Homogalacturonan is a polysaccharide present in plant cell walls. The diagram illustrates a molecule of the monomer that joins together to make homogalacturonan. A student examined the structure of this monomer and compared it with the structure of the monomer used to make cellulose. Which carbon atoms in the monomer shown in the diagram have hydroxyl groups in positions that differ from those in the cellulose monomer?
- Acarbon one and carbon four
- Bcarbon one only
- Ccarbon three and carbon four
- Dcarbon three only