Monosaccharides, cellulose, starch, and lactose are all carbohydrates, but they belong to different categories within the carbohydrate classification.

1. Monosaccharides:

   • Monosaccharides are the simplest carbohydrates and cannot be further hydrolyzed into smaller sugars.
   • They consist of a single sugar unit and have a general formula of (CH2O)n, where “n” is typically between 3 and 7.
   • Monosaccharides are classified based on the number of carbon atoms they contain:
     • Trioses: Monosaccharides with three carbon atoms (e.g., glyceraldehyde).
     • Pentoses: Monosaccharides with five carbon atoms (e.g., ribose, deoxyribose).
     • Hexoses: Monosaccharides with six carbon atoms (e.g., glucose, fructose, galactose).

2. Cellulose:

   • Cellulose is a complex carbohydrate and a type of polysaccharide.
   • It is made up of repeating units of glucose monosaccharides linked together through β-1,4-glycosidic bonds.
   • Cellulose is classified as a structural polysaccharide and is a major component of plant cell walls.

3. Starch:

   • Starch is another complex carbohydrate and a type of polysaccharide.
   • It is composed of repeating glucose units linked together through α-1,4-glycosidic bonds.
   • Starch serves as a storage polysaccharide in plants, storing excess glucose as an energy reserve.
   • It can be further divided into two forms: amylose (unbranched) and amylopectin (branched).

4. Lactose:

   • Lactose is a disaccharide, which means it consists of two monosaccharide units linked together.
   • It is composed of one glucose molecule and one galactose molecule linked by a β-1,4-glycosidic bond.
   • Lactose is primarily found in milk and serves as a source of energy for infants.