Unicellular eukaryotes

Eukaryotes unicellular and multicellular organisms with nuclear membranes and DNA in the form of chromosomes. 

The Foraminiferida (informally referred to as foraminifera) are eukaryotic unicellular organisms, classified in the Kingdom Protoctista, Phylum Granuloreticulosa, Class Foraminifera (Sen Gupta 1999). They range from the Early Cambrian to the present day and are either planktonic or benthic in life habitat. Of the approximately 10 000 extant foraminiferal species known, only 50 are planktonic, the remainder being benthic. 

Tubulins arose very early during the course of evolution of unicellular eukaryotes and provide the machinery for the equipartitioning of chromosomes in mitosis, cell locomotion, and the maintenance of cell shape. The primordial genes that coded for tubulins likely were few in number. As metazoan evolution progressed, natural selection processes conserved multiple and mutant tubulin genes in response to the requirements for differentiated cell types (Sullivan, 1988). 

Although many prokaryotic organisms are single-celled (unicellular), some exist as multicellular filaments or collections of cells. Eukaryotic organisms may be unicellular or multicellular. Most eukaryotic cells are at least 5 pm in diameter, but many are much larger. The cells of most prokaryotes are small, ranging from 0.2 to 1 / m in diameter, but a few are much larger. 

LGT is not expected to be common among or play the same role in the evolution of multicellular plants and animals, especially those with sequestered germ lines, and there simply is no extensive data on LGT in unicellular eukaryotes. 

Fig. 10.11 The modified tree of life still has the usual tree-like structure and also confirms that the eukaryotes originally took over mitochondria and chloroplasts from bacteria. It does, however, also show a network of links between the branches. The many interconnections indicate a frequent transfer of genes between unicellular organisms. The modified tree of life is not derived, as had previously been assumed, from a single cell (the hypothetical primeval cell ). Instead, the three main kingdoms are more likely to have developed from a community of primitive cells with different genomes (Doolittle, 2000)...

Unicellular Eukaryotes Chemotypes (About One and a Half Billion Years Ago )... 

Additional Distributions of Elements in Unicellular Eukaryote Compartments the Eukaryote Metallome and the Advantages of Compartmentalised... 

Spheromorph Acritarchs, primitive unicellular eukaryotes Atmosphere oxidising Endosymbiosis. Aerobic respiration 0.3%... 

Many unicellular eukaryotes are free-living cells, but may form huge local communities, which are especially beneficial to the homeostasis of the ocean/atmos-phere carbon cycle, e.g. coccoliths. Many others are not free-living, but are extremely valuable in symbiotic relationship with multi-cellular plants and animals. Unfortunately, some unicellular eukaryotes are the causes of disease, for example Trypanosoma, which are animals and cause sleeping sickness in humans (see Section 8.9 for parallel diseases of plants). These facts are reminders that while we consider that the whole ecosystem works to one general purpose (Section 4.4), this does not exclude the obvious feature that within its overall associations we can see diseases inflicted on one species by another or competition between similar species. Many bacteria are also causes of serious eukaryote diseases. Even so at the end of... 

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