Fructose and glucose are simple sugars, monosaccharides, with the general formula C6H12O6.
Fructose, or fruit sugar, occurs naturally in fruits, some root vegetables, cane sugar and honey and is the sweetest of the sugars.
Glucose, dextrose or grape sugar, occurs naturally in fruits and plant juices and is the primary product of photosynthesis. Most ingested carbohydrates are converted into glucose during digestion and it is the form of sugar that is transported around the bodies of animals in the bloodstream.
Sucrose is a compound sugar, disaccharide, with the general formula C12H22O11. Sucrose is found in the stems of sugarcane and roots of sugar beet. It also occurs naturally alongside fructose and glucose in other plants, in particular fruits and some roots (carrots). A molecule of sucrose is formed by the combination of a molecule of glucose with a molecule of fructose, and it is split into these parts during digestion.
The different proportions of sugars found in plant foods determines their sweetness.