Learning Objectives

Differentiate in between bacteria, archaea, and eukarya.Draw the phylogenetic relationships in between bacteria, archaea, and eukarya.Identify ways that archaea and also bacteria gain power and also carbon.Explain the fossil, chemical, and also genetic proof for essential occasions for advancement of the three domains of life (bacteria, archaea, eukarya)Exsimple why the prospering of cyanobacteria resulted in the oxygenation of the environment.Place the development of the 3 domain names of life on the geologic time range.Describe the prominence of prokaryotes (bacteria and also archaea) with respect to humale health and also environmental processes.

You are watching: Which of the following correctly summarizes why bacteria and archaea are not in the same kingdom?

Three domain names of life on Earth

DNA sequence comparisons and structural and also biochemical comparisons repeatedly categorize all living organisms right into 3 primary domains: Bacteria, Archaea, and also Eukarya (likewise called Eukaryotes; these terms can be used interchangeably). Both Bacteria and Archaea are prokaryotes, single-celled microorganisms with no nuclei, and also Eukarya includes us and also all other pets, plants, fungi, and also single-celled protists – all organisms whose cells have actually nuclei to encshed their DNA apart from the rest of the cell. The fossil document suggests that the first living organisms were prokaryotes (Bacteria and Archaea), and eukaryotes emerged a billion years later.

Study Tip: It is suggested that you develop a chart to compare and comparison the 3 domains of life as you check out.


The indevelopment listed below was adapted from OpenStax Biology 22.2

Archaea and also Bacteria share a variety of features, however are also unique domains of life:

Both Archaea and Bacteria are unicellular organisms. In this means they are different from eukaryotes, which incorporate both unicellular and multicellular organismsArchaea and bacterial cells absence organelles or other interior membrane-bound frameworks. Therefore, unlike eukaryotes, archaea and bacteria perform not have a nucleus separating their hereditary material from the remainder of the cell.Archaea and also Bacteria generally have actually a solitary circular chromosome– a piece of circular, double-stranded DNA located in a room of the cell called the nucleoid. In comparison, many kind of eukaryotes have multiple, direct chromosomes.Archaea and Bacteria reproduce via fission, a process wright here an individual cell reproduces its single chromosome and splits in two. Eukaryotes recreate with mitosis, which has extra measures for replicating and correctly separating multiple chromosomes between two daughter cells. Many eukaryotes likewise recreate sexually, wbelow a process dubbed meiosis reduces the number of chromosome by half to produce haploid cells (typically dubbed sperm or eggs), and also then 2 haploid cells fuse to create a new organism. Archaea and bacteria cannot reproduce sexually.Almany all prokaryotes have actually a cell wall, a protective framework that allows them to survive in extreme problems, which is located exterior of their plasma membrane. In contrast, some eukaryotes carry out have cell walls, while others carry out not. The complace of the cell wall differs considerably in between the domains Bacteria and Archaea. Bacterial cell walls are created of peptidoglydeserve to, a complicated of protein and also sugars, while archaeal cell walls are created of polysaccharides (sugars). The composition of their cell wall surfaces additionally differs from the eukaryotic cell walls found in plants (cellulose) or fungi and insects (chitin). Some bacteria have an outer capsule external the cell wall.Other frameworks are current in some prokaryotic species, however not in others. For example:The capsule found in some species enables the organism to affix to surdeals with, protects it from dehydration and strike by phagocytic cells, and makes pathogens more resistant to our immune responses.Some species additionally have flagella (singular, flagellum) provided for locomotion, and pili (singular, pilus) provided for attachment to surencounters.Plasmids, which consist of extra-chromosomal DNA, are additionally current in many type of species of bacteria and also archaea.Prokaryotes, specifically Archaea, have the right to make it through in excessive environments that are unwelcoming for most living points.
The features of a typical prokaryotic cell are shown. Image credit: OpenStaxes Biology 22.2

Metabolic diversity of prokaryotes 

The information below was adapted from OpenStax Biology 22.3 

Prokaryotes have been and also are able to live in every atmosphere by using whatever energy and also carbon sources are easily accessible. Prokaryotes fill many kind of niches on Earth, consisting of being associated in nutrient cycles such as nitrogen and also carbon cycles, dewriting dead organisms, and prospering inside living organisms, consisting of humans. The very wide range of environments that prokaryotes occupy is possible because they have actually varied metabolic processes. Phototrophs (or phototrophic organisms) attain their energy from sunlight. Chemotrophs (or chemoman-made organisms) achieve their power from chemical compounds.

Prokaryotes not just deserve to use different sources of energy yet additionally different sources of carbon compounds. Respeak to that organisms that are able to fix inorganic carbon (for example, carbon dioxide) into organic carbon (for example, glucose) are called autotrophs. In comparison, heterotrophs need to attain carbon from organic compounds. The terms that define how prokaryotes attain energy and carbon can be merged. Therefore, photoautotrophs use power from sunlight, and carbon from carbon dioxide and water, whereas chemoheterotrophs obtain power and carbon from an organic chemical source. Chemoautotrophs obtain their power from not natural compounds, and they construct their facility molecules from carbon dioxide. Finally, photoheterotrophs usage light as an power resource, however require an organic carbon source (they cannot fix carbon dioxide into organic carbon). In comparison to the great metabolic diversity of prokaryotes, eukaryotes are just photoautotrophs (plants and some protists) or chemoheterotrophs (animals, fungi, and also some protists). The table below summarizes carbon and also energy sources in prokaryotes.


The videos listed below provide even more thorough overviews of Archaea and also Bacteria, including general attributes and metabolic diversity:

Phylohereditary relationships in between Archaea, Bacteria, and also Eukarya

While the term prokaryote (“before-nucleus”) is commonly offered to describe both Archaea and also Bacteria, you deserve to see from the phylohereditary Tree of Life listed below that this term does not define a monophyletic group:

A phylohereditary tree of living points, based on RNA information and proposed by Carl Woese, mirroring the separation of bacteria, archaea, and eukaryotes. By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute, uncovered in an article, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1201601

In truth, Archaea and Eukarya form a monophyletic group, not Archaea and Bacteria. These relationships suggest that archaea are even more carefully concerned eukaryotes than to bacteria, also though superficially archaea show up to be much even more equivalent to bacteria than eukaryotes.

Key occasions and also evidence in the advancement of the 3 domain names of life on Earth

Early life on Earth: The Earth is around 4.6 billion years old based on radiometric dating. While it is formally possible that life developed in the time of the Hadean eon, conditions may not have been stable enough on the earth to sustain life bereason big numbers of asteroids were thneed to have collided through the world in the time of the finish of the Hadean and beginning of the Archean eons. Evidence from microfossils (literally “microscopic fossils”) says that the life was current on Planet at leastern 3.8 billion years back. The earliest chemical proof of life, in the develop of chemical signatures produced just by living organisms, dates to roughly 3.6 billion years ago. What were these early life develops like? For the initially billion years of Earth’s existence, the atmosphere was anoxic, interpretation that there was no molecular oxygen (O2). Therefore the initially living things were single-celled, prokaryotic anaerobes (living without oxygen) and likely chemotrophic. 

The Oxygen Revolution: The development of water-separating and also oxygen-generating photosynthesis by cyanobacteria led to the first totally free molecular oxygen about 2.6 billion years earlier. The cost-free oxygen produced by cyanobacteria automatically reacted with soluble iron in the oceans, bring about iron oxide (rust) to precipitate out of the oceans. Oxygen didn’t accumulate all at once, and also evidence indicates that the seas weren’t totally oxygenated until 850 million years back (Mya). Today we check out evidence of the sluggish build-up of oxygen in the environment via banded iron formations existing in sedimentary rocks from that duration.

