Campbell Biology Chapter 27 Review: Bacteria and Archaea

27.1 How a prokaryotic cell is built

pp. 556–561

On the AP exam? Yes

Topics 2.1, 2.4, 2.10 and 6.1 test how prokaryotic cells differ from eukaryotic ones: no nucleus, a peptidoglycan wall in bacteria, ribosomes in every cell, and a circular chromosome plus plasmids. Gram staining, capsules, fimbriae, flagellum structure and endospores won't be on the exam.

In the course: Topic 2.1 Cell Structure and Function, Topic 2.2 Cell Size, Topic 2.4 Membrane Permeability, Topic 2.7 Tonicity and Osmoregulation, Topic 2.10 Origins of Cell Compartmentalization, Topic 6.1 DNA and RNA Structure, Topic 8.1 Responses to the Environment (notes, videos and more questions)

Key points

Prokaryotes are mostly single cells, about 0.5–5 µm across, which is far smaller than a typical eukaryotic cell. Being tiny gives them a lot of membrane for their volume, so materials move in and out fast. Common shapes are spheres (cocci), rods (bacilli) and spirals.
Almost every prokaryote has a cell wall that holds its shape and keeps it from bursting when water flows in. Bacterial walls contain peptidoglycan, a mesh of sugar chains linked by short peptides. Archaeal walls are built from other materials. In a strongly hypertonic setting, like brine or syrup, a cell loses water and can't divide.
The Gram stain splits bacteria into two groups. Gram-positive cells have a thick peptidoglycan layer and stay purple. Gram-negative cells have a thin layer under an outer membrane studded with lipopolysaccharides, and they end up pink. That outer membrane can make them harder to treat with antibiotics. Human cells make no peptidoglycan at all, so a drug that sabotages wall-building can hit bacteria and leave you unharmed.
Many cells have extras on the outside: a sticky capsule or slime layer for clinging to surfaces and dodging immune cells, short fimbriae for attaching, and pili that reel in a partner cell so DNA can pass between them.
About half of prokaryotes can steer toward food or away from poisons and other cues, which is called taxis. Most use spinning flagella. Bacterial, archaeal and eukaryotic flagella are built from different proteins and evolved separately, so they're analogous, not homologous.
Inside, there's no nucleus and usually no membrane-bound organelles. The main chromosome is usually one circle of DNA in a region called the nucleoid, often joined by small extra circles called plasmids. Some species have folded inner membranes for respiration or photosynthesis. Their ribosomes differ from yours, which lets some antibiotics target them.
Prokaryotes reproduce by binary fission, sometimes as often as every 20 minutes or so in ideal conditions. Some bacteria survive hard times as endospores, dormant cells that can withstand boiling and drying. Huge numbers and short generations let their populations evolve quickly, so a simple cell plan doesn't mean they're any less evolved than we are.

Key terms (14)

prokaryote: A cell with no nucleus and usually no membrane-bound organelles. Bacteria and archaea are prokaryotes.
cell wall: A stiff layer outside the plasma membrane that gives a cell its shape and stops it from bursting when water moves in.
peptidoglycan: The main building material of bacterial cell walls: long sugar chains tied together by short chains of amino acids. Archaea and eukaryotes don't make it.
Gram stain: A dye test that sorts bacteria into two groups by how their cell walls are built. It helps doctors choose a first antibiotic.
gram-positive: Describes bacteria with a thick peptidoglycan wall and no outer membrane. They hold onto the purple dye in a Gram stain.
gram-negative: Describes bacteria with a thin peptidoglycan layer covered by an outer membrane. They lose the purple dye and look pink.
capsule: A dense, sticky coat of sugars or proteins around some prokaryotes. It helps them stick to things and can hide them from immune cells.
fimbriae: Many short, hair-like threads on the surface of some prokaryotes that let them grip surfaces or other cells.
pilus: A longer surface tube that reaches out, grabs another prokaryote and draws it close so DNA can be handed over. Plural: pili.
taxis: Moving toward or away from something, like a chemical or light. Chemotaxis is the version that responds to chemicals.
nucleoid: The region of a prokaryotic cell where the chromosome sits. Unlike a nucleus, it has no membrane around it.
plasmid: An extra, small loop of DNA that replicates on its own schedule. Its handful of genes often help only in certain settings, like resisting a drug.
binary fission: How prokaryotes reproduce: the cell copies its chromosome, grows, and pinches into two cells.
endospore: A tough, dried-out, dormant cell some bacteria form when conditions turn bad. It can survive heat and drying, then revive later.

