{"id":4594,"date":"2013-06-29T06:52:18","date_gmt":"2013-06-29T06:52:18","guid":{"rendered":"http:\/\/www.mometrix.com\/academy\/?page_id=4594"},"modified":"2026-03-25T12:46:06","modified_gmt":"2026-03-25T17:46:06","slug":"aerobic-respiration","status":"publish","type":"page","link":"https:\/\/www.mometrix.com\/academy\/aerobic-respiration\/","title":{"rendered":"Aerobic Respiration"},"content":{"rendered":"\n\t\t\t<div id=\"mmDeferVideoEncompass_QTCnaBEbtm4\" style=\"position: relative;\">\n\t\t\t<picture>\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.webp\" type=\"image\/webp\">\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" type=\"image\/jpeg\"> \n\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" loading=\"eager\" id=\"videoThumbnailImage_QTCnaBEbtm4\" data-source-videoID=\"QTCnaBEbtm4\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" alt=\"Aerobic Respiration Video\" height=\"464\" width=\"825\" class=\"size-full\" data-matomo-title = \"Aerobic Respiration\">\n\t\t\t<\/picture>\n\t\t\t<\/div>\n\t\t\t<style>img#videoThumbnailImage_QTCnaBEbtm4:hover {cursor:pointer;} img#videoThumbnailImage_QTCnaBEbtm4 {background-size:contain;background-image:url(\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/1404-aerobic-respiration-1.webp\");}<\/style>\n\t\t\t<script defer>\n\t\t\t  jQuery(\"img#videoThumbnailImage_QTCnaBEbtm4\").click(function() {\n\t\t\t\tlet videoId = jQuery(this).attr(\"data-source-videoID\");\n\t\t\t\tlet helpTag = '<div id=\"mmDeferVideoYTMessage_QTCnaBEbtm4\" style=\"display: none;position: absolute;top: -24px;width: 100%;text-align: center;\"><span style=\"font-style: italic;font-size: small;border-top: 1px solid #fc0;\">Having trouble? <a href=\"https:\/\/www.youtube.com\/watch?v='+videoId+'\" target=\"_blank\">Click here to watch on YouTube.<\/a><\/span><\/div>';\n\t\t\t\tlet tag = document.createElement(\"iframe\");\n\t\t\t\ttag.id = \"yt\" + videoId;\n\t\t\t\ttag.src = \"https:\/\/www.youtube-nocookie.com\/embed\/\" + videoId + \"?autoplay=1&controls=1&wmode=opaque&rel=0&egm=0&iv_load_policy=3&hd=0&enablejsapi=1\";\n\t\t\t\ttag.frameborder = 0;\n\t\t\t\ttag.allow = \"autoplay; fullscreen\";\n\t\t\t\ttag.width = this.width;\n\t\t\t\ttag.height = this.height;\n\t\t\t\ttag.setAttribute(\"data-matomo-title\",\"Aerobic Respiration\");\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_QTCnaBEbtm4\").html(tag);\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_QTCnaBEbtm4\").prepend(helpTag);\n\t\t\t\tsetTimeout(function(){jQuery(\"div#mmDeferVideoYTMessage_QTCnaBEbtm4\").css(\"display\", \"block\");}, 2000);\n\t\t\t  });\n\t\t\t  \n\t\t\t<\/script>\n\t\t\n<p><script>\nfunction g57_Function() {\n  var x = document.getElementById(\"g57\");\n  if (x.style.display === \"none\") {\n    x.style.display = \"block\";\n  } else {\n    x.style.display = \"none\";\n  }\n}\n<\/script><\/p>\n<div class=\"moc-toc hide-on-desktop hide-on-tablet\">\n<div><button onclick=\"g57_Function()\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2024\/12\/toc2.svg\" width=\"16\" height=\"16\" alt=\"show or hide table of contents\"><\/button><\/p>\n<p>On this page<\/p>\n<\/div>\n<nav id=\"g57\" style=\"display:none;\">\n<ul>\n<li class=\"toc-h2\"><a href=\"#Glycolysis\" class=\"smooth-scroll\">Glycolysis<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#The_Connecting_Step\" class=\"smooth-scroll\">The Connecting Step<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#The_Krebs_Cycle\" class=\"smooth-scroll\">The Krebs Cycle<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Oxidative_Phosphorylation\" class=\"smooth-scroll\">Oxidative Phosphorylation<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Review\" class=\"smooth-scroll\">Review<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Frequently_Asked_Questions\" class=\"smooth-scroll\">Frequently Asked Questions<\/a><\/li>\n<\/ul>\n<\/nav>\n<\/div>\n<div class=\"accordion\"><input id=\"transcript\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"transcript\">Transcript<\/label><input id=\"FAQs\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"FAQs\">FAQs<\/label>\n<div class=\"spoiler\" id=\"transcript-spoiler\">\n<p>Hi, and welcome to this video about aerobic respiration! <\/p>\n<p>What exactly is aerobic respiration, and what steps are involved? We\u2019ll answer both of those questions later on in this video. But first, let\u2019s talk about metabolism and how that relates to aerobic respiration. Remember that metabolism is a series of reactions where molecules are degraded or synthesized. If a metabolic reaction degrades molecules, it\u2019s called a catabolic reaction.