aerobic respiration the very basics so the best place to start is to learn the word equation and then the balanced equation they're asked frequently at higher and ordinary levels so learn them so aerobic respiration is a two-stage process stage one is called glycolysis and it means the splitting of glucose where does this stage take place it happens in the cytosol of the cell the liquid part of the cytoplasm is oxygen involved in this stage no oxygen plays no role in glycolysis so we start with glucose a six carbon molecule and at the end of glycolysis we have it split into two three carbon molecules of pyruvic acid so forming these pyruvic acid molecules involved the removal of pairs of hydrogen atoms hydrogen atoms contain electrons and protons and these go to form nadh that molecule that transfers electrons and protons so you remember go back revise nad plus how it combines with two electrons and a proton to form nadh there's only a net gain of two atp in glycolysis not much energy made so we have pyruvic acid this three carbon molecule there are two of them but we'll just discuss one and if there is oxygen present it will enter stage two oxygen is essential where does stage two take place it takes place in the mitochondria of the cells the powerhouses so each one of these pyruvic acid molecules is going to be immediately broken down into a two carbon molecule called acetyl coa this happens by removing a carbon dioxide and also a pair of hydrogen atoms those hydrogen atoms remember contain electrons and protons and they get picked up to form nadh so acetyl coa this two carbon molecule now enters into this cycle of reactions known as krebs cycle or the citric acid cycle and i know students really don't like this so let's make this very simple acetyl-coa joins with a four-carbon molecule and makes a six carbon molecule and the whole cycle is about breaking down that six carbon molecule to get back to the four carbon molecule this happens by removing carbon dioxides two of them and also pairs of hydrogen atoms the removal of hydrogen atoms is really important because they contain electrons and protons and they get picked up by nad plus to form nadh so one of the most important products of krebs cycle are the nadh molecules that are made they're really important there's not much energy made in krebs cycle only one atp and the associated water molecule so what can you say happens to the acetyl-coa well it eventually gets converted to water and carbon dioxide a previous exam question so know that the products of krebs cycle are three nadh molecules one atp and the two carbon dioxide molecules so we're still in stage two and remember stage two is taking place in the mitochondria of the cells so don't forget that so all of stage two is in the mitochondria and this part the last part deals with the electron transport chain so nadh transfers electrons and protons and it transfers the electrons to the electron transport chain this is a series of molecules and the electrons pass from molecule to molecule over this chain and as they do they release energy and some of this energy is used to make atp some of it's lost as heat also at the end of this process the now low energy electrons combine with protons and oxygen to form water really important don't forget that nadh once it transfers the electrons and protons reverts to nad plus so now if you are comfortable with the topic and you know all about stage one pause the video and see if you can answer these exam questions after this then move on to stage two these are sometimes more tricky but they're really straightforward pause the video and see if you can answer these questions so once you've done that you should know most of what happens in aerobic respiration so the best way to practice is to do exam papers and to use your textbook