Cellulose is a polymer made up of glucose monomers. A polymer is a large molecule composed of repeating subunits called monomers. In the case of cellulose, these monomers are glucose molecules.

Option 1, fructose, is not correct because fructose is a different type of sugar and is not used to make cellulose.

Option 2, galactose, is also not correct. Galactose is another type of sugar that is not involved in the formation of cellulose.

Option 4, sucrose, is a disaccharide made up of glucose and fructose molecules. While glucose is a component of cellulose, sucrose as a whole is not involved in its formation.

Therefore, the correct answer is option 3, glucose. Glucose molecules are linked together through chemical bonds to form cellulose, which serves as a structural component in the cell walls of plants.