<\/p>\n<p>Catabolic reactions take fuel like <a class=\"ylist\" href=\"https:\/\/www.mometrix.com\/academy\/carbohydrates\/\">carbohydrates<\/a> or fat and break the molecules down into useful energy with carbon dioxide and water as byproducts. If a reaction is anabolic, however, it takes useful energy and single precursors and synthesizes more complex molecules for the body to use. Basically, aerobic respiration is a type of catabolic metabolic process that requires oxygen to proceed. It\u2019s made up of three stages that each have multiple steps: glycolysis, the Krebs cycle, and oxidative phosphorylation.<\/p>\n<p>Let\u2019s go over each of these processes in a little more depth.<\/p>\n<h2><span id=\"Glycolysis\" class=\"m-toc-anchor\"><\/span>Glycolysis<\/h2>\n<p>\nThe first step of both aerobic and anaerobic respiration is <a class=\"ylist\" href=\"https:\/\/www.mometrix.com\/academy\/glycosis\/\">glycolysis<\/a>, which does not require oxygen in either case. The purpose of glycolysis is to break down our starting material, glucose, which is a common simple sugar and jam-packed with energy potential. During the process of glycolysis 2 pyruvate molecules, 2 NADH molecules, and 4 ATP are produced. <\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2022\/02\/glycolysis.png\" alt=\"\" width=\"652\" height=\"348\"\/><\/p>\n<p>Glycolysis occurs in the cytoplasm of our cells in two phases.<\/p>\n<h3><span id=\"Phase_1\" class=\"m-toc-anchor\"><\/span>Phase 1<\/h3>\n<p>\nDuring the first phase, one molecule of glucose is cleaved into two phosphorylated 3-carbon compounds through a series of five reactions. This is accomplished through investing 2 net molecules of ATP, so we can think of this as the energy investment phase. The resulting compounds from phase one are two molecules of glyceraldehyde 3-phosphate or GAP.<\/p>\n<h3><span id=\"Phase_2\" class=\"m-toc-anchor\"><\/span>Phase 2<\/h3>\n<p>\nEach molecule of GAP will go through the second phase, where these 3-carbon compounds are oxidized to form two pyruvate molecules as well as four molecules of ATP and two molecules of NADH in a series of five more reactions. Each of these reactions are oxidation-reduction reactions where electrons are essentially transferred from one compound to another. Therefore, this phase is known as the energy harvesting phase. <\/p>\n<p>So in summary, we started with one molecule of glucose and ended with two molecules of pyruvate that will eventually be converted into more ATP. Glycolysis also produces two molecules of NADH that we\u2019ll use during the Krebs cycle. <\/p>\n<h2><span id=\"The_Connecting_Step\" class=\"m-toc-anchor\"><\/span>The Connecting Step<\/h2>\n<p>\nHowever, before we can enter the Krebs cycle, we have to check in with our oxygen levels. At this point the body will ask itself, is oxygen present? If the answer is yes, we move on to the Krebs cycle and the electron transport chain. If the answer is no, the body is forced to undergo anaerobic respiration through a process called fermentation.<\/p>\n<p>It would be inefficient for the body to go through any more processing past this point without considering oxygen levels, because the conversion of pyruvate to acetyl coenzyme A is an irreversible step. We don\u2019t want to convert molecules into compounds we can\u2019t use due to the oxygen conditions. This step is called the connecting step. Once that\u2019s complete, we can move on to stage two<\/p>\n<h2><span id=\"The_Krebs_Cycle\" class=\"m-toc-anchor\"><\/span>The Krebs Cycle<\/h2>\n<p>\nSince we\u2019re talking about aerobic respiration in this video, let\u2019s assume that oxygen is present and that both pyruvate molecules were converted into two molecules of acetyl CoA, effectively committing to the Krebs cycle. The Krebs cycle is simply a series of oxidation-reduction reactions that take place in the mitochondrial matrix of eukaryotes where carbon molecules are oxidized to harvest electrons.<\/p>\n<p>A pre-existing molecule, oxaloacetate, reacts with acetyl CoA to form citrate, also known as citric acid. Through a series of redox reactions, carbon dioxide is produced along with NADH and FADH<sub>2<\/sub>. Oxaloacetate is regenerated so that the cycle can begin again for our second molecule of acetyl CoA. FADH<sub>2<\/sub> and NADH are high-energy electron carriers that will donate their electrons during the electron transport chain to generate ATP. Although the Krebs cycle nets 2 molecules of ATP, this is an insignificant amount compared to the amount we\u2019ll generate later on in the process. <\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2022\/02\/krebs-cycle.png\" alt=\"\" width=\"635\" height=\"306\"\/><\/p>\n<h2><span id=\"Oxidative_Phosphorylation\" class=\"m-toc-anchor\"><\/span>Oxidative Phosphorylation<\/h2>\n<p>\nThe last stage we\u2019ll talk about today is oxidative phosphorylation, which is a process the electron transport chain (ETC) uses to generate ATP. The purpose of the ETC is to produce a proton gradient (H<sup>+<\/sup> ) using energy from those high-energy electrons in NADH and FADH<sub>2<\/sub> that are carried over from glycolysis and the Krebs cycle. This proton gradient will eventually serve as a proton motive force to synthesize ATP.