Final answer:
Starch, chitin, and cellulose are all polysaccharides made up of multiple monosaccharides linked together. While starch and cellulose are composed of glucose units, chitin includes a modified form of glucose.
Step-by-step explanation:
Starch, chitin, and cellulose are all similar because they are polysaccharides. These substances are comprised of long chains of monosaccharides linked together through glycosidic bonds. Starch and cellulose consist of glucose units, but cellulose has a linear chain while starch may have branched chains as seen in amylopectin.
On the other hand, chitin is composed of a modified form of glucose and is an important structural polysaccharide in arthropods and fungi.