Which of the following polysaccharides are digestible?

Question

BlackTom AI · Accepted Answer

We start by parsing the question: Which of the following polysaccharides are digestible?

Option 1: Pectin. Pectin is a complex carbohydrate found in plant cell walls that humans generally cannot digest due to lack of enzymes to break its galacturonic acid-rich backbone. It mostly passes through the gastrointestinal tract as fiber and is fermented slowly by gut bacteria, not digested into simple sugars that are absorbed.

Option 2: Hemicellulose. Hemicellulose is another component of plant cell walls. It has a heterogeneous, branched structure and is largely resistant to human amylolytic enzymes. While some parts may be partially fermented by the microbiota, it is not digestible into absorbable monosaccharides in the human small intestine.

Option 3: Cellulose. Cellulose consists of long chains of β-1,4-linked glucose units. Humans lack the enzyme cellulase to cleave these β-1,4 bonds, so cellulose is not digestible and is considered dietary fiber that passes through the gut largely intact.

Option 4: Amylopectin. Amylopectin is a highly branched polymer of α-1,4- and α-1,6-linked glucose found in starch. Humans possess digestive enzymes (amylase, isomylase, and disaccharidases) that can hydrolyze these linkages, breaking amylopectin down into maltose, maltotriose, and glucose for absorption. Therefore, it is digestible.

Summarizing the contrasts: the digestible option is the starch-derived component that humans can enzymatically cleave to absorbable sugars, whereas the other listed polysaccharides are largely resistant to human digestive enzymes and are classified as dietary fiber. Each of the first three options—pectin, hemicellulose, and cellulose—lacks the necessary enzymes for complete digestion in the human small intestine, which is why they are not considered digestible in the same sense as amylopectin.

Which of the following polysaccharides are digestible?单项选择题

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