Learning Objectives

Differentiate between bacteria, archaea, and eukarya.Draw the phylogenetic relationships between bacteria, archaea, and also eukarya.Identify methods that archaea and also bacteria gain energy and carbon.Explain the fossil, chemical, and also genetic proof for key events for advancement of the three domains of life (bacteria, archaea, eukarya)Explain why the thriving of cyanobacteria led to the oxygenation the the atmosphere.Place the advancement of the three domain names of life top top the geologic time scale.Describe the importance of prokaryotes (bacteria and archaea) through respect to human being health and environmental processes.

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Three domain names of life ~ above Earth

DNA succession comparisons and also structural and also biochemical comparisons continuously categorize every living organisms right into 3 primary domains: Bacteria, Archaea, and also Eukarya (also called Eukaryotes; these terms can be supplied interchangeably). Both Bacteria and also Archaea space prokaryotes, single-celled microorganisms through no nuclei, and Eukarya consists of us and also all other animals, plants, fungi, and also single-celled protists – every organisms whose cells have nuclei come enclose your DNA except the remainder of the cell. The fossil record indicates that the an initial living organisms were prokaryotes (Bacteria and also Archaea), and also eukaryotes developed a billion year later.

Study Tip: that is argued that you create a graph to compare and also contrast the three domain names of life as you read.


The information below was adapted from OpenStax biologic 22.2

Archaea and also Bacteria share a number of features, yet are additionally distinct domains of life:

Both Archaea and also Bacteria are unicellular organisms. In this means they are various from eukaryotes, which include both unicellular and also multicellular organismsArchaea and also bacterial cells lack organelles or other inner membrane-bound structures. Therefore, unlike eukaryotes, archaea and also bacteria execute not have a cell core separating their hereditary material from the remainder of the cell.Archaea and also Bacteria usually have a single circular chromosome– a piece of circular, double-stranded DNA located in an area of the cell referred to as the nucleoid. In contrast, numerous eukaryotes have actually multiple, straight chromosomes.Archaea and also Bacteria reproduce with fission, a process where one individual cell reproduces its solitary chromosome and also splits in two. Eukaryotes reproduce with mitosis, i m sorry includes extr steps because that replicating and also correctly separating multiple chromosomes in between two daughter cells. Countless eukaryotes likewise reproduce sexually, wherein a process called meiosis reduce the number of chromosome by fifty percent to create haploid cells (typically dubbed sperm or eggs), and also then two haploid cell fuse to develop a new organism. Archaea and also bacteria can not reproduce sexually.Almost all prokaryotes have actually a cabinet wall, a protective structure that permits them to survive in excessive conditions, i beg your pardon is located exterior of their plasma membrane. In contrast, some eukaryotes do have actually cell walls, while others perform not. The ingredient of the cell wall surface differs significantly in between the domain names Bacteria and Archaea. Bacterial cell walls space composed of peptidoglycan, a facility of protein and also sugars, when archaeal cabinet walls are composed of polysaccharides (sugars). The composition of their cell walls additionally differs indigenous the eukaryotic bio cell walls found in plants (cellulose) or fungi and insects (chitin). Some bacteria have an outer capsule outside the cabinet wall.Other frameworks are current in some prokaryotic species, yet not in others. For example:The capsule uncovered in some types enables the biology to attach to surfaces, protects that from dehydration and attack by phagocytic cells, and makes pathogens an ext resistant come our immune responses.Some species also have flagella (singular, flagellum) provided for locomotion, and pili (singular, pilus) offered for attachments to surfaces.Plasmids, i m sorry consist the extra-chromosomal DNA, are additionally present in many species of bacteria and archaea.Prokaryotes, especially Archaea, deserve to survive in extreme environments that are unwelcoming for many living things.
The attributes of a usual prokaryotic cell room shown. Image credit: OpenStax biologic 22.2

Metabolic diversity the prokaryotes 

The information below was adjusted from OpenStax biological 22.3 

Prokaryotes have been and also are able to live in every environment by using everything energy and carbon resources are available. Prokaryotes fill numerous niches on Earth, including being connected in nutrient cycles such together nitrogen and carbon cycles, decomposing dead organisms, and thriving inside living organisms, including humans. The an extremely broad variety of environments that prokaryotes accounting is possible because lock have varied metabolic processes. Phototrophs (or phototrophic organisms) obtain their energy from sunlight. Chemotrophs (or chemosynthetic organisms) achieve their energy from chemical compounds.

