Cellular Organelles I | Biology

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>Cellular Organelles I | Biology | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/biology/2/cellular-organelles-i/195"> <meta name="description" content="Evolution isn't always about competition. It can also be about cooperation, as is the case with the development of chloroplasts and mitochondria from free-living bacteria. This module explains the theory of endosymbiosis along with its origins. Convincing evidence in support of the theory is presented. The evolution of the nucleus and other organelles through invagination of the cell membrane is also discussed."> <meta name="keywords" content="science, education, STEM, math, biology, chemistry, physics, earth science, online learning"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/biology/2/cellular-organelles-i/195" }, "name": "Cellular Organelles I", "headline": "Cellular Organelles I: Endosymbiosis and membrane-bound organelles", "author": [ { "@type": "Person", "name": "Donna Hesterman" } , { "@type": "Person", "name": "Nathan H Lents, Ph.D." }], "datePublished": "2013-09-24 14:43:09", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_195-23061209062726.jpeg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "Evolution isn't always about competition. It can also be about cooperation, as is the case with the development of chloroplasts and mitochondria from free-living bacteria. This module explains the theory of endosymbiosis along with its origins. Convincing evidence in support of the theory is presented. The evolution of the nucleus and other organelles through invagination of the cell membrane is also discussed.", "keywords": "science, education, STEM, math, biology, chemistry, physics, earth science, online learning", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2013"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/biology/2/cellular-organelles-i/195"> <meta property="og:title" content="Cellular Organelles I | Biology | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Evolution isn't always about competition. It can also be about cooperation, as is the case with the development of chloroplasts and mitochondria from free-living bacteria. This module explains the theory of endosymbiosis along with its origins. Convincing evidence in support of the theory is presented. The evolution of the nucleus and other organelles through invagination of the cell membrane is also discussed."> <meta property="og:image" content="https://visionlearning.com/images/logo.png"> <meta property="fb:admins" content="100000299664514"> <link rel="stylesheet" type="text/css" href="/css/visionlearning.css">  <link rel="stylesheet" type="text/css" href="/css/visionlearning-icons.css">  <link rel="preconnect" as="font" href="https://fonts.gstatic.com" crossorigin> <link href="https://fonts.googleapis.com/css2?family=Open+Sans:ital,wght@0,400;0,700;1,400;1,700&family=Schoolbell&display=swap" rel="stylesheet"> <style> textarea.myEditor { width: 90%; height: 350px; } </style> <script type="text/x-mathjax-config" src="/js/mathjax-config.js"></script> <script id="MathJax-script" async src="/js/mathjax/tex-svg.js"></script> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script> </head> <body>  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Control Earth's Temperature</a></li> <li><a href="/en/library/earth-science/6/circulation-in-the-atmosphere/255">Circulation in the Atmosphere</a></li> </ul> </div> <button class="accordion__button" id="acc-button-hazards" data-accordion="button" aria-controls="acc-panel-hazards" aria-expanded="false"> <span class="accordion__button__label"> Hazards </span> </button> <div class="accordion__panel" id="acc-panel-hazards" data-accordion="panel" aria-labelledby="acc-button-hazards" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/natural-hazards-and-risk/288">Natural Hazards and Risk</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-history" data-accordion="button" aria-controls="acc-panel-earth-history" aria-expanded="false"> <span class="accordion__button__label"> Earth History </span> </button> <div class="accordion__panel" id="acc-panel-earth-history" data-accordion="panel" aria-labelledby="acc-button-earth-history" 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</span> </button> <div class="accordion__panel" id="acc-panel-ecology" data-accordion="panel" aria-labelledby="acc-button-ecology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/biodiversity-i/276">Biodiversity I</a></li> <li><a href="/en/library/environmental-science/61/biodiversity-ii/281">Biodiversity II</a></li> <li><a href="/en/library/environmental-science/61/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/environmental-science/61/population-biology/287">Population Biology</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/environmental-science/61/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-general-science" data-accordion="button" aria-controls="acc-panel-general-science" aria-expanded="false"> <span class="accordion__button__label"> General Science </span> </button> <div class="accordion__panel" id="acc-panel-general-science" data-accordion="panel" aria-labelledby="acc-button-general-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-methods" data-accordion="button" aria-controls="acc-panel-methods" aria-expanded="false"> <span class="accordion__button__label"> Methods </span> </button> <div class="accordion__panel" id="acc-panel-methods" data-accordion="panel" aria-labelledby="acc-button-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-scientific-method/45">The Scientific Method</a></li> </ul> </div> <button class="accordion__button" id="acc-button-measurement" data-accordion="button" aria-controls="acc-panel-measurement" aria-expanded="false"> <span class="accordion__button__label"> Measurement </span> </button> <div class="accordion__panel" id="acc-panel-measurement" data-accordion="panel" aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span class="accordion__button__label"> Math in Science </span> </button> <div class="accordion__panel" id="acc-panel-math-in-science" data-accordion="panel" aria-labelledby="acc-button-math-in-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-equations" data-accordion="button" aria-controls="acc-panel-equations" aria-expanded="false"> <span class="accordion__button__label"> Equations </span> </button> <div class="accordion__panel" id="acc-panel-equations" data-accordion="panel" aria-labelledby="acc-button-equations" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/unit-conversion/144">Unit Conversion</a></li> <li><a href="/en/library/math-in-science/62/linear-equations/194">Linear Equations</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-i/206">Exponential Equations I</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/the-nature-of-light/132">The Nature of Light</a></li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-process-of-science" data-accordion="button" aria-controls="acc-panel-process-of-science" aria-expanded="false"> <span class="accordion__button__label"> Process of Science </span> </button> <div class="accordion__panel" id="acc-panel-process-of-science" data-accordion="panel" aria-labelledby="acc-button-process-of-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-introduction" data-accordion="button" aria-controls="acc-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-panel-introduction" data-accordion="panel" aria-labelledby="acc-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-the-culture-of-science" data-accordion="button" aria-controls="acc-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177">Theories, Hypotheses, and Laws</a></li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-button-data" data-accordion="button" aria-controls="acc-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-panel-data" data-accordion="panel" aria-labelledby="acc-button-data" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/data-analysis-and-interpretation/154">Data Analysis and Interpretation</a></li> <li><a href="/en/library/process-of-science/49/uncertainty-error-and-confidence/157">Uncertainty, Error, and Confidence</a></li> <li><a href="/en/library/process-of-science/49/statistics-in-science/155">Statistics in Science</a></li> <li><a href="/en/library/process-of-science/49/using-graphs-and-visual-data-in-science/156">Using Graphs and Visual Data in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-communication" data-accordion="button" aria-controls="acc-panel-scientific-communication" aria-expanded="false"> <span class="accordion__button__label"> Scientific Communication </span> </button> <div