Changes In The Atmosphere Causing Multicellularity :: essays research papers

Changes in the Atmosphere Causing MulticellularityAbout 2.5 billion years ago, oxygen began slowly to accumulate in theatmosphere, as a resultant of the photosynthetic activity of the cyanobacteria.Those prokaryotes that were able to use oxygen in adenosine triphosphate production gained a strongadvantage, and so they began to prosper and increase. Some of these cells whitethorn wee-wee evolved into modern forms of aerobic bacteria. Other cells whitethorn have nonplussymbionts with larger cells and evolved into mitochondria. As the amount ofoxygen and other atmospheric gasses increased, they started blockade out deadlyu.v. rays from the sun. The suns rays made life foreign of water nearlyim possible. These changes made life on land possible and evolution occurred asprokaryotes gave rise to land living eukaryotes.The microfossil record indicates that the firstborn eukaryotes evolved at least1.5 billion years ago. Eukaryotes are distinguished from prokaryotes by theirlarger siz e, the separation of nucleus from cytoplasm by a thermo thermonuclear envelope, theassociation of DNA with histone proteins and its organization into a number off unmistakable chromosomes, and complex organelles, among which are chloroplasts andmitochondria. Scientists believe that eukaryotic organisms such as the protistsevolved from the prokaryotes. thither are two main theories which describe howthis transition may have occurred. The first is the endo dependent theory, orenosymbiosis, and the other is the autogenous theory, or autogenisis. These twotheories are not mutually exclusive, meaning one or the other could visor fordifferent parts of eukaryotic cells. The endosymbiotic theory states that theformation of eukaryotic cells were symbiotic associations of prokaryotic cellsliving inside larger prokaryotes. The endosymbiotic hypothesis accounts for thepresence in eukaryotic cells of complex organelles not found in the far simplerprokaryotes. many another(prenominal) modern organisms contain intracellular symbiotic bacteria,cyanobacteria, or photosynthetic protists, indicating that such associations arenot difficult to establish and maintain. Endosymbiosis is said to becreditworthy for the presence of chloroplasts and mitochondria in eukaryotes.Autogenisis, the alternative to the endosymbiotic theory is specialization ofinternal membranes derived in the beginning from the plasma membrane of a prokaryote.Autogenisis could be responsible for structures like the nuclear membrane andendoplasmic reticulum in eukaryotes.There are two scenarios for which multicellularity may have occurred. Thefirst is unicellular organisms came together to form a compound organism, then