Check yourself: 27.1 How a prokaryotic cell is built

4 questions on 27.1 How a prokaryotic cell is built. Pick an answer to see if you got it, and why.

Question 1 of 4

A microbiologist studies a single-celled organism from a hot spring. Which observation, on its own, would show that the organism is a prokaryote?

Question 2 of 4

A new drug weakens the cross-links that hold a bacterium's peptidoglycan together, but it doesn't harm the cells while they grow in a medium that has the same solute concentration as their cytoplasm. What would most likely happen if the treated bacteria were moved into distilled water?

Question 3 of 4Calculator allowed

A spherical bacterium is 1 µm in diameter, and a spherical animal cell is 20 µm in diameter. For a sphere, surface area ÷ volume = 3 ÷ radius. How many times larger is the bacterium's surface area-to-volume ratio?

Question 4 of 4

An antibiotic binds to bacterial ribosomes and stops protein synthesis, but it barely affects the ribosomes in a human cell's cytoplasm. At high doses, though, it can harm human tissues that use a lot of energy, like heart muscle. What is the best explanation?

0 of 4 answered

27.2 Why prokaryote populations vary so much

pp. 561–564

On the AP exam? Yes

Topic 6.7 names transformation, transduction and conjugation, and Topic 7.8 uses antibiotic resistance as evidence that evolution is still happening. F⁺, F⁻ and Hfr cells aren't on the exam.

In the course: Topic 6.7 Mutations, Topic 7.2 Natural Selection, Topic 7.8 Continuing Evolution, Topic 6.1 DNA and RNA Structure (notes, videos and more questions)

Key points

Natural selection only works if a population varies, and prokaryote populations vary a lot, even though they don't reproduce sexually.
Any one gene rarely mutates during a single division. But a population of billions dividing again and again turns out new mutants every day, so variation builds fast.
Prokaryotes also mix DNA from different cells in three ways. Transformation: a cell picks up loose DNA from its surroundings. Transduction: a phage accidentally carries a bit of one host's DNA into another host. Conjugation: one cell passes DNA to another through a direct connection, always in one direction.
Gene movement between different species is called horizontal gene transfer. It lets useful genes jump across species lines.
In E. coli, the ability to donate DNA by conjugation comes from a set of genes called the F factor. Cells with the F plasmid (F⁺) donate to cells without it (F⁻), and the recipient becomes F⁺. When the F factor sits inside the chromosome (an Hfr cell), chromosome genes can be passed on and swapped in.
R plasmids carry genes that defeat antibiotics, sometimes several at once, and many can move by conjugation. Using an antibiotic kills sensitive cells and leaves resistant ones to multiply. It doesn't create the resistance; it selects it.

Key terms (11)

genetic recombination: Any process that mixes DNA from two separate origins, creating a new combination of genes.
horizontal gene transfer: Passing genes to an organism that isn't your offspring, often one of a different species. It's common in prokaryotes.
transformation: When a prokaryote takes in loose DNA from its surroundings and adds it to its own genome.
transduction: When a virus that infects bacteria accidentally carries a piece of one host cell's DNA into another host cell.
bacteriophage: A virus that infects bacteria. Often shortened to phage.
conjugation: A bacterium passing DNA straight into a partner cell it's attached to. The DNA flows only one way, from donor to recipient.
F factor: A stretch of DNA, mostly genes for building pili, that makes an E. coli cell a DNA donor. It may float free as a plasmid or sit inside the main chromosome.
F plasmid: The F factor when it's a separate circle of DNA. Cells with it (F⁺) act as donors; cells without it (F⁻) are recipients.
Hfr cell: A bacterium whose F factor has joined its chromosome, so it can pass chromosome genes to another cell during conjugation.
R plasmid: A plasmid carrying genes that protect a bacterium from one or more antibiotics. Many can move between cells by conjugation.
recombinant cell: A cell that has mixed DNA from another cell into its own genome.

Check yourself: 27.2 Why prokaryote populations vary so much

4 questions on 27.2 Why prokaryote populations vary so much. Pick an answer to see if you got it, and why.

Question 1 of 4Calculator allowed

A patient's infection contains about 1 × 10¹⁰ bacteria. In any one cell, resistance to drug X arises by mutation with a chance of 1 × 10⁻⁸, and resistance to drug Y with a chance of 1 × 10⁻⁷. The two mutations happen independently. About how many cells in the infection would be expected to carry both resistance mutations?

