![]() ![]() There is no clear evidence of life on Earth during the first 600 million years of its existence. This means archaea collectively have over 100 times the collective biomass of humans, and bacteria over 1000 times. These figures can be contrasted with the estimate for the total biomass for animals on the planet, which is about 2 Gt C, and the total biomass of humans, which is 0.06 Gt C. This is made up of 7 Gt C for archaea and 70 Gt C for bacteria. In 2018 it was estimated the total biomass of all prokaryotes on the planet was equivalent to 77 billion tonnes of carbon (77 Gt C). ![]() Prokaryotes live throughout the biosphere. Marine prokaryotes are responsible for significant levels of the photosynthesis that occurs in the ocean, as well as significant cycling of carbon and other nutrients. Some prokaryotes are pathogenic, causing disease and even death in plants and animals. Prokaryotes play important roles in ecosystems as decomposers recycling nutrients. The three-domain system of classifying life adds another division: the prokaryotes are divided into two domains of life, the microscopic bacteria and the microscopic archaea, while everything else, the eukaryotes, become the third domain. Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane. All cellular life forms can be divided into prokaryotes and eukaryotes. They are defined by their habitat as prokaryotes that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. ![]() Marine prokaryotes are marine bacteria and marine archaea. ![]()
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