Question 21M.2.SL.TZ2.6a
| Date | May 2021 | Marks available | [Maximum mark: 3] | Reference code | 21M.2.SL.TZ2.6a |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | a | Adapted from | N/A |
Outline the structures in M. tuberculosis that are not present in a human cell.
[3]
a. cell wall ✔
b. pili/flagella ✔
c. 70S ribosomes ✔
d. nucleoid / circular DNA
OR
naked DNA ✔
e. plasmids ✔
As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted.
Ignore references to membrane bound organelles.
(attempted by about 60 % of the cohort)
Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.
