Final answer:
Cellulose, pectin, and lignin are types of Carbohydrates, specifically polysaccharides, which are important for plant structure and dietary fiber.
Step-by-step explanation:
Cellulose, pectin, and lignin are types of Carbohydrates. These substances are all polysaccharides, which are a type of carbohydrate consisting of long chains of monosaccharide units bonded together. Cellulose is a primary structural component of plant cell walls, providing rigidity and strength. This polysaccharide is the most abundant organic compound on Earth and is crucial in the diet as dietary fiber, which humans cannot digest. Pectin is also found in plant cell walls and is often used in food as a gelling agent. Lignin, different from cellulose and pectin, adds additional structural support to the cell walls of plants and is not a carbohydrate on its own but is commonly discussed alongside other structural polysaccharides.