Question 1

Who pioneered the discovery of the three domains of life?

Accepted Answer

In the late 20th century, the pioneering work of Carl Woese and others compared sequences of small-subunit ribosomal RNA (SSU rRNA), which resulted in a more fundamental way to group organisms on Earth than before. Based on the differences in the structure of cell membranes and in rRNA, Woese and his colleagues proposed that all life on Earth evolved along three lineages, called domains, Bacteria, Archaea, and Eukarya.

Question 2

When did prokaryotes first appear on Earth?

Accepted Answer

About 3.5 to 3.8 billion years ago, indicated by the presence of fossilized microbial mats. The first microbial mats likely obtained their energy from chemicals found near hydrothermal vents. Fossilized microbial mats represent the earliest record of life on Earth.

Question 3

What are some examples of environments that are inhabited by prokaryotes?

Accepted Answer

Prokaryotes are abundant and ubiquitous. They are found in both moderate and extreme environments, such as boiling springs to permanently frozen environments in Antarctica; from salty environments like the Dead Sea to environments under tremendous pressure, such as the depths of the ocean; and from areas without oxygen, such as a waste management plant, to radioactively contaminated regions, such as Chernobyl. Prokaryotes reside in the human digestive system and on the skin, are responsible for certain illnesses, and serve an important role in the preparation of many foods.

Question 4

What is an acidophile?

Accepted Answer

Organism with optimal growth in pH of three or below.

Question 5

What is an alkaliphile?

Accepted Answer

Organism with optimal growth pH of nine or above.

Question 6

What are anaerobic organisms?

Accepted Answer

Refers to the organisms that grow without oxygen.

Question 7

What does it mean to be anoxic?

Accepted Answer

Without oxygen.

Question 8

What is a biofilm?

Accepted Answer

Microbial community that is held together by a gummy-textured matrix that consists primarily of polysaccharides secreted by the organisms, together with some proteins and nucleic acids. Biofilms grow attached to surfaces. Some of the best-studied biofilms are composed of prokaryotes, although fungal biofilms have also been described as well as some composed of a mixture of fungi and bacteria.

Question 9

What is an extremophile?

Accepted Answer

Organism that grows under extreme or harsh conditions.

Question 10

What is a halophile?

Accepted Answer

Organism that requires a salt concentration of at least 0.2 M.

Question 11

What is a hydrothermal vent?

Accepted Answer

Fissure in Earth's surface that releases geothermally heated water.

Question 12

What is a hyperthermophile?

Accepted Answer

Organism that grows at temperatures between 80-122 C.

Question 13

What is a microbial mat?

Accepted Answer

Multi-layered sheet of prokaryotes that may include bacteria and archaea. They are a few centimeters thick, and typically grow where different types of materials interface, mostly on moist surfaces. The various types of prokaryotes that comprise them carry out different metabolic pathways, and that is the reason for their various colors. Prokaryotes in a microbial mat are held together by a glue-like sticky substance that they secrete called extracellular matrix.

Question 14

What is a nutrient?

Accepted Answer

Essential substances for growth, such as carbon and nitrogen.

Question 15

What is an osmophile?

Accepted Answer

Organism that grows in a high sugar concentration.

Question 16

What is a phototroph?

Accepted Answer

Organism that is able to make its own food by converting solar energy to chemical energy.

Question 17

What is a psychrophile?

Accepted Answer

Organism that grows at temperatures of -15 C or lower.

Question 18

What is a radioresistant organism?

Accepted Answer

Organism that grows in high levels of radiation.

Question 19

What is resuscitation?

Accepted Answer

Process by which prokaryotes that are in the VBNC state return to viability.

Question 20

What is a stromatolite?

Accepted Answer

Layered sedimentary structure formed by precipitation of minerals by prokaryotes in microbial mats. Stromatolites form layered rocks made of carbonate or silicate.

Question 21

What is a thermophile?

Accepted Answer

Organism that lives at temperatures between 60-80 C.

Question 22

What is a viable-but-non-culturable (VBNC) state?

