<u>Answer</u>:
1. The purpose of the uninoculated control tubes used in the oxidation fermentation test is to serve as basis of the medium for the color comparison and that it is sterile.
2. It is necessary to use two controls in order to illustrate the no color change (green color) under both aerobic and anaerobic conditions.
3. The purpose of the experiment is to determine if the organisms utilize the carbohydrate and thus is fermentative. This will result in a color change from green to yellow.
Thus, the medium in one tube is sealed with a layer of paraffin to prevent diffusion of oxygen. This tube will show that the medium is unaffected by the lack of oxygen.
The second tube will allow the diffusion of oxygen. This tube will show that the medium does not change color naturally in the presence of oxygen. Thus, the color changes will be caused only by the fermentation process of the organisms.
