What key factor makes starch easier to convert into ethanol than cellulose?

Starch is easier to convert into ethanol compared to cellulose primarily due to its simple sugar structure. Starch is made up of glucose units linked together by alpha-glycosidic bonds, making it more amenable to enzymatic breakdown. The enzymes used in the conversion process, such as amylases, are well-suited for these alpha bonds, allowing starch to be hydrolyzed efficiently into fermentable sugars.

In contrast, cellulose consists of glucose units linked by beta-glycosidic bonds, which are much tougher to break down. The enzymes required to convert cellulose into sugars, such as cellulases, are less efficient and require harsher conditions or additional treatments. This complexity in structure and the associated challenges in enzyme interactions mean that converting cellulose to ethanol is generally less efficient compared to using starch.

The other factors listed, such as commercial availability or moisture content, while they may influence practical applications, do not fundamentally alter the biochemical processes that govern the conversion of these carbohydrates into ethanol. Higher enzyme activity might aid in the conversion process but is not the primary reason that starch is more easily converted than cellulose. Thus, the structural simplicity of starch makes it the more favorable substrate for ethanol production.