| Date | May 2011 | Marks available | 1 | Reference code | 11M.3.sl.TZ1.B1 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | B1 | Adapted from | N/A |
Question
Starch and cellulose are polysaccharides found in plants.
Compare the structural features of starch and cellulose.
Humans can digest starch but cannot digest cellulose. Explain why humans cannot digest cellulose.
Markscheme
both are polymers of glucose;
starch has \(\alpha \)-1,4 (and \(\alpha \)-1,6) linkages / bonds / \(\alpha \) glucose;
cellulose has \(\beta \)-1,4 linkages / bonds / \(\beta \) glucose;
absence of cellulase enzyme (in humans);
Examiners report
Very few candidates seemed familiar with the structures of the required polysaccharides and whilst most knew that cellulose could not be digested because humans lack the required enzyme, far fewer could name this enzyme.
Very few candidates seemed familiar with the structures of the required polysaccharides and whilst most knew that cellulose could not be digested because humans lack the required enzyme, far fewer could name this enzyme.
