Which type of carbohydrate is not made up of saccharide units?

The correct choice is lignin because it is not classified as a carbohydrate and does not consist of saccharide units. Lignin is a complex organic polymer found in the cell walls of plants, particularly in woody plants. It provides structural support, helping to strengthen the cell walls and make them more rigid, which is a different function compared to carbohydrates.

In contrast, oligosaccharides, disaccharides, and starch are all types of carbohydrates composed of various numbers of saccharide units. Oligosaccharides are made up of 2 to 10 monosaccharides, disaccharides consist of two monosaccharides, and starch is a polysaccharide made up of numerous glucose units linked together. Therefore, lignin stands out as the correct answer since it is fundamentally different from the other options in terms of both structure and function within plants.