<\/p>\n<p>Oxidative phosphorylation is when electrons are used to reduce oxygen to form water\u2013during which we release a lot of energy. And so our bodies use all of this energy to generate ATP.<\/p>\n<p>Let\u2019s break it down!<\/p>\n<p>The ETC is located within the inner membrane of the mitochondrion in eukaryotes and is made up of four protein complexes labeled I-IV. The process starts with our molecules of NADH which have a lot of energy or electron-transfer potential. Electrons from NADH enter protein complex I via an oxidation reaction and form NAD<sup>+<\/sup>, H<sup>+<\/sup>, and two electrons. <\/p>\n<p>The electrons flow through the complex until they reach the mobile electron carrier called ubiquinone (Q), which is reduced to QH<sub>2<\/sub>. This part of the process gives us enough energy to pump protons from the matrix into the intermembrane space to start building up our proton gradient. <\/p>\n<p>Nearly simultaneously, FADH<sub>2<\/sub> enters protein complex II and is oxidized to FAD, transferring its electrons to ubiquinone (Q) and later reduced to QH<sub>2<\/sub>. Unlike complex I, complex II only accepts protons from FADH<sub>2<\/sub> and does not contribute any protons to the proton gradient.<\/p>\n<p>QH<sub>2<\/sub> then travels through the membrane to deliver the electrons collected to complex III. The transfer of electrons into complex III allows protons to be pumped from the mitochondrial matrix to the intermembrane space to help build up the proton gradient some more. From here, the electrons are passed on to another mobile electron carrier called cytochrome C. Cytochrome C takes those electrons and passes them on to complex IV, the last protein complex in the ETC. <\/p>\n<p>Complex III becomes supercharged with electrons just like we saw in complexes I and II, so complex III is also able to pump protons from the matrix into the intermembrane space. <\/p>\n<p>At this point, we have a proton gradient where there are more protons in the intermembrane space than there are in the matrix, and we have lone electrons in complex IV. We know from basic chemistry that those lone electrons are not stable and will be looking to bind to something.<\/p>\n<p>This is where the oxygen comes in. Since we established that oxygen is in fact present, those lone electrons will react with oxygen (O<sub>2<\/sub>), splitting it into two oxygen ions. Now each oxygen ion will bond with two protons (H<sup>+<\/sup>) to form two water molecules (H<sub>2<\/sub>O). The important thing to note here is that oxygen acts as the final electron acceptor, helping the reaction come to completion and remain stable. This effectively brings the electron transport chain to an end.<\/p>\n<p>The reason we transfer electrons in a chain-like fashion versus giving them straight to oxygen is because the reaction is more controlled and easier to use when we transfer energy a little bit at a time. <\/p>\n<p>Finally, a protein called ATP-synthase will utilize the proton motive force generated by the ETC and protons to phosphorylate adenosine diphosphate (ADP), which is less energetic, to become adenosine triphosphate (ATP). As a whole, the process will net about 30 to 32 ATP molecules. From the electron transport chain through ATP synthase, we essentially converted the electron-transfer potential of NADH and FADH<sub>2<\/sub> into ATP, a more energetic molecule.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2022\/02\/oxidative-phosphorylation-1.png\" alt=\"\" width=\"680\" height=\"369\"\/><\/p>\n<hr>\n<h2><span id=\"Review\" class=\"m-toc-anchor\"><\/span>Review<\/h2>\n<p>\nNow that we\u2019ve covered the different steps of aerobic respiration, let\u2019s look at a couple of review questions to test your knowledge.<\/p>\n<p>1. Which protein complexes in the electron transport chain directly contribute to the proton gradient?<\/p>\n<ol style=\"list-style-type: upper-alpha;\">\n<li>Complex I<\/li>\n<li>Complex II<\/li>\n<li>Complex III<\/li>\n<li>Cytochrome C<\/li>\n<li>Complex IV<\/li>\n<\/ol>\n<div style=\"text-align: center; margin-bottom: 20px;\"><button class=\"buttontranscript\" onClick=\"toggle('Answer1')\">Show Answer<\/button><\/div>\n<div id=\"Answer1\" style=\"display:none; box-shadow: 1.5px 1.5px 5px grey; background-color:#E0E0E0; padding: 30px; padding-bottom: 15px; width: 60%; margin: auto; text-align: center;\">\n<strong>The answers are A, C, and E!