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Cellular respiration pathway – glycolysis, link reaction, Krebs cycle, electron transport chain and fermentation

BiologyCell BiologyAges 15–16

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Step through glycolysis in the cytoplasm, the link reaction and Krebs cycle in the mitochondrial matrix, and oxidative phosphorylation on the inner membrane, with a running tally of carbon atoms, CO₂, NADH, FADH₂, ATP and O₂ per glucose (about 30–32 ATP). In the live model, remove O₂, add cyanide or the uncoupler DNP, switch stages on and off, or change from muscle to yeast cells, and watch the proton gradient, ATP level, ATP yield per glucose, glucose and O₂ uptake and lactate or ethanol formation; record each run in a results table.

Lesson: Cellular respiration: glycolysis, link reaction, Krebs cycle, electron transport chain and chemiosmosis (oxidative phosphorylation), anaerobic respiration (fermentation)

What it shows

Cellular respiration releases the energy in glucose to make ATP. Glycolysis in the cytoplasm splits glucose into two pyruvate, giving 2 ATP and 2 NADH. In the mitochondrial matrix the link reaction and the Krebs cycle release all six carbons as CO₂ and load NADH and FADH₂. On the inner membrane the electron transport chain uses their electrons to pump H⁺; oxygen is the final electron acceptor, and H⁺ flowing back through ATP synthase makes most of the ATP. Without oxygen, fermentation to lactate or ethanol regenerates NAD⁺ so glycolysis can continue.

How to use

In Step through, press Next step to follow one glucose stage by stage and read the tally table. In Live model, untick O₂ present, tick Add cyanide, raise DNP uncoupler, or untick a stage, then watch the graph and the per-glucose table. Press Record result once the lines level off to compare conditions. Switch Cell to yeast to see alcoholic fermentation.

Parameters you can change

  • View Step through one glucose, Live model
  • Oxygen present
  • Add cyanide (blocks complex IV)
  • DNP uncoupler dose 0–100 %
  • Cell type Animal muscle cell (lactate fermentation), Yeast (alcoholic fermentation)
  • Glycolysis working
  • Link reaction working
  • Krebs cycle working
  • Electron transport chain working

Questions to explore

  1. Why does the Krebs cycle stop without oxygen, even though it does not use oxygen directly?
  2. Cyanide and DNP both reduce ATP production; why does oxygen uptake rise with DNP but stop with cyanide?
  3. Why does a cell use glucose faster when it switches to fermentation?

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