Chapter 17 – Viruses, Bacteria, and Protists (Essentials of Biology, 6e)

These 63 question-and-answer flashcards review key concepts from Chapter 17, covering viruses, viroids, prions, prokaryotes (bacteria & archaea), and diverse protist supergroups.

What two basic components make up every virus?

An outer protein capsid and an inner core of genetic material (DNA or RNA).

Why are viruses described as "obligate intracellular parasites"?

They can reproduce only inside a host cell by taking over its metabolic machinery.

What characteristic determines viral host specificity?

The virus must be able to attach to a matching receptor on the host cell’s surface.

Name the five stages of the lytic cycle.

Attachment, penetration, biosynthesis, maturation, and release.

In the lysogenic cycle, what is a prophage?

Viral DNA integrated into the host chromosome that can remain latent before entering the lytic cycle.

How does a bacteriophage differ from an animal virus?

A bacteriophage infects bacteria, while animal viruses infect animal cells and may possess an outer envelope derived from the host membrane.

What plant virus is the best studied and causes mottling in tobacco leaves?

Tobacco Mosaic Virus (TMV).

Which human viruses can remain latent as a provirus and be reactivated by stress?

Herpesviruses (e.g., herpes simplex causing cold sores, genital herpes, and chickenpox).

Define a retrovirus.

An RNA virus that uses reverse transcriptase to make a DNA copy, which integrates into the host genome.

What enzyme allows HIV to convert its RNA into DNA?

Reverse transcriptase.

What is an emerging virus?

A virus that has recently infected large numbers of people for the first time.

Give five examples of emerging viruses.

HIV, West Nile virus, hantavirus, SARS coronavirus, and Ebola virus.

List three ways a virus can emerge or re-emerge.

Being transported to a new location, infecting a new species, or acquiring a new mode of transmission.

Why is it difficult to develop antiviral drugs?

Viruses use the host cell’s own machinery, so drugs must target the virus without harming host processes.

How do nucleoside analog drugs such as acyclovir or remdesivir work?

They mimic nucleotides and interfere with viral genome synthesis.

Retroviruses contain which key enzyme?

Reverse transcriptase (answer to concept check).

How does a viroid differ from a virus?

A viroid is a naked strand of circular RNA without a protein capsid.

What human diseases are caused by prions?

Creutzfeldt-Jakob disease, variant CJD (mad cow in humans), and kuru.

How was kuru traditionally transmitted among the Fore people of Papua New Guinea?

Through ritualistic cannibalism, especially consumption of brain tissue.

What method of reproduction is used by bacteria and archaea?

Binary fission (asexual cell division).

Name three processes that increase bacterial genetic diversity.

Conjugation, transformation, and transduction.

What is an endospore and why is it medically important?

A dormant, resistant bacterial cell formed under harsh conditions; it allows pathogens like Bacillus anthracis to survive drying and heat.

Which bacterial shapes correspond to bacilli, cocci, and spirilla?

Rods (bacilli), spheres (cocci), and spirals (spirilla/spirochetes).

What complex polymer strengthens most bacterial cell walls?

Peptidoglycan.

How do bacterial flagella differ from eukaryotic flagella?

Bacterial flagella rotate like propellers and lack the 9+2 microtubule structure found in eukaryotes.

Which photosynthetic bacteria are photoautotrophs similar to plants?

Cyanobacteria.

Describe chemoautotrophic bacteria.

They obtain energy by oxidizing inorganic molecules (e.g., H₂, H₂S) and use that energy to fix CO₂—common at deep-sea vents.

What is a saprotroph?

An organism that secretes digestive enzymes outside its body and absorbs the resulting nutrients; many chemoheterotrophic bacteria are saprotrophs.

Define mutualism and give a bacterial example.

A symbiosis where both partners benefit; gut bacteria that synthesize vitamins K and B₁₂ for humans.

Why are decomposer bacteria essential to ecosystems?

They recycle nutrients by breaking down dead organic matter into inorganic forms used by producers.

What role do Rhizobium bacteria play in the nitrogen cycle?

They fix atmospheric N₂ into ammonia in legume root nodules, making nitrogen available to plants.

What is bioremediation?

The use of microbes to detoxify or remove pollutants such as oil spills, pesticides, or plastics.

How is lactic acid fermentation by bacteria used in food production?

It curdles milk into cheese, ferments cucumbers into pickles, and adds tangy flavors.

In 2001 anthrax letters, why could dry powder cause infection?

It contained dormant anthrax endospores that germinated inside victims’ bodies (correct answer B).

Which domain possesses peptidoglycan in its cell wall?

Bacteria only; archaea and eukaryotes lack peptidoglycan.

What unique feature of archaeal membranes allows survival at high temperatures?

Unusual branched lipid molecules that stabilize membranes under extreme heat.

List the three major physiological groups of archaea.

Methanogens, halophiles, and thermoacidophiles.

Where do methanogens live and what do they produce?

Anaerobic environments like swamps and intestines; they produce methane (CH₄).

Why are halophiles pinkish and able to make ATP in saline water?

They use pigmented proteins to absorb light and pump chloride ions, driving ATP synthesis.

At what conditions do thermoacidophiles thrive?

Temperatures above 80 °C and pH 1–2 (very hot, acidic environments).

What evidence links archaea more closely to eukaryotes than to bacteria?

Shared ribosomal proteins, similar types of tRNAs, and similar initiation of transcription.

State the endosymbiotic theory.

Mitochondria and chloroplasts originated as free-living bacteria that were engulfed and became symbiotic organelles in early eukaryotes.

Define a protist.

Any eukaryote that is not classified as a plant, animal, or fungus; typically unicellular or simple multicellular.

Name the three traditional nutritional categories of protists.

Algae (photosynthetic), protozoa (ingestive), and slime/water molds (absorptive).

List the five eukaryotic supergroups.

Archaeplastids, Amoebozoans, SAR, Excavates, and Opisthokonts.

What unites the supergroup Archaeplastids?

Chloroplasts derived from endosymbiotic cyanobacteria; includes red algae, green algae, and land plants.

Give two examples of green algae.

Chlamydomonas, Volvox, or Spirogyra (any two).

How do amoebozoans move and feed?

By extending pseudopods to engulf food particles.

What three major clades compose the SAR supergroup?

Stramenopiles, Alveolata, and Rhizaria.

Provide one example each of stramenopiles and alveolates.

Stramenopile: brown algae or diatom; Alveolate: dinoflagellate, apicomplexan (Plasmodium), or ciliate (Paramecium).

Which alveolate causes malaria?

Plasmodium (an apicomplexan).

What harmful phenomenon is produced by toxin-secreting dinoflagellates?

Red tides (harmful algal blooms).

How do ciliates such as Paramecium move?

By coordinated beating of numerous cilia covering the cell surface.

What are the hard shells made by foraminifera and radiolarians called?

Tests, composed of calcium carbonate (forams) or silica (radiolarians).

Which characteristic defines Excavata?

Flagellated protists with an excavated feeding groove and often reduced or absent mitochondria.

Why is Giardia medically significant?

It is an intestinal parasite that causes severe diarrhea in humans and other mammals.

What groups are included in Opisthokonts?

Animals, fungi, choanoflagellates, and related filaments/flagellates.

How are choanoflagellates related to animals?

They are the closest protistan relatives of animals and resemble sponge collar cells (choanocytes).

Which algal group is directly associated with red tide events?

Dinoflagellates (concept check answer E).