class="accordion__panel" id="acc-panel-scientific-communication" data-accordion="panel" aria-labelledby="acc-button-scientific-communication" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-díaz/219">Franklin Chang Díaz</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Biology </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-biological-molecules" data-accordion="button" aria-controls="acc-sub-panel-biological-molecules" aria-expanded="false"> <span class="accordion__button__label"> Biological Molecules </span> </button> <div class="accordion__panel" id="acc-sub-panel-biological-molecules" data-accordion="panel" aria-labelledby="acc-sub-button-biological-molecules" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/carbohydrates/61">Carbohydrates</a></li> <li><a href="/en/library/biology/2/fats-and-proteins/62">Fats and Proteins</a></li> <li><a href="/en/library/biology/2/biological-proteins/243">Biological Proteins</a></li> <li><a href="/en/library/biology/2/blood-biology-i/242">Blood Biology I</a></li> <li><a href="/en/library/biology/2/lipids/207">Lipids</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-cell-biology" data-accordion="button" aria-controls="acc-sub-panel-cell-biology" aria-expanded="false"> <span class="accordion__button__label"> Cell Biology </span> </button> <div class="accordion__panel" id="acc-sub-panel-cell-biology" data-accordion="panel" aria-labelledby="acc-sub-button-cell-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/discovery-and-structure-of-cells/64">Discovery and Structure of Cells</a></li> <li><a href="/en/library/biology/2/respiration/285">Respiration</a></li> <li><a href="/en/library/biology/2/membranes-i/198">Membranes I</a></li> <li><a href="/en/library/biology/2/membranes-ii/204">Membranes II</a></li> <li class="current">Cellular Organelles I</li> <li><a href="/en/library/biology/2/cell-division-i/196">Cell Division I</a></li> <li><a href="/en/library/biology/2/cell-division-ii/212">Cell Division II</a></li> <li><a href="/en/library/biology/2/membranes-and-chemical-transport/106">Membranes and Chemical Transport</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-energy-in-living-systems" data-accordion="button" aria-controls="acc-sub-panel-energy-in-living-systems" aria-expanded="false"> <span class="accordion__button__label"> Energy in Living Systems </span> </button> <div class="accordion__panel" id="acc-sub-panel-energy-in-living-systems" data-accordion="panel" aria-labelledby="acc-sub-button-energy-in-living-systems" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/energy-metabolism-i/215">Energy Metabolism I</a></li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225">Energy Metabolism II</a></li> <li><a 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class="module__header"> <span class="subcategory"> <strong><em>Cell Biology</em></strong> </span> <h1>Cellular Organelles I: <sub><em>Endosymbiosis and membrane-bound organelles</em></sub></h1> <p class="byline">by Donna Hesterman, Nathan H Lents, Ph.D.</p> </header> <nav class="module__tabs"> <ul class="tabs-nav tabs-nav--pill tabs-nav--horizontal--md library"> <li> <a href="/en/library/biology/2/cellular-organelles-i/195/reading" class="is-active" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/biology/2/cellular-organelles-i/195/quiz" >Quiz</a> </li> <li> <a href="/en/library/biology/2/cellular-organelles-i/195/resources" >Teach with this</a> </li> </ul> </nav> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_195.mp3", "description": "Recording of Cellular Organelles I : Evolution isn't always about competition. It can also be about cooperation, as is the case with the development of chloroplasts and mitochondria from free-living bacteria. This module explains the theory of endosymbiosis along with its origins. Convincing evidence in support of the theory is presented. The evolution of the nucleus and other organelles through invagination of the cell membrane is also discussed.", "encodingFormat": "mp3", "name": "module_195.mp3" } </script> <div class="module__audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_195.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> <hr class="module__divider" />  <div class="module__tools"> <aside class="module__tools__container border-radius box-shadow-1"> <div class="tabs tabs--toggle-mobile--lg" role="tablist"> <ul class="tab__buttons"> <li> <button class="button button--icon-over-text" aria-label="In this module" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="button__icon"> <span class="icon icon-list" aria-hidden="true"></span> </span> <span class="button__text">Contents</span> </button> </li> <li> <button class="button button--icon-over-text" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="button__icon"> <span class="icon icon-glossary-highlight"></span> </span> <span class="button__text">Glossary Terms</span> </button> </li> </ul> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <div class="table-of-contents"> <p class="table-of-contents__title"> Table of Contents </p> <ul class="table-of-contents__nav"> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc_1">The origin of eukaryotic cells</a> </li> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc_2">The theory of endosymbiosis</a> </li> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc_3">Confirming the theory</a> </li> <li> <ul> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc2_1">Major evidence for the endosymbiotic theory</a> </li> </ul> </li> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc_4">The evolution of other organelles</a> </li> <li><a href="/en/library/biology/2/cellular-organelles-i/195#toc_5">The endomembrane system</a> </li> </ul> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> <div class="glossary-container"></div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. Once highlighted, you can click on them to view these standards. </em> </p> </div> </div> <div class="ngss-container"></div> </div> </div> </aside> <div class="margin-3"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-9561344156007092" data-ad-slot="7634263342" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> </div>     <div class="module__main"> <div class="module__main__container"> <div class="accordion">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that “survival of the fittest” is not the only explanation for the success of a species over time? Cooperation can be just as important when it comes to how species adapt in order to survive. According to Lynn Margulis, who proposed that modern-day mitochondria and chloroplasts evolved through endosymbiosis, “Life did not take over the globe by combat, but by networking.”</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"><li><p>One of the main differences between eukaryotic cells and prokaryotic cells is the presence of a nucleus and other membrane-bound organelles.</p></li> <li><p>Chloroplasts and mitochondria have specialized roles in producing energy for the cell and have several unique features including some of their own DNA. Because of this, scientists believe that both of these organelles originated through endosymbiosis when one small cell began to live inside a larger one.</p></li> <li><p>Membrane-bound organelles evolved as folds of the plasma membrane; this allowed these cells to establish compartments with different environments appropriate for the specific function that the organelle performs.</p></li></ul> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt><a href="/en/glossary/view/algae">algae </a></dt> <dd> mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic </dd> <dt><a href="/en/glossary/view/bacteria">bacteria </a></dt> <dd> a large group of one-celled organisms that are found almost everywhere </dd> <dt><a href="/en/glossary/view/membrane">membrane </a></dt> <dd> layer of tissue that forms the boundary of a cell or cell part</dd> </dl> </div> </div> </div> <section> <p>When we think of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, we tend to think of a competition where the fittest survive. Male rams with giant curling horns defeat smaller males and earn the privilege of passing on their <mark class="term" data-term="trait" data-term-def="A specific characteristic that is genetically determined." data-term-url="/en/glossary/view/trait/8271">traits</mark> – big strong bodies and massive curling horns – to the next <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generation</mark>. Similarly, male birds with showy, colorful feathers win the competition for mates against dull-looking males, and give their offspring the gift of flashy plumage. But the story of evolution isn't always about competition. In fact, sometimes, evolution can be about cooperation. Such is the case with <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>.