<\/strong><\/p>\n<\/div>\n<p>\n&nbsp;<br \/>\n2. Which best describes the purpose of the Krebs cycle in aerobic respiration?<\/p>\n<ol style=\"list-style-type: upper-alpha;\">\n<li>It produces low-energy electron carriers in the form of NAD<sup>+<\/sup> and FAD<\/li>\n<li>It\u2019s a series of oxidative phosphorylation reactions that generate ATP for various cellular processes<\/li>\n<li>It recycles enzymes from glycolysis so the process can repeat<\/li>\n<li>It produces high-energy electron carriers in the form of NADH and FADH<sub>2<\/sub><\/li>\n<\/ol>\n<div style=\"text-align: center; margin-bottom: 20px;\"><button class=\"buttontranscript\" onClick=\"toggle('Answer2')\">Show Answer<\/button><\/div>\n<div id=\"Answer2\" style=\"display:none; box-shadow: 1.5px 1.5px 5px grey; background-color:#E0E0E0; padding: 30px; padding-bottom: 15px; width: 60%; margin: auto; text-align: center;\">\n<strong>The answer is D!<\/strong><\/p>\n<\/div>\n<p>\n&nbsp;<br \/>\nI hope this review was helpful! Thanks for watching, and happy studying!<\/p>\n<ul class=\"citelist\">\n<li><a href=\"https:\/\/medium.com\/countdown-education\/3-simple-stages-in-cellular-respiration-and-how-they-work-4de3abc5f819\"target=\"_blank\">Wolfe, Ernest. 2016. \u201c3 Simple Stages in Cellular Respiration and How They Work.\u201d<\/a><\/li>\n<\/ul>\n<\/div>\n<div class=\"spoiler\" id=\"FAQs-spoiler\">\n<h2 style=\"text-align:center\"><span id=\"Frequently_Asked_Questions\" class=\"m-toc-anchor\"><\/span>Frequently Asked Questions<\/h2>\n<div class=\"faq-list\">\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What is aerobic respiration?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>Aerobic cellular respiration is a series of enzyme-controlled chemical reactions in which oxygen reacts with glucose to produce carbon dioxide and water, releasing energy in the form of adenosine triphosphate (ATP).<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">Where does aerobic respiration occur?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>The majority of aerobic respiration occurs in the mitochondria, but the first step known as glycolysis takes place in the cytoplasm. <\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What is the difference between aerobic and anaerobic respiration?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>Aerobic respiration is a type of catabolic metabolic process that requires oxygen to proceed, while anaerobic respiration does not need oxygen.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">How many ATP are produced in aerobic respiration?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>As a whole, the process will produce about 36 net ATP molecules; 2 net ATP from glycolysis, 2 from the Krebs cycle, and 32 from oxidation phosphorylation.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What are the products of aerobic respiration?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>The products of aerobic respiration are carbon dioxide, water, and ATP.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n<div class=\"home-buttons\">\n<p><a href=\"https:\/\/www.mometrix.com\/academy\/biology\/\">Return to Biology Videos<\/a><\/p>\n<\/div>\n<p><script>\nfunction toggle(obj) {\n          var obj=document.getElementById(obj);\n          if (obj.style.display == \"block\") obj.style.display = \"none\";\n          else obj.style.display = \"block\";\n}\n<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Return to Biology Videos<\/p>\n","protected":false},"author":1,"featured_media":100447,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"","meta":{"footnotes":""},"class_list":{"0":"post-4594","1":"page","2":"type-page","3":"status-publish","4":"has-post-thumbnail","6":"page_category-biological-processes-videos","7":"page_type-video","8":"subject_matter-science"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/4594","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/comments?post=4594"}],"version-history":[{"count":5,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/4594\/revisions"}],"predecessor-version":[{"id":261142,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/4594\/revisions\/261142"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media\/100447"}],"wp:attachment":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media?parent=4594"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}