Please provide a narrative/summary of "The Origin of Multicellular Life."© BrainMass Inc. brainmass.com October 2, 2022, 11:59 pm ad1c9bdddf
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To understand how multicellular life began, it is important to first briefly explore how life began at all. According to geological dating methods, the Earth is roughly 4.5 billion years old, and roughly 4 billion years ago it accumulated substantial amounts of liquid water. Liquid water is a necessary component for life as almost all chemical reactions in living things take place in aqueous solution.
Around 4 billion years ago, when water began to accumulate, it set up the conditions needed to produce micelles and lipid bilayers. The amphipathic (hydrophobic and hydrophilic regions) of lipids caused them to form both micelles and liposomes. Liposomes are the precursors to cells and are important because they provide a barrier between what is inside the liposome and what is in the external environment. This condition is necessary if living cells are to control their physiology. From there, the progression is unclear, but it seems that amino acids probably formed early on along with RNA. These self-replicating molecules became captured within liposomes and constituted the first early cells.
Early cells were individual and prokaryotic, which means they lacked a nucleus or any significant organelles. They were all anerarobic and probably used heat from hydrothermal vents and other sources to produce energy. These unicellular organisms where soon followed (about 3 billion years ago) by autotrophs, which use sunlight to make energy and, importantly, produce oxygen as a byproduct. Oxygen is important for aerobic respiration, which is much more efficient than anaerobic respiration.
About 2 billion years ago, there was probably enough oxygen for the first eukaryotes to make an appearance. These cells have a true nucleus and lots of organelles and need lots of energy to maintain this high degree of order. Very few eukaryotes use anaerobic respiration all of the time (though some can use it in rough situations when oxygen is limited). Sometime, around 650 million years ago we seen the first true multicellular eukaryotes. It is thought that the situation arose from symbiosis and community living. Unicellular organisms lived together in close proximity for survival. The longer they lived together, the more specialized individual cells became, until at some point they were completely dependent on one another. At that point, they became true multicellular organisms. Over time, the complexity of these organisms increased, providing more elaborate species. In essence, the development of multicellular life from unicellular life comes down to division of labor. The more that cells lived together in communities, the more valuable it came to have cells specialize in different tasks. This specialization benefited the whole group, but meant cells had to give up their independence. The result was a progression from unicellular organisms living together in harmony to individual cells that were so dependent on each other they could not separate.
Some good sources are:
http://www.americanscientist.org/science/pub/yeast-suggests-speedy-start-for-multicellular-life© BrainMass Inc. brainmass.com October 2, 2022, 11:59 pm ad1c9bdddf>