"An organic being is a microcosm, a little universe formed of a host of self propagating organisms inconceivably minute, and as numerous as the stars in heaven."
|The "Big Bang" Creation of Eukaryotes
The sudden appearance of eukaryotes at about 1.8 Ba, with no clear predecessors and with major structural and genetic changes, has been described as a "Biological Big Bang (BBB)"1. Not only do the eukaryotes appear on the scene suddenly and without warning or obvious predecessors, but even within the major classes of eukaryotes there is no clear line of antecedence -- no clear "archeotype." Indeed the eukaryotes appear to be examples of "reductive evolution" -- the ancestor appears to be more complex than the descendents. This is a recurring theme in the development of species.
"The origin of eukaryotes is a huge enigma and a major challenge for evolutionary biology."1.1 At root, the problem is twofold: first, there is a great chasm between the most complex prokaryote and the least complex eukaryote; and second, there are six major groups of eukaryotes, with no evident common ancestor1.2 -- which leads to the assertion that the "ancestor" must have been more complex than any existing eukaryote, and the present strains derived from that complex ancestor by reductive evolution -- see the box on reductive evolution. In summary, eukaryotes appear suddenly with no known ancestors, and the inferred ancestor was more complex than any eukaryotes that exist today! -- hence the remark that the Eukaryotes began in a "likely 'big bang' of early eukaryote radiation." [ibid.]
"Even the most widely accepted notion that eukaryotes originated from prokaryotes is problematic because traits unique to eukaryotes, such as the nucleus, endomembrane system, cytoskeleton, and mitosis, are found in all taxa with no intermediate stages left as signposts of their evolution." 1.3
To confuse the issue even more, the genes of eukaryotes are "an uneven mix of genes of apparent archaeal origin, genes of probable bacterial origin, and genes that so far seem eukaryote-specific, without convincing evidence of ancestry in either of the two prokaryote domains."1.4
Reductive evolution refers to the concept that the ancestors of a given species are more complex than the descendents. The reduction of functionality seems to be a general (or at least a common) feature of species development. When this reduction reflects the elimination of redundant functionality, or elimination of an un-needed function, it is a plausible "advancement." But when the ancestors suddenly appear (or are inferred), with novel and complex features that then disappear in the descendents, reductive evolution contradicts some basic assumptions of evolution that argue for a progressive advancement in species complexity.
At the beginnings of modern geology, a number of early geologists remarked that the fossil record often began with the sudden appearance of a complex species which then evolved over time by losing functionality, so that the later appearances were more specialized and less complex than the ancestors. This phenomenon -- later termed Reductive Evolution -- was widely regarded by some early geologists as plausible evidence for a divine Creator because of the lack of fossil precursors, and as a counterpoint to the apparent general rule of progressive development (which is also clear in the fossil record)1.5. Perhaps the classic example of this is the trilobite, discussed in a later chapter, which appeared full-formed as one of the earliest animal fossils.
When Darwin's Theory of Evolution appeared in 1859, there was a wholesale movement towards the adoption of evolution by purely natural means. This meant, in effect, that the sudden appearance of novel classes was overlooked, "removed into a more distant and dimmer region" as Lydia Miller noted about 10 years later, in 1869. As she noted, the facts still remained but were de-emphasized.
Given the complex ancestor, one may construct a plausible chain of evolutionary events to explain reductive evolution: the elimination of superfluous features (such as the eyes of blind cave fish) or the elimination of redundant and overlapping genes. Such change towards simplification may be understood to be plausible and reasonable; but this reasoning does not explain a complex ancestor that appears to have no precedent. The usual "explanation" is the incompleteness of the fossil record, or the lack of hard parts which can be fossilized -- such as the exoskeletons of shellfish.
With the recent advent of detailed gene studies, one might have hoped that the problem of complexity of the first "proto-eukaryotes" might be solved, but such is not the case. Consider the following statement regarding the identity of the very earliest eukaryotes, summarizing a decade of intensive genetic research on the origin of eukaryotes:
The terminology in this quotation perhaps needs some interpretation:
• "no grounds to consider any group of eukaryotes primitive": The general groupings of (protist) eukaryotes do not exhibit a hierarchy of development from one of their own kind.
• "most ... evolved from more complex ancestral forms by reductive evolution.": all examples appear to come from an unknown, more complex ancestor, of unknown connection with existing prokaryotes (the presumed antecedents of the first eukaryote).
