Question

6. A student reads that both plants and animals use carbohydrates, but for different reasons. He learns that plants make cellulose for structure and starch for energy storage, while animals store carbohydrates as glycogen. During lunch, his class discusses how carbohydrates from food enter the body. They recall that large carbohydrates like starch and cellulose are too big to pass directly into the bloodstream.

Which of the following statements accurately describe how carbohydrates from food are processed and used by the body? (Select all that apply.):

Responses

A. Large carbohydrates must be broken down into smaller sugar molecules to be absorbed.
A. Large carbohydrates must be broken down into smaller sugar molecules to be absorbed.

B. The small intestine absorbs simple sugars like glucose into the bloodstream.
B. The small intestine absorbs simple sugars like glucose into the bloodstream.

C. Humans can digest cellulose because it is made of glucose molecules.
C. Humans can digest cellulose because it is made of glucose molecules.

D. Enzymes in the digestive system store carbohydrates in the liver before they are broken down.
D. Enzymes in the digestive system store carbohydrates in the liver before they are broken down.

E. Undigested carbohydrates like cellulose are eliminated from the body as part of waste.

Answer 1

Correct answers: A, B, E.

- A — True. Large polysaccharides must be enzymatically broken down into smaller sugars (disaccharides/monosaccharides) before absorption.
- B — True. The small intestine absorbs simple sugars (mainly glucose, fructose, galactose) into the bloodstream.
- C — False. Cellulose is made of glucose but has beta-1,4 linkages that human enzymes (cellulases) cannot break, so humans cannot digest it.
- D — False. Digestive enzymes do not store carbohydrates in the liver. After monosaccharides are absorbed, the liver can convert excess glucose into glycogen for storage.
- E — True. Undigested carbohydrates (dietary fiber such as cellulose) largely pass through the gut and are eliminated, though some fiber is partially fermented by gut bacteria.