| Date | May 2015 | Marks available | 1 | Reference code | 15M.2.SL.TZ2.4 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Define | Question number | 4 | Adapted from | N/A |
Question
Define pathogen.
Explain antibody production.
Explain why antibiotics are effective against bacterial diseases but not against viral diseases.
Markscheme
Organism (or virus) that causes a disease.
a. many types of lymphocytes (B and T) exist;
b. produced/ stored in the lymph nodes;
c. each type recognizes one specific antigen/pathogen;
d. each type responds by dividing to form a clone;
e. (a clone) (B) lymphocyte secretes (specific) antibody against the antigen;
f. antibodies are produced as part of a specific immune response;
g. some reference to plasma/memory cells;
a. antibiotics block metabolic pathways of bacteria / reference to a specific pathway;
b. viruses have no metabolic pathways / viruses reproduce using the host cell’s metabolic pathways;
c. (host cell’s) metabolic pathways are not affected by antibiotics / (antibiotics) do not affect host cells because they are metabolically different from bacteria;
Examiners report
A disturbing number could not give a definition for pathogen in part a. (6.3.1).
In b, some teachers seem to have over-taught antibody production including the HL components, with the result that the students were giving very confused answers and missing out the basics. There were a few G2 comments that the command term for part b should have been "describe" rather than explain.
The reasons why antibiotics are effective against bacteria and not viruses was quite well understood, by those students who had covered it.