Question 2 of 4

Two bacterial strains are put in the two arms of a U-shaped tube, separated by a filter whose pores let viruses and DNA through but not cells. An enzyme that destroys free DNA is added to both sides. Some cells on one side later gain a gene from the other strain. Which process most likely moved the gene?

Question 3 of 4

Which treatment would block gene transfer by transformation but leave gene transfer by conjugation working?

Question 4 of 4

A culture starts with 10% F⁺ cells, which carry the F plasmid, and 90% F⁻ cells, which don't. The cells are mixed and allowed to conjugate for several hours without dividing much. What is the most likely result?

0 of 4 answered

27.3 How prokaryotes get energy and carbon

pp. 564–565

On the AP exam? Yes

Topic 8.2 tests that producers capture energy from light or from chemicals and that nitrogen gets fixed, and Topic 3.5 tests respiration versus fermentation. Names like photoheterotroph and facultative anaerobe help in class but aren't required on the exam.

In the course: Topic 8.2 Energy Flow Through Ecosystems, Topic 3.4 Photosynthesis, Topic 3.5 Cellular Respiration (notes, videos and more questions)

Key points

Sort any organism's nutrition with two questions. Where does its energy come from: light (photo-) or chemicals (chemo-)? Where does its carbon come from: CO₂ alone (auto-) or organic molecules made by others (hetero-)?
That gives four modes. Photoautotrophs use light and CO₂, like cyanobacteria and plants. Chemoautotrophs pull energy from inorganic chemicals such as hydrogen sulfide, ammonia, hydrogen gas or iron ions and use CO₂; only prokaryotes do this. Photoheterotrophs use light for energy but need organic carbon; this is mostly found in certain prokaryotes. Chemoheterotrophs get both from organic molecules, like most bacteria, fungi and you.
Oxygen splits prokaryotes too. Some can't live without O₂ (obligate aerobes). For others, O₂ is toxic (obligate anaerobes); they ferment, or they run anaerobic respiration, passing electrons to a stand-in acceptor such as nitrate. Facultative anaerobes can do either, depending on what's around.
Only prokaryotes can fix nitrogen, turning N₂ from the air into ammonia (NH₃) that can be built into amino acids and nucleotides. Plants and animals depend on that fixed nitrogen.
The nitrogen-fixing enzyme is wrecked by O₂, so photosynthetic cyanobacteria keep the two jobs apart. Some filaments have thick-walled cells called heterocysts that fix nitrogen and trade it with neighbors for sugar; other species fix nitrogen only at night.
Many prokaryotes live in biofilms, slimy communities stuck to a surface, like the coating on a stream rock or inside a water pipe. Cells signal each other, share resources and are protected by the slime, which also makes biofilms hard to clean off.
Taken together, prokaryotes have a far wider range of ways to make a living than eukaryotes do.

Key terms (15)

phototroph: An organism that gets its energy from light.
chemotroph: An organism that gets its energy from chemicals, either organic ones like sugar or inorganic ones like H₂S.
autotroph: An organism that can build all its organic molecules using CO₂ as the only carbon source.
heterotroph: An organism that can't build its organic molecules from CO₂ alone and must take in some ready-made organic compounds.
photoautotroph: Uses light for energy and CO₂ for carbon. Cyanobacteria, algae and plants work this way.
chemoautotroph: Gets energy by reacting inorganic chemicals like H₂S or NH₃ and builds sugars from CO₂. Only prokaryotes do this.
photoheterotroph: Uses light to make ATP but must take in organic molecules for carbon. Found mainly in certain prokaryotes.
chemoheterotroph: Gets both energy and carbon from organic molecules. Most bacteria, all fungi and all animals, including you.
obligate aerobe: An organism that relies on O₂ as the final electron acceptor in respiration, so it stops growing when O₂ runs out.
obligate anaerobe: An organism for which O₂ is toxic. It makes ATP by fermentation or by anaerobic respiration.
facultative anaerobe: An organism that respires with O₂ when it can get it and falls back on fermentation or anaerobic respiration when it can't.
anaerobic respiration: Cellular respiration whose electron transport chain hands its electrons to something besides O₂, like nitrate or sulfate.
nitrogen fixation: Turning N₂ gas into ammonia (NH₃), a form living things can use. Only some prokaryotes can do it.
heterocyst: A specialized, thick-walled cell in some filament-forming cyanobacteria that fixes nitrogen while keeping O₂ out.
biofilm: A slimy community of microbes, often several species, attached to a surface and held together by the sugars and proteins they secrete.