Accepted Answer

Survival mechanism of bacteria facing environmental stress conditions.

Question 23

What were the conditions on earth likely like when the first organisms arose?

Accepted Answer

Earth had a very different atmosphere (containing less molecular oxygen) and was subjected to strong radiation, so the first organisms would have flourished where they were more protected, such as in ocean depths or beneath the surface of the Earth. Strong volcanic activity was also common, so life was likely adapted to very high temperatures and other harsh conditions.

Question 24

Are stromatolites formed present day?

Accepted Answer

Although most stromatolites are artifacts from the past, there are places on Earth where stromatolites are still forming. For example, growing stromatolites have been found in the Anza-Borrego Desert State Park in San Diego County, California, and in Shark Bay, Australia. Fossilized stromatolites found in Glacier National Park, Montana, are nearly 1.5 billion years old.

Question 25

What was the constitution of the atmosphere of early Earth and how did aerobic organisms evolve?

Accepted Answer

Evidence indicates that during the first two billion years of Earth's existence, the atmosphere was anoxic (lacking molecular oxygen). Phototrophs appeared within one billion years of the formation of Earth. Cyanobacteria evolved from these simple phototrophs one billion years later, which began the oxygenation of the atmosphere. Increased atmospheric oxygen allowed the development of more efficient O2-utilizing catabolic pathways. It also opened up the land to increased colonization, because some O2 is converted into ozone, and ozone effectively absorbs the ultraviolet light that would otherwise cause lethal mutations in DNA. Ultimately, the increased in O2 concentrations allowed the evolution of other life forms.

Question 26

How do cell walls help prokaryotes survive?

Accepted Answer

Almost all prokaryotes have a cell wall, which allows them to survive in both hyper- and hypo-osmotic conditions.

Question 27

What is an endospore?

Accepted Answer

A dormant, tough, and non-reproductive structure produced by some soil bacteria. Endospores resist heat and drought, which allows the organism to survive until favorable conditions recur.

Question 28

What are some environments that extremophiles have been found in?

Accepted Answer

The depth of the oceans, hot springs, the Artic and Antarctic, in very dry places, deep inside the Earth, in harsh chemical environments, and in high radiation environments.

Question 29

What is Deinococcus radiodurans ?

Accepted Answer

A prokaryote that can tolerate very high doses of ionizing radiation. It has developed DNA repair mechanisms that allow it to reconstruct its chromosome even if it has been broken into hundreds of pieces by radiation or heat.

Question 30

What is the Dead Sea?

Accepted Answer

A hypersaline basin that is located between Jordan and Israel. In the Dead Sea, the sodium concentration is 10 times higher than that of seawater, and the water contains high levels of magnesium (about 40 times higher than in seawater) that would be toxic to most living things. Taken together, the high concentration of divalent cations, the acidic pH (6.0) and the intense solar radiation flux make the Dead Sea a unique, and uniquely hostile, ecosystem.

Question 31

What is a divalent ion?

Accepted Answer

Doubly-charged monatomic ions, such as Fe2+, Ca2+, and Mg2+.

Question 32

What is hard water?

Accepted Answer

Water that has high mineral content, such as iron, calcium, and magnesium divalent cations.

Question 33

What sort of prokaryotes live in the Dead Sea?

Accepted Answer

Extremely salt-tolerant microbial mats, including Halobacterium , Haloferax volcanii , Halorubrum sodomense , Halobaculum gomorrense , and Haloarcula marismortui .

Question 34

How are prokaryotes grown in culture?

Accepted Answer

Microbiologists typically grow prokaryotes in the laboratory using an appropriate culture medium containing all the nutrients needed by the target organism. The medium can be liquid, broth, or solid. After an incubation time at the right temperature, there should be evidence of microbial growth. The process of culturing bacteria is complex and is one of the greatest discoveries of modern science.

Question 35

How was the process of culturing bacteria discovered?

Accepted Answer

German physician Robert Koch is credited with discovering the techniques for pure culture, including staining and using growth media. His assistant Julius Petri invented the Petri dish whose use persists in today's laboratories.

