Changes In The Atmosphere Causing Multicellularity :: essays research papers

Changes in the Atmosphere Causing MulticellularityAbout 2.5 billion years ago, group O began slowly to accumulate in theatmosphere, as a result of the photosynthetic activity of the cyanobacteria.Those prokaryotes that were able to use oxygen in ATP production gained a strongadvantage, and so they began to prosper and increase. Some of these cells may hold back evolved into modern body-builds of aerobic bacteria. Other cells may have becomesymbionts with larger cells and evolved into mitochondria. As the tot up ofoxygen and other atmospheric gasses increased, they started blocking out deadlyu.v. rays from the sun. The suns rays made feeling outside of water nearlyimpossible. These changes made life on land possible and evolution occurred asprokaryotes gave rise to land living eukaryotes.The microfossil record indicates that the first eukaryotes evolved at least1.5 billion years ago. Eukaryotes argon distinguished from prokaryotes by theirlarger size, the separation of nucleus fr om cytoplasm by a nuclear envelope, theassociation of DNA with histone proteins and its organization into a number killdistinct chromosomes, and colonial organelles, among which are chloroplasts andmitochondria. Scientists believe that eukaryotic organisms such as the protistsevolved from the prokaryotes. There are two main theories which describe howthis transition may have occurred. The first is the endosymbiotic theory, orenosymbiosis, and the other is the autogenous theory, or autogenisis. These twotheories are not mutually exclusive, meaning one or the other could account for antithetical 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 modern organisms contain intracellular symbiotic bacteria,cyanobacteria, or photosynthetic protists, indicating that such associations arenot grueling to establish and maintain. Endosymbiosis is said to beresponsible for the presence of chloroplasts and mitochondria in eukaryotes.Autogenisis, the alternative to the endosymbiotic theory is specialization ofinternal membranes derived originally 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 colonial organism, then