HL 1 Biology

8.1a Aerobic Respiration

<<Mitochondrion Structure>>


  • in almost all cytoplasms of eukaryotic cells
  • discovered by Carl Benda (at end of 19th century) using light microscope
  • structure details observed through electron microscopes
    • Outer and inner membrane; Double membrane
    • Intermembrane Space: space between inner and outer membranes
    • Matrix: the large space inside inner membrane
    • Enzymes
    • Ribosomes
    • one/more small loops of naked DNA
    • Cristae: inner mitochondrial membrane has folds/invaginations

<<Oxidative Phosphorylation>>

Oxidative phosphorylation

  • final part of aerobic respiration (ADP phosphorylated to produce ATP, using energy released by oxidation)
  • NADH + H+ : main substance oxidised
  • energy released by small steps, performed by a chain of electron carriers (because more energy can be trapped in ATP
  • Chemiosmosis: the coupling of ATP synthesis to electron transport via a concentration gradient of protons; chemical substance (H+) moves across membrane, down concentration gradient; releases energy needed for enzyme ATP synthase to make ATP


  1. NADH + H+ gives hydrogen atom pairs o first carrier in the chain, with NAD+ returning to matrix
  2. Hydrogen atoms split and release 2 electron, pass from carrier to carrier in chain
  3. Energy released as electron pass from carrier to carrier & 3 of them use energy to transfer protons (H+) across inner mitochondrial membrane (from matrix to intermembrane space)
  4. Concentration gradient of protons build up, with more protons moving across inner mitochondrial membrane; proton gradient: store of potential energy
  5. electrons must be transferred to terminal electron acceptor at the end of the chain, to allow electrons to continue to flow (Aerobic respiration: its oxygen which becomes O-2 yet combines two H_ ions from matrix to become water)
  6. With ATP synthase, protons pass back rom intermembrane space to matrix; the energy released as protons move down the concentration gradient is used by ATP synthase to phosphorylate ADP.


Oxygen consumption by mitochondria (p. 97)

1) Oxygen consumption by the  mitochondria could not begin unless pyruvate had been added because pyruvate is the substrate for the aerobic respiration, thus it is the one that could start the function of the enzymes. Without oxygen, the pyruvate cannot break down in the link reaction. Also, the reduced molecules produced from the pyruvate breakdown is essential during oxygen consumption in the process of oxidative phosphorylation.

2) Oxygen consumption was prevented due to the fact that ADP is a raw material for the process of the Krebs cycle, and is needed to be added for the Krebs cycle to function. Without ADP, it would mean the Krebs cycle would not occur and no electron transport chain would be present. And thus without the electron transport chain, oxygen consumption would be prevented.

3) If the ADP had not been added at point III, the oxygen level would have stayed constant instead of declining any lower. As mentioned previously, without the ADP added, no Krebs cycle would occur and thus no electron transport would occur as well.

4) After ADP was added at point IV, the oxygen consumption may not have resumed because the Krebs cycle stopped occurring as all the pyruvate have been used up. Due to the stop in the Krebs cycle, there will no longer be any oxygen consumption in the electron transport chain. Therefore, the ADP is no longer enough to resume the oxygen consumption as it is not rate limiting any more.

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