Which carbohydrate is the building block of starch and cellulose?

The correct answer is glucose because it is the fundamental monosaccharide from which both starch and cellulose are synthesized. In plants, glucose is produced through photosynthesis and serves as a primary energy source.

In the case of starch, which is a polysaccharide, glucose units are linked together by α-1,4 glycosidic bonds, forming long chains or branched structures that store energy in plants. On the other hand, cellulose, a structural component of plant cell walls, is composed of glucose units linked by β-1,4 glycosidic bonds, which results in a straight-chain configuration that allows for strong hydrogen bonding between the chains, providing rigidity to plant cells.

Both starch and cellulose are polymers of glucose, underscoring the significance of glucose as a key building block in plant biology. The other choices—sucrose, fructose, and lactose—are not polymers comprised solely of glucose; instead, they are disaccharides or combinations of different monosaccharides.