Support:
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Support for the Endosymbiotic Theory can be found by examining the external structure of chloroplasts and mitochondria. A chloroplast has a distinctive inner membrane space, which rests between the inner and outer envelope membranes, the stroma space, which is located between the inner envelope and thylakoid membrane, and the thylakoid lumen, which is the space between the thylakoid membranes (Heldt, 1997). All of these membranes are selectively permeable to different macromolecules which differ from the plant cell itself. Chloroplasts and other plastids also have their own distinct DNA which is also different from the rest of the plant cell. Similar to chloroplasts, mitochondria also have a layered membrane that is selectively permeable to macromolecules different from the cell, and from other membrane bound organelles within the same cell as well as their own mitochondrial DNA and ribosomal DNA. In recent years, studies of the outer envelope proteins have helped understand organelle movement and membrane lipid remodeling, activities that are vital for plant survival according to (Inoue, K 2011). Another crucial line of evidence, supporting a singular origin of plastids, is the apparent similarity in the mechanisms by which the products of genes transferred to the nucleus are linked back to the organelle and their ability to code for proteins (McFadden & Dooren , 2004). Although mitochondrian also aid in energy production, for the purpose of this discussion we will narrow in on chloroplast and its unique ability to promote energy production through the use of photosynthesis.