Part of the difficulty is that:
• Eukaryotes are a radical advance in organizational complexity over all prokaryotes
• All eukaryotes display a large package of genes that are unknown -- let alone separately existing -- in any prokaryotes.
• The genes that do appear to be shared with prokaryotes seem to be indiscriminately selected from both archaea and bacteria. There is no plausible scenario in which this might occur -- even given lateral gene transfer (LGT), which is well-established and demonstrated in the laboratory.
A number of the early gelogists remarked on this apparent inversion of what one would expect. This is the sense of Hugh Miller's remark that "The magnates walk first" -- see below.
Buckland, Geology and Mineralology (2nd Ed. 1837) p.294 "[regarding fossil fish] a kind of retrograde development, from complex to simple forms, may be said to have taken place. As some of the more early Fishes united in a single species, points of organization which, at a later period, are found distinct in separate families, these changes would seem to indicate in the class of Fishes a process of Division, and of Subtraction from more perfect, rather than of Addition to less perfect forms. ... In no kingdom of nature, therefore, does it seem less possible to explain the successive changes of organization, disclosed by geology, without the direct interposition of repeated acts of Creation."
Hugh Miller, Foot-prints of the Creator, (3rd. Edition, 1858) p. 325 "We know, further, so far at least as we have yet succeeded in deciphering the record, -- that the several dynasties were introduced, not in their lower, but in their higher forms; that, in short, in the imposing programme of creation it was arranged, as a general rule, that in each of the great divisions of the procession the magnates should walk first." [See also the box.]
Edward & Charles Hitchcock, Elementary Geology (1860) p. 363 "Sixth Law. -- Complexity and perfection of organization as well as intelligence increase as we ascend in the rocks. This is true as a general fact; but in particular tribes we find the reverse, viz., retrogradation from a lower to higher, condition. 'All our most ancient fossil fishes,' says Professor Sedgwick, 'belong to a high organic type; and the very oldest species that are well determined, fall naturally into an order of fishes which Owen and Miller place, not at the bottom, but at the top of the whole class.' ... 'The Cephalopods, the most perfect of the molluscs, which lived in the early period of the world,' says D'Orbigny, 'show a progress of degradation in their generic forms. The molluscs as to their classes have certainly retrograded from the compound to the simple, or from the more to the less simple.'" p. 367 "Thirteenth Law -- Many of the fossil animals had a combination of characters which among living animals are found only in several diferent types or classes. Agassiz very appropriately calls such types Prophetic Types. For they form the pattern of animals that were to appear afterward."
Alexander Winchell, Sketches of Creation (1870). p. 314 "Nature has always issued her bulletins. It is a most interesting fact in the history of the animal creation that Nature advertised her plans in the very earliest creative acts. In our study of the relics of the primeval ages we do not find the grand and fundamental purposes of Infinite Wisdom unfolding themselves by degrees as type after type of organic life made its advent upon our planet. ...Nature had her plans, and these were mature in the very beginning. ...  [U]pon the very threshold of Paleozoic Time representatives of Radiates, Molluscs, and Articulates burst into multifarious being almost simultaneously. So nearly simultaneous was the appearance of each of these types, that all hypothesis of their genealogical succession is rationally precluded. ...  There is no successional relation between the four sub-kingdoms of animals, nor even between the several classes of the invertebrate sub-kingdoms; but among the orders of the several classes and the classes of the Vertebrates we find generally a progress from lower to higher in the order of introduction. But there is another principle, complementary to this, which needs to be united to it in order to present us with a true view of Nature's method. There has generally been a downward as well as an upward unfolding of each type from the central forms in which it was first embodied. Trilobites, the first representatives of the Crustacean type, belong indeed to the lowest group, but do not lie at the bottom of the group. The earliest reptiles were not the lowest of the Amphibians, but Labyrinthodonts, the highest Amphibians; Vertebrates began, not with the lowest fishes, but with a grade of fishes above the mean level of the type... We shall arrive, therefore, at the truest expression of the plan of Nature in reference to the succession of organic beings by saying that each type was first introduced at a nodal point, from which the stream of development proceeded in both directions...."
