| Date | May 2015 | Marks available | 1 | Reference code | 15M.1.SL.TZ1.4 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 1 |
| Command term | Label | Question number | 4 | Adapted from | N/A |
Question
What is the structure labeled X in the electron micrograph of a rat liver cell?
[Source: “0315 Mitochondrion new” by OpenStax College - Anatomy & Physiology, Connexions Web site.
http://cnx.org/content/col11496/1.6/, Jun 19, 2013.. Licensed under CC BY 3.0 via Wikimedia Commons -
https://commons.wikimedia.org/wiki/File:0315_Mitochondrion_new.jpg#/media/File:0315_Mitochondrion_new.jpg]
A. Ribosome
B. Lysosome
C. Mitochondrion
D. