Worksheets20.1 Viruses, Viroids, and Prions: Introduction
Total questions: 92
Worksheet time: 46mins
Which statement best distinguishes viruses from cellular life?
They are noncellular infectious agents
They metabolize independently in hosts
They contain both DNA and RNA genomes
They perform photosynthesis for energy
A hallmark of viral replication is that viruses
depend on host metabolic machinery
translate proteins without ribosomes
synthesize ATP in their own organelles
divide by binary fission outside cells
Which pair correctly matches a viral component with its nature?
Genome — both DNA and RNA together
Core enzymes — photosynthetic proteins
Envelope — rigid carbohydrate layer
Capsid — protein shell around core
What technological advance first allowed scientists to see viruses directly?
The electron microscope invention
The Gram staining technique
The light microscope refinement
The ultracentrifuge method
Louis Pasteur contributed to virology by proposing that
viroids are misfolded infectious proteins
all viruses possess lipid envelopes
viruses are self-replicating without hosts
an agent smaller than bacteria caused rabies
Which feature is used to classify viruses?
Presence of chlorophyll pigments
Ability to produce peptidoglycan
Mode of cellular respiration used
Type of nucleic acid core present
A virus described as “naked” most likely lacks which component?
A lipid envelope surrounding capsid
A protein capsid enclosing genome
Any nucleic acid in the inner core
Any proteins associated with enzymes
A newly discovered virus is 50 nanometers in diameter and contains single‑stranded RNA. Which is the most justified conclusion from this information?
It must contain double‑stranded DNA
It cannot infect animals or plants
It could be enveloped or nonenveloped
It can replicate without host cells
In the adenovirus diagram, which structural feature is located at each vertex of the polyhedral capsid?
A base plate with pins
A helical sheath segment
A fiber extending outward
A short neck connector
Which statement best distinguishes the heads of adenovirus and a T-even bacteriophage in the diagrams?
Both are polyhedral, but only the bacteriophage has a neck
Only adenovirus has a polyhedral head structure
Both heads are helical with DNA coiled inside
Only the bacteriophage head lacks enclosed nucleic acid
According to the bacteriophage diagram, what structure directly connects the head to the tail sheath?
A corner fiber
A base plate ring
A capsid protein
A small neck region
Which sequence correctly traces from the bacteriophage head to the point of initial host contact shown in the diagram?
Capsid → neck → tail sheath → base plate → pins
Capsid → base plate → neck → pins → sheath
DNA → base plate → neck → sheath → pins
Capsid → fiber → neck → pins → sheath
In the adenovirus figure, what composes the outer shell enclosing the DNA?
Cellulose-protein hybrid wall
Peptidoglycan lattice shell
Lipid bilayer with glycoproteins
Protein units forming a capsid
A researcher engineers a mutant T-even bacteriophage lacking tail fibers but retaining the base plate and pins. Which outcome is most likely during host recognition?
Enhanced DNA packing within the head
No change to initial adsorption dynamics
Reduced attachment efficiency to the host
Improved neck stability during infection
Which statement best identifies the nucleic acid composition of a single virion?
Either DNA or RNA, never both
Both DNA and RNA together
Mostly proteins with some RNA
Primarily lipids with some DNA
In the left diagram of the tobacco mosaic virus, what structural feature is highlighted by the cylinder of repeating units?
Tail fibers for host attachment
Helical capsid surrounding RNA
Icosahedral capsid around DNA
Enveloped membrane with spikes
Which component is present in influenza virions but absent in the tobacco mosaic virus shown?
Capsid composed of proteins
Single-stranded RNA genome
Helical capsid protein shell
Membranous envelope with spikes
A virus has a spherical capsid surrounded by a membrane studded with proteins. Which feature most directly aids host cell recognition?
Phospholipids in the membrane
Length of the RNA genome
Capsid protein subunit pattern
Glycoprotein spikes on the envelope
If a newly discovered virus contains both DNA and RNA in its core, which conclusion is most justified?
It must infect only plant cells
The sample is contaminated, not a single virion
It represents a typical enveloped virus
It likely has no protein capsid
Two viruses enter a cell: Virus A has a helical capsid without an envelope; Virus B has a spherical capsid with an envelope and spikes. Which prediction is best supported about their entry mechanisms?
Virus B likely fuses or endocytoses via spikes
Virus A uses envelope-mediated membrane fusion
Both rely solely on DNA injection through tails
Neither requires host receptors for attachment
Which statement best defines viruses as obligate intracellular parasites?
They reproduce in cell-free nutrient media
They reproduce independently using viral ribosomes
They reproduce only inside living cells
They reproduce best in sterile saline solutions
During which stage of the viral reproductive cycle are new viral genomes and proteins synthesized using host machinery?
Release stage exiting through lysis
Penetration stage injecting the genome
Attachment stage matching surface molecules
Biosynthesis stage using host resources
What primarily determines host specificity during viral attachment to a cell?
Presence of cell wall and capsule thickness
Rate of host cell division and size
Concentration of nutrients in the medium
Complementary viral proteins and host receptors
Which sequence correctly orders the five common stages of viral reproduction?
Attachment, penetration, biosynthesis, maturation, release
Release, biosynthesis, maturation, penetration, attachment
Penetration, attachment, maturation, biosynthesis, release
Maturation, release, attachment, penetration, biosynthesis
A bacteriophage immediately replicates and causes host cell lysis, releasing many virions. Which cycle is described?
Retroviral cycle with reverse transcription
Lytic cycle with immediate reproduction
Endosymbiotic cycle with mutual benefit
Lysogenic cycle with genome latency
In the lysogenic cycle of a bacteriophage, the integrated viral DNA is called a what?
Prion lacking nucleic acids
Prophage integrated in host genome
Provirus outside the cytoplasm
Plasmid carrying viral enzymes
Which outcome distinguishes the lysogenic cycle from the lytic cycle in bacteria?
Rapid virion assembly and cell bursting
Viral genome latency without immediate lysis
Release only by budding from membranes
No integration and immediate transcription
A toxin-producing bacterium causes disease only when carrying phage DNA integrated into its genome. Which mechanism explains this?
Horizontal transfer by transformation
Conjugation forming an F plasmid
Lytic burst increasing cell motility
Lysogenic conversion via a prophage
A researcher blocks host ribosomes after viral entry. Which stage will be directly impaired first?
Biosynthesis of viral components
Attachment to host receptors
Penetration of the capsid or genome
Release of virions by lysis
Which statement best contrasts viruses with living cells in this context?
Viruses contain all metabolic enzymes for replication
Viruses grow by cell division independent of hosts
Viruses are active or inactive rather than alive or dead
Viruses can be cultured on nutrient agar plates
Which event directly distinguishes the lytic cycle from the lysogenic cycle in bacteriophages?
Host cell rapidly lyses and releases virions
Viral DNA enters through cell envelope
Viral genome integrates into host chromosome
Phage capsid attaches to bacterial receptor
During attachment, what molecular interaction is depicted between the bacteriophage and the bacterium?
Capsid proteins bind specific surface receptors
Tail fibers fuse with lipid bilayer
Capsid injects proteins into cytoplasm
Viral RNA base-pairs with cell wall
In the lysogenic cycle, what is the fate of viral DNA after entry into the host?
It immediately directs virion assembly
It remains circular in the cytoplasm
It is degraded by host restriction enzymes
It integrates as a prophage within host DNA
Which sequence best matches the lytic cycle stages?
Attachment, penetration, biosynthesis, maturation, release
Attachment, integration, maturation, biosynthesis, release
Penetration, integration, maturation, release, attachment
Integration, biosynthesis, maturation, release, penetration
A prophage is indicated in the lysogenic cycle. Which outcome is emphasized when the host cell divides?
Phage receptors are downregulated
Viral genome is copied into daughter cells
New virions are released by lysis
Capsid proteins are assembled rapidly
Under certain conditions, cells in the lysogenic state enter the lytic cycle. Which trigger is most consistent with the diagram’s emphasis on outcomes?
