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Question: List three key differences between starch and cellulose and explain their implications for the biological roles they play in plants and their digestibility by humans. Answer: Three key differences between starch and cellulose are: 1. Glucose linkage - Starch has α(1→4) glycosidic linkages, while cellulose has β(1→4) glycosidic linkages. This difference in linkages influences their shape, properties, and digestibility. 2. Structure - Starch can be linear or branched (amylose or amylopectin), while cellulose is linear. The linear and rigid structure of cellulose makes it an essential component for plant cell walls, whereas the structure of starch allows it to serve as an energy storage molecule. 3. Digestibility - Humans can digest starch due to the presence of enzymes that break down α(1→4) linkages but cannot digest cellulose, which has β(1→4) linkages. Hence, cellulose acts as dietary fiber in our diet.