The Pasteur Effect

In 1861 Louis Pasteur observed that yeast, a facultative anaerobe, could grow in a sugar and protein broth without air, i.e. Oxygen. For every gram of yeast in a culture, 60-80 grams of sugar disappeared from the broth. When the yeasts are cultured with air 4-10 grams of sugar are consumed for every gram of yeast added to the culture. When the yeasts were cultured only on protein broth, only yeast culture with air grew. Below is a table that summarizes the conditions that allowed the yeast to grow.

1 g of yeastWithout oxygen60-80 g sugar
1 g of yeastWith oxygen4-10 g of sugar
1 g of yeastWith oxygenProtein broth, no sugar
  • How does this data demonstrate yeast are facultative anaerobes?
  • Is the ratio of sugar required without oxygen compared to the sugar required with oxygen like the ratio of ATP produced with fermentation and with aerobic respiration?
  • How did the yeast without sugar grow?
  • Why did the yeast with only protein in the broth require oxygen to grow?
  • Explain the Pasteur Effect.

Expert Answer

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