Banded iron formation, Karijini National Park, Western Australia. By Graeme Churcdifficult from Bristol, UK – Dales GorgeUploaded by PDTillguy, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=30889569

The increase in oxygen, called “The Oxygen Revolution,” permitted the evolution of larger bodies and also organs and also tissues, such as brains, via high metabolic prices. The boost in oxygen is a dramatic example of how life can transform the planet. Evolution of oxygenic photosynthesis adjusted the planet’s environment over billions of years, and also in turn brought about radical shifts in the biosphere: from an anoxic environment occupied by anaerobic, single-celled prokaryotes, to eukaryotes living in a micro-aerophilic (low-oxygen) atmosphere, to multicellular-organisms in an oxygen-wealthy setting. The video listed below offers a summary of the Oxygen Radvancement (aka, the Oxygen Catastrophe), consisting of its detrimental effects on the organisms that lived at the time:

Origins of eukaryotes: How did eukaryotes arise? The leading hypothesis, dubbed the endosymbiotic theory, is that eukaryotes occurred as a result of a blend of Archaean cells through bacteria, wright here an ancient Archaean engulfed (yet did not eat) an ancient, aerobic bacterial cell. The engulfed (endosymbiosed) bacterial cell remained within the archaean cell in what might have been a mutualistic relationship: the engulfed bacterium permitted the organize archean cell to use oxygen to release power stored in nutrients, and the host cell safeguarded the bacterial cell from predators. Microfossil evidence suggests that eukaryotes occurred at some time in between 1.6 and also 2.2 billion years earlier. The descendants of this primitive engulfed cell are existing in all eukaryotic cells now as mitochondria. We’ll discuss the endosymbiotic theory for the beginning of eukaryotes even more in the following analysis. 

Complex life forms: Much of the life on Planet was singled celled until shortly prior to the Cambrian “explosion,” once we watch introduction of all modern-day pet phyla. The Cambrian radiation (interpretation rapid evolutionary diversification) emerged approx. 540 Mya. The “explosion” term describes a boost in biodiversity of multicellular organisms at the begin of the Cambrian, 540 million years ago. Multicellular life appeared only a number of 10s of millions of years prior to the start of the Cambrian, as bizarre-looking fossils (Ediacaran biota/Doushantuo fossils) and also exhibiting body plans unlike anything seen contemporary animals. These species greatly disshowed up and were reput by Cambrian fauna, whose selection includes every one of the body plans discovered in present-day animal phyla. The appearance of Cambrian fauna expectancy millions of years; they did not all appear simultaneously as the term “explosion” inaccurately suggests.

Placing crucial events on the geologic time scale

How do each of these events map onto geologic time? Many of them are not “instantaneous” occasions, and so they expectancy multiple time durations as follows:

Hadean eon (4.6-4 BYA): No life present on EarthArchean eon (4 to 2.5 BYA)Origin of life (prokaryotic, anaerobic), 2.8-2.6 BYAFirst cyanobacteria, qualified of creating oxygen with photosynthesis, ~2.5 BYAProterozoic eon (2.5 BYA to 542 MYA)Oxygen radvancement (or catastrophe, depending upon your suggest of view) and development of Banded Iron Formations, occurs over a period from 2.5 to 1.9 BYAFirst single-celled eukaryotes, ~1.6 BYAFirst multicellular algaes, ~1.4 BYAFirst multicellular animals, ~635 MYAPhanerozoic eon (542 MYA to current day)Cambrian explosion (the majority of major pet phyla appeared in the fossil record), 542 MYAObviously many various other events happen in the Phanerozoic, and also we’ll spfinish a lot of of the rest of this module discussing them

Links to human wellness and ecological processes

The indevelopment listed below was adapted from OpenStax Biology 22.4 Some prokaryotic species deserve to harm humale health and wellness as pathogens: Devastating pathogen-borne illness and plagues, both viral and bacterial in nature, have impacted people because the start of human history, however at the time, their reason was not construed. Gradually, people pertained to realize that remaining apart from afflicted persons (and also their belongings) tfinished to reduce one’s opportunities of acquiring sick. For a microorganism to reason condition, it have to have the ability to reproduce in the host’s body and damages the organize in some way, and to spcheck out, it need to pass to a brand-new hold. In the 21st century, transmittable illness remain among the leading causes of death global, despite advancements made in clinical research and also treatments in recent years. The indevelopment listed below was adjusted from OpenStaxation Biology 22.5 Not all prokaryotes are pathogenic; pathogens reexisting only a really small percentage of the diversity of the microbial world. In fact, our life would not be feasible without prokaryotes. Some prokaryotic species are directly beneficial to huguy health:

