Using a redox indicator
A redox indicator can be used to investigate factors that alter respiration in yeast. Its colour changes when its oxidation state changes.
DCPIP and methylene blue are suitable indicators in this investigation.
| State of DCPIP or methylene blue | Appearance |
|---|---|
| Oxidised | Blue |
| Reduced | Colourless |
Respiration repeatedly involves oxidation and reduction. NAD becomes reduced during glycolysis, while both NAD and FAD are reduced in the Krebs cycle. When the indicator is present, the dye can become the substance being reduced rather than NAD or FAD, causing its colour to change.
A higher respiration rate means hydrogen is released more rapidly, so the redox indicator is reduced more quickly and loses its blue colour sooner.
faster respiration → faster indicator reduction → shorter time to colour loss