Learning Objectives

Differentiate in between bacteria, archaea, and also eukarya.Draw the phylogenetic relationships in between bacteria, archaea, and also eukarya.Identify means that archaea and bacteria gain energy and also carbon.Explain the fossil, chemical, and also genetic proof for crucial events for advancement of the three domain names of life (bacteria, archaea, eukarya)Explain why the growing of cyanobacteria resulted in the oxygenation the the atmosphere.Place the development of the three domains of life ~ above the geologic time scale.Describe the prominence of prokaryotes (bacteria and also archaea) through respect to person health and also environmental processes.

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Three domain names of life ~ above Earth

DNA sequence comparisons and structural and biochemical comparisons consistently categorize every living organisms into 3 primary domains: Bacteria, Archaea, and also Eukarya (also called Eukaryotes; this terms can be provided interchangeably). Both Bacteria and also Archaea room prokaryotes, single-celled microorganisms v no nuclei, and Eukarya contains us and also all various other animals, plants, fungi, and also single-celled protists – every organisms who cells have nuclei come enclose your DNA except the rest of the cell. The fossil record suggests that the first living organisms to be prokaryotes (Bacteria and also Archaea), and eukaryotes occurred a billion year later.

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


The information below was adjusted from OpenStax biological 22.2

Archaea and also Bacteria re-superstructure a number of features, yet are likewise distinct domain names of life:

Both Archaea and Bacteria room unicellular organisms. In this method they are different from eukaryotes, which encompass both unicellular and multicellular organismsArchaea and also bacterial cells absence organelles or other interior membrane-bound structures. Therefore, unlike eukaryotes, archaea and also bacteria execute not have a nucleus separating their genetic material from the remainder of the cell.Archaea and also Bacteria generally have a single circular chromosome– a item of circular, double-stranded DNA situated in an area of the cell called the nucleoid. In contrast, many eukaryotes have actually multiple, linear chromosomes.Archaea and Bacteria reproduce with fission, a process where an individual cabinet reproduces its single chromosome and splits in two. Eukaryotes reproduce with mitosis, i m sorry includes extr steps for replicating and also correctly separating multiple chromosomes between two daughter cells. Numerous eukaryotes also reproduce sexually, wherein a procedure called meiosis reduces the number of chromosome by fifty percent to develop haploid cells (typically dubbed sperm or eggs), and also then 2 haploid cells fuse to create a brand-new organism. Archaea and also bacteria cannot reproduce sexually.Almost every prokaryotes have a cell wall, a protective framework that permits them to make it through in extreme conditions, which is located exterior of your plasma membrane. In contrast, some eukaryotes do have actually cell walls, if others carry out not. The composition of the cell wall differs significantly in between the domain names Bacteria and also Archaea. Bacterial cabinet walls space composed that peptidoglycan, a complex of protein and sugars, if archaeal cell walls are composed the polysaccharides (sugars). The composition of your cell walls additionally differs native the eukaryotic bio cell walls uncovered in tree (cellulose) or fungi and also insects (chitin). Part bacteria have actually an outer capsule outside the cell wall.Other structures are existing in some prokaryotic species, yet not in others. For example:The capsule uncovered in some species enables the biology to affix to surfaces, protects the from dehydration and also attack by phagocytic cells, and also makes pathogens more resistant come our immune responses.Some species also have flagella (singular, flagellum) provided for locomotion, and pili (singular, pilus) offered for attachment to surfaces.Plasmids, i m sorry consist the extra-chromosomal DNA, are additionally present in many types of bacteria and archaea.Prokaryotes, specifically Archaea, deserve to survive in extreme atmospheres that are unwelcoming for many living things.
The attributes of a usual prokaryotic cell are shown. Picture credit: OpenStax biological 22.2

Metabolic diversity that prokaryotes 

The information below was adapted from OpenStax biology 22.3 

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

Prokaryotes not only can use various sources of energy but additionally different resources of carbon compounds. Recall that organisms that are able to fix not natural carbon (for example, carbon dioxide) right into organic carbon (for example, glucose) space called autotrophs. In contrast, heterotrophs must obtain carbon native organic compounds. The terms that describe how prokaryotes acquire energy and also carbon have the right to be combined. Thus, photoautotrophs use energy from sunlight, and also carbon indigenous carbon dioxide and water, whereas chemoheterotrophs acquire energy and carbon from an organic chemistry source. Chemoautotrophs achieve their power from not natural compounds, and they construct their facility molecules indigenous carbon dioxide. Finally, photoheterotrophs usage light together an power source, yet require an organic carbon source (they cannot deal with carbon dioxide right into organic carbon). In comparison to the good metabolic diversity the prokaryotes, standard scale are just photoautotrophs (plants and some protists) or chemoheterotrophs (animals, fungi, and some protists). The table below summarizes carbon and also energy resources in prokaryotes.