Prokaryotes no only have the right to use various sources of energy but also different resources of carbon compounds. Recall that organisms that room able come fix inorganic carbon (for example, carbon dioxide) into organic carbon (for example, glucose) room called autotrophs. In contrast, heterotrophs must obtain carbon indigenous organic compounds. The state that describe how prokaryotes acquire energy and also carbon have the right to be combined. Thus, photoautotrophs use energy from sunlight, and carbon from carbon dioxide and water, whereas chemoheterotrophs acquire energy and also carbon from an organic chemistry source. Chemoautotrophs acquire their energy from not natural compounds, and also they develop their facility molecules indigenous carbon dioxide. Finally, photoheterotrophs usage light as an energy source, but require an necessary carbon source (they cannot resolve carbon dioxide into organic carbon). In contrast to the good metabolic diversity that prokaryotes, eukaryotes are only photoautotrophs (plants and also some protists) or chemoheterotrophs (animals, fungi, and also some protists). The table listed below summarizes carbon and energy resources in prokaryotes.


The videos below provide an ext detailed overviews the Archaea and also Bacteria, including general features and also metabolic diversity:

Phylogenetic relationships between Archaea, Bacteria, and Eukarya

While the term prokaryote (“before-nucleus”) is widely provided to describe both Archaea and Bacteria, you deserve to see indigenous the phylogenetic Tree the Life listed below that this ax does not describe a monophyletic group:

A phylogenetic tree of living things, based upon RNA data and proposed through Carl Woese, reflecting the separation the bacteria, archaea, and eukaryotes. By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute, discovered in an article, public Domain, https://commons.wikimedia.org/w/index.php?curid=1201601

In fact, Archaea and also Eukarya form a monophyletic group, no Archaea and also Bacteria. These relationships suggest that archaea are much more closely pertained to eukaryotes 보다 to bacteria, even though superficially archaea appear to it is in much much more similar to bacteria 보다 eukaryotes.

Key events and evidence in the advancement of the three domains of life ~ above Earth

Early life ~ above Earth: The planet is approximately 4.6 billion years old based on radiometric dating. While it is formally possible that life developed during the Hadean eon, problems may not have actually been stable enough on the planet to sustain life because huge numbers that asteroids were assumed to have actually collided through the planet throughout the finish of the Hadean and beginning of the Archean eons. Proof from microfossils (literally “microscopic fossils”) argues that the life was present on earth at least 3.8 billion year ago. The earliest chemical evidence of life, in the type of chemistry signatures created only by life organisms, dates to about 3.6 billion years ago. What were these beforehand life forms like? because that the first billion year of earth’s existence, the atmosphere was anoxic, definition that there was no molecule oxygen (O2). For this reason the very first living things were single-celled, prokaryotic anaerobes (living there is no oxygen) and likely chemotrophic. 

The Oxygen Revolution: The advancement of water-splitting and also oxygen-generating photosynthesis through cyanobacteria resulted in the very first free molecular oxygen around 2.6 billion year ago. The complimentary oxygen developed by cyanobacteria immediately reacted through soluble iron in the oceans, resulting in iron oxide (rust) to precipitate the end of the oceans. Oxygen no accumulate every at once, and also evidence indicates that the seas weren’t totally oxygenated till 850 million years back (Mya). This particular day we see evidence of the slow build-up of oxygen in the environment through banded steel formations present in sedimentary rocks from that period.