</p> <p><section id="toc_1" class=""> <h2>The origin of eukaryotic cells</h2></p> <p><em>Eukaryotic</em> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> differ from <em>prokaryotic</em> cells in that most of the various <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> in <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells are encapsulated in <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark>, while <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> cells have only free-floating organelles (Figure 1). The difference is a very obvious one, even when viewed through the simplest microscopes. As early as the late 1800s, scientists were already debating how <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> may have given rise to these two very distinct <mark class="term" data-term="lineage" data-term-def="In organisms, lineage is the line of descent from an ancestor." data-term-url="/en/glossary/view/lineage/5291">lineages</mark> (Mereschkowski, 1910).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6495.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6495-130909100918.jpg" alt="Figure 1: A eukaryotic cell (left) has membrane bound organelles, while a prokaryotic cell (right) does not." /> </button> <figcaption> <p><strong>Figure 1:</strong> A eukaryotic cell (left) has membrane bound organelles, while a prokaryotic cell (right) does not.</p> <span class="credit">image ©J Thorpe</span> </figcaption> </figure> </div> <p>Konstantin Mereschkowski (Figure 2) originally proposed the idea that <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> in plants evolved from a symbiotic relationship like the one he had seen in his <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> with <mark class="term" data-term="lichen" data-term-def="Fungi that live symbiotically with photosynthetic algae or bacteria." data-term-url="/en/glossary/view/lichen/6541">lichens</mark>. Lichens, he had observed, were really composite <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> formed by a fungus and photosynthetic <mark class="term" data-term="algae" data-term-def="(plural form of <b>alga</b>) Mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic." data-term-url="/en/glossary/view/algae/8678">algae</mark> living together <mark class="term" data-term="symbiosis" data-term-def="The intimate living together of two dissimilar organisms in a mutually beneficial relationship." data-term-url="/en/glossary/view/symbiosis/2184">symbiosis</mark>. The fungus part of the organism provides a safe <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environment</mark> for the photosynthetic algae, and the algae <mark class="term" data-term="photosynthesize" data-term-def="The act of performing photosynthesis." data-term-url="/en/glossary/view/photosynthesize/7077">photosynthesize</mark> <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> for the lichen. Mereschkowski suspected that the chloroplasts in plant <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> descended from organisms similar to the algae in his lichens. Unfortunately, he had no real <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> to support his <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark>, so no one took it very seriously at the time. However, when an American biologist named Lynn Margulis (Figure 2) proposed the idea again in 1967, things were different. Technology was becoming available that would allow scientists to gather <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> and investigate the claim fully. Mereschkowski's idea finally got some attention, although 100 years later.</p> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="9090201191"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6496.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6496-130909100923.jpg" alt="Figure 2: Konstantin Mereschkowski (left), a Russian biologist, originally proposed the idea that chloroplasts in plant cells were the distant relatives of photosynthetic single-celled organisms. Lynn Margulis (right) revived this idea and provided a detailed mechanistic theory which was later confirmed by many lines of evidence." /> </button> <figcaption> <p><strong>Figure 2:</strong> Konstantin Mereschkowski (left), a Russian biologist, originally proposed the idea that chloroplasts in plant cells were the distant relatives of photosynthetic single-celled organisms. Lynn Margulis (right) revived this idea and provided a detailed mechanistic theory which was later confirmed by many lines of evidence.</p> <span class="credit">image ©Wikimedia Commons</span> </figcaption> </figure> </div> </section> <section id="toc_2"> <h2>The theory of endosymbiosis</h2><p>The idea proposed by Margulis is called the <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <em>endosymbiosis</em>. This theory states that modern-day <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> and <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> are actually the descendants of ancient bacteria-like <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> that began living inside <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> when Earth was very young (Sagan, 1967).</p><p>The story begins over two billion years ago when Earth was still hot and mostly barren. There was no oxygen <mark class="term" data-term="gas" data-term-def="The state of matter characterized by its non-condensed nature and ability to flow. Unlike liquids, molecules within a gas remain far&hellip;" data-term-url="/en/glossary/view/gas/8725">gas</mark> (O<sub>2</sub>) in the <mark class="term" data-term="atmosphere" data-term-def="The collective mass of gases that surrounds the Earth or another planet." data-term-url="/en/glossary/view/atmosphere/8529">atmosphere</mark>, and the only life forms on Earth were single-celled <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> similar to present-day <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>. Some of these <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark>, called <em>cyanobacteria</em>, evolved the ability to capture the <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> in sunlight to make <mark class="term" data-term="organic" data-term-def="Originating from a living organism; a compound that contains hydrocarbons." data-term-url="/en/glossary/view/organic/8530">organic</mark> <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark>. Because of their new abilities, these photosynthetic bacteria flourished and began to release free oxygen gas (O<sub>2</sub>) into the ocean water.</p><p>Oxygen <mark class="term" data-term="gas" data-term-def="The state of matter characterized by its non-condensed nature and ability to flow. Unlike liquids, molecules within a gas remain far&hellip;" data-term-url="/en/glossary/view/gas/8725">gas</mark> was purely a byproduct of <mark class="term" data-term="photosynthesis" data-term-def="Formation of carbohydrates from carbon dioxide and a source of hydrogen (as water) in the chlorophyll-containing tissues of plants exposed to light." data-term-url="/en/glossary/view/photosynthesis/2194">photosynthesis</mark> and hadn’t previously existed on the planet. Because oxygen is reactive, it was toxic to most of the <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark> living at that time and caused many of them to go <mark class="term" data-term="extinction" data-term-url="/en/glossary/view/extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism.">extinct</mark>. However, a small number of prokaryotes evolved the ability to tolerate the oxygen, and some of their descendants later evolved the ability to utilize oxygen to aid their <mark class="term" data-term="metabolism" data-term-def="A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the&hellip;" data-term-url="/en/glossary/view/metabolism/1606">metabolism</mark>, much like we do today.</p><p>Cells that can use oxygen for <mark class="term" data-term="metabolism" data-term-def="A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the&hellip;" data-term-url="/en/glossary/view/metabolism/1606">metabolism</mark> are called <em>aerobic</em>, while those that cannot are called <em>anaerobic.</em> <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">Aerobic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> have a powerful advantage because oxygen allows them to get much more <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> out of the food <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> they consume.