Final answer:
In the described assay, glucose concentration is directly proportional to optical density as the enzymatic reaction produces a color change whose intensity correlates with glucose levels.
Step-by-step explanation:
The concentration of glucose using the described assay is directly proportional to optical density. In the enzymatic method, the enzyme glucose oxidase reacts with glucose to produce gluconic acid and hydrogen peroxide. The hydrogen peroxide then reacts with a chromogenic substance to develop a color whose intensity can be measured. This intensity is directly proportional to the glucose concentration in the blood sample. In other words, as the amount of glucose increases, the color's intensity deepens, which corresponds to a higher optical density reading.