Final answer:
Glucose is the monosaccharide that does not exist by itself in food but combines with other sugars to form disaccharides, starch, or dietary fiber.
Step-by-step explanation:
Monosaccharides in Foods
The monosaccharide that does not usually exist in food by itself, but is rather joined to other sugars to form disaccharides, starch, or dietary fiber, is glucose. Glucose is a simple six-carbon sugar that can act as a monomer for complex carbohydrates. In the form of disaccharides, glucose can be bonded to another monosaccharide like fructose to form sucrose, or to another glucose molecule to form maltose. It is also joined together in long chains (polysaccharides), such as in the straight-chain amylose or the branched-chain amylopectin, both of which are forms of starch. In the digestive process, these complex carbohydrates are broken down into their monosaccharide components, which are then readily used by the body for energy.