Banded steel formation, Karijini nationwide Park, western Australia. By Graeme Churchard native Bristol, UK – Dales GorgeUploaded through PDTillman, CC by 2.0, https://commons.wikimedia.org/w/index.php?curid=30889569

The rise in oxygen, dubbed “The Oxygen Revolution,” allowed the evolution of bigger bodies and also organs and also tissues, such together brains, through high metabolic rates. The rise in oxygen is a dramatic instance of exactly how life can transform the planet. Evolution of oxygenic photosynthesis adjusted the planet’s atmosphere over billions that years, and in turn brought about radical move in the biosphere: indigenous an anoxic atmosphere populated through anaerobic, single-celled prokaryotes, to eukaryotes life in a micro-aerophilic (low-oxygen) environment, come multicellular-organisms in one oxygen-rich environment. The video clip below provides an overview of the Oxygen revolution (aka, the Oxygen Catastrophe), including its detrimental impacts on the organisms that lived at the time:

Origins that eukaryotes: How did eukaryotes arise? The top hypothesis, referred to as the endosymbiotic theory, is the eukaryotes arose as a result of a fusion of Archaean cells v bacteria, where an old Archaean engulfed (but did not eat) an ancient, aerobic bacter cell. The engulfed (endosymbiosed) bacter cell continued to be within the archaean cell in what may have been a mutualistic relationship: the engulfed bacterium permitted the hold archean cell to usage oxygen to release energy stored in nutrients, and the host cell safeguarded the bacterial cabinet from predators. Microfossil evidence argues that eukaryotes occurred sometime in between 1.6 and 2.2 billion years ago. The descendants of this ancient engulfed cell are current in all eukaryotic bio cells today as mitochondria. We’ll comment on the endosymbiotic theory for the beginning of eukaryotes more in the next reading. 

Complex life forms: Much of the life on planet was singled celled until shortly before the Cambrian “explosion,” once we see appearance of all modern animal phyla. The Cambrian radiation (meaning rapid evolutionary diversification) developed approx. 540 Mya. The “explosion” term refers to rise in biodiversity of multicell organisms in ~ the start of the Cambrian, 540 million year ago. Multicell life showed up only numerous tens of millions of years before the begin of the Cambrian, as bizarre-looking fossils (Ediacaran biota/Doushantuo fossils) and exhibiting human body plans unequal anything seen present-day animals. These species largely disappeared and were replaced by Cambrian fauna, whose selection includes all of the body plans found in present-day pet phyla. The illustration of Cambrian fauna span millions that years; castle did no all appear simultaneously together the term “explosion” inaccurately implies.

Placing an essential events top top the geologic time scale

How do each that these events map onto geologic time? most of them are not “instantaneous” events, and also so they expectations multiple time periods as follows:

Hadean eon (4.6-4 BYA): No life present on EarthArchean eon (4 come 2.5 BYA)Origin that life (prokaryotic, anaerobic), 2.8-2.6 BYAFirst cyanobacteria, qualified of producing oxygen through photosynthesis, ~2.5 BYAProterozoic eon (2.5 BYA to 542 MYA)Oxygen revolution (or catastrophe, depending upon your suggest of view) and formation the Banded iron Formations, occurs end a duration 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 existing day)Cambrian explosion (most major animal phyla showed up in the fossil record), 542 MYAObviously countless other events occur in the Phanerozoic, and also we’ll spend most of the remainder of this module discussing them

Links to human health and also environmental processes

The information listed below was adjusted from OpenStax biological 22.4 Some prokaryotic species can injury human health and wellness as pathogens: Devastating pathogen-borne diseases and plagues, both viral and also bacterial in nature, have affected humans since the start of person history, yet at the time, their cause was not understood. End time, people pertained to realize that remaining apart from afflicted persons (and your belongings) often tended to minimize one’s possibilities of obtaining sick. For a virus to cause disease, that must have the ability to reproduce in the host’s body and damage the hold in some way, and also to spread, it need to pass come a new host. In the 21st century, infectious diseases remain among the leading reasons of fatality worldwide, despite advancements made in medical research and also treatments in current decades. The information listed below was adjusted from OpenStax biological 22.5 Not every prokaryotes room pathogenic; pathogens represent just a very little percentage that the diversity that the microbial world. In fact, ours life would certainly not be feasible without prokaryotes. Part prokaryotic species are directly useful to human health:

