The monomers that help plants build their own sugars are called monosaccharides. Monosaccharides are simple sugars that can be linked together through a process called dehydration synthesis to form more complex sugars, such as disaccharides and polysaccharides.
Plants use monosaccharides like glucose and fructose to build more complex sugars like starch and cellulose, which are used for energy storage and structural support, respectively. Monosaccharides are produced by photosynthesis, in which plants use energy from sunlight to convert carbon dioxide and water into glucose and oxygen. The glucose is then used to build more complex sugars, or it is stored in the plant's cells for later use.