BSC 314 Lecture Notes - Lecture 44: Phloem, Xylem, Smallest Organisms
27 Jun 2018
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Systematics
The oldest known fossils are suspected to be bacteria, ancestors of the modern
prokaryotes.
Fossil record
Prokaryotes were the first organisms when the atmosphere of the new Earth
was anoxic (without oxygen) and there was extensive volcanic activity. Bacterium like ‐
filaments have been found in 3.5 billion year old rocks in western Australia, and ‐ ‐
bacterium like spheroids of the same age occur in South Africa. ‐
Fossil stromatolites are present in many ancient sedimentary rocks worldwide.
Stromatolites are layered columns or mushroom shaped domes a few inches wide and ‐
a foot or more in height that formed when bacterial mats (composed primarily of
cyanobacteria growing in primeval ponds) trapped sediments. Together sediment and
bacteria solidified into rock over the ensuing eons. Stromatolites are forming today in
many places in the same way by descendants of the same organisms.
Phylogeny
Data from molecular sequencing of DNA has changed—and continues to change—the
ideas concerning bacterial relationships. At this time there is no clear consensus among
microbiologists concerning the lineages among the prokaryotes. With only an estimated
10percent of the bacteria named, and the majority of those identified not yet studied in
detail, the task appears formidable.
Ecology
Attributing life or death importance to organisms too small to be seen without great ‐ ‐
magnification is difficult, but consider that the prokaryotes:
Decompose complex organic molecules and return to the soil and air the elements
needed for growth of all organisms.
Participate in complex biogeochemical webs that concentrate minerals—iron,
manganese, copper, and others.
Maintain soil fertility by fixing atmospheric nitrogen, thus assuring the supply of
available nitrogen for protein and nucleic acid synthesis by all organisms.
Are the base of food webs on land and in the oceans.
Are crucial links in the sulfur, phosphorus, carbon, oxygen, and nitrogen cycles.
Using novel metabolic pathways, both discharge into the atmosphere and extract
from it all of the major reactive gases: nitrogen, oxygen, carbon dioxide, carbon
monoxide, sulfur-containing gases, hydrogen, methane, and ammonia.
Human Interest
Humans have a love–hate relationship with the prokaryotes. They cause terrible
diseases, but by recycling the indispensable materials that all organisms need, make
life possible on Earth.
Plant pathology
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Document Summary
The oldest known fossils are suspected to be bacteria, ancestors of the modern prokaryotes. Prokaryotes were the first organisms when the atmosphere of the new earth was anoxic (without oxygen) and there was extensive volcanic activity. Bacterium like filaments have been found in 3. 5 billion year old rocks in western australia, and bacterium like spheroids of the same age occur in south africa. Fossil stromatolites are present in many ancient sedimentary rocks worldwide. Stromatolites are layered columns or mushroom shaped domes a few inches wide and a foot or more in height that formed when bacterial mats (composed primarily of cyanobacteria growing in primeval ponds) trapped sediments. Together sediment and bacteria solidified into rock over the ensuing eons. Stromatolites are forming today in many places in the same way by descendants of the same organisms. Data from molecular sequencing of dna has changed and continues to change the ideas concerning bacterial relationships.
