# Question #298ac

Using yeast to make bread dough rise.

#### Explanation:

During the process of respiration, organisms such as yeast break down molecules of sugar to make ATP. Wastes produced by respiration include carbon dioxide and water.

Yeast are capable of...

1. alcohol fermentation, which does not depend on the presence of oxygen.

$S u g a r \to e t h a n o l + C {O}_{2}$

1. aerobic respiration, which does depend on the presence of oxygen

$S u g a r + {O}_{2} \to C {O}_{2} + {H}_{2} O$

Yeast evolved the ability to produce alcohol as a means to kill off other microbes with whom the yeast compete for food.

The yeast produce alcohol. The rising alcohol levels kill off their competition, and then the yeast can later "digest" the alcohol to produce the ATP they need for life processes.

This video shows an experiment conducted to determine the effect of altering the temperature on the rate of respiration in yeast.

Hope this helps!