(saccharide) A polyhydroxy aldehyde or ketone or a derivative of such a compound. Many carbohydrates have the structural formula (CH2
0)n, which suggests that they were originally hydrates of carbon. The simplest carbohydrates are the *monosaccharides
or simple sugars. They are single polyhydroxy aldehyde (see aldose
) or ketone (see ketose
) units, most commonly containing five or six carbons. *Oligosaccharides
are more complex carbohydrates containing between two and ten monosaccharide units. *Polysaccharides contain many monosaccharide units in long linear or branched chains. They function as energy storage molecules and as structural elements in the plant body.