James Dana, Manual of Geology, (1896) p1031 "No successional lines among Insects appear to have passed between the higher tribes of Neuropters, Orthopters, Coleopters, Lepidopters, Hymenopters; but each was derived from some early [unwitnessed - dcb] comprehensive forms."
-- p.487 ""The Lower Cambrian species have not the simplicity of structure that would naturally be looked for in the earliest Paleozoic life. They are perfect of their kind and highly specialized structures. No steps from simple kinds leading up to them have been discovered; no line from Protozoans up to Corals, Echinoderms, or Worms, or from either of these groups up to Brachiopods, Mollusks, Trilobites, or other Crustaceans. This appearance of abruptness in the introduction of Cambrian life is one of the striking facts made known by geology."
DNA in Prokaryotes and Eukaryotes
Cell Size Scale
Note relative size of Mars "fossils"
Common Features of All Eukaryotes
sometimes called the "cellular power plants" are the reason why all
eukaryotes are oxygen-breathers03. They "burn" oxygen
(forming water) to produce ATP, the "batteries" universally used to
provide energy for cell metabolism. Many bacteria also have
mitochondria, but the eukaryote mitochondria are much larger and more
The mitochondria contain their own bacteria-like (circular) genetic material, and reproduce independently from the cell's own genetic material. This is one reason why biologists conclude that it originated as a bacterial cell which took up residence in an ancestral eukaryote.
cytoskeleton (Figure 4) is a unique feature of the eukaryotic
cell that provides a number of important features.
• Structural support throughout the cell's interior
• Internal transport network connecting all cell components
There is no comparable structure to be found in bacteria; it leads to major improvements found only in eukaryotes:
1. Another characteristic feature of the eukaryotic cell is the fact that it has internal structure. Bacteria come in only a few typical shapes that can be characterized as "balloon shapes" (Figure 5) that form as a result of turgid pressure. These shapes are what result when the surface membrane provides the only structure, and the shape is maintained by turgid pressure -- spheres, tubular shapes and spiral shapes. There is little or no internal structural support.
In contrast, a proper cell has a cytoskeleton for internal structural support. The cytoskeleton allows the proper cell to assume a fantastic range of shapes and sizes (Figure 6), including sizes that are easily visible to the naked eye.
2. The movement of food and waste in bacteria is limited to random diffusion. In eukaryotes these movements are controlled by a highly developed transport system moving along microtubules, which involves the Kinesin linear motor molecule. See the Kinesin Transport Molecule box below. The consequence is that bacteria are limited in size to a maximum on the order of 10 µm, the practical limit of diffusion (Figure 7)3.1. In contrast, eukaryotic cells can be relatively very large.
logical order is: first the cytoskeleton, then nuclear membranes
attached to the cytoskeleton, which in turn form the organelles
including the most prominent visual one, the nucleus.
Internal membranes are used to provide a special local environment to conduct specialized tasks. An example in bacteria is the chloroplast of cyanobacteria used in photosynthesis. Eukaryotes make a much richer use of membranes, which form a number of specialized organelles that are joined by the cytoskeleton. The nucleus is the most visible organelle, bounded by a specialized membrane that uses special access ports to control traffic to the nucleus interior. Many other organelles also exist, each with its own specialized functions. Not all organelles (other than ribosomes and the nucleus) exist in every eukaryote.
The nuclear membrane is a double membrane.
The separation between transcription and translation
?? the cytoplasm outside the nucleus is structured by the cytoskeleton. So where does the genetic info go? Inside its own environment inthe nucleus. Doesn't therefore use (?) the transport mech of the cytoskeleton (so how does the mRNA etc move???)
The organelles are small "factories" contained within the eukaryotic cell. Each organelle is bounded by a membrane to form a controlled microenvironment that specializes in a particular cell function. Figure 8 shows some of the organelles found in all eukaryotes. See the box on Organelles for a description of some of these organelles and their functions.
bacteria and archaea have circular DNA, in which the genetic
information is contained in complementary strands of nucleotides
forming the DNA "ladder". All eukaryotes have the DNA in chromosomes,
each containing two complete copies of its complement of DNA. In the
"condensed" (compact) state a chromosome appears in the diploid "X"
form as shown in Figure 9. Chromosomes can also be a single (haploid)
strand of DNA (a chromatid).
reproduction, the egg and sperm are both haploid, and they
combine to form the diploid chromosomes in the fertilized egg.
