Cellular Respiration in Yeast
Background
Yeast are tiny single-celled fungi. The organisms in Kingdom Fungi are not capable of making
their own food. Fungi, like any other organism, need food for energy. They rely on
...
Cellular Respiration in Yeast
Background
Yeast are tiny single-celled fungi. The organisms in Kingdom Fungi are not capable of making
their own food. Fungi, like any other organism, need food for energy. They rely on sugar
found in their environment to provide them with this energy so that they can grow and
reproduce.
Yeast, like bacteria, grow in or on their food source. They produce and release digestive
proteins (enzymes) into their environment where the sugar molecules are found. Sugar
molecules then break down into smaller molecules that can be absorbed by the yeast and
used for food (energy).
Yeast is a facultative anaerobe, meaning that it can participate in aerobic respiration when
possible, but when it is not, it respires anaerobically. When using yeast in making dough, the
yeast will use the initial oxygen up very quickly, and then start to undergo anaerobic
respiration.
The final equation for cellular respiration plus alcoholic fermentation is
C6H12O6 = 2CH3CH2OH + 2CO2 + 2 ATP
For the yeast cell, this chemical reaction is necessary to produce the energy for life. The
alcohol and carbon dioxide are waste products produced by the yeast. It is these waste
products that we take advantage of. CO2 creates gas bubbles causing bread to rise.
Gluten is a wheat protein that allows bread to stretch when rising. The heat from baking kills
the yeast and also evaporates the alcohol.
1. Are yeast autotrophs or heterotrophs? Identify which one and explain why.
Heterotroph because they cannot make their own energy.
2. Most recipes for bread have you add a small amount of sugar to the mixture. What
purpose does the sugar serve?
The sugar provides energy for the yeast to help it rise
3. What are the two products (other than energy) that are produced by yeast
undergoing alcoholic fermentation?
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