</p><p>The cooperation between the two <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark> came about when a large anaerobic <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> engulfed (but failed to digest) a smaller, <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">aerobic</mark> cell. The aerobic cell, now living inside the anaerobic cell, continued to efficiently metabolize food <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> using oxygen, and shared its excess <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> (chemical storage form of energy) with its host, the large anaerobe. The arrangement would have been similar to the one we see in our own digestive system: Millions of microbes live happily in our intestines, helping us to digest and metabolize the foods we eat. Like the microbes living in our guts today, the aerobic cell lived entirely inside its host.</p><p>Over millions of <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generations</mark>, the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> continued to grow, divide, and multiply, and their relationship evolved into a mutually beneficial cooperation – a <mark class="term" data-term="symbiosis" data-term-def="The intimate living together of two dissimilar organisms in a mutually beneficial relationship." data-term-url="/en/glossary/view/symbiosis/2184">symbiosis</mark>. In time, most (but not all) of the <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> from the smaller <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">aerobic</mark> cell made its way into the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> of the host cell and the two separate <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> became one – the ancestor of all the <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells we see today. The descendants of that small aerobic cell evolved into the <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelle</mark> we call <em>mitochondria</em>. <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">Mitochondria</mark> still pass on some of their own DNA to their <mark class="term" data-term="daughter" data-term-def="A material that is derived from the breakdown or division of another. For example, a product of the radioactive decay of&hellip;" data-term-url="/en/glossary/view/daughter/10177">daughter</mark> cells, just as DNA from the nucleus is passed on to the nucleus of its daughter cells. The <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossil</mark> <mark class="term" data-term="record" data-term-def="A written account or description. <br> <b>[verb]</b> To write an account or description." data-term-url="/en/glossary/view/record/8239">record</mark> shows us that mitochondria and modern eukaryotic cells look much different than the precursors did because they have continued to evolve and change over two billion years.</p><p>The endosymbiotic <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> goes on to say that <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> evolved in a similar fashion. It proposes that a small cyanobacteria (the photosynthetic <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> mentioned earlier as the first source of oxygen gas) was engulfed by a larger, <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">aerobic</mark>, non-photosynthetic <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>. This large non-photosynthetic cell, a descendent of the <mark class="term" data-term="symbiosis" data-term-def="The intimate living together of two dissimilar organisms in a mutually beneficial relationship." data-term-url="/en/glossary/view/symbiosis/2184">symbiosis</mark> described above, already had <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> living inside it. It was either an early <mark class="term" data-term="eukaryote" data-term-def="A single- or multi-cellular organism whose cells contain a distinct nucleus that encloses the organism's genetic material." data-term-url="/en/glossary/view/eukaryote/5297">eukaryote</mark> or an advanced <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryote</mark> that shared some features with eukaryotes. And just as before, when the larger cell engulfed the smaller cell, it failed to digest it. The cyanobacteria, like the aerobic cell before it, lived happily tucked inside the larger cell. The larger cell now had <i>both</i> an aerobic cell and a photosynthetic cell living within it!</p><p>The arrangement could have been very similar to what we see in modern day single <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> called <em>Paramecium bursaria. P. bursaria</em> commonly live in ponds and eat large quantities of photosynthetic <mark class="term" data-term="algae" data-term-def="(plural form of <b>alga</b>) Mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic." data-term-url="/en/glossary/view/algae/8678">algae</mark> that they do not digest. The algae continue to <mark class="term" data-term="photosynthesize" data-term-def="The act of performing photosynthesis." data-term-url="/en/glossary/view/photosynthesize/7077">photosynthesize</mark> inside the almost completely transparent host, providing the paramecium with an onboard renewable food source. The paramecium host contributes to the <mark class="term" data-term="symbiosis" data-term-def="The intimate living together of two dissimilar organisms in a mutually beneficial relationship." data-term-url="/en/glossary/view/symbiosis/2184">symbiosis</mark> by transporting the algae to sunny spots in the pond while protecting it from more harmful, less accommodating predators. It also shares food that it is able to find with the algae during times when sunlight is scarce.</p><p>Just as with the earlier <mark class="term" data-term="symbiosis" data-term-def="The intimate living together of two dissimilar organisms in a mutually beneficial relationship." data-term-url="/en/glossary/view/symbiosis/2184">symbiosis</mark>, the cooperative arrangement between the photosynthetic <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> and the larger cell was mutually beneficial. The small photosynthesizer was provided with protection and all the <mark class="term" data-term="nutrient" data-term-def="A chemical substance (e.g., minerals, vitamins, proteins) that is needed by an organism to survive and grow. See also: macronutrient and micronutrient." data-term-url="/en/glossary/view/nutrient/7058">nutrients</mark> that it needed, including lots of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark> since the large cell was <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">aerobic</mark>. The large cell benefited even more. With the small cyanobacteria inside it, the cell no longer had to search around for food to eat – it had a built-in source of high-energy <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> made by its new photosynthetic helper. Over millions of years, the cooperation became closer, and the descendants of the small cyanobacteria are now an entirely dependent <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelle</mark> called the <em>chloroplast</em>. The large cell, now both aerobic and photosynthetic, gave rise to all plants and <mark class="term" data-term="algae" data-term-def="(plural form of <b>alga</b>) Mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic." data-term-url="/en/glossary/view/algae/8678">algae</mark> that we see today.</p><p>The <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="endosymbiosis" data-term-def="A symbiosis where one organism lives entirely within another." data-term-url="/en/glossary/view/endosymbiosis/6546">endosymbiosis</mark> sounds pretty far-fetched, and the scientific community didn't buy it at first. But Lynn Margulis was persistent and worked tirelessly to gather hard <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> to support her theory. She finally got the proof she needed in the late 1970s when scientists developed a new tool for identifying the ancestral <mark class="term" data-term="lineage" data-term-def="In organisms, lineage is the line of descent from an ancestor." data-term-url="/en/glossary/view/lineage/5291">lineage</mark> of <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6535"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Evolutionary changes</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6535-0-option-a" name="quiz-option-6535" type="radio" value="must be driven by competition." > <span class="option__label"> <span class="screen-reader-only">a.</span> must be driven by competition. </span> </label> <span class="quiz__response" id="response-6535-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6535-1-option-b" name="quiz-option-6535" type="radio" value="may be driven by cooperation." > <span class="option__label"> <span class="screen-reader-only">b.