Learning Objectives

Differentiate in between bacteria, archaea, and also eukarya.Draw the phylogenetic relationships between bacteria, archaea, and eukarya.Identify means that archaea and also bacteria get energy and also carbon.Explain the fossil, chemical, and genetic proof for an essential events for advancement of the three domains of life (bacteria, archaea, eukarya)Explain why the growing of cyanobacteria led to the oxygenation that the atmosphere.Place the development of the three domain names of life top top the geologic time scale.Describe the prestige of prokaryotes (bacteria and also archaea) with respect to person health and also environmental processes.

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Three domains of life ~ above Earth

DNA succession comparisons and structural and also biochemical comparisons repetitively categorize every living organisms into 3 primary domains: Bacteria, Archaea, and also Eukarya (also called Eukaryotes; these terms can be used interchangeably). Both Bacteria and also Archaea are prokaryotes, single-celled microorganisms through no nuclei, and Eukarya has us and also all other animals, plants, fungi, and single-celled protists – all organisms whose cells have actually nuclei come enclose your DNA apart from the remainder of the cell. The fossil record shows that the an initial living organisms to be prokaryotes (Bacteria and Archaea), and eukaryotes developed a billion years later.

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


The information listed below was adjusted from OpenStax biological 22.2

Archaea and also Bacteria re-publishing a variety of features, yet are likewise distinct domains of life:

Both Archaea and Bacteria are unicellular organisms. In this means they are various from eukaryotes, which encompass both unicellular and multicellular organismsArchaea and bacterial cells lack organelles or other inner membrane-bound structures. Therefore, unequal eukaryotes, archaea and bacteria perform not have actually a cell core separating their genetic material indigenous the rest of the cell.Archaea and Bacteria typically have a solitary circular chromosome– a piece of circular, double-stranded DNA situated in an area the the cell called the nucleoid. In contrast, plenty of eukaryotes have actually multiple, straight chromosomes.Archaea and also Bacteria reproduce with fission, a process where one individual cell reproduces its single chromosome and also splits in two. Eukaryotes reproduce through mitosis, which includes additional steps for replicating and correctly separating multiple chromosomes in between two daughter cells. Numerous eukaryotes additionally reproduce sexually, whereby a procedure called meiosis reduces the number of chromosome by fifty percent to develop haploid cells (typically called sperm or eggs), and also then two haploid cell fuse to produce a new organism. Archaea and also bacteria can not reproduce sexually.Almost every prokaryotes have actually a cell wall, a protective framework that allows them to make it through in too much conditions, which is located exterior of their plasma membrane. In contrast, some eukaryotes do have actually cell walls, if others perform not. The composition of the cell wall surface differs significantly between the domain names Bacteria and also Archaea. Bacterial cell walls are composed of peptidoglycan, a complicated of protein and also sugars, while archaeal cell walls room composed of polysaccharides (sugars). The composition of their cell walls also differs from the eukaryotic cell walls uncovered in plants (cellulose) or fungi and insects (chitin). Part bacteria have actually an outer capsule outside the cabinet wall.Other structures are current in some prokaryotic species, yet not in others. Because that example:The capsule found in some species enables the biology to connect to surfaces, protects that from dehydration and attack by phagocytic cells, and also makes pathogens much more resistant to our immune responses.Some species also have flagella (singular, flagellum) supplied for locomotion, and pili (singular, pilus) offered for attachments to surfaces.Plasmids, which consist the extra-chromosomal DNA, are also present in many varieties of bacteria and archaea.Prokaryotes, specifically Archaea, can survive in extreme atmospheres that are unwelcoming for many living things.
The attributes of a usual prokaryotic cell space shown. Picture credit: OpenStax biological 22.2

Metabolic diversity the prokaryotes 

The information below was adjusted from OpenStax biologic 22.3 

Prokaryotes have been and are able come live in every environment by using whatever energy and carbon resources are available. Prokaryotes fill countless niches top top Earth, including being involved in nutrient cycles such together nitrogen and also carbon cycles, decomposing dead organisms, and thriving within living organisms, including humans. The really broad range of settings that prokaryotes occupy is possible because lock have diverse metabolic processes. Phototrophs (or phototrophic organisms) achieve their power from sunlight. Chemotrophs (or valence organisms) obtain their power from chemical compounds.

Prokaryotes not only can use various sources of power but likewise different resources of carbon compounds. Recall the organisms that space able come fix inorganic carbon (for example, carbon dioxide) right into organic carbon (for example, glucose) space called autotrophs. In contrast, heterotrophs must acquire carbon indigenous organic compounds. The state that define how prokaryotes attain energy and carbon can be combined. Thus, photoautotrophs use power from sunlight, and carbon native carbon dioxide and also water, vice versa, chemoheterotrophs attain energy and also carbon native an organic chemical source. Chemoautotrophs achieve their energy from inorganic compounds, and also they construct their facility molecules indigenous carbon dioxide. Finally, photoheterotrophs use light together an power source, however require an necessary carbon resource (they cannot fix carbon dioxide into organic carbon). In comparison to the great metabolic diversity the prokaryotes, eukaryotes are only photoautotrophs (plants and some protists) or chemoheterotrophs (animals, fungi, and also some protists). The table listed below summarizes carbon and also energy resources in prokaryotes.


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

Phylogenetic relationships between Archaea, Bacteria, and also Eukarya

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

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

In fact, Archaea and Eukarya type a monophyletic group, no Archaea and also Bacteria. These relationships show that archaea are more closely related to eukaryotes 보다 to bacteria, also though superficially archaea show up to it is in much more similar come bacteria 보다 eukaryotes.

Key events and also evidence in the evolution of the three domains of life top top Earth

Early life ~ above Earth: The planet is approximately 4.6 billion year old based on radiometric dating. While it is formally feasible that life arose during the Hadean eon, conditions may not have actually been stable enough on the world to sustain life because large numbers of asteroids were assumed to have actually collided through the planet throughout the end of the Hadean and beginning the the Archean eons. Evidence from microfossils (literally “microscopic fossils”) suggests that the life was current on planet at the very least 3.8 billion year ago. The earliest chemical proof of life, in the type of chemical signatures created only by life organisms, days to roughly 3.6 billion year ago. What to be these beforehand life forms like? because that the very first billion year of earth’s existence, the atmosphere was anoxic, meaning that there was no molecular oxygen (O2). Hence the an initial living points were single-celled, prokaryotes anaerobes (living without oxygen) and likely chemotrophic. 

The Oxygen Revolution: The evolution of water-splitting and also oxygen-generating photosynthesis by cyanobacteria brought about the an initial free molecular oxygen about 2.6 billion year ago. The totally free oxygen developed by cyanobacteria automatically reacted with soluble iron in the oceans, causing iron oxide (rust) come precipitate the end of the oceans. Oxygen didn’t accumulate every at once, and evidence shows that the seas weren’t completely oxygenated till 850 million years earlier (Mya). Now we see proof of the slow build-up of oxygen in the environment through banded steel formations present in sedimentary rocks from the period.

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

The increase in oxygen, called “The Oxygen Revolution,” permitted the development of bigger bodies and organs and also tissues, such as brains, v high metabolic rates. The rise in oxygen is a dramatic instance of just how life can transform the planet. Evolution of oxygenic photosynthesis readjusted the planet’s atmosphere over billions the years, and also in turn brought about radical shifts in the biosphere: native an anoxic setting populated by anaerobic, single-celled prokaryotes, come eukaryotes living in a micro-aerophilic (low-oxygen) environment, to multicellular-organisms in one oxygen-rich environment. The video below provides an introduction of the Oxygen change (aka, the Oxygen Catastrophe), including its detrimental effects on the biology that live at the time:

Origins that eukaryotes: How did standard scale arise? The leading hypothesis, referred to as the endosymbiotic theory, is that eukaryotes occurred as a an outcome of a combination of Archaean cells through bacteria, where an ancient Archaean engulfed (but did no eat) one ancient, aerobic bacter cell. The engulfed (endosymbiosed) bacterial cell remained within the archaean cell in what may have been a mutualistic relationship: the engulfed bacterium enabled the organize archean cell to use oxygen come release power stored in nutrients, and the host cell protected the bacterial cabinet from predators. Microfossil evidence says that eukaryotes arose sometime in between 1.6 and also 2.2 billion years ago. The descendants of this old engulfed cell are current in all eukaryotic bio cells now as mitochondria. We’ll discuss the endosymbiotic concept for the beginning of eukaryotes much more in the next reading. 

Complex life forms: Much the the life on planet was singled celled till shortly prior to the Cambrian “explosion,” once we see emergence of all modern animal phyla. The Cambrian radiation (meaning quick evolutionary diversification) arisen approx. 540 Mya. The “explosion” hatchet refers to boost in biodiversity of multicellular organisms at the begin of the Cambrian, 540 million year ago. Multicell life appeared only numerous tens of countless years prior to the begin of the Cambrian, together bizarre-looking fossils (Ediacaran biota/Doushantuo fossils) and also exhibiting human body plans uneven anything seen contemporary animals. These species largely disappeared and also were replaced by Cambrian fauna, whose range includes all of the human body plans discovered in present-day animal phyla. The appearance of Cambrian fauna expectations millions that years; lock did no all show up simultaneously as the ax “explosion” inaccurately implies.