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

Phylogenetic relationships between Archaea, Bacteria, and Eukarya

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

A phylogenetic tree of living things, based on RNA data and proposed by Carl Woese, mirroring the separation of bacteria, archaea, and also eukaryotes. By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute, discovered in one 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. This relationships show that archaea are much more closely concerned eukaryotes than to bacteria, also though superficially archaea appear to it is in much much more similar come bacteria 보다 eukaryotes.

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

Early life top top Earth: The planet is roughly 4.6 billion years old based on radiometric dating. While that is formally feasible that life arose during the Hadean eon, problems may not have actually been stable enough on the earth to sustain life because large numbers the asteroids were believed to have collided v the planet during the finish of the Hadean and beginning that the Archean eons. Evidence from microfossils (literally “microscopic fossils”) says that the life was present on planet at least 3.8 billion year ago. The more quickly chemical proof of life, in the kind of chemistry signatures developed only by life organisms, days to about 3.6 billion year ago. What to be these early life develops like? because that the an initial billion year of earth existence, the environment was anoxic, meaning that there was no molecule oxygen (O2). Therefore the an initial living points were single-celled, prokaryotes anaerobes (living without oxygen) and also likely chemotrophic. 

The Oxygen Revolution: The evolution of water-splitting and oxygen-generating photosynthesis by cyanobacteria led to the first free molecule oxygen around 2.6 billion years ago. The totally free oxygen developed by cyanobacteria instantly reacted through soluble steel in the oceans, causing iron oxide (rust) to precipitate out of the oceans. Oxygen no accumulate every at once, and evidence suggests that the oceans weren’t totally oxygenated until 850 million years back (Mya). This day we see evidence of the slow build-up of oxygen in the environment through banded steel formations present in sedimentary rocks from the period.

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

The increase in oxygen, referred to as “The Oxygen Revolution,” enabled the development of larger bodies and organs and tissues, such as brains, with high metabolic rates. The rise in oxygen is a dramatic instance of exactly how life can alter the planet. Advancement of oxygenic photosynthesis changed the planet’s setting over billions of years, and also in turn resulted in radical shifts in the biosphere: indigenous an anoxic atmosphere populated by anaerobic, single-celled prokaryotes, come eukaryotes life in a micro-aerophilic (low-oxygen) environment, to multicellular-organisms in one oxygen-rich environment. The video below provides review of the Oxygen transformation (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 top hypothesis, dubbed the endosymbiotic theory, is that eukaryotes occurred as a an outcome of a blend of Archaean cells with bacteria, where an old Archaean engulfed (but did not eat) an ancient, aerobic bacter cell. The engulfed (endosymbiosed) bacter cell stayed within the archaean cabinet in what may have been a mutualistic relationship: the engulfed bacterium permitted the organize archean cell to use oxygen to release power stored in nutrients, and the hold cell defended the bacterial cell from predators. Microfossil evidence suggests that eukaryotes occurred sometime in between 1.6 and also 2.2 billion year ago. The descendants of this old engulfed cabinet are present in all eukaryotic cells today as mitochondria. We’ll comment on the endosymbiotic theory for the origin of eukaryotes more in the following reading. 

Complex life forms: Much that the life on planet was singled celled until shortly before the Cambrian “explosion,” once we see introduction of all modern animal phyla. The Cambrian radiation (meaning fast evolutionary diversification) occurred approx. 540 Mya. The “explosion” term refers to boost in biodiversity of multicellular organisms in ~ the begin of the Cambrian, 540 million years ago. Multicellular life showed up only numerous tens of millions of years before the start of the Cambrian, as bizarre-looking fossils (Ediacaran biota/Doushantuo fossils) and also exhibiting human body plans unlike anything seen contemporary animals. These types largely disappeared and were replaced by Cambrian fauna, whose variety includes every one of the human body plans uncovered in present-day pet phyla. The illustration of Cambrian fauna span millions that years; castle did not all show up simultaneously as the hatchet “explosion” inaccurately implies.

Placing crucial events ~ above the geologic time scale

How execute each the these occasions map onto geologic time? most of them are not “instantaneous” events, and so they span multiple time durations as follows:

Hadean eon (4.6-4 BYA): No life existing on EarthArchean eon (4 to 2.5 BYA)Origin that life (prokaryotic, anaerobic), 2.8-2.6 BYAFirst cyanobacteria, capable of producing oxygen through photosynthesis, ~2.5 BYAProterozoic eon (2.5 BYA come 542 MYA)Oxygen revolution (or catastrophe, depending on your allude of view) and formation that Banded iron 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 present day)Cambrian explode (most major animal phyla appeared in the fossil record), 542 MYAObviously many other occasions occur in the Phanerozoic, and we’ll spend most of the remainder of this module mentioning them

