Respiration

• Glycolysis: Cytoplasm


  1. Glucose is phosphorylated to glucose phosphate by (2x) ATP

  2. Glucose phosphate splits into 2x triose phosphate (TP)

  3. (2x) TP is oxidised to (2x) pyruvate

  • Net gain of (2x) reduced NAD & (2x) ATP per glucose
• Glycolysis


  The first stage of anaerobic & aerobic respiration, occurs in the cytoplasm, is an anaerobic process
• Aerobic respiration


  1. Glycolysis

  2. Link reaction: Oxidation of pyruvate to acetate, producing NADH

  3. Krebs cycle

  4. Oxidative Phosphorylation via ETC
• Link Reaction: Mitochondrial matrix

  • Oxidation of pyruvate to acetate - produces NADH
  • Acetate combines with coenzyme A (CoA), producing acetyl coenzyme A

  Acetyl coenzyme A reacts with a 4-C compound, releasing CoA & producing a 6-C compound that enters the Krebs cycle.
• Anaerobic respiration


  1. Only glycolysis continues

  2. Pyruvate is converted to ethanol or lactate using reduced NAD
• If respiration is aerobic

  Pyruvate from glycolysis enters the mitochondrial matrix by active transport
• Krebs Cycle: Mitochondrial Matrix

  Series of redox reactions produces:

  • ATP by substrate-level phosphorylation
  • Reduced coenzymes (NADH)
  • CO2 is lost
• Oxidative Phosphorylation via ETC: Inner membrane of cristae

  NADH (Krebs cycle) split into H & NAD; H split into a proton & an e-:

  • e- passed through ETC down energy gradient, releasing energy;
  • Energy used to actively pump H+ against their conc gradient into inter membrane space. Creates an electrochemical gradient & causes H+ to diffuse back into mitochondria via ATPase
  • Energy from this is used to phosphorylate ADP (& Pi) to ATP - catalysed by ATP synthase

  Oxygen acts as the final electron acceptor - H2O byproduct
• ETC: Oxygen

  Acts as the final electron acceptor; The leftover proton, combines with oxygen & electron to produce water
• Respiratory substrates


  Breakdown products of lipids (glycerol & fatty acids) & amino acids, which enter Krebs cycle
• The benefit of an ETC rather than a single reaction is that energy is released gradually + less energy is released as heat
• Lipids as respiratory substrate

  1. Lipid → glycerol + fatty acids

  2. Phosphorylation of glycerol -› TP for glycolysis

  3. Fatty acid -> acetate; acetate enters link reaction

  4. H atoms produced for oxidative phosphorylation
• Anaerobic respiration in animals


  1. Only glycolysis continues

  2. Reduced NAD + pyruvate → oxidised NAD (for further glycolysis) + lactate
• Anaerobic respiration in some microorganisms e.g. yeast & some plant cells


  1. Only glycolysis continues

  2. Pyruvate is decarboxylated to form ethanal

  3. Ethanal is reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis
• Advantage of producing ethanol/ lactate during anaerobic respiration

  It converts reduced NAD back into NAD so glycolysis can continue
• Disadvantage of producing ethanol during anaerobic respiration


  Cells die when ethanol concentration is over 12%; Ethanol dissolves cell membranes
• Disadvantage of producing lactate during anaerobic respiration

  Acidic, so decreases pH; Results in muscle fatigue
• Similarities between aerobic & anaerobic respiration

  • Both involve glycolysis; Both require NAD; Both produce ATP
• Difference between aerobic & anaerobic respiration

  Aerobic produces ATP by substrate-level phosphorylation & oxidative phosphorylation, & produces much more ATP. Anaerobic produces ATP by substrate-level phosphorylation only, produces fewer ATP & produces ethanol or lactate.
• Investigating the effect of a named variable on the rate of respiration of a single-celled organism

  1. Use a respirometer (pressure changes in the boiling tube cause a drop of coloured liquid to move)

  2. Use a dye as the terminal electron acceptor for the ETC

  3. Rate of respiration using a respirometer = V of 0 produced or CO, consumed/ time x mass of sample

  4. Volume = distance moved by coloured drop x (0.5 x capillary tube diameter)2 × m