Histones are proteins that assist in packing the DNA "spools around which DNA winds". Highly "conserved" proteins -- throughout eukaryotes and some archaea, but not found in bacteria. They are "spindles" that the dna wraps around so that it can be stored in compact form in the chromosomes. Chromatin is DNA + histones.
Protist chromosome numbers: amoeba 12 chromosomes; paramecium 50 chromosomes; some rhizopods reported to be as high as 1500.
All eukaryotes duplicate by a complex process called mitosis. This is a non-sexual form of duplication in which a parent cell divides into two eactly identical daughter cells. In prokaryotes, duplication is done by a different and simpler process called binary fission. In mitosis the parent first duplicates the chromosomes and then uses special cytoskeleton structure called the mitotic spindle to separate the new chromosomes to opposite sides of the cell, after which the cell divides using a process called cytokinesis.
Multicellular species all begin as a single cell and grow by mitosis, which is also used for repair and replacement of cells in mature bodies.
reproduction is by meiosis. It is associated with chromosomes, so no
prokaryotes conduct meiosis, or can reproduce sexually. However
bacteria can share dna between individuals through genetic
recombination and in other ways that may achieve results comparable to
Meiosis is the stage of the sexual cycle in which a diploid cell, ordinarily having two complete sets of chromosomes, gives rise to haploid cells (gametes) each having one set of chromosomes. Two such gametes arising from different individual organisms may fuse by the process of syngamy (fertilization) to generate a new diploid individual, thus completing the sexual cycle.
All eukaryotes except some members of the protist group excavata have meiosis 3.2.
is there something unique shared by eukaryotes?
is a small regulatory protein (76 amino acids) found in all eukaryotes
but entirely absent in prokaryotes. It directs protein recycling
(programmed death) in the proteasome.
The nucleus protects the DNA from damage by contact with food or cell invaders. When the DNAs genes are copied prior to building the various proteins and other complex molecules of life, the genes are processed within the nucleus to remove un-needed information, and to correct copying errors.
It is hard to overemphasize how this contrasts with bacteria. The DNA of bacteria comes in constant contact with the cell contents, and as a result is subject to both random and deliberate changes in the DNA code itself. That is how viral infection works: a virus injects its genetic material into a bacterial cell, and the material then inserts itself into the cell's own DNA. From this point the cell begins to reproduce the virus, using the cell's own genetic machinery.
Bacteria are designed in this loose genetic way because
strong points about bacteria is the ability to respond to environmental
changes by changing its genetic make-up. Bacteria can even share
of DNA from other bacterial species, perhaps through snips of DNA that
enter the cell as food. This is why bacterial species, such as the
E. Coli have so many different subspecies, both harmful and beneficial.
One biologist, Lynn Margulis, argued that the concept of species is not
really appropriate for bacteria because there is so much genetic
She notes: "Because bacteria that differ in nearly every
trait can receive and permanently incorporate any number of genes from
each other or from the environment, the concept of 'species,'
to named eukaryotes, seems inappropriate for the Prokarya.
For higher species, that advantage is overshadowed by the need
to guard the genetic code's accuracy. The code is much more complex,
changes are very likely to be unwelcome. So for eukaryotes, the
is on limiting changes in the code and controlling the accuracy when
code is copied. This work takes place within the nucleus.
More remarks along these lines will be made in the
When mid-19th Century biologists looked at cells through a microscope, they saw the cell protoplasm as an amorphous jelly. The prominent evolutionary proponent Ernst Haeckel viewed the protoplasm as the "life force" of living cells, and assumed that it, and therefore the essence of life, to be essentially simple05. However, by the end of the 19th century it was generally understood through numerous scientific investigations that there is much more structure and content to the protoplasm06.
The basic problem is the resolution of light microscopes which can only see things down to a dimension of a few microns -- the size of small bacteria. Therefore the elaborate structure within a bacterial cell was almost completely invisible.
The structural content of the "protoplasm" is built up of cytoskeleton threads that are only a few nanometers in diameter (a few molecules across), and can be viewed only with electron microscopes, first built in the 1940s. Even then, the essentially colorless threads can only be viewed if they were tagged with dyes or doped with heavy atoms such as gold.
