Variables, along with the hypothesis, help the design and construction of the experiment. They include the independent variable, the dependent variable, the controlled variables, and the standard of comparison.

The independent variable is what we control and change in our experiment. It is what we test in order to derive results. In our project specifically, we had two independent variables. The first consisted of the type of algae we grew, and the second the type of sugar we used for fermentation. The algae types we tested were green algae (Nannochloropsis oculata), red algae (Porphyridium cruentum), and brown algae (Isochrysis galbana). Because we were testing for ethanol content through heterotrophic fermentation (fermentation under low oxygen and sunlight levels), we tested growing these different algae types on three different sugars for food. These sugars included fructose (monosaccharide), sucrose (disaccharide), and glucose (monosaccharide).

A control group, or standard of comparison, allows for a benchmark measurement which can be compared to the measurements of the actual experimentation. We did indeed have a control group which was the ethanol production of algae with no sugars added for fermentation. For the green, red, and brown algae, we made up a separate solution of the nutrient salts and algae bloom starter to create a generic growth serum. We then monitored this algae group for the same amounts of time as the fermenting algae and used it as a standard of comparison. By finding whether or not the ethanol measurements by mass are different in each solution than that of the standard serum, we can see the benefits or negatives of using heterotrophic fermentation with the three different sugars sucrose, glucose, and fructose.