</span> may be driven by cooperation. </span> </label> <span class="quiz__response" id="response-6535-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>Confirming the theory</h2><p>Margulis originally conceived of the idea of <mark class="term" data-term="endosymbiosis" data-term-def="A symbiosis where one organism lives entirely within another." data-term-url="/en/glossary/view/endosymbiosis/6546">endosymbiosis</mark> based on what she observed in the laboratory as she studied <em>Euglena</em>, a single-celled, photosynthetic <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark>. The <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> inside the <em>Euglena</em> reminded Margulis of <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> she had studied before. The chloroplasts had <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> that was circular like the DNA in bacteria (Figure 3).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6497-130909100926.jpg" alt="Figure 3: DNA in mitochondria and chloroplasts are circular like DNA in bacteria." /> </button> <figcaption> <p><strong>Figure 3:</strong> DNA in mitochondria and chloroplasts are circular like DNA in bacteria.</p> </figcaption> </figure> </div> <p> The <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> in <em>Euglena</em> also had similarities to free-living <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>. For example, they pinched themselves in half as a means of reproduction in a <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> that looks a lot like <strong>binary fission</strong> (Figure 4) (see our <a href="/library/module_viewer.php?mid=196">Cell Division I: The Cell Cycle</a> module for more information).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6498-130909100928.jpg" alt="Figure 4: Bacteria and mitochondria both split in half to reproduce." /> </button> <figcaption> <p><strong>Figure 4:</strong> Bacteria and mitochondria both split in half to reproduce.</p> </figcaption> </figure> </div> <p>Just because <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> look like <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> wasn’t enough to convince most scientists that the <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> actually descended from bacterial ancestors. Gathering conclusive <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> that present-day mitochondria and <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> are distantly related to bacteria was a very difficult thing to do in the 1960s. However, in the 1970s, scientists developed a <mark class="term" data-term="method" data-term-def="A procedure or process; a systematic way of performing a task or conducting research." data-term-url="/en/glossary/view/method/8238">method</mark> for reading the precise sequence of <mark class="term" data-term="nucleotide" data-term-def="The building blocks of DNA and RNA, consisting of a nitrogen base, a five-carbon sugar, and one or more phosphate groups." data-term-url="/en/glossary/view/nucleotide/1603">nucleotides</mark> present in an organism’s <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>. The new technique allowed scientists to compare the <mark class="term" data-term="genome" data-term-def="All of the genetic material of an organism, carried in its DNA." data-term-url="/en/glossary/view/genome/8517">genome</mark> of one <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> to that of another and look for similarities that indicate relatedness. More similarities between the genomes of two species suggest that they are more related. Fewer similarities suggest that two <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> are less related.</p><p>Using the new <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> sequencing techniques, Ford Doolittle and Michael Gray, scientists working at Dalhousie University in Halifax, Nova Scotia, found the <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> needed to convince the scientific community that Margulis was right. They compared the DNA from <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> to DNA from the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> of the same <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>. Then they compared the chloroplast DNA to an ancient line of free-living photosynthetic <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>.</p> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="3321739899"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> <p>They found that the <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplast</mark> <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> appeared to be more closely related to the <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> than to the nuclear DNA of plants or <mark class="term" data-term="algae" data-term-def="(plural form of <b>alga</b>) Mostly aquatic plantlike organisms that range in size from one cell to large multi-celled seaweed and are photosynthetic." data-term-url="/en/glossary/view/algae/8678">algae</mark>. Not long after that, they showed that mitochondrial DNA, or mtDNA, was more closely related to an ancient line of free-living <mark class="term" data-term="aerobic" data-term-def="An organism or cell that requires oxygen to carry out its metabolic processes; a process that requires oxygen." data-term-url="/en/glossary/view/aerobic/6538">aerobic</mark> bacteria than to nuclear DNA of the <mark class="term" data-term="eukaryote" data-term-def="A single- or multi-cellular organism whose cells contain a distinct nucleus that encloses the organism's genetic material." data-term-url="/en/glossary/view/eukaryote/5297">eukaryotes</mark> that host the <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark>. The reaction in the scientific community was swift. Margulis's explanation for the origin of mitochondria and chloroplasts in <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> quickly became the dominant view. More <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> continued to pour in and by the early 1990s there was solid scientific consensus that the <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> of the endosymbiotic origin of mitochondria and chloroplasts was indeed correct (see list below). It was the first documented example of cooperation, rather than competition, driving a major evolutionary innovation.</p></section> <section id="toc2_1"><h3>Major evidence for the endosymbiotic theory</h3><ol> <li>Mitochondria and <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> have some of their own <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>, and it is located on a circular <mark class="term" data-term="chromosome" data-term-def="The organized genetic structure of DNA with associated proteins that contains the hereditary information necessary for reproduction, protein manufacture, and other functions." data-term-url="/en/glossary/view/chromosome/3760">chromosome</mark> (similar to bacteria).</li> <li>Mitochondria and chloroplasts have their own ribosomes, and they are similar to bacterial ribosomes, not to the <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> ribosomes found in the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark>.</li> <li>Proteins that are made inside <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> and chloroplasts begin with N-formyl-methionine, like bacterial <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark>, not like eukaryotic proteins, which always begin with regular methionine.</li> <li>Mitochondria and chloroplasts divide and replicate on their own in a manner very similar to how <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> divide, called <em>binary fission</em>.</li> <li>There are transport proteins found in the <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> of mitochondria and chloroplast, called <em>porins,</em> that are found in bacterial, but not in eukaryotic, <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membranes</mark>.</li> <li>Mitochondrial DNA sequences are more similar to bacteria <mark class="term" data-term="gene" data-term-def="Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function." data-term-url="/en/glossary/view/gene/3294">genes</mark> than to any eukaryotic genes.</li> <li>The modern-day bacteria whose DNA is most similar to mitochondrial DNA is the <em>Rickettsia</em> <mark class="term" data-term="genus" data-term-def="(plural: <strong>genera</strong>) A taxonomic category one rank or step above species in the Linnaean system, and which may include one or&hellip;" data-term-url="/en/glossary/view/genus/886">genus</mark>. These bacteria live inside large eukaryotic <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> as <mark class="term" data-term="parasite" data-term-def="An organism that lives on or in a host organism of another species. Parasites derive their food from and are detrimental&hellip;" data-term-url="/en/glossary/view/parasite/5272">parasites</mark>.