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March 17, 2017

What is the multicellularity’s origin?

Before directly on the study of the earliest multicellular organisms, let us think: why, strictly speaking, this multicellular necessity? What advantages does it offer? Can be viewed from different angles on this subject, but we start to see the environment. In other words, do not give that is not the most multicellular organism and ecosystem and eventually enter the biosphere. Small size phytoplankton organisms (primarily prokaryotic) faced with another problem, the first attention attracted to hydrobiologist B. Vilenkin. Delivery of single nutrients and dissolved gases is by diffusion through the cell wall; it seems to be for the miniaturization of the cell in order to maximize the ratio of its surface area to volume. However, a very small body is not able to stand out from the surrounding mass of water, passively floating in the water column (and remains stationary with respect to it), it quickly creates a “desert” itself – eats directly from the surrounding aqueous layer all nutrients. It fills out the water organics that cannot diffuse in the cell due to the same high surface area / volume ratio. The fact that this irrevocably lost more than a third of the cell product – not so bad; Poorer than that consumed for the oxidation of organic material oxygen and the aqueous layer of the organism eutrophic.

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In a word, Piglet was unforgettable: living “very small beings” full of difficulties. Troubles of them can only be avoided by forcing the body to compel the surrounding waters to move relatively. This can be accomplished in two ways: either begin to actively move in thickness, or, on the contrary, to attach to a solid substrate so that the water moves over you. The second possibility to construct prokaryotes immediately by mat. But with the first method (seemingly simple and obvious) they have great problems – for an effective enforcement of movement, such as flagella and cilia eukaryotic protozoa, prokaryotes do not occur, and the creation of cell aggregates, capable of coordinated movements (e.g., wavy) of the extreme weakness of intercellular interactions.

Therefore, the “generic line”, this method will only form the appearance of eukaryotes of the situation of highly integrated cellular aggregations, except for today is multicellular. Multicellular led among other things to create a strong increase in the ability of the body in your body to supply nutrients. Virtually without these stocks, protozoans (especially prokaryotes) are doomed to fail to change the content of nutrients in the environment the only way to react to change the density of the population. (An example of such behavior is the “flowering” of the waters when the rapid multiplication unicellular and thread algae leads quickly to depletion of the resources of the ecosystem, because of the heavily overgrown population suddenly dies, and the oxidation of dead organic substance consumed and then almost the entire oxygen reservoir – “suffocation’). Substitutions and securing large biomass of organisms make their population more independent of resource fluctuations and their density stabilize. In turn, geochemical cycles that exist in the ecosystem gaining these large organisms’ secured securities has powerful stabilizing effect at all these cycles. This “mutual stabilization” seems to be one of the most important ecological consequences of the formation of multicellular organisms (although to say correctly – macroscopic, thus with the naked eye) organisms. The last sentence is not accidental.

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