Question 36

What were Robert Koch's postulates?

Accepted Answer

Koch's postulates include that an organism can be identified as the cause of disease when it is present in all infected samples and absent in all healthy samples, and it is able to reproduce the infection after being cultured multiple times.

Question 37

Why are some prokaryotes unculturable?

Accepted Answer

For the most part, this is due to a lack of knowledge as to what to feed these organisms and how to grow them; they have special requirements for growth that remain unknown to scientists, such as needing specific micronutrients, pH, temperature, pressure, co-factors, or co-metabolites. Some bacteria cannot be cultured because they are obligate intracellular parasites and cannot be grown outside a host cell.

Question 38

Where can biofilms be found?

Accepted Answer

Biofilms are present almost everywhere: they can cause the clogging of pipes and readily colonize surfaces in industrial settings. In large-scale outbreaks of bacterial contamination of food, biofilms have played a major role. They also colonize household surfaces, such as kitchen counters, cutting boards, sinks, and toilets, as well as places on the human body, such as the surfaces of our teeth.

Question 39

Why are biofilms more robust than free-living prokaryotes?

Accepted Answer

Interactions among the organisms that populate a biofilm, together with their protective exopolysaccharide (EPS) environment, make these communities more robust than free-living, or planktonic, prokaryotes. The sticky substance that holds bacteria together also excludes most antibiotics and disinfectants, making biofilm bacteria hardier than their planktonic counterparts. Overall, biofilms are very difficult to destroy because they are resistant to many common forms of sterilization.

Question 40

What are the five stages of biofilm development?

Accepted Answer

During stage 1, initial attachment, bacteria adhere to a solid surface via weak van der Waals interactions. During stage 2, irreversible attachment, hairlike appendages called pili permanently anchor the bacteria to the surface. During stage 3, maturation I, the biofilm grows through cell division and recruitment of other bacteria. An extracellular matrix composed primarily of polysaccharides holds the biofilm together. During stage 4, maturation II, the biofilm continues to grow and takes on a more complex shape. During stage 5, dispersal, the biofilm matrix is partly broken down, allowing some bacteria to escape and colonize another surface.

Question 41

Why do bacteria in biofilms often show increased resistance to antibiotics and detergents?

Accepted Answer

The extracellular matrix and outer layer of cells protects the inner bacteria. The close proximity of cells also facilitates later gene transfer (of genes with antibiotic resistance, for example). Exo-enzymes that destroy antibiotics may save neighboring bacteria as well.

Question 42

What is a capsule?

Accepted Answer

External structure that enables a prokaryote to attach to surfaces and protects it from dehydration. It can also protect the organism from attack by phagocytic cells, and makes pathogens more resistant to host organism immune responses.

Question 43

What is conjugation?

Accepted Answer

Process by which prokaryotes move DNA from one individual to another using a pilus. The DNA transferred can be in the form of a plasmid or as a hybrid, containing both plasmid and chromosomal DNA.

Question 44

What are some characteristics of the cell wall and envelope of Gram-negative bacteria?

Accepted Answer

Bacterium whose cell wall contains little peptidoglycan but has an outer membrane. They have a relatively thin cell wall composed of a few layers of peptidoglycan (only 10% of the total cell wall), surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. Porins are proteins in this cell membrane that allow substances to pass through the outer membrane. This outer envelope is sometimes referred to as a second lipid bilayer. The chemistry of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes.

Question 45

What is a Gram-positive bacterium?

Accepted Answer

Bacterium that contains mainly peptidoglycan in its cell walls. They typically lack the outer membrane found in Gram-negative organisms. Up to 90% of the cell wall is composed of peptidoglycan, and most of the rest is composed of acidic substances called teichoic acids. Teichoic acids may be covalently linked to lipids in the plasma membrane to form lipoteichoic acids. Lipoteichoic acids anchor the cell wall to the cell membrane.

Question 46

What is peptidoglycan?

Accepted Answer

Material composed of polysaccharide chains cross-linked to unusual peptides.

