There is compelling evidence that mitochondria and chloroplasts were once primitive bacterial cells. This evidence is described in the endosymbiotic theory. How did this theory get its name? Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell. Show
It's Just a TheoryIn everyday speech, people use the word theory to mean an opinion or speculation not necessarily based on facts. But in the field of science, a theory is a well established explanation based on extensive experimentation and observation. Scientific theories are developed and verified by the scientific community and are generally accepted as fact. Mitochondria Have DNAMitochondria and chloroplasts have striking similarities to bacteria cells. They have their own DNA, which is separate from the DNA found in the nucleus of the cell. And both organelles use their DNA to produce many proteins and enzymes required for their function. A double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested by a primitive host. The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division. \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
Learning Objectives
It is thought that life arose on earth around four billion years ago. The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship. Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell. Mitochondria and chloroplasts cannot grow outside their host cell. Evidence for this is based on the following:
Although evidence is less convincing, it is also possible that flagella and cilia may have come from spirochetes.  Example \(\PageIndex{1}\)
Solutions
SummaryThe endosymbiotic theory states that mitochondria and chlopoplasts in today's eukaryotic cells were once separate prokaryotic microbes. This page titled 7.8: The Endosymbiotic Theory is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Gary Kaiser via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. Which is an observation that supports the theory of endosymbiosis?Single stranded, circular DNA is found exclusively in prokaryotes. This evidence supports the endosymbiosis theory because these characteristics would allow the mitochondria and chloroplasts to survive on their own.
What are the 3 pieces of evidence that support the endosymbiotic theory?Evidence for endosymbiosis. Membranes — Mitochondria have their own cell membranes, just like a prokaryotic cell does.. DNA — Each mitochondrion has its own circular DNA genome, like a bacteria's genome, but much smaller. ... . Reproduction — Mitochondria multiply by pinching in half — the same process used by bacteria.. What evidence supports the endosymbiotic theory quizlet?The endosymbiotic hypothesis is supported by the physiology and metabolism of chloroplasts and mitochondria with the sequence and structures of their genomes.
Which of the following best describes the main idea of the endosymbiotic theory?Which of the following best describes the main idea of the endosymbiotic theory? Modern day mitochondria evolved from simple prokaryotic cells taken up by larger prokaryotes.
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