foreign welcome back to our IB Biology video series this is the second video in IB Biology topic 8 metabolism respiration and photosynthesis where we will be looking at respiration including mitochondria glycolysis the link reaction the Krebs cycle and oxidative phosphorylation before watching this video we recommend completing our topic 2 video series to ensure you have a solid foundation in metabolism and respiration in the final video we introduced respiration as the process by which a cell releases energy in the form of ATP from its organic compounds we discuss the two forms of respiration aerobic and anaerobic including their equations for the IB Biology higher level syllabus you must recall both forms of respiration in far more detail as a summary anaerobic respiration involves just one stage known as glycolysis aerobic respiration begins just like anaerobic with glycolysis however it then has an additional three stages these are the link reaction the Krebs cycle and oxidative phosphorylation this generates 34 more molecules of ATP for every glucose used within each of these stages are many reduction and oxidation reactions covered throughout this video for those of you not studying IB chemistry let's quickly Define what is meant by these reduction reactions involve the gain of electrons whilst oxidation reactions involve the loss of electrons however the movement of electrons is not immediately obvious so we can also Define reduction as either the gain of hydrogen or the loss of oxygen and oxidation reactions as either the loss of hydrogen or gain of oxygen so what are the reactions Within These stages well for you to follow them in detail we must first summarize the structure of a mitochondria mitochondria are organelles within which the three additional stages of aerobic respiration occur they have a unique structure which you must draw and annotate they have a jewel membrane with a narrow intermembrane space facilitating the buildup of a h plus concentration gradient the inner membrane contains the electron transport chain and is folded to form crystali which increase the surface area present for oxidative phosphorylation they contain a matrix like a cytoplasm which contains the enzymes required for the link reaction and Krebs cycle they contain their own DNA and 70s ribosomes to synthesize proteins and enzymes in recent years electron tomography has produced 3D images of this structure deepening our understanding of mitochondrial function whilst you don't need to worry about this for your exam you do need to recognize these structures on electron micrographs for example like this so with that covered let's discuss the stages of respiration starting with glycolysis glycolysis occurs in the cytoplasm and involves the conversion of glucose into two pyruvate molecules it can be considered as four stages glucose is phosphorylated using 2 ATP to form an unstable phosphorylated six carbon molecule this unstable phosphorylated six carbon molecule then split by lysis T form two three carbon phosphorylated molecules each of these then undergoes oxidation transferring one hydrogen to NAD plus which is reduced to form nadh each also undergoes D phosphorylation producing two ATP the resulting molecule formed is named pyruvate therefore two nadh 480p and two pyruvates are formed in total since 280p were required and four were produced we say the net production of glycolysis is 2 ATP one important concept that arises in exams is that for glycolysis to continue there must be adequate supply of NAD Plus for anaerobic respiration the fermentation of pyruvate to h plus and lactate or ethanol regenerates this NAD Plus however in aerobic respiration NAD plus is regenerated during the electron transport chain at this stage anaerobic respiration is complete let's continue the stages of aerobic respiration starting with the link reaction the link reaction occurs in the Matrix of the mitochondria and involves the conversion of each pyruvate into an acetyl molecule it therefore occurs twice for each molecule of glucose before the link reaction can occur each pyru rate must be transported from the cytoplasm to The Matrix this requires one ATP each so a total of two the link reaction can be considered as three stages each pyruvate undergoes oxidation transferring one hydrogen to NAD plus which is reduced to form nadh once again each is also decarboxylated producing one CO2 the resulting two carbon molecule formed is named acetyl so a total of two CO2 2ndh and two acetyl molecules are formed each of the two acetyl molecules combines with its own coenzyme a to form acetyl COA therefore at the end of the link reaction two acetyl-coa molecules are present from a single molecule of glucose these are then passed to the Krebs cycle the Krebs cycle occurs in the same location as the link reaction The Matrix of the mitochondria it involves the conversion of each acetal molecule into a six carbon molecule used for oxidation it therefore occurs twice for each molecule of glucose the Krebs cycle can be considered as six stages first each acetyl-coa releases its acetyl which combines with a four carbon molecule to form a six carbon molecule thus two six carbon molecules are formed in total each six carbon molecule then undergoes oxidation transferring one hydrogen to NAD plus to produce nadh each is also decarboxylated producing one CO2 the result is a five carbon molecule thus 2co2 2ndh and two five carbon molecules are formed in total each five carbon molecule then undergoes oxidation transferring 1H to NAD plus to produce nadh each is also decarboxylated producing one CO2 the result is a full carbon molecule thus two CO2 two nadh and two four carbon molecules are formed in total it is important to note that each five carbon molecule also forms 180p directly in this stage so a total of 280p are also produced each of the four carbon molecules then undergoes oxidation reducing fad to fadh2 each then undergoes oxidation again transferring one H to NAD plus to produce nadh thus between the two cycles two fadh2 and two nadh form this last stage results in the formation of the original four carbon molecule this can then combine with a new acetyl molecule and allow the Krebs cycle to repeat but how does this make ATP well this is the role of oxidative phosphorylation you've now reached the end of the preview for this IB science video if you want to check out the full video head over to our website and select a membership plan today