Question

Compare and contrast Anaerobic Respiration versus Fermentation. Explain the (1) electron transport system and how many ATP are produced, (2) where the electrons go (the final electron acceptor), and (3) give an example of an organism that carries out anaerobic respiration and an example of an organism that uses fermentation

Answer 1

Fermentation, say by yeast is the incomplete oxidation of glucose under anaerobic conditions where Pyruvic acid is converted to CO2 and ethanol which is catalaysed by pyruvic acid decarboxylase and alcohol dehydrogenase.Other organisms like some bacteria produce lactic acid with the help of lactate dehydrogenase.CO2 is released.It requires a small amount of oxygen.It is an extracellular process.Glycolysis doesn't follow citric acid cycle and ETC.

Anaerobic respiration is an intracellular process occuring in the absence of oxygen.CO2 is not released.It starts with breakdown of glucose as in Fermentation,but does not produce ethanol and CO2. Glycolysis follows citric acid cycle and ETC.

1.The metabolic pathway through which an electron passes from one carrier to another finally leading to the synthesis of ATP is called Electron transport system.It is present in the inner mitochondrial membrane.Electrons from NADH and FADH2 produced in the mitochondrial matrix during citric acid cycle are transported along the ETC containing Complexes I to V.

Complex I is NADH dehydrogenase,Complex II is Succinic dehydrogenase,Complex III is Cytochrome bc1 complex,Complex IV is Cytochrome C oxidase and Complex V is ATP synthase.

The electrons from NADH and FADH2 are transported via these Complexes in the ETC and are coupled to ATP synthesis.

ATP produced through ETC :

In glycolysis 4 ATP are produced from NADH via ETC.

In Oxidative decarboxylation of pyruvic acid 6 ATP are produced from NADH

In Krebs cycle 18 ATP are produced from NADH and 4 ATP are produced from FADH2.

The total ATP generated via ETC is 32 ATP.

2.The final electron acceptor in the ETC is oxygen.The role of oxygen is limited to terminal stage of the process.It drives the whole process by removing hydrogen from the system.In the final step Oxygen is converted to H2O.

3.Anaerobic respiration occurs in certain species of bacteria and Archaea. Ex: Clostridium,E coli.

Fermentation occurs in yeast,Aspergillus, Saccharomyces sps.