Check yourself: 27.3 How prokaryotes get energy and carbon

4 questions on 27.3 How prokaryotes get energy and carbon. Pick an answer to see if you got it, and why.

Question 1 of 4

A bacterium in the runoff from an old mine gets its energy by converting dissolved Fe²⁺ to Fe³⁺, and it builds all its organic molecules from CO₂. Which nutritional mode does it use?

Question 2 of 4

Question 3 of 4

Three bacterial species are grown in tall tubes of soft agar, where oxygen is plentiful at the top and absent near the bottom. Species X grows only in a band at the top, species Y grows only near the bottom, and species Z grows all through the tube but most thickly near the top. Which description fits species Z?

Question 4 of 4

A bacterium in oxygen-free mud passes electrons down an electron transport chain to nitrate (NO₃⁻) instead of O₂. Which statement about this bacterium is correct?

0 of 4 answered

27.4 Sorting prokaryotes with DNA: bacteria and archaea

pp. 565–570

On the AP exam? Background

The exam won't ask you to name archaeal clades or groups of bacteria. It does expect you to read trees built from DNA data (Topic 7.9), to see shared features as evidence of common ancestry (Topic 7.7), and to know that mitochondria and chloroplasts came from bacteria (Topic 2.10).

In the course: Topic 7.9 Phylogeny, Topic 7.7 Common Ancestry, Topic 6.7 Mutations, Topic 6.8 Biotechnology, Topic 2.10 Origins of Cell Compartmentalization (notes, videos and more questions)

Key points

Older schemes grouped prokaryotes by how they looked and behaved, which says little about ancestry. Comparing DNA sequences, especially ribosomal RNA genes that every cell carries, showed that prokaryotes fall into two very old domains: Bacteria and Archaea.
Archaea share some traits with bacteria (no nucleus, a circular chromosome) and others with eukaryotes (an RNA polymerase built like eukaryotes', proteins started with methionine, histones in some, and resistance to antibiotics like streptomycin). They also have their own: no peptidoglycan, and membrane lipids with branched chains.
Newer DNA data suggest eukaryotes may have branched off from within the archaea. One recently found archaeal group, the Asgard archaea, seems to be eukaryotes' closest living relative, and the mitochondrion came later from a bacterium.
Sequencing DNA taken straight from soil or water (genetic prospecting, now often whole-genome metagenomics) shows that most prokaryotes have never been grown in a lab. New branches keep being added to the tree.
A large share of many prokaryote genomes was borrowed from distant species by horizontal gene transfer. Trees built from different genes can disagree, which makes the deepest branches hard to pin down.
Many archaea are extremophiles: extreme halophiles love salt, and extreme thermophiles have heat-stable proteins and DNA. Methanogens release methane and are strict anaerobes in swamps and animal guts. Plenty of archaea also live in ordinary soil, lakes and seawater.
Bacteria cover every nutritional mode. Big groups include the proteobacteria (whose relatives gave rise to mitochondria), the cyanobacteria (the only prokaryotes with oxygen-releasing photosynthesis, and the source of chloroplasts), the gram-positive bacteria, spirochetes and chlamydias.

Key terms (12)

molecular systematics: Working out how species are related by comparing DNA, RNA or protein sequences.
ribosomal RNA (rRNA) gene: A gene for the RNA that forms part of the ribosome. Every cell has one, so it's a favorite for comparing distant groups.
domain: The broadest level of classification. Life is split into three: Bacteria, Archaea and Eukarya.
Archaea: The domain of prokaryotes whose walls lack peptidoglycan and whose genes and proteins share many features with eukaryotes.
genetic prospecting: Sequencing genes straight from environmental samples like soil or seawater to find microbes nobody has grown in the lab.
metagenomics: Sequencing all the DNA in an environmental sample at once to piece together the genomes of the many species living there.
extremophile: An organism that thrives in conditions most life can't handle, like boiling water, strong acid or brine.
extreme halophile: A prokaryote that lives in very salty water, many times saltier than the ocean.
extreme thermophile: A prokaryote that thrives in very hot places, such as hot springs, thanks to heat-stable proteins and DNA.
methanogen: An archaeon that releases methane as it gets energy. Oxygen poisons it, so it lives in places like swamp mud and animal guts.
proteobacteria: A huge, varied group of gram-negative bacteria. The bacterium that became the mitochondrion came from this group.
cyanobacteria: Bacteria that carry out photosynthesis that releases O₂, the way plants do. A cyanobacterium gave rise to the chloroplast.