The bacteria that inhalittle bit our skin and also gastrointestinal tract perform a host of great things for us. They defend us from pathogens, help us digest our food, and also develop some of our vitamins and also other nutrients. More freshly, researchers have actually gathered evidence that these bacteria may additionally aid control our moods, affect our task levels, and also even help manage weight by affecting our food choices and also absorption trends. The Person Microbiome Project has started the procedure of cataloging our normal bacteria (and also archaea) so we deserve to much better understand these features.Scientists are likewise learning that the absence of specific crucial microbes from our intestinal tract may collection us up for a selection of difficulties. This seems to be particularly true regarding the correct functioning of the immune mechanism. Tbelow are intriguing findings that imply that the absence of these microbes is a crucial contributor to the development of allergies and some autoimmune disorders. Research is presently undermeans to test whether including certain microbes to our interior ecosystem might aid in the treatment of these difficulties and in treating some forms of autism.A especially fascinating instance of our normal flora relates to our digestive systems. People that take high doses of antibiotics tfinish to shed many of their normal gut bacteria, permitting a naturally antibiotic-resistant species called Clostridium difficile to overthrive and reason major gastric problems, particularly chronic diarrhea. Obviously, trying to treat this problem with antibiotics just renders it worse. However, it has actually been efficiently treated by providing the patients fecal transplants (so-dubbed “poop pills”) from healthy and balanced donors to recreate the normal intestinal microbial neighborhood. Clinical trials are undermeans to encertain the safety and also efficiency of this technique.

See more: Calculate The Rms Speed Of An Oxygen Gas Molecule, O2, At 21.0 ∘C .

Carbon cycle; Image modified from “Nitrogen cycle” by Johann Dréo (CC BY-SA 3.0). The modified picture is licensed under a CC BY-SA 3.0 license._

Other prokaryotes instraight, however substantially, affect humale wellness through their functions in environmental processes:

Prokaryotes play a critical function in biogeochemical cycling of nitrogen, carbon, phosphorus, and other nutrients. The function of prokaryotes in the nitrogen cycle is critical. Nitrogen is a really crucial element to living things, bereason it is component of nucleotides and amino acids that are the building blocks of nucleic acids and proteins, respectively. Nitrogen is generally the a lot of limiting aspect in terrestrial ecodevices, via atmospheric nitrogen, N2, providing the biggest pool of obtainable nitrogen. However before, eukaryotes cannot usage atmospheric, gaseous nitrogen to synthedimension macromolecules. Fortunately, nitrogen can be “addressed,” meaning it is converted into ammonia (NH3) either biologically or abiotically. Abiotic nitrogen fixation occurs as an outcome of lightning or by industrial procedures. Biological nitrogen fixation (BNF) is specifically lugged out by prokaryotes: soil bacteria, cyanobacteria, and Frankia spp. (filamentous bacteria interacting through actinorhizal plants such as alder, bayberry, and also sweet fern). After photosynthesis, BNF is the second a lot of necessary biological procedure on Earth.Prokaryotes are likewise important in microbial bioremediation, the use of prokaryotes (or microbial metabolism) to remove pollutants, such as agricultural chemicals (pesticides, fertilizers) that leach from soil right into groundwater and the subsurface, and certain toxic steels and also oxides, such as selenium and arsenic compounds. One of the a lot of advantageous and also exciting examples of the use of prokaryotes for bioremediation objectives is the cleanup of oil spills, consisting of the Exxon Valdez spill in Alaska (1989), and more recently, the BP oil spill in the Gulf of Mexico (2010). To clean up these spills, extra inorganic nutrients that aid bacteria to thrive are added to the area, and also the development of bacteria breaks down the excess hydrocarbons.
a) Cleaning up oil after the Valdez spill in Alaska, employees hosed oil from beaches and then supplied a floating boom to corral the oil, which was finally skimmed from the water surface. Some species of bacteria are able to solubilize and also degrade the oil. (b) One of the a lot of catastrophic aftermath of oil spills is the damages to fauna. (crmodify a: alteration of work by NOAA; credit b: alteration of job-related by GOLUBENKOV, NGO: Saving Taman; from https://cnx.org/resources/b3178fe3228bf3c1f1ce0feae58ed67d7d1dad07/Figure_22_05_03ab.jpg)