</li> <li>Chloroplast DNA sequences are more similar to cyanobacteria genes than to any eukaryotic genes. Cyanobacteria are modern-day photosynthetic bacteria.</li> </ol><p>The advent of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> sequencing and the ability to compare DNA between different <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> has also shed light on the likely identity of the large <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> that first engulfed the ancestor of the <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark>. While the mitochondria and the <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> appear to be descended from <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>, the DNA in the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> of <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells is more similar to modern-day <mark class="term" data-term="archaea" data-term-def="(plural of archaeon) One of three domains of life on Earth (the other two being <a href="http://www.visionlearning.com/en/glossary/index/B#term-8679">Bacteria</a> and <a href="http://www.visionlearning.com/en/glossary/index/E#term-5297">Eukaryota</a>), consisting&hellip;" data-term-url="/en/glossary/view/archaea/10172">archaea</mark> than to that of bacteria. We tend to think of archaea as arcane <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> relegated to life in extreme <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environments</mark>, far outnumbered by their fellow <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark>, the bacteria. However, they were once the <mark class="term" data-term="dominant" data-term-def="Designating a genetic trait that is expressed when an organism has inherited two different variations (alleles) of a gene for that&hellip;" data-term-url="/en/glossary/view/dominant/8736">dominant</mark> life forms on the planet, and scientists today are finding them in more and more surprising places. Due to the similarity of our nuclear DNA to theirs, it is probable that the large cell that engulfed the ancestor of the mitochondria was an archaea, which means that all <mark class="term" data-term="eukaryote" data-term-def="A single- or multi-cellular organism whose cells contain a distinct nucleus that encloses the organism's genetic material." data-term-url="/en/glossary/view/eukaryote/5297">eukaryotes</mark> – including us – are descendents of archaeans through our nucleus, and of bacteria through our mitochondria. It’s almost as if the two <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> domains of life, bacteria and archaea, joined together and gave rise to the eukaryotic branch of the tree of life.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6536"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">The most convincing evidence that organelles such as mitochondria and chloroplasts descended from bacteria was</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6536-0-option-a" name="quiz-option-6536" type="radio" value="similarities in DNA." > <span class="option__label"> <span class="screen-reader-only">a.</span> similarities in DNA. </span> </label> <span class="quiz__response" id="response-6536-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6536-1-option-b" name="quiz-option-6536" type="radio" value="similarities in reproductive behavior." > <span class="option__label"> <span class="screen-reader-only">b.</span> similarities in reproductive behavior. </span> </label> <span class="quiz__response" id="response-6536-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>The evolution of other organelles</h2><p>But what about the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> found in <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells? How did that evolve? The membrane-bound nucleus, perhaps the single-most defining characteristic of eukaryotic <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>, in no way resembles any free-living <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> or achaean. The nucleus and other <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> evolved in a very different manner than did the <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> and <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark> (Figure 5).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6499.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6499-130909100931.jpg" alt="Figure 5: The nucleus containing DNA is clearly visible in this eukaryotic cell." /> </button> <figcaption> <p><strong>Figure 5:</strong> The nucleus containing DNA is clearly visible in this eukaryotic cell.</p> <span class="credit">image ©Image courtesy of Judith Beekman</span> </figcaption> </figure> </div> <p>Biologists cannot say for certain the exact order in which all of the <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> evolved. The <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossil</mark> <mark class="term" data-term="record" data-term-def="A written account or description. <br> <b>[verb]</b> To write an account or description." data-term-url="/en/glossary/view/record/8239">record</mark> is difficult to read when it comes to tiny, fluid-filled microorganisms from billions of years ago. Further complicating the matter is the fact that some organelles appear to have evolved more than once in different <mark class="term" data-term="lineage" data-term-def="In organisms, lineage is the line of descent from an ancestor." data-term-url="/en/glossary/view/lineage/5291">lineages</mark> over evolutionary time. In short, there is still some <mark class="term" data-term="debate" data-term-def="A reasoned discussion of opposing points in an argument." data-term-url="/en/glossary/view/debate/8242">debate</mark> about the details of the chronology, but scientists can infer the basic sequence of events based on what we know about how the organelles function today.</p><p>Early <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>, the first forms of life on Earth, probably had a rigid cell wall, like <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark> do today. Inside the cell wall there was a plasma <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membrane</mark>, like all cells have (see our <a href="/library/module_viewer.php?mid=198">Membranes I: Introduction to Biological Membranes</a> module). Somehow, perhaps as the result of a <mark class="term" data-term="mutation" data-term-def="A change in gene sequences of cell DNA." data-term-url="/en/glossary/view/mutation/8757">mutation</mark>, the <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membrane</mark> began to fold in on itself, creating a small cavern or – invagination – inside the cell wall (Figure 6). Over many thousands of <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generations</mark>, this invagination grew and eventually surrounded the cell’s <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>, creating a nuclear envelope. This architectural enhancement gave these cells an advantage over other prokaryotic cells because their DNA was now better protected from damaging <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> found in the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> of the cells.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6500.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6500-130909100933.jpg" alt="Figure 6: The first eukaryotic cells probably evolved as a result of invaginations, or a folding in, of the outer membrane." /> </button> <figcaption> <p><strong>Figure 6:</strong> The first eukaryotic cells probably evolved as a result of invaginations, or a folding in, of the outer membrane.</p> </figcaption> </figure> </div> <p>The <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> offered another important benefit. Inside the protective <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environment</mark> created by the nucleus, the <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> was able to evolve in ways that it never had before. Free from the interference from the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>'s <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark>, new <mark class="term" data-term="chemical reaction" data-term-def="A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that&hellip;" data-term-url="/en/glossary/view/chemical+reaction/1547">chemical reactions</mark> that power <mark class="term" data-term="gene" data-term-def="Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function." data-term-url="/en/glossary/view/gene/3294">gene</mark> recombination, DNA repair, and gene expression eventually evolved, and the structure of DNA itself began to change. DNA evolved from its ancient form – the simple ring-like structure seen in <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> – to the long intricate strings of <mark class="term" data-term="nucleotide" data-term-def="The building blocks of DNA and RNA, consisting of a nitrogen base, a five-carbon sugar, and one or more phosphate groups." data-term-url="/en/glossary/view/nucleotide/1603">nucleotides</mark> that make up our own DNA. With a single evolutionary change – the development of a nucleus – <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells were set on a course for greater diversity and specialization than <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> cells could ever achieve.