.

The major lytic stages are attachment, penetration, biosynthesis of viral genomes and proteins, assembly, and release. The question begins after attachment, so B gives the correct remaining sequence.

The bacterium benefits from the association while the host is harmed, so the relationship is parasitism. In predation, a predator captures and consumes prey.

The E. coli trp operon encodes enzymes for tryptophan biosynthesis. Tryptophan acts as a corepressor: binding to the repressor enables it to bind the operator and reduce transcription. Lactose metabolism is regulated by the lac operon.

Prions are infectious, misfolded forms of proteins and contain no DNA or RNA. In contrast, viruses have nucleic acid genomes protected by protein coats.

The plasma membrane is the selective barrier that regulates nutrient uptake and waste transport. The cell wall provides structural support and helps prevent osmotic lysis in hypotonic environments. Thus, A, B, and C are primarily membrane functions.

Vancomycin generally acts against susceptible gram-positive bacteria; the gram-negative outer membrane usually prevents entry. Vancomycin binds cell-wall precursor peptides, while penicillins inhibit penicillin-binding proteins. Susceptibility also depends on the bacterial strain and resistance mechanisms.

Mutation and horizontal gene transfer can create genetic variation in bacterial populations. Transformation, conjugation, and transduction are mechanisms of horizontal transfer.

All are correct except A. Adenoviruses are DNA viruses.

The prefix diplo- indicates pairs, staphylo- indicates clusters, and strepto- indicates chains. Cocci are spherical, bacilli are rod-shaped, and spirilla are spiral-shaped.

Microbes can cause disease, support other organisms, decompose organic matter, and recycle nutrients. For example, some intestinal bacteria synthesize vitamin K.

Prions are infectious misfolded proteins that can cause neurodegenerative diseases, including bovine spongiform encephalopathy (BSE), Creutzfeldt-Jakob disease, and scrapie.

Viruses are acellular particles with a protein capsid and, in some cases, a lipid envelope. Plant and oomycete walls contain cellulose; fungal walls contain chitin and other polysaccharides. Most bacterial walls contain peptidoglycan, outside a separate plasma membrane. Some bacteria lack a cell wall.

Some animal viruses replicate their genomes in the host nucleus, and some acquire envelopes from host membranes. T4 attaches to a susceptible bacterial cell and injects its DNA through a tail apparatus; its genome replication occurs in the bacterial cytoplasm.

T4 is a virulent, double-stranded DNA bacteriophage that infects susceptible bacteria such as E. coli. It has a head, tail sheath, and tail fibers and follows a lytic cycle. Temperate phages such as lambda can establish lysogeny.

Analogous structures perform similar functions but have independent evolutionary origins. Most bacterial walls contain peptidoglycan, whereas plant walls are rich in cellulose. Their similar protective and supporting functions do not make them homologous.

All are found in bacterial cells except B. Lysosomes are found in most eukaryotic animal cells.

Taxis is directed movement toward or away from a stimulus. E. coli can move toward attractants and away from repellents. Kinesis is a nondirectional change in movement rate or turning frequency in response to a stimulus. Flagella can propel many bacteria.

Bacteria do not undergo meiosis. Binary fission is asexual cell division, while horizontal gene transfer can introduce genetic variation. Biofilms are communities attached to a surface and embedded in an extracellular matrix. Some plasmids mediate horizontal transfer. Therefore, II and III are correct; I and IV are false.

Viroids are RNA pathogens of plants and lack protein capsids.

Influenza viruses are enveloped. Adenoviruses, tobacco mosaic virus, papillomaviruses, and phage T4 are nonenveloped. Bacteriophages as a group are diverse; some, such as phage phi6, do have envelopes.

Allolactose normally binds the lac repressor and reduces its affinity for the operator. Without allolactose, the repressor remains able to bind the operator, so lactose cannot produce normal induction and transcription stays low. Expression also depends on glucose availability.

Capsids are protein coats that normally protect viral genomes and can help deliver them into host cells. Their normal role is not to enclose bacterial chromosomes. During transduction, a phage capsid can accidentally package bacterial DNA.

Retroviruses use reverse transcriptase to copy their RNA into DNA. The DNA can integrate into the host genome, and transcription produces new viral RNA. T4 is a DNA phage that follows a lytic cycle; it does not normally replicate by integrating its genome into bacterial DNA.

Facultative anaerobes, including E. coli, can grow with or without oxygen. They use aerobic respiration when oxygen is available and can use fermentation or anaerobic respiration when it is absent. Obligate aerobes require oxygen for growth; obligate anaerobes do not grow in oxygenated conditions.

T4 is a double-stranded DNA virus that infects susceptible E. coli cells and reproduces through a lytic cycle in the bacterial cytoplasm. Other bacteriophages can have different host ranges, genomes, or life cycles; some are temperate, and some have RNA genomes.

Transduction is transfer of bacterial DNA by a bacteriophage. Conjugation transfers DNA through direct contact between bacterial cells. Transformation is uptake of free DNA from the environment. Binary fission is asexual cell division.

Viruses lack cellular structures and independent metabolism and require host cells to produce progeny. They do not use bacterial conjugation. Conjugation is direct DNA transfer between bacterial cells. Therefore, I, II, and III are correct; IV is false.

HIV is a retrovirus whose virions carry an RNA genome. It makes a DNA intermediate during infection, but that does not make it a DNA-genome virus. Adenoviruses have DNA genomes, and viral proteins are translated by host ribosomes.