Random mutations prevent DNA replication
Low temperature permanently inhibits phage genes
Nutrient abundance stabilizes prophage integration
Environmental stress induces prophage excision
Which step immediately follows entry of an animal virus into a host cell?
Assembly of mature virions
Budding from the plasma membrane
Uncoating releases viral nucleic acid
Integration into host chromosomes
During budding of animal viruses, what happens to the virion?
Degrades host plasma membrane
Acquires a membranous envelope
Loses its capsid structure
Replicates host ribosomal RNA
What enzymatic activity defines retroviruses such as HIV?
Reverse transcriptase synthesizing cDNA
RNA-dependent RNA polymerase
Integrase removing proviral DNA
DNA-dependent DNA polymerase
In HIV replication, which event creates the provirus state?
Biosynthesis of viral proteins
Packaging RNA into the capsid
Budding from the host membrane
cDNA integration into host DNA
Which sequence best represents early HIV life cycle steps inside a cell?
Budding, maturation, entry
Integration, attachment, biosynthesis
Attachment, entry, reverse transcription
Reverse transcription, attachment, release
Why can HIV remain latent for years in infected cells?
Proviral cDNA is replicated with host DNA
Envelope proteins are constantly changing
Viral capsid hides from immune cells
Budding prevents immune recognition
Which outcome directly results from transcription of integrated HIV DNA?
Insertion of additional host promoters
Production of viral RNA genomes and mRNA
Formation of double-stranded host plasmids
Induction of cell wall biosynthesis
A drug blocks the acquisition of a membranous envelope by virions. Which stage is most directly inhibited?
Release by budding from the membrane
Integration into nuclear chromatin
Attachment to host cell receptors
Reverse transcription inside the cytosol
Which event allows HIV contents to enter the host cytoplasm during initial infection?
Lysis of the host membrane by toxins
Membrane fusion between viral and host envelopes
Active transport through nuclear pores
Endocytosis without membrane interaction
After attachment to the cell, what directly enables HIV to bind the host membrane?
Hydrolysis of host membrane phospholipids
Interactions between viral proteins and host receptors
Insertion of viral DNA into the membrane
Random collisions with the lipid bilayer
Which step converts HIV RNA into a form that can integrate into the host chromosome?
RNA replication yields double-stranded RNA
Ribosomal translation produces integrase protein
Reverse transcription generates cDNA for integration
Transcription from host DNA creates viral RNA
Once integrated, which process produces new viral genomes using host machinery?
Degradation of host mRNA by viral nucleases
Biosynthesis of viral RNA from the DNA copy
Replication of host mitochondrial genomes
Translation of viral RNA into envelope proteins
What sequence correctly orders late-stage events of HIV replication?
RNA synthesis, release from cell, assembly of particles
Release from cell, assembly of particles, RNA synthesis
Assembly of particles, RNA synthesis, release from cell
RNA synthesis, assembly of particles, release from cell
Which function is primarily associated with the hemagglutinin (H) spike on influenza viruses?
Binding to host cell receptors
Packaging the RNA genome segments
Cleaving sialic acid on virions
Blocking host immune interferons
The neuraminidase (N) spike most directly facilitates which step during influenza infection?
Attachment to epithelial receptors
Replication of viral RNA segments
Assembly of the capsid proteins
Exit of mature virions from cells
How many distinct types of H and N spikes are commonly noted for influenza A viruses, respectively?
9 H and 16 N types
12 H and 12 N types
16 H and 9 N types
18 H and 11 N types
Why can novel H and N spike combinations hinder preexisting immunity in human populations?
Antibodies target known spike epitopes
T cells only recognize internal proteins
Macrophages ignore viral envelopes
Interferons block all spike variants
In the bird flu diagram, which process best explains gradual changes in spike genes within a bird host over time?
Accumulation of point mutations
Horizontal gene transfer
Binary fission of virions
Photosynthetic gene drift
A human cell co-infected with human and bird influenza can generate a new strain through which mechanism?
