Question 20N.2.SL.TZ0.a
| Date | November 2020 | Marks available | [Maximum mark: 3] | Reference code | 20N.2.SL.TZ0.a |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Draw | Question number | a | Adapted from | N/A |
Life is based on carbon compounds.
Draw a molecular diagram of alpha-D-glucose.
[3]
a. hexagonal ring structure with O at one point (between C1 and C5);
b. correct orientation of OH groups (on carbons 1 to 4); Hydrogens not required
c. CH2OH group shown on fifth carbon with correct orientation;
OR
d. 6 carbon chain with oxygen on first C;
e. H and OH groups correctly orientated;
Carbons do not need to be numbered.
Allow boat or chair diagrams.
Allow [2 max] if linear structure drawn.
This was the less favourite option question, generally attempted by the better candidates. In part (a) the candidates tended to gain either 3 for a correct structure or zero. A G2 comment asked whether the different forms of glucose were needed; knowledge of the structure of alpha-glucose is stated in the syllabus.
Most gained some marks for what was really a description of photosynthesis in part (b), and the transformations of carbon compounds in the carbon cycle was quite well known. Some students lost marks by continuing to use the term ‘carbon compounds’ instead of carbon dioxide and the specific compounds. Many went off on a tangent to write about carbon dioxide and climate change etc. Many drew some quite detailed flow charts of the carbon cycle from which some marks could be gleaned or ambiguous statements clarified.