The bacteria the inhabit ours skin and also gastrointestinal tract carry out a organize of great things for us. They safeguard us indigenous pathogens, assist us digest our food, and produce several of our vitamins and other nutrients. More recently, scientists have gathered evidence that these bacteria might also help regulate our moods, influence our activity levels, and even assist control load by affecting ours food choices and absorption patterns. The person Microbiome task has begun the procedure of cataloging our common bacteria (and archaea) so us can far better understand this functions.Scientists are also discovering that the absence of certain an essential microbes from our intestinal street may collection us up because that a selection of problems. This appears to be an especially true about the proper functioning of the immune system. There are intriguing result that indicate that the absence of this microbes is crucial contributor come the breakthrough of allergies and also some autoimmune disorders. Research is at this time underway to check whether adding specific microbes come our internal ecosystem may assist in the treatment of this problems and in dealing with some develops of autism.A specifically fascinating example of our common flora relates come our digestive systems. People who take it high doses of antibiotics often tend to lose plenty of of their regular gut bacteria, allowing a normally antibiotic-resistant species called Clostridium difficile to overgrow and also cause severe gastric problems, specifically chronic diarrhea. Obviously, trying to treat this trouble with antibiotics just makes it worse. However, it has actually been effectively treated by providing the patient fecal transplants (so-called “poop pills”) from healthy donors to reestablish the common intestinal microbial community. Clinical trials space underway come ensure the safety and also effectiveness that this technique.

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Carbon cycle; image modified native “Nitrogen cycle” by Johann Dréo (CC BY-SA 3.0). The modified image is license is granted under a CC BY-SA 3.0 license._

Other prokaryotes indirectly, however dramatically, influence human health through their duties in environmental processes:

Prokaryotes pat a crucial role in biogeochemical to ride bicycle of nitrogen, carbon, phosphorus, and also other nutrients. The function of prokaryotes in the nitrogen cycle is critical. Nitrogen is a very important aspect to living things, since it is component of nucleotides and amino mountain that space the building blocks of nucleic acids and proteins, respectively. Nitrogen is usually the most limiting facet in terrestrial ecosystems, with atmospheric nitrogen, N2, providing the largest pool of easily accessible nitrogen. However, standard scale cannot use atmospheric, gaseous nitrogen to synthesize macromolecules. Fortunately, nitrogen deserve to be “fixed,” an interpretation it is converted right into ammonia (NH3) one of two people biologically or abiotically. Abiotic nitrogen continuous occurs as a an outcome of lightning or by commercial processes. Biological nitrogen fixation (BNF) is exclusively lugged out through prokaryotes: floor bacteria, cyanobacteria, and Frankia spp. (filamentous bacteria interacting with actinorhizal plants such as alder, bayberry, and also sweet fern). ~ photosynthesis, BNF is the second most crucial biological process on Earth.Prokaryotes are additionally essential in microbial bioremediation, the use of prokaryotes (or microbial metabolism) to eliminate pollutants, such as farming chemicals (pesticides, fertilizers) that leach from soil into groundwater and the subsurface, and certain toxic metals and oxides, such as selenium and also arsenic compounds. One the the most useful and also interesting instances of the use of prokaryotes for bioremediation purposes is the cleanup that oil spills, including the Exxon Valdez pour out in Alaska (1989), and an ext recently, the BP oil pour out in the Gulf that Mexico (2010). To clean up this spills, added inorganic nutrients that assist bacteria to prosper are included to the area, and also the development of bacteria breaks down the overfill hydrocarbons.
a) clean up oil ~ the Valdez spill in Alaska, employees hosed oil from beaches and then supplied a floating eight to corral the oil, which was ultimately skimmed indigenous the water surface. Some types of bacteria space able to solubilize and also degrade the oil. (b) one of the most catastrophic after-effects of oil pour out is the damages to fauna. (credit a: modification of work-related by NOAA; credit transaction b: change of job-related by GOLUBENKOV, NGO: saving Taman; from https://cnx.org/resources/b3178fe3228bf3c1f1ce0feae58ed67d7d1dad07/Figure_22_05_03ab.jpg)