Links to person health and also environmental processes

The information listed below was adjusted from OpenStax biological 22.4 Some prokaryotic varieties can harm human health as pathogens: Devastating pathogen-borne diseases and plagues, both viral and also bacterial in nature, have affected humans since the beginning of human history, however at the time, their reason was no understood. Over time, people came to realize that remaining apart from afflicted persons (and your belongings) tended to minimize one’s possibilities of acquiring sick. For a pathogen to cause disease, it must have the ability to reproduce in the host’s body and damage the organize in some way, and to spread, it have to pass come a new host. In the 21st century, infectious diseases remain among the leading causes of fatality worldwide, despite breakthroughs made in clinical research and also treatments in current decades. The information below was adapted from OpenStax biological 22.5 Not all prokaryotes are pathogenic; pathogens represent just a very little percentage the the diversity of the microbial world. In fact, our life would certainly not be possible without prokaryotes. Part prokaryotic varieties are directly valuable to person health:

The bacteria the inhabit ours skin and gastrointestinal tract execute a hold of an excellent things because that us. They safeguard us from pathogens, help us digest our food, and produce few of our vitamins and also other nutrients. An ext recently, scientists have gathered evidence that these bacteria might also aid regulate ours moods, affect our activity levels, and also even aid control weight by affecting our food choices and also absorption patterns. The human Microbiome project has begun the process of cataloging our typical bacteria (and archaea) so we can better understand these functions.Scientists are also discovering that the absence of certain vital microbes from our intestinal street may collection us up for a variety of problems. This appears to be particularly true about the appropriate functioning that the immune system. There are intriguing findings that imply that the absence of this microbes is an essential contributor come the development of allergies and also some autoimmune disorders. Research study is at this time underway to test whether adding certain microbes to our internal ecosystem may aid in the therapy of these problems and also in treating some creates of autism.A particularly fascinating instance of our normal flora relates to our digestive systems. Human being who take it high doses of antibiotics tend to lose plenty of of their typical gut bacteria, enabling a naturally antibiotic-resistant types called Clostridium difficile to overgrow and also cause severe gastric problems, specifically chronic diarrhea. Obviously, trying to treat this problem with antibiotics just makes that worse. However, it has actually been efficiently treated by giving the patient fecal transplants (so-called “poop pills”) from healthy donors come 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; photo modified indigenous “Nitrogen cycle” through Johann Dréo (CC BY-SA 3.0). The modified picture is license is granted under a CC BY-SA 3.0 license._

Other prokaryotes indirectly, yet dramatically, affect human wellness through their roles in eco-friendly processes:

Prokaryotes pat a vital role in biogeochemical cycling of nitrogen, carbon, phosphorus, and also other nutrients. The function of prokaryotes in the nitrogen bicycle is critical. Nitrogen is a very important aspect to living things, due to the fact that it is component of nucleotides and amino mountain that are the structure blocks of nucleic acids and also proteins, respectively. Nitrogen is usually the most limiting aspect in terrestrial ecosystems, through atmospheric nitrogen, N2, offering the biggest pool of easily accessible nitrogen. However, eukaryotes cannot use atmospheric, gas nitrogen come synthesize macromolecules. Fortunately, nitrogen deserve to be “fixed,” meaning it is converted into ammonia (NH3) one of two people biologically or abiotically. Abiotic nitrogen permanent occurs as a result of lightning or by commercial processes. Biological nitrogen fixation (BNF) is exclusively lugged out by prokaryotes: floor bacteria, cyanobacteria, and Frankia spp. (filamentous bacteria communicating with actinorhizal plants such together alder, bayberry, and sweet fern). ~ photosynthesis, BNF is the 2nd most crucial biological process on Earth.Prokaryotes are additionally essential in microbial bioremediation, the usage of prokaryotes (or microbial metabolism) to remove pollutants, such as agricultural chemicals (pesticides, fertilizers) that leach indigenous soil into groundwater and the subsurface, and details toxic metals and oxides, such as selenium and also arsenic compounds. One of the most useful and also interesting examples of the use of prokaryotes for bioremediation functions is the cleanup of oil spills, including the Exxon Valdez pour out in Alaska (1989), and an ext recently, the BP oil pour out in the Gulf of Mexico (2010). Come clean up this spills, additional inorganic nutrient that help bacteria to flourish are added to the area, and also the expansion of bacteria breaks under the excess hydrocarbons.
a) cleaning up oil after ~ the Valdez pour out in Alaska, employees hosed oil from beaches and also then offered a floating eight to corral the oil, i beg your pardon was lastly skimmed indigenous the water surface. Some varieties of bacteria space able come solubilize and also degrade the oil. (b) among the many catastrophic consequences of oil spills is the damage to fauna. (credit a: alteration of work-related by NOAA; credit transaction b: modification of occupational by GOLUBENKOV, NGO: conserving Taman; native https://cnx.org/resources/b3178fe3228bf3c1f1ce0feae58ed67d7d1dad07/Figure_22_05_03ab.jpg)