What functional groups glucose have? Is it an aldehyde or a ketone and why?

glucose, as a solid, has five hydroxyl (OH) groups, and
one aldehyde group (CHO) at the end in a linear structure. However, in the body glucose
is generally found in a ring form as a alcohol. (see link
below)

Aldehydes in general have the structure R-CHO where
R is any carbon containing group attached to the carbon, and their is a double bond
between the carbon and the oxygen.  Ketones are similar but their general structure is
RCOR' , where both R and R' are carbon containing groups, and there is a double bond
between the carbon and the oxygen.