Aldoses and ketoses are two types of monosaccharides, which are the simplest carbohydrates. Monosaccharides are made up of a single sugar unit and cannot be broken down into smaller sugars by hydrolysis.

Aldoses are monosaccharides that contain an aldehyde group (-CHO) on the first carbon atom. The most common aldoses are glucose, galactose, and mannose.

Ketoses are monosaccharides that contain a keto group (=O) on the second carbon atom. The most common ketoses are fructose and ribose.

Aldoses and ketoses can be interconverted by isomerization reactions. Isomerization reactions are chemical reactions that convert one isomer of a compound into another isomer. In the case of aldoses and ketoses, isomerization reactions can convert an aldose into a ketose or vice versa.

The type of monosaccharide (aldose or ketose) is determined by the location of the carbonyl group. In aldoses, the carbonyl group is located at the end of the carbon chain, while in ketoses, the carbonyl group is located in the middle of the carbon chain.