Placing an essential events on the geologic time scale

How execute each that these occasions map onto geologic time? most of them space not “instantaneous” events, and so they span multiple time periods 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 producing oxygen v photosynthesis, ~2.5 BYAProterozoic eon (2.5 BYA to 542 MYA)Oxygen transformation (or catastrophe, depending upon your point of view) and also formation of Banded steel Formations, occurs over a duration from 2.5 come 1.9 BYAFirst single-celled eukaryotes, ~1.6 BYAFirst multicell algaes, ~1.4 BYAFirst multicellular animals, ~635 MYAPhanerozoic eon (542 MYA to current day)Cambrian to explode (most major animal phyla appeared in the fossil record), 542 MYAObviously countless other occasions occur in the Phanerozoic, and we’ll spend many of the rest of this module stating them

Links to person health and also environmental processes

The information listed below was adapted from OpenStax biology 22.4 Some prokaryotic varieties can damage human wellness as pathogens: Devastating pathogen-borne diseases and plagues, both viral and also bacterial in nature, have influenced humans because the start of human history, yet at the time, their reason was not understood. Over time, people pertained to realize that continuing to be apart native afflicted persons (and their belongings) tended to mitigate one’s chances of acquiring sick. For a virus to reason disease, the must be able to reproduce in the host’s body and also damage the host in some way, and also to spread, it should pass to a brand-new host. In the 21st century, contagious diseases remain amongst the leading reasons of death worldwide, despite breakthroughs made in medical research and treatments in recent decades. The information below was adjusted from OpenStax biologic 22.5 Not all prokaryotes are pathogenic; pathogens represent just a very tiny percentage that the diversity the the microbial world. In fact, ours life would certainly not be feasible without prokaryotes. Some prokaryotic varieties are directly beneficial to human health:

The bacteria the inhabit our skin and also gastrointestinal tract do a host of great things because that us. They protect us native pathogens, aid us digest ours food, and produce several of our vitamins and other nutrients. More recently, scientists have actually gathered evidence that these bacteria might also assist regulate our moods, influence our task levels, and even aid control load by affecting our food choices and also absorption patterns. The human being Microbiome project has started the procedure of cataloging our common bacteria (and archaea) so us can better understand these functions.Scientists are additionally discovering the the absence of certain crucial microbes from our intestinal street may collection us up for a variety of problems. This appears to be specifically true concerning the ideal functioning of the immune system. There room intriguing findings that suggest that the absence of this microbes is vital contributor come the advance of allergies and some autoimmune disorders. Research is at this time underway to test whether adding details microbes to our inner ecosystem may help in the therapy of these problems and also in treating some forms of autism.A an especially fascinating instance of our common flora relates to our digestive systems. People who take high sheep of antibiotics tend to lose countless of their regular gut bacteria, enabling a normally antibiotic-resistant varieties called Clostridium difficile to overgrow and cause significant gastric problems, especially chronic diarrhea. Obviously, trying come treat this problem with antibiotics just makes it worse. However, it has been effectively treated by providing the patient fecal transplants (so-called “poop pills”) from healthy donors come reestablish the normal intestinal microbial community. Clinical trials are underway come ensure the safety and also effectiveness the this technique.

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

Other prokaryotes indirectly, yet dramatically, affect human wellness through their roles in environmental processes:

Prokaryotes pat a an important role in biogeochemical to ride bicycle of nitrogen, carbon, phosphorus, and other nutrients. The function of prokaryotes in the nitrogen bike is critical. Nitrogen is a very important facet to living things, due to the fact that it is part of nucleotides and amino acids that room the structure blocks of main point acids and also proteins, respectively. Nitrogen is typically the many limiting facet in terrestrial ecosystems, v atmospheric nitrogen, N2, offering the biggest pool of available nitrogen. However, eukaryotes cannot usage atmospheric, gaseous nitrogen to synthesize macromolecules. Fortunately, nitrogen can be “fixed,” definition it is converted into ammonia (NH3) either biologically or abiotically. Abiotic nitrogen fixation occurs together a an outcome of lightning or by industrial processes. Biological nitrogen fixation (BNF) is exclusively lugged out by prokaryotes: soil bacteria, cyanobacteria, and Frankia spp. (filamentous bacteria communicating with actinorhizal plants such together alder, bayberry, and also sweet fern). ~ photosynthesis, BNF is the second most vital biological process on Earth.Prokaryotes are likewise essential in microbial bioremediation, the use of prokaryotes (or microbial metabolism) to eliminate pollutants, such as agricultural chemicals (pesticides, fertilizers) that leach indigenous soil right into groundwater and the subsurface, and particular toxic metals and oxides, such together selenium and also arsenic compounds. One the the many useful and also interesting instances of the usage of prokaryotes because that bioremediation purposes is the cleanup the oil spills, including the Exxon Valdez pour out in Alaska (1989), and much more recently, the BP oil spill in the Gulf of Mexico (2010). To clean up these spills, additional inorganic nutrient that help bacteria to thrive are included to the area, and the development of bacteria breaks under the overfill hydrocarbons.
a) cleaning up oil after ~ the Valdez spill in Alaska, workers hosed oil native beaches and then used a floating boom to corral the oil, i m sorry was finally skimmed from the water surface. Some varieties of bacteria room able come solubilize and also degrade the oil. (b) among the many catastrophic after-effects of oil spills is the damage to fauna. (credit a: alteration of job-related by NOAA; credit transaction b: change of job-related by GOLUBENKOV, NGO: saving Taman; indigenous https://cnx.org/resources/b3178fe3228bf3c1f1ce0feae58ed67d7d1dad07/Figure_22_05_03ab.jpg)