The cytoskeleton performs a number of functions in the cell (see Figure 8): it provides:
• Structure, support and spatial organization;
• Food and waste transport between cell organelles and the cell wall;
• Contraction, dilation and movement;
The food and waste transport involves the Kinesin transport molecule which is a linear motor that carrys waste and food along the microtubules which connect the cell wall and all internal organelles. All eukaryotic cells have a microtubular organizing center, the centrosome, near the nucleus, generally associated with the golgi apparatus. The centrosome is used to anchor the mitotic bundles during mitosis. See the video on cytoskeleton microtubules.
The idea of isolating part of the cell to perform a special function is not new with eukaryotes. The earliest cyanobacteria used such protected environments to conduct photosynthesis -- ATP synthase, for example, is a rotary motor embedded in a closed membrane with an acidic (high H+) interior and is powered by the flow of H+ through the motor. In addition, nitrogen fixation in specialized cells (the heterocysts) also required the provision of a specialized (oxygen-free) local environment to drive the nitrogenase molecule.
Aside from photosynthesis, many other early bacteria also had mitochondria to produce ATP from oxygen. These bacterial mitochondria did not require the cytoskeleton network, because the bacterial cell was very small and relied on ordinary diffusion to distribute products to the "work site" where they were needed. When the production rate or the transport time was too slow, the solution was to proliferate many mitochondria throughout the cell so that local needs could be met with local industry, so to speak. A similar thing happens in eukaryotes.
In eukaryotes, the cytoskeleton with its built-in transport system allowed the cells to support many more of these specialized membrane-bound "factories", the organelles, with the ability to move the raw materials, products and waste from specialized sites to the general cell.
The Kinesin molecule transports food and wastes between the organelles of a eukaryotic cell, moving along microtubules of the cell's cytoskeleton (Figure 9).
Kinesin motors were first discovered by accident in 1981 by a Dartmouth professor, Robert D. Allen, when he used a television video camera to view squid nerve fiber under a light microscope07. By adjusting the image brightness it was discovered that details could be seen that are a tenth of the size that is normally visible in a light microscope, and for the first time, it was actually possible to see little objects moving along the nerve fiber. These turned out to be kinesin moving along microtubules.
The microtubules have a "polarity" which determines the direction in which the kinesin molecule moves. The "minus" ends in a centrosome. The kinesin move preferrentially in the "plus" direction along a microtubule (away from the centrosome), and the dynein molecule moves in the "minus" direction (towards the centrosome) between the endoplastic reticulum and the golgi apparatus08.
Bacteria rely on ordinary diffusion to move food and waste within a cell. Diffusion depends on random movement due to molecular collisions, and is typified by the dispersion of a dye in a beaker of water (Figure 10):
Eukaryotic ReproductionA bacterial cell reproduces by cell division.
Mitosis, Meiosis and Sexual Differentiation (dimorphism).
Because eukaryotes have a cell nucleus and the DNA exists in chromosomes instead of the circular dna of bacteria, something more complex than the bacterial cell division is needed.
?ALL HAVE MITOSIS? MEIOSIS? NOT
?Are all chromosomes diploid (at some stage)?
Eukaryotic chromosomes occur in the cell in greater numbers than prokaryotic chromosomes. The condensed replicated chromosomes have several points of interest. The kinetochore is the point where microtubules of the spindle apparatus attach. Replicated chromosomes consist of two molecules of DNA (along with their associated histone proteins) known as chromatids. The area where both chromatids are in contact with each other is known as the centromere the kinetochores are on the outer sides of the centromere. Remember that chromosomes are condensed chromatin (DNA plus histone proteins).
Q: DO ALL EUK HAVE MITOSIS?
IS MITOSIS THE FIRST STEP IN MEIOSIS? OR ARE THEY ALTOGETHER DIFFERENT?
ARE ALL CHROMOSOMES DIPLOID AT SOME STAGE IN EXISTENCE? (CONTRA BACTERIA).
"All animals have a characteristic number of chromosomes in their body cells called the diploid (or 2n) number." -- all protists too???
Eukaryote cell cycle: do all go through a diploid as well as a haploid stage???
gametes are necessarily haploid -- ?one stage in meiosis??
Wiki: The only supergroup of eukaryotes which does not have meiosis in all organisms is excavata.
==>> ALL EUKARYOES HAVE MITOSIS(???) ==> PROBABLY UNIVERSAL - e.g. in multicellular ....
==>> ALL MULTICELLED EUKARYOTES HAVE MEIOSIS!(??)
