Exploring the Endosymbiotic Theory and its Implications

DO NOT WRITE ON THIS PAPER! Background information: Endosymbiotic theory proposes that mitochondria and chloroplasts, important organelles in eukaryotic cells, were once independent prokaryotic cells that somehow were incorporated into larger host cells, perhaps as prospective parasites or intended meals that somehow escaped digestion. They might have instead started to provide the host cells with crucial nutrients (in the case of the primitive chloroplast) or help to exploit oxygen for extracting energy (in the case of the primitive mitochondrion) and, in turn, would have received protection and a steady environment in which to live. Multiple lines of evidence support the endosymbiotic theory. Not only is endosymbiosis observed elsewhere in biology, but mitochondria and chloroplasts have DNA that is different from what is found in the nucleus of a eukaryotic cell, and their structure, biochemistry, and genetic makeup is similar to certain prokaryotes. Endosymbiosis Cartoon Activity – Draw a cartoon that illustrates the concept of endosymbiosis. It can be funny or silly. It should show how aerobic bacteria were engulfed to be mitochondria and how photosynthetic bacteria were engulfed and eventually became chloroplasts. Please have at least 6 cartoon panels. Above is a serious illustration that describes endosymbiosis to help get you started. Your drawings do not have to be professional though I would like them to be recognizable (25 points), describe what is going on either through dialogue or a description (50 points), and colored (25 points). This activity is worth 100 points. On the board is a simple and not very good cartoon that I drew to also get your mind working. Name: ____________________________ Period: _________ Date: ______ Questions to answer: 1. Describe Endosymbiotic Theory: ________________________________________________ The Endosymbiotic Theory proposes that eukaryotic cells, which are the building blocks of complex life forms like plants, animals, fungi, and protists, evolved from the symbiotic relationship between different types of prokaryotic cells. According to this theory, a host cell engulfed a smaller prokaryotic cell through endocytosis, forming a symbiotic relationship rather than digesting it. Over time, this symbiotic relationship became mutually beneficial, leading to the smaller cell (the endosymbiont) evolving into specialized organelles within the host cell 2. What two organelles came about because of endosymbiosis? __________________________ The two organelles that are believed to have originated from endosymbiotic events are mitochondria and chloroplasts. Mitochondria are thought to have evolved from an endosymbiotic relationship between an ancestral eukaryotic cell and aerobic bacteria, possibly related to today's Rickettsiales. Chloroplasts, found in plants and algae, are believed to have evolved from the endosymbiosis of a photosynthetic cyanobacterium within a eukaryotic host cell 3. What evidence is there to support endosymbiosis? ____________________________________ There are several lines of evidence supporting the endosymbiotic theory: - - - Mitochondria and chloroplasts have their own DNA, ribosomes, and membranes, which are similar to those found in prokaryotic cells, suggesting they were once independent organisms The DNA of mitochondria and chloroplasts is circular, similar to bacterial DNA, rather than linear, as found in the nucleus of eukaryotic cells Both mitochondria and chloroplasts reproduce independently of the host cell through a process similar to binary fission, similar to bacteria Phylogenetic studies show that the DNA sequences of mitochondria and chloroplasts are more closely related to certain groups of bacteria than to eukaryotic nuclear DNA, supporting the idea of a shared evolutionary history Some protists, such as amoebas, contain vestigial remnants of engulfed prokaryotes, providing further evidence of past endosymbiotic events