Check yourself: 27.4 Sorting prokaryotes with DNA: bacteria and archaea

4 questions on 27.4 Sorting prokaryotes with DNA: bacteria and archaea. Pick an answer to see if you got it, and why.

Question 1 of 4

Why are the genes for small-subunit ribosomal RNA so useful for working out how distantly related prokaryotes are related?

Question 2 of 4

A microbe from oxygen-free lake mud has these features: no nucleus, a cell wall with no peptidoglycan, membrane lipids with branched hydrocarbon chains, and protein synthesis that starts with methionine rather than formyl-methionine. Which group does it most likely belong to?

Question 3 of 4

A phylogenetic tree based on ribosomal RNA shows the Bacteria branching off first. Later, a second split separates the Archaea from the Eukarya. Which statement is supported by this tree?

Question 4 of 4

Researchers count the differences between the small-subunit ribosomal RNA genes of four newly sequenced prokaryotes, W, X, Y and Z (invented data). Pair | Differences per 1,000 bases W–X | 12 W–Y | 141 W–Z | 146 X–Y | 144 X–Z | 149 Y–Z | 31 Which conclusion is best supported?

0 of 4 answered

27.5 Prokaryotes keep ecosystems running

pp. 570–571

On the AP exam? Yes

Topic 8.2 covers producers that use chemical energy and how matter, including nitrogen, cycles, and Topic 8.5 covers mutualism, commensalism and parasitism. Expect scenarios, not microbe names.

In the course: Topic 8.2 Energy Flow Through Ecosystems, Topic 8.5 Community Ecology (notes, videos and more questions)

Key points

Life on Earth leans hard on prokaryotes. They recycle elements, feed food webs and partner with countless species, so losing them would bring down many ecosystems.
Atoms in living things cycle between organisms and the soil, water and air. Bacteria and fungi do most of the decomposing: as they feed on dead bodies and wastes, they return carbon, nitrogen, phosphorus and other elements to forms that producers can take up again.
Prokaryotes also make raw materials usable. Nitrogen fixers turn N₂ into ammonia, nitrifying bacteria and archaea convert ammonium to nitrite and then nitrate, and photosynthetic and chemosynthetic prokaryotes build sugars from CO₂ that the rest of the food web eats. Cyanobacteria add O₂ to the air as they do it.
Microbes can raise or lower the nutrients plants can reach. They can free minerals from rock and soil, but they can also lock nutrients up in their own cells for a while.
Symbiosis is a close relationship between two species, usually a larger host and a smaller symbiont. In mutualism both benefit, in commensalism one benefits and the other is barely affected, and in parasitism the parasite gains at the host's expense. Parasites that cause disease are pathogens.
In places with no sunlight, such as rock deep underground or the dark ocean floor, chemoautotrophic prokaryotes are the producers, and every other organism there depends on them.

Key terms (10)

decomposer: An organism, usually a bacterium or fungus, that breaks down dead matter and wastes and returns nutrients to the soil, water and air.
chemical cycling: The constant movement of elements like carbon and nitrogen between living things and their nonliving surroundings.
nitrification: Microbes turning ammonium into nitrite and then nitrate, the form most plants take up best.
symbiosis: Two species living closely together, in direct contact, over a long time.
host: The larger partner in a symbiosis, which the smaller partner lives on or in.
symbiont: The smaller partner in a symbiosis, living on or in its host.
mutualism: A partnership where both species come out ahead.
commensalism: A relationship that benefits one species and has little or no effect on the other.
parasitism: A one-sided relationship: the parasite lives on or in its host and takes nutrients from it, doing the host harm.
chemosynthesis: Making sugars from CO₂ using energy from inorganic chemicals instead of light. It's how chemoautotrophs feed food webs in the dark.

Check yourself: 27.5 Prokaryotes keep ecosystems running

4 questions on 27.5 Prokaryotes keep ecosystems running. Pick an answer to see if you got it, and why.

Question 1 of 4

Aphids feed only on plant sap, which lacks several amino acids they need. Bacteria living inside special aphid cells make those amino acids, and the aphid supplies the bacteria with sugars and a home. Aphids that lose their bacteria grow poorly and have few young. What kind of relationship is this?

Question 2 of 4

A bacterium lives on the skin of a frog species. Which result would best show that the relationship is mutualism rather than commensalism?

Question 3 of 4

Bags of fallen leaves are buried in two kinds of soil for six months (invented data). Soil | Leaf mass remaining Sterilized soil | 92% Untreated soil | 41% Which conclusion is best supported?