Question 47

What is a pilus?

Accepted Answer

Surface appendage of some prokaryotes used for attachment to surfaces including other prokaryotes.

Question 48

What is pseudopeptidoglycan?

Accepted Answer

Component of archaeal cell walls that is similar to peptidoglycan in morphology but contains different sugars.

Question 49

What is an S-layer protein?

Accepted Answer

Surface-layer protein present on the outside of cell walls of archaea and bacteria.

Question 50

What is teichoic acid?

Accepted Answer

Polymer associated with the cell wall of Gram-positive bacteria.

Question 51

What is transduction?

Accepted Answer

Process by which a bacteriophage moves DNA from one prokaryote to another.

Question 52

What is transformation?

Accepted Answer

Process by which a prokaryote takes in DNA found in its environment that is shed by other prokaryotes.

Question 53

What are the three basic categories of prokaryotes, according to their shape?

Accepted Answer

Cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped).

Question 54

What are proteobacteria?

Accepted Answer

A major phylum of Gram-negative bacteria. There are five primary classes of proteobacteria: alpha, beta, gamma, delta, and epsilon.

Question 55

What are alpha proteobacteria?

Accepted Answer

Some species are photoautotrophic but some are symbionts of plants and animals and others are pathogens. Eukaryotic mitochondria are thought to be derived from bacteria in this group.

Question 56

What are beta proteobacteria?

Accepted Answer

This group of bacteria is diverse. Some species play an important role in the nitrogen cycle.

Question 57

What are gamma proteobacteria?

Accepted Answer

Many are beneficial symbionts that populate the human gut, but others are familiar human pathogens. Some species from this subgroup oxidize sulfur compounds.

Question 58

What are delta proteobacteria?

Accepted Answer

Some species generate a spore-forming fruiting body in adverse conditions. Others reduce sulfate and sulfur.

Question 59

What are epsilon proteobacteria?

Accepted Answer

Many species inhabit the digestive tract of animals as symbionts or pathogens. Bacteria from this group have been found in deep-sea hydrothermal vents and cold seep habitats.

Question 60

What are some representative organisms of alpha proteobacteria?

Accepted Answer

Rhizobium : nitrogen-fixing endosymbiont associated with the roots of legumes Rickettsia : obligate intracellular parasite that causes typhus and Rocky Mountain Spotted Fever (but not rickets, which is caused by vitamin D deficiency)

Question 61

What are some representative organisms of beta proteobacteria?

Accepted Answer

Nitrosomonas : species from this group oxidize ammonia into nitrite Spirillum minus : causes rat-bite fever

Question 62

What are some representative organisms of gamma proteobacteria?

Accepted Answer

Escherichia coli : normally beneficial microbe of the human gut, but some strains cause disease Salmonella : certain strains cause food poisoning or typhoid fever Yersinia pestis : causative agent of Bubonic plague Pseudomonas aeruginosa : causes lung infections Vibrio cholera : causative agent of cholera Chromatium : sulfur-producing bacteria that oxidize sulfur, producing H2S

Question 63

What are some representative organisms of delta proteobacteria?

Accepted Answer

Myxobacteria : generate spore-forming fruiting bodies in adverse conditions Desulfovibrio vulgaris : anaerobic, sulfate-reducing bacterium

Question 64

What are some representative organisms of epsilon proteobacteria?

Accepted Answer

Campylobacter : causes blood poisoning and intestinal inflammation Helicobacter pylori : causes stomach ulcers

22: Prokaryotes - Bacteria and Archaea Flashcards

Prokaryotic Diversity, Structure of Prokaryotes, Prokaryotic Metabolism, Bacterial Diseases in Humans, Beneficial Prokaryotes

Brainscape's Knowledge GenomeTM

22: Prokaryotes - Bacteria and Archaea Flashcards

Prokaryotic Diversity, Structure of Prokaryotes, Prokaryotic Metabolism, Bacterial Diseases in Humans, Beneficial Prokaryotes

Brainscape's Knowledge Genome^TM