Question 19M.2.SL.TZ1.4c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ1.4c |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | c | Adapted from | N/A |
Outline how the structure of cellulose makes it suitable as a component of cell walls.
[2]
a. chains of glucose/1-4 glycosidic linkages/covalent bonding between glucose ✔
b. beta glucose so alternating orientation of glucose units
OR
beta glucose forms straight chains ✔
c. forms microfibrils/long and thin/thin fibres/parallel bundles of cellulose molecules
OR
hydrogen bonding/cross linkage between cellulose molecules holds them together ✔
d. high tensile strength/rigid/doesn’t stretch so provides support/allows turgidity ✔
Many candidates found this question the hardest in Section A. There were a few knowledgeable accounts that easily scored the two marks, but far more revealed little or no understanding of the structure of cellulose. It might be thought to be an obscure topic, but cellulose may be the most abundant biochemical on Earth. It is the key to how plants support themselves and grow. The paper that candidates wrote their answers on was mostly cellulose and nearly all candidates will have been wearing clothes composed largely of it. One misunderstanding that was often evident was that cellulose is freely permeable. The cell wall as a whole has this property, but it is due to the gaps between cellulose microfibrils, not to the cellulose itself. Another common mistake was to state that cellulose is made of starch, so contrasts between these two polysaccharides should be emphasised more widely.
