A Level Biology Practice Exam

What type of glucose has its functional group above the plane of the ring?

1. Beta-glucose

2. Gamma-glucose

3. Alpha-glucose

4. Epsilon-glucose

The correct answer is: Alpha-glucose

The correct answer is beta-glucose. In the context of glucose, the structure includes a ring form where the hydroxyl (–OH) functional group on the first carbon can either be positioned above or below the plane of the ring. For beta-glucose, the hydroxyl group on the first carbon is above the plane, which is significant in defining its properties and reactivity compared to alpha-glucose. In alpha-glucose, this hydroxyl group is below the plane of the ring. Gamma-glucose and epsilon-glucose are not standard terms in the context of the common six-carbon sugars and don't correspond to specific ring structures that are characterized by the positioning of the hydroxyl group in the same manner. The distinction between alpha and beta forms is critical, especially in biochemistry, as it affects how glucose molecules interact with each other and form larger structures like starch and cellulose. The orientation of the functional groups influences properties such as solubility, reactivity, and how organisms metabolize these sugars.