in this video we're going to talk about the difference between aerobic respiration and anaerobic respiration aerobic respiration occurs in the presence of oxygen anaerobic respiration occurs without oxygen and so that's the key difference between these two processes cellular respiration which converts glucose into carbon dioxide and water that is an example of aerobic respiration so in that process we start with glucose and in glycolysis glucose is converted into pyruvate now glycolysis doesn't require oxygen by the way but the other steps will that is once we get to the electron transport chain pyruvate is converted into acetyl enzyme a during pyruvic oxidation and then in the krebs cycle acetylchoenzyme a is oxidized to two carbon dioxide molecules and the electrons that are removed from acetyl coenzyme a is used to reduce nadplus into nadh and fad into fadh2 so those electron carriers go to the electron transport chain and they give up their electrons to oxygen which produces water so in aerobic cellular respiration glucose reacts with oxygen to ultimately produce carbon dioxide and water now i do want to add that one molecule of glucose yields two molecules of pyruvate which yields two molecules of acetylchoenzyme a and during pyruvate oxidation we get one molecule of co2 so for two private molecules we would get two molecules of co2 during oxidation and four molecules of co2 during the krebs cycle which would equate to the six molecules of glucose so the overall chemical equation for aerobic cellular respiration is this we take one glucose molecule c6h12o6 react it with six oxygen molecules to produce six co2 molecules and six water molecules so that's the overall chemical equation which you can't see all of that from here that's just a basic overview now in anaerobic respiration that is without oxygen there's two common pathways you need to be familiar with the first one is ethanol fermentation ethanol fermentation occurs when yeasts have access to glucose but do not have access to o2 the other one is lactic acid fermentation so this form of anaerobic respiration occurs in your muscle cells so let's say if you're working out and you're depleting the amount of oxygen in your muscle tissue your body can switch to lactic acid fermentation to give your muscles the energy that it needs so that's what you need to know about these two types of fermentation lactic acid fermentation occurs in your muscle cells ethanol fermentation typically occurs with fungi such as yeast so let's begin our discussion with ethanol fermentation let's see what happens during this particular form of anaerobic respiration so the first step is with glucose c6h12o6 so keep in mind glycolysis doesn't require oxygen to work so during this first step or during glycolysis glucose is converted to two molecules of pyruvate pyruvate has a methyl group a carbonyl group and a carboxylate group it's a three carbon ion now in this process that is in glycolysis two molecules of adp is converted to two molecules of atp and so this is the energy that we get from anaerobic respiration now in order to generate those atp molecules glycolysis nad plus into two molecules of nadh now in order for the cell to keep making atp without o2 we need to generate more of the energy plus because as glycolysis continues we're going to run out of nad plus so in the next step we're going to convert pyruvate into two molecules of acetaldehyde and this involves decarboxylation that is the removal of carbon dioxide so we're going to lose two carbon dioxide molecules for the two pyruvate ions that we have here the final step is the reduction of acetaldehyde into ethanol so this is our end product ethanol now in order to reduce ethanol something has to be oxidized and that something is nadh so nadh is oxidized back into nad plus now keep in mind oxidation involves a loss of electrons reduction involves a gain of electrons so now that we've regenerated energy plus this can go back into glycolysis this allowing the cycle to continue given all the atp that we need for the yeast cells to keep functioning so that's how yeast cells can convert glucose into ethanol in the absence of o2 now let's move on to lactic acid fermentation now this form of fermentation has some similarities to ethanol fermentation the first step being glycolysis so once again we're going to start with glucose and then we're going to convert it into two molecules of pyruvate so this part is going to stay the same and just like before we're going to generate two molecules of atp and we are going to reduce two ions of nad plus and to make that into two molecules of nadh now just like before in order for glycolysis to continue we need to regenerate the nad plus so that we can keep making atp so that's important so the next step we are going to reduce pyruvate into lactate so notice what happened as we went from pyruvate to lactate what is the difference between the two structures so notice that the carbonyl group was reduced into an alcohol functional group so if pyruvate is reduced to lactate what is oxidized in this case is going to be nadh so two molecules of nadh is oxidized back into two ions of nad plus and this is important because now the cycle can continue and so we can regenerate the nad plus that we need so that we can keep making atp in glycolysis so both in lactic acid fermentation and in ethanol fermentation we get two atp molecules per glucose molecule and keep in mind this occurs in the tissues of muscle cells so that's a basic review of ethanol fermentation and lactic acid fermentation which are two forms of anaerobic respiration now let's work on some review questions let's see if you were paying attention number one how many atp molecules are generated from glucose during lactic acid fermentation is it 2 6 18 36 or 38 what would you say feel free to pause the video if you want to try it the answer is two both during lactic acid fermentation and ethanol fermentation two molecules of atp are produced now in an anaerobic cellular respiration the maximum is 38 according to some textbooks and some will say 36 if you take into account the two atp molecules that are needed to transport pyruvate into the mitochondria so these numbers would occur for cellular respiration that's how much atp can be produced during that event but during lactic acid fermentation the answer is a number two which of the following statements is false so go ahead and pause the video again take a minute to work on this example so let's start with answer choice a aerobic cellular respiration requires o2 to occur this is a true statement so we can eliminate this answer this is the conversion of glucose into carbon dioxide and water use an oxygen so it's c6h12o6 plus o2 turn it into co2 and water so that's aerobic cellular respiration now for b ethanol fermentation is a form of anaerobic respiration that's true for yeast cells to convert glucose into ethanol they do not require the use of o2 so that's a type of anaerobic respiration now c lactic acid fermentation occurs in the tissues of muscle cells that is true that's just one of the things that you need to know when you're working out and you burn up all your oxygen supply and your muscle tissues you get the buildup of lactate and then eventually you feel tired d lactic acid fermentation produces co2 which we release during exhalation now while it's true that we do breathe out co2 co2 is not produced in lactic acid fermentation so d is false which is the answer we're looking for so to review during lactic acid fermentation we have glucose converted into two molecules of pyruvate and then from pyruvate we get lactate two molecules of lactate now in ethanol fermentation we start with glucose which turns into two molecules of pyruvate and then that turns into two molecules of acetaldehyde which becomes two molecules of ethanol now i'm going to draw pyruvate because here's what's important pyruvate is a three carbon molecule acetaldehyde is a two carbon molecule to convert pyruvate into acetaldehyde we need to lose a carbon and so the carbon atom that we lose will be in the form of carbon dioxide so it's important to understand that carbon dioxide is released during ethanol fermentation and not in lactic acid fermentation now let's move on to part e ethanol fermentation occurs in four steps is that true or false this is step one step two step three so this is false it looks like there's two answers so d and e i should have put circle each one so ethanol fermentation occurs in three steps lactic acid fermentation occurs it occurs in two steps so d and e are the correct answers so that's it for this video so now you understand the difference between aerobic respiration which occurs with oxygen and anaerobic respiration which occurs without oxygen and keep in mind ethanol fermentation and lactic acid fermentation are two forms of anaerobic respiration