Question

Discuss the endosymbiosis theory. Analyze the evidence that supports the theory, and the problems that refute the theory. Please be at least 7 sentences and include all the main points.

Answer 1

• Endosymbiotic theory is a theory proposed to explain the origin of semi-autonomous cell organelles- mitochondria and chloroplast about 1.5bya.
• An early prokaryotic cell engulfed anaerobic proteobacteia which could break down energy. Slowly this proteobacteia became mitochondria and is present in both plant and animal cells.
• Next, some of these cells , engulfed another bacteria which could perform photosynthesis. Later, this bacteria became plastids (chloroplast) . It is found only in plant cells.
• Evidence in support of theory: (i)cells cannot regenerate mitochondria/plastid if these organelles are removed from cell., (ii) mitochondria and plastid have their own genome and translation machinery (like single cells do )., (iii) mitochondria &plastid have circular genomes with similarities to bacterial genomes, (iv) New mitochondria and plastid are formed by the same mode as used by bacteria to divide, binary fission.
• Evidence against the theory: (i) mode of replication is different for bacterial DNA and that of mitochondria or plastid, (ii) structure of outer membrane of bacteria and mitochondria/plastid is not same., (iii) absence of organism with intermediate properties which could form a link between simple eukaryotic cell and a modern eukaryotic cell containing mitochondria/plastid.