| Date | May 2011 | Marks available | 2 | Reference code | 11M.3.SL.TZ2.11 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Outline | Question number | 11 | Adapted from | N/A |
Question
Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere.
Markscheme
(prokaryotes) used hydrogen from water in synthesis and released oxygen;
(prokaryotes) produced oxygen during photosynthesis;
atmosphere changed from a reducing atmosphere to an oxidizing atmosphere;
current life forms depend upon an oxygen-rich atmosphere;
Examiners report
D2 (b) presented a problem for many candidates who could not outline the contribution of prokaryotes to an oxygen rich atmosphere.