Question 4 of 4

Water-filled cracks in rock a kilometer underground get no sunlight. Bacteria there get energy by oxidizing hydrogen gas (H₂) released by reactions in the rock, and they make sugars from CO₂. Tiny worms graze on films of these bacteria, and predatory worms eat the grazers. What is the original source of the energy in a predatory worm's body?

0 of 4 answered

27.6 Prokaryotes and people: partners, pathogens and tools

pp. 571–573

On the AP exam? Yes

Topic 7.8 tests antibiotic resistance and new diseases as evidence of ongoing evolution, Topic 6.7 covers genes moving between bacteria, and Topic 6.8 covers bacteria as biotech tools. Exotoxins, endotoxins and named diseases are background.

In the course: Topic 7.8 Continuing Evolution, Topic 6.7 Mutations, Topic 6.8 Biotechnology, Topic 8.5 Community Ecology (notes, videos and more questions)

Key points

Only a tiny share of prokaryotes cause disease. Your gut holds hundreds of bacterial species that digest fibers you can't, make vitamins, and crowd out invaders. Newer counts put gut bacteria at roughly the same number as your own cells, not ten times more as older books say.
Every known disease-causing prokaryote is a bacterium; no archaeon has been clearly shown to make people sick. Bacterial diseases can spread through air, water, food, contact or the bites of other animals.
Pathogens often harm you with poisons. Exotoxins are proteins a bacterium makes and releases while it's alive; because the poison acts on its own, food can still sicken you after the bacteria in it are dead. Endotoxins are lipopolysaccharides built into the extra outer layer that wraps gram-negative cells, and they pour out when those cells break apart.
Antibiotic resistance is spreading because drug use selects for resistant cells, fast reproduction multiplies them, and horizontal gene transfer hands resistance genes to other strains and species.
Horizontal gene transfer can also turn a harmless strain into a dangerous one by bringing in virulence genes, such as genes for a toxin. That's one way new diseases appear.
People put prokaryotes to work: cleaning up oil, solvents and sewage (bioremediation), copying genes on plasmids, making insulin and other medicines, carrying new genes into crop plants, fermenting milk into yogurt and cheese, and producing fuels and plastics that break down.

Key terms (9)

gut microbiota: The huge community of bacteria and other microbes living in your intestines. Many help digest food and keep harmful microbes out.
pathogen: An organism or virus that causes disease. All known disease-causing prokaryotes are bacteria.
exotoxin: A poisonous protein that a bacterium makes and releases. The poison can still cause illness after the bacteria themselves are dead or gone.
endotoxin: A poison built into the extra outer layer that wraps gram-negative cells (a lipopolysaccharide). It floods out when those cells burst or die.
virulence: How strongly a pathogen can cause disease. Genes for toxins or for clinging to host cells raise it.
antibiotic resistance: A bacterium's inherited ability to survive a drug that would normally kill it or stop its growth.
bioremediation: Using living things, often prokaryotes, to break down or remove pollutants from soil, water or air.
gene cloning: Putting a gene into a carrier like a plasmid and letting bacteria copy it, often so they'll make the protein it codes for.
emerging disease: A disease that's new to a population or quickly spreading, often because a pathogen gained new genes or a new host.

Check yourself: 27.6 Prokaryotes and people: partners, pathogens and tools

4 questions on 27.6 Prokaryotes and people: partners, pathogens and tools. Pick an answer to see if you got it, and why.

Question 1 of 4

A patient with a serious gram-negative infection starts a powerful antibiotic that makes bacterial cells burst. Within hours, the patient's fever and blood-pressure drop get worse before improving. What best explains this?

Question 2 of 4

A hospital tracks how often one bacterial species resists drug Z (invented data). Year | Use of drug Z | Isolates resistant 2015 | Low | 4% 2017 | High | 18% 2019 | High | 37% 2021 | Cut back sharply | 30% 2023 | Low | 22% Resistant cells grow a little more slowly than sensitive cells when no drug is present. Which explanation best fits the change after 2019?

Question 3 of 4

A harmless bacterial strain picks up, in a single transfer event, a cluster of about 40 genes from another species, including genes for a toxin and for attaching to host cells. Why can horizontal gene transfer like this create a new pathogen much faster than point mutations can?

Question 4 of 4

A team wants bacteria to make a human hormone. They insert the hormone's gene, copied straight from human chromosomal DNA, into a plasmid and put it into bacteria. The bacteria make a protein, but it's longer than the hormone and doesn't work. What change would most likely fix the problem?

0 of 4 answered