Complement fixation cascade
Reverse transcription inhibition
Homologous recombination
Gene segment reassortment
Which scenario would most likely produce an H7N9 strain capable of human transmission?
Loss of neuraminidase activity in avian strains
Point mutations increasing bacterial receptor binding
Fusion of capsid proteins into one large subunit
Reassortment mixing bird H7 with human-adapted genes
A public health team detects an influenza virus with a novel H spike but familiar N spike. Which consequence is most plausible?
Autoimmunity against host membrane proteins
No immunity because N dominates recognition
Partial immunity with reduced attachment neutralization
Complete immunity due to known neuraminidase
Which statement best defines an emerging virus?
A virus newly recognized in human populations
A virus confined to a single animal reservoir
A virus eliminated by long-standing vaccines
A virus causing only mild seasonal symptoms
Which scenario illustrates viral range extension?
Latent herpes reactivation in a single patient
West Nile establishing in birds and mosquitoes in the US
Influenza antigenic drift within a human population
Eradication of smallpox through global vaccination
Why is a new influenza vaccine recommended each year?
Rapid mutation alters circulating flu strains annually
Avian reservoirs eliminate prior human immunity
Vaccine immunity disappears after two weeks
Global production quotas limit long-term protection
Which example reflects emergence via genetic mutation crossing species barriers?
Polio transmission halted by sanitation measures
Rabies persisting in bats without human cases
H5N1, H1N1, and H7N9 arising from animal flu viruses
Measles outbreaks in unvaccinated children
Examine the global map of outbreaks. Which region shows documented emergence of both SARS (2003) and a novel coronavirus (2012)?
South America along the Amazon basin
Western Europe and the British Isles region
Sub-Saharan Africa and Madagascar coasts
East Asia and the Arabian Peninsula region
Since 1992, more than twenty emerging diseases have been noted worldwide. Which inference is most supported by this trend?
Human immunity universally declines with modern medicine
Vaccination programs are the primary cause of emergence
New virulence factors or environments can expand host range
All pathogens become less transmissible over time
A public health team sees chikungunya appear where the mosquito vector recently established. Which intervention most directly targets the mechanism of emergence?
Promotion of probiotics to boost general microbiomes
Mass antibiotic distribution to asymptomatic residents
Vector control reducing newly established mosquito populations
Quarantine of only recovered travelers after illness
Which statement best distinguishes viroids from viruses and prions?
Viroids are lipid particles treated by antibiotics
Viroids are naked RNA causing many crop diseases
Viroids are DNA viruses with metabolic enzymes
Viroids are misfolded proteins with tertiary structure
Why are antibiotics ineffective against viral infections such as herpes or HIV?
Viruses lack metabolism targeted by antibiotics
Viruses hide only in plant host tissues
Viruses are larger than bacterial cells
Viruses are prions with contagious folds
Transmissible spongiform encephalopathies (TSEs) are best described as
Viral cancers cured by broad-spectrum antibiotics
Plant infections caused by naked DNA circles
Bacterial disorders prevented by conventional vaccines
Neurodegenerative diseases destroying brain nerve tissue
Which scenario most plausibly explains transmission of bovine spongiform encephalopathy (BSE) to humans?
Consuming infected cattle neural tissue spreads prion folds
Mosquito bites transfer viral particles between species
Aerosolized bacteria from barns colonize the lungs
Eating undercooked plants with viroid sequences
A new fatal livestock disease shows no nucleic acids but a contagious tertiary structure. Which agent is most likely responsible?
A prion producing neurodegeneration
An RNA virus with metabolism
A DNA virus with antibiotics
A viroid infecting crop species
Which domains include organisms that are prokaryotes?
Eukarya only
Archaea and Eukarya
Bacteria and Eukarya
Bacteria and Archaea
What does the term prokaryote literally mean?
Primitive organism
Without ribosomes
Before a nucleus
Tiny single cell
Typical bacterial cell dimensions are best described as which range?
1–10 micrometers long, 0.7–1.5 micrometers wide
10–100 micrometers long, 2–5 micrometers wide
0.01–0.1 millimeters long, 1–2 micrometers wide
100–1000 nanometers long, 10–20 nanometers wide
Where are prokaryotes most abundantly found in everyday environments?
Deep-sea vents exclusively
Inside animal nuclei only
Only in sterile laboratory flasks
Air, water, soil, and on objects
In Pasteur’s first experiment, briefly opened flasks outside showed more growth than those opened inside. Which hypothesis does this pattern support?
Glass flasks create nutrients
Boiling generates new organisms
Life arises spontaneously in broth
Airborne bacteria contaminate broth
Pasteur’s second experiment used a swan-neck flask that allowed air in but trapped particles. What was the key outcome?
Broth became cloudy immediately
Spontaneous generation was proven
No growth occurred in the broth
Growth increased due to airflow
Which reasoning best explains why the outside-opened flasks had higher contamination than inside-opened flasks?
Boiling temperature was lower outdoors
Broth quality was poorer outdoors
Sunlight sterilized the indoor air
Higher airborne bacterial concentrations outdoors
A student sets up a sterile broth in a flask open to filtered air that removes bacteria but not gases. Predict the most likely result after several days.
Broth becomes cloudy with growth
Particles generate cells spontaneously
Broth remains clear without growth
Microbes appear from nutrients alone
Which structure houses the primary DNA in a prokaryotic cell?
Thylakoid stacks for photosynthesis
Conjugation pilus extension
Membrane-bound nucleus compartment
Nucleoid region of cytoplasm
What component primarily makes up most bacterial cell walls?
Peptidoglycan polymer network
Cholesterol-rich lipid bilayer
Cellulose microfibril scaffold
Silica-based mineral lattice
Which appendage is specialized for motility in many prokaryotes?
Flagellum rotating propeller
Fimbriae adhesive bristles
Conjugation pilus bridge
Glycocalyx capsule shell
Plasmids in bacteria are best described as which of the following?
Accessory rings of DNA
Protein-only episomes
Linear chromosomal arms
Membranous micronuclei
A bacterium attaches firmly to a surface before forming a biofilm. Which structure most directly mediates this initial adhesion?
Thylakoid membrane stacks
Nucleoid DNA complex
Flagella long helical filaments
Fimbriae short protein fibers
During conjugation, genetic material is transferred between bacterial cells primarily through which structure?
Peptidoglycan pores
Ribosomal exit tunnel
Glycocalyx slime layer
Conjugation pilus bridge
Which statement distinguishes prokaryotes from eukaryotes?
They enclose DNA in nucleus
They possess chloroplast systems
They lack membranous organelles
They contain mitochondria arrays
Which structure in a bacterium is a gel-like coating outside the cell wall made of polysaccharide called glycocalyx?
Fimbriae
Nucleoid
Basal body
Capsule
Ribosome
In the bacterial cell, which structure regulates the entrance and exit of molecules by surrounding the cytoplasm?
Cell wall
Cytoplasm gel
Capsule layer
Plasma membrane
Conjugation pilus
Which component provides support and shape to the bacterial cell according to the diagram?
Plasma membrane
Capsule coat
Fimbrial network
Cytoplasm matrix
Cell wall
What is identified as the location of the bacterial chromosome within the cell?
Plasmid ring
Vesicle
Nucleoid
Ribosome
Nucleus
Which structure is described as hairlike bristles that allow adhesion to surfaces?
Fimbriae
Flagellum
Conjugation pilus
Ribosomes
Capsule
According to the flagellum inset, which part connects the filament to the cell envelope and enables rotation?
Fimbriae and hook
Plasma and wall
Capsule and wall
Ribosome and hook
Hook and basal body
Which bacterial structure is the site of protein synthesis shown within the cytoplasm?
Plasma membrane
Capsule
Nucleoid
Cell wall
Ribosome
Which appendage is an elongated hollow tube used to transfer DNA to other cells?
Conjugation pilus
Flagellum
Basal body
Filament
Fimbriae