Mitosis is the basis for formation of a multicellular body from a single cell (zygote), for growth in a multicellular species, and for cell replacement or regeneration in the event of damage.
?? All eukaryotes can reproduce by mitosis -- for example that's how multicellular species grow.
?? All (?) eukaryotes (except some single-celled excavata) can also reproduce by meiosis.
HOW COMPARE WITH BACTERIA?
Error-detecting and correcting schemes ensure the accuracy of the dna and rna copies. In bacteria, insertions and changes to the dna code occur frequently, because the dna is located in the cell cytoplasm and can come in contact with portions of dna derived from food and viruses. In addition the transcription of the bacterial dna is more prone to errors. Overall for a bacterial dna, transcription accuracy is on the order of one transcription error per ??? codons. In contrast, overall transcription accuracy for a eukariotic cell is on the order of one error per billion codons. [CHECK]. This still results in about ??? errors per cell per second. [CHECK]
# Both are highly regulated by elaborate sensing systems ("chemical noses”) that make them aware of the reactions within them and the environment around them.
HOW COMPARE WITH BACTERIA?
Mitochondria are, in one
sense, the key feature, next to the nucleus, of eukaryotes, because
they are the "cellular power plants" -- they generate most of a cell's
requirements for ATP -- that explain why eukaryotes use oxygen as a
prime engine of metabolism. (??)
How do mitochondria use oxygen? redox reactions (oxidative phosphorylation).
conversion of oxygen to water
Four membrane-bound complexes have been identified in mitochondria. Each is an extremely complex transmembrane structure that is embedded in the inner membrane. Three of them are proton pumps.
distinction between dna that codes for genes and other dna.
Introns absent from bacteria, present in eukaryotes and some archaea.
Alternative splicing is widely used to generate multiple proteins from a single gene
Q: do all eukar dna code for genes? (prob not -- or maybe expression is suppresses? e.g. e coli genome is huge relative to what is actually xlated???
A becterial cell reproduces by cell division.
ALL EUKARYOTES HAVE JUNK DNA???
Transcription & translation regulation?
HOW COMPARE WITH BACTERIA?
centromere teleomere -- essential parts of chromosome. Not coding to specific genes.
Jonathan Wells The Myth of Junk DNA (2011)
|"Major transitions in
biological evolution show the same pattern of sudden emergence of
diverse forms at a new level of complexity. The relationships between
major groups within an emergent new class of biological entities are
hard to decipher and do not seem to fit the tree pattern that,
following Darwin's original proposal, remains the dominant description
of biological evolution. The cases in point include the origin of
complex RNA molecules and protein folds; major groups of viruses;
archaea and bacteria, and the principal lineages within each of these
prokaryotic domains; eukaryotic supergroups; and animal phyla."
flagellate protozoa - the only group that does not have meiosis (sexual
reproduction) in all organisms. Includes slime molds which have a life
cycle that includes an
amoeba-like multicellular aggregation phase.
|Amoebozoa||Most lobose amoeboids and slime moulds|
|Opisthokonta||Animals, fungi, choanoflagellates, etc.|
|Rhizaria||Foraminifera, Radiolaria, and various other amoeboid protozoa.|
|Chromalveolata||Stramenopiles (or Heterokonta), Haptophyta, Cryptophyta (or cryptomonads), and Alveolata.|
|Archaeplastida (or Primoplantae)||Land
plants, green algae, red algae, and glaucophytes.
Kingdom: Develop from
a Blastula. Together with fungi they form the Opisthokonta
listed in the preceeding table
listed in the preceeding table.
|Supergroup Excavata||Euexcavatae||The Excavata
listed above. The excavate is a groove that runs longitudinally on the
cell surface and associated with at least one recurrent
flagellum, which set up currents in the groove to concentrate
suspended particles and move them to a cytostome.
|Supergroup Chromalveolata||Eukaryomonadae||The references
are to the
bag-like sacs that underlie the cell membrane and that many taxa are
The Chromalveolata listed above
|Supergroup Rhizaria||The reference is to the fine, filose, and often branching pseudopodia in this group. The Rhizaria listed above|
|Supergroup Archaeplastida||The reference
is to this
supergroup having the chloroplasts that came from a primary
endosymbiosis with a cyanobacterium.
The Archaeplastida listed above.
Posted 20 Decembe