| Date | November 2012 | Marks available | 3 | Reference code | 12N.3.SL.TZ0.12 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Discuss | Question number | 12 | Adapted from | N/A |
Question
Discuss the endosymbiotic theory for the origin of eukaryotes.
Markscheme
(both) mitochondria and chloroplasts have evolved from independent prokaryotic cells;
endocytosis originally led to symbiotic relationship;
(mitochondria and chloroplasts) grow and divide like cells;
naked loop of DNA, like prokaryotes;
have 70S ribosomes, like prokaryotes;
have double membranes as would expect when taken in by endocytosis;
Examiners report
The general idea of the endosymbiotic theory for the origin of eukaryotes was understood by many for part (b) but few described this well; candidates were still able to gain 2 of the 3 marks.
