So we essentially have the beta D glucose molecule in its cyclic form. Now, even though the cyclic form is more stable and it's going to predominate at equilibrium, we're still going to form a very tiny amount with less than 1% of the open chain of this deglucose molecule. And in the open chain we see that we have the aldehyde. Now, what's the big deal about the aldehyde group? Well, from organic chemistry we know that when an aldehyde group is in the presence of some type of oxidizing agent, for example a copper ion with a charge of positive two, that will basically undergo an oxidation reduction reaction. So this will basically act as the reducing agent and the C two, the oxidizing agent, while that will act as the oxidizing agent and what we'll have is, will form a carboxylic acid.