On page 132 to 133, Shubin talks about the differences between sponges, single celled organisms, and organisms with body plans. Describe how as time went on organisms were able to become more complex, becoming multicellular and even developing different types of tissues that hold the body together. Discuss the “old parts” that were used in new ways from one organism to another and give examples.
(Alex Sapozhnikov marijio@gmail.com)
Looking at the timeline on page 121, Shubin lays out the time gap from the first life to the first bodies to the first land animals to the first modern humans. Generally speaking, the first single cellular organisms had billions of years to change. Based on their surrounding environment, the single cellular organisms began clumping in ways that make living in the extreme conditions of early earth a much easier task. The symbiotic theory states that unicellular organisms began clumping together and upon doing so, the cells became dependent on each other. By becoming dependent on each other, different cells performed different roles. Granted, this took millions of years to occur as evolution is a timely process. However, as Shubin shows, these organisms had time to evolve into more complex organisms with more efficient styles of life. As time continued to move along, specialization of cells occurred because it provided an energy efficient way to live. Thus, when going through life, these multicellular organisms were able to provide efficient ways to support themselves through “teamwork”. As a team, the cells would work together to create necessary elements of life, such as food. Upon continuation of evolution of the group of cells, different tissues would begin forming as the organism would be able to create them in need to stay clumped together and protected from outside danger. For example, in the endosymbiotic theory, one cell surrounded another cell and divided, however, it created a similar organism with the same interior cell and one larger exterior cell. For example, in a normal cell with mitochondria, the mitochondria were not always there. Millions of years before, it used to just be the outer cell with no mitochondria. Mitochondria began appearing and performing functions that work for the cell that surrounded it, even though there were different DNA’s in both the cells. Thus, mitochondria used to be individual cells. However, upon the grouping of cells and endosymbiosis, mitochondria became a part of multicellular organisms. The functions of the mitochondria changed as it began using food (glucose) to create ATP for the cells to use. Thus, as time moved on, different unicellular organisms began grouping together and their functions began changing upon grouping together.
ReplyDeleteSources:
http://facstaff.gpc.edu/~pgore/students/w96/joshbond/symb.htm
Shreeraj Patel
shreeraj.patel1@gmail.com
As Shreeraj said, the symbiotic theory can help to explain the change from unicellular to multicellular organisms. Unicellular organisms would come together which caused these cells to become dependent on their surrounding cells. As these cells were coming together, there needed to be a way to hold and keep the cells together in the multicellular organisms. All of these organisms, from placazoans and sponges to humans have the molecular apparatus that holds bodies together present. This apparatus includes “the rivets that hold cells together; the various devices that help cells signal to one another; and many of the molecules that lie between cells” (132). However, even though both sponges and humans contain these features, the sponge is a much more simple and primitive organism. For example, a human would have “hundreds of different types of molecular rivets, [while] sponges have a small fraction of that number” (132). This shows how humans developed and became more complex organisms than sponges.
ReplyDeleteAs organisms became even more complex, they began to use “old parts” in new ways. This usually resulted in more efficient selective advantages in organisms. For example, the evolution of reptiles to mammals is seen partly in the ear of the mammal. A reptile’s ear only contains the stapes while a mammal’s ear contains three bones: the malleus, incus, and stapes. It was discovered that the malleus and the incus in mammals “evolved from bones set in the back of the reptilian jaw” (161). These “new” bones in the mammals “act[ed] to amplify sound waves and transfer them from the air to the liquid contained in the inner ear's spiral-shaped cochlea”(Bartlett). In other words, the extra bones in mammals’ ears allowed them to have better hearing than reptiles. This shows how the mammals were becoming more complex organisms by using the “old parts” of the reptiles in new ways in order to have more success while living.
Sources:
Your Inner Fish
http://www.cosmosmagazine.com/news/1105/humans-ear-bones-began-reptile-jaws - by Sarah Bartlett
Danielle Webb (dwebb456@gmail.com)
Even though it may seem like a long stretch to compare sponges to actual bodies, it is sponge that allows us to understand the origin and evolution of bodies. Sponges and bodies share very similar properties: The cells have a division of labor; the cells communicate with one another; and the array of cells functions as a single individual (130, Your Inner Fish). Sponges also have cell adhesion that we have. They even have collagen (a protein found throughout the body to hold tissues together, sponges have two, humans have twenty one). As you can see, placozoans (the simplest structure of all non-parasitic multi-cellular animals) and sponges share much in common with evolved body plans.
ReplyDeleteTo discover the transition from simple to complex body-plans, Nicole King, from UC-Berkeley, was able to make some vital discoveries. King used choanoflagellates in her experiments (closest microbe (unicellular organism) to be related with bodies and sponges). King discovered that many of the genes that were active in choanoflagellates were also found to be active in animals with bodies. Proteins that contain functions of cell adhesion and communication in bodies are all present in choanoflagellates. Proteins made from single-celled organisms have aided the functions in the multi-cellular organisms. This is an example of co-option (evolutionary process in which existing biological structure is adapted for a new function), which in this case is for multi-cellular animals. The protein mechanisms for multicellularity had evolved even before the origin of multicellularity itself, and “old parts” gave way to benefit a multicellular organism in an entirely new fashion.
Although it is unclear to determine where multicellularity arose there has been clues throughout evolutionary history that guide us. Choanoflagellates are unicellular organisms that formed colonies (several individual organisms of same species living closely together). Colonial organisms like these were most likely the first step towards multicellular organisms via natural selection in evolution. In a colony, cells can survive on their own while cells in a multicellular body are unable to do so. Sponges, one of the oldest living multi-cellular organisms, like I have said are very morphologically similar to unicellular choanoflagellates. It is believed that unicellular groups of organisms gave rise to multicellular individuals. Cells grouped together may have been able to slowly evolve and adhere to one another, taking on different cell roles to survive. Like Danielle and Shreeraj have mentioned, independent cells become dependent upon one another due to the “clumping” of unicellular organisms. In extreme conditions where unicellular organisms are in danger of becoming extinct, cells becoming dependent on each other would be advantageous in staying alive (food scavenging, defense, energy cost).
This transition from unicellular to multicellular life forms have caused a trade-off. Multicellular organisms have cells reliant on each other, but offer better defense mechanisms and protection. Multicellular organisms are also much more mobile, but require more ATP. Multicellular organisms also contain a complex digestive system, but require more nutrients.
Sources:
http://sciencematters.berkeley.edu/archives/volume2/issue17/story1.php
Campbell
Your Inner Fish
http://facstaff.gpc.edu/~pgore/students/w96/joshbond/symb.htm
Kyle Kim, piece847@gmail.com