Final answer:
Cellulose is a complex carbohydrate composed of a long straight chain of glucose molecules. It serves as a structural component in plants, forming their cell walls. Chitin is another complex carbohydrate with a complex arrangement of chitin molecules, serving as a structural component in fungi and insects.
Step-by-step explanation:
Cellulose is considered a complex carbohydrate because it is composed of a long straight chain of glucose molecules. Polysaccharides like cellulose are made up of multiple monosaccharide molecules and serve as structural components in living organisms, such as forming the cell walls of plants. While cellulose is made up of glucose molecules, chitin is a complex carbohydrate that is composed of a complex arrangement of chitin molecules, which make up the cell walls of fungi and the exoskeletons of insects.