Explain ETS. OR Illustrate the mechanism of electron transport system.

1. NADH₂ and FADH₂ produced during glycolysis, connecting link reaction and Krebs cycle are oxidized with the help of various electron carriers and enzymes. 

2. These carriers and enzymes are arranged on inner mitochondrial membrane in the form of various complexes as complex I, II, III, VI and V. 

3. NADH+H⁺ is oxidised by NADH dehydrogenase (complex I) and it’s electrons are transferred to ubiquinone (coenzyme Q-CoQ) present on inner membrane of mitochondria. Reduced ubiquinone is called as ubiqunol. 

4. FADH₂ is oxidised by complex II (Succinate dehydrogenase) and these electrons are also transferred to CoQ. 

5. The open end of the glass tube (delivery tube) is dipped into lime water containing in a test tube (Tube B). 

6. Stoppers of both the tubes are fitted tightly to prevent leakage of gases. First test tube is placed in warm water (37° C-38° C) in a beaker. 

7. Lime water gradually turns milky, indicating the evolution of carbon dioxide from the yeast preparation. 

8. Level of the lime water in the delivery tube does not rise, showing that there is no decline in volume of gas in test tube A and consequently no utilization of oxygen by yeast. Preparation is stored for a day or two. 

9. When we open the stopper of tube A we will notice a smell of alcohol indicating the formation of ethanol. 

10. From this activity it may be inferred that yeast respires anaerobically to ferment glucose to ethanol and carbon dioxide.