</p><p>Later on in their <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, when <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> acquired <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> and <mark class="term" data-term="chloroplast" data-term-def="Organelle in plant and algae cells where photosynthesis occurs." data-term-url="/en/glossary/view/chloroplast/6543">chloroplasts</mark>, they gained another advantage. Eukaryotic cells could now find and utilize food sources better than their <mark class="term" data-term="prokaryotic" data-term-def="Cells that do not have a nuclei, nor any other membrane bound organelles." data-term-url="/en/glossary/view/prokaryotic/6540">prokaryotic</mark> cousins. Eukaryotic cells began to grow larger. (The average eukaryotic cell today is 100 to 1,000 times larger than a <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryote</mark>.) And as the cells became larger, their outer <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membrane</mark> continued folding in on itself in the same way that it had when the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> was formed. More folds created more channels inside the cell, and the same <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of invagination that formed the nucleus began to fashion the remaining membrane-bound <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark>.</p><p>The compartments (or organelles) created spaces where new processes could evolve without interference from the rest of the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>. Membrane-bound <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> gave <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells the same benefit that a proper laboratory gives a chemist – an environment where <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reactions</mark> can be controlled. Inside the newly formed organelles, complex processes like <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">protein</mark> <mark class="term" data-term="synthesis" data-term-def="The production of a chemical compound by combining simpler compounds or elements." data-term-url="/en/glossary/view/synthesis/8756">synthesis</mark> were able to evolve without chemical disruption from other cell functions like <mark class="term" data-term="respiration" data-term-def="The physical and chemical processes by which an organism supplies its cells and tissues with the oxygen needed for metabolism and&hellip;" data-term-url="/en/glossary/view/respiration/2195">respiration</mark> or <mark class="term" data-term="photosynthesis" data-term-def="Formation of carbohydrates from carbon dioxide and a source of hydrogen (as water) in the chlorophyll-containing tissues of plants exposed to light." data-term-url="/en/glossary/view/photosynthesis/2194">photosynthesis</mark>. Eventually, pathways and other features developed in cells that enabled them to communicate with each other. And once cells were able to pass signals and cooperate, they began to develop larger symbiotic relationships that ultimately gave rise to the tissues and organs that make up our bodies (Figure 7).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6501.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6501-130909100937.jpg" alt="Figure 7: A neuron has a nucleus and many other organelles common to all eukaryotic cells, but they have also evolved specialized structures like axons and dendrites that are found only in nerve cells." /> </button> <figcaption> <p><strong>Figure 7:</strong> A neuron has a nucleus and many other organelles common to all eukaryotic cells, but they have also evolved specialized structures like axons and dendrites that are found only in nerve cells.</p> <span class="credit">image ©Image copyright 2013 by David G. King, used with permission</span> </figcaption> </figure> </div> <p>While the explanation above is an educated guess, it is bolstered by <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> from modern-day <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark>, the <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>. Many bacteria have invaginations in their <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> that they use for a variety of purposes. In fact, most bacteria have extensive in-foldings of their <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membranes</mark> that process food <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> the same way that <mark class="term" data-term="mitochondria" data-term-def="Organelles that convert energy from food molecules into ATP, the main energy currency inside cells." data-term-url="/en/glossary/view/mitochondria/6542">mitochondria</mark> metabolize food in <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark>. What this shows is that the <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> of membrane folds into internal compartments is not a far-fetched possibility. In fact, it still happens today and can provide clear advantages for cells.</p><p>The <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> surrounding the <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> of <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> do more than just provide a barrier between organelles and <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark>, however. They serve as a <mark class="term" data-term="network" data-term-def="An interconnected system; an interrelated net-like arrangement of parts." data-term-url="/en/glossary/view/network/8740">network</mark> that provides a means of communication and transport throughout the cell. The <mark class="term" data-term="endomembrane system" data-term-def="A network of membrane-bound organelles that exchange materials and function cooperatively. Components include the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosome,&hellip;" data-term-url="/en/glossary/view/endomembrane+system/6549">endomembrane system</mark>, also thought to have evolved via the <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> of invagination, illustrates this point nicely.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6537"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Complex processes like nerve impulses are more likely to be found in __________ cells.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6537-0-option-a" name="quiz-option-6537" type="radio" value="prokaryotic" > <span class="option__label"> <span class="screen-reader-only">a.</span> prokaryotic </span> </label> <span class="quiz__response" id="response-6537-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6537-1-option-b" name="quiz-option-6537" type="radio" value="eukaryotic" > <span class="option__label"> <span class="screen-reader-only">b.</span> eukaryotic </span> </label> <span class="quiz__response" id="response-6537-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_5"> <h2>The endomembrane system</h2><p>Camillo Golgi, an Italian physician working in the late 1800s, is said to have discovered the <mark class="term" data-term="golgi apparatus" data-term-def="An organelle in eukaryotic cells responsible for packaging, modifying, and delivering newly formed proteins to their proper destination." data-term-url="/en/glossary/view/golgi+apparatus/6548">Golgi apparatus</mark> when he was looking at <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> from the body's central nervous <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>. The <em>internal reticular apparatus</em>, as he called it, appeared to be an individual structure when viewed through his microscope, which was the cutting edge technology of the day (Figure 8). Today, we know that the Golgi apparatus is connected to a larger <mark class="term" data-term="endomembrane system" data-term-def="A network of membrane-bound organelles that exchange materials and function cooperatively. Components include the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosome,&hellip;" data-term-url="/en/glossary/view/endomembrane+system/6549">endomembrane system</mark>.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6502.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6502-130909100940.jpg" alt="Figure 8: The Golgi apparatus is part of a larger system of organelles called the endomembrane system." /> </button> <figcaption> <p><strong>Figure 8:</strong> The Golgi apparatus is part of a larger system of organelles called the endomembrane system.</p> <span class="credit">image ©Julian Thorpe</span> </figcaption> </figure> </div> <p>The <mark class="term" data-term="endomembrane system" data-term-def="A network of membrane-bound organelles that exchange materials and function cooperatively. Components include the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosome,&hellip;" data-term-url="/en/glossary/view/endomembrane+system/6549">endomembrane system</mark> divides the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>'s <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> into separate compartments, or <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark>, that each performs specialized tasks within the cell. The separate compartments, however, aren't entirely separate. Some are actually connected by shared <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark>, as is the case with the <mark class="term" data-term="rough endoplasmic reticulum" data-term-def="A system of membranes present in most eukaryotic cells that separates the cytoplasm into compartments. In comparison to the smooth endoplasmic&hellip;" data-term-url="/en/glossary/view/rough+endoplasmic+reticulum/9844">rough endoplasmic reticulum</mark> and the nuclear membrane. This particular <mark class="term" data-term="network" data-term-def="An interconnected system; an interrelated net-like arrangement of parts." data-term-url="/en/glossary/view/network/8740">network</mark> forms a pathway for large <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> and signals to pass between the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> and the <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environment</mark> outside the cell.</p><p>Compartments that don't share a direct physical connection pass signals, <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark>, and waste via tiny membrane-bound sacs called <em>vesicles</em>. <mark class="term" data-term="vesicle" data-term-def="A small, self-enclosed sac inside of cells containing fluid and other material. The vesicles organize the cell's metabolism, help store enzymes&hellip;" data-term-url="/en/glossary/view/vesicle/2610">Vesicles</mark> form when part of an <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelle</mark>'s <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membrane</mark> pinches off, forms a lipid-bound sac, and floats through the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> to deliver its cargo between organelles. The <mark class="term" data-term="vesicle" data-term-url="/en/glossary/view/vesicle" data-term-def="A small, self-enclosed sac inside of cells containing fluid and other material. The vesicles organize the cell's metabolism, help store enzymes&hellip;">vesicles</mark>, being formed of the same <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membrane</mark> that surrounds the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> and all the organelles, easily merges with the membranes surrounding each compartment. Vesicles containing basic proteins synthesized in the <mark class="term" data-term="rough endoplasmic reticulum" data-term-def="A system of membranes present in most eukaryotic cells that separates the cytoplasm into compartments. In comparison to the smooth endoplasmic&hellip;" data-term-url="/en/glossary/view/rough+endoplasmic+reticulum/9844">rough endoplasmic reticulum</mark> travel to the <mark class="term" data-term="golgi apparatus" data-term-def="An organelle in eukaryotic cells responsible for packaging, modifying, and delivering newly formed proteins to their proper destination." data-term-url="/en/glossary/view/golgi+apparatus/6548">Golgi apparatus</mark> for final processing via vesicles. Vesicles containing the finished protein leave the Golgi apparatus and deliver the final product out to another organelle (Figure 9).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6503.jpg" data-lightbox="image"> <img src="/img/library/modules/mid195/Image/VLObject-6503-130909100943.jpg" alt="Figure 9: Depiction of vesicles containing newly synthesized protein leaving the Golgi apparatus." /> </button> <figcaption> <p><strong>Figure 9:</strong> Depiction of vesicles containing newly synthesized protein leaving the Golgi apparatus.</p> <span class="credit">image ©University of Dundee/Wellcome Images</span> </figcaption> </figure> </div> <p>Our current understanding of the <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membranes</mark> surrounding <mark class="term" data-term="organelle" data-term-def="Structure or compartment within a cell that performs a specialized function such as respiration or photosynthesis. An organelle is analogous to&hellip;" data-term-url="/en/glossary/view/organelle/5281">organelles</mark> has come from new techniques in biochemistry that give researchers greater access to the inner workings of <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> than the scientists of Margulis's day had. Researchers today can sift through cell samples using centrifuges and isolate individual organelles for closer scrutiny. They can also track the movement of specific chemicals and <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark> through a cell's <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark> and witness first-hand the flow of chemicals and signals from one organelle to another. The result has been a greater understanding of the true spirit of cooperation that was the basis of the <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> of the <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cell in the first place. As Lynn Margulis and her son wrote in one of their many books, “Life did not take over the globe by combat, but by networking."</p></section> <footer class="module__main__footer"> <hr class="border-color-dark"> <p class="citation"> <em> Donna Hesterman, Nathan H Lents, Ph.D. “Cellular Organelles I” Visionlearning Vol. BIO (1), 2013. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li><p>Gray, M. W. (1983). The bacterial ancestry of plastids and mitochondria. <em>BioScience, 33,</em> 693–699.</li> <li>Margulis, L. (1970). <em>Origin of Eukaryotic Cells</em>. New Haven, CT: Yale University Press.</li> <li>Mereschkowsky, K. (1910). Theorie der zwei Plasmaarten als Grundlage der Symbiogenesis, einer neuen Lehre von der Ent‐stehung der Organismen. (The nature and origins of chromatophores in the plant kingdom.) <em>Biol Centralbl, 30,</em> 353‐367.</li> <li>Sagan, L. (1967). On the origin of mitosing cells. <em>Journal of Theoretical Biology, 14,</em> 225–274.</p></li> </ul> </div> </footer> </div>    </article> </div> </div> </main>   <footer class="position-relative box-shadow-1 font-size-md" id="global-footer"> <h2 class="screen-reader-only">Page Footer</h2> <div class="back-to-top"> <div class="container wide"> <button class="button button--has-icon font-size-sm"> <span class="icon icon-arrow-up"></span> <span class="button__text">Back to top</span> </button> </div> </div> <div class="container wide padding-y-2"> <div class="grid grid--column-2--md grid--column-4--lg gap-4 grid--divider--fill-x"> <nav> <ul class="nav font-weight-bold"> <li> <a href="/en/library" title="Readings & quizzes"> Library </a> </li> <li> <a href="/en/glossary" title="Science terms"> Glossary </a> </li> <li> <a href="/en/classroom" title="Courses & bookmarks"> Classroom </a> </li> </ul> </nav> <nav> <ul class="nav"> <li><a href="/en/about">About</a></li> <li><a href="/en/help">Contact</a></li> <li><a href="/en/about/jobs">Jobs</a></li> <li><a href="/en/help/faq">FAQ</a></li> </ul> </nav> <div> <ul class="nav nav--horizontal margin-bottom-2"> <li> <a class="display-flex" href="https://www.nsf.gov" target="_blank" rel="noopener"> <img src="/images/sponsor-nsf.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> <li> <a class="display-flex" href="https://www.ed.gov/" target="_blank" rel="noopener"> <img src="/images/sponsor-doe.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> </ul> <p>Visionlearning is supported by the The National Science Foundation and the U.S. Department of Education. 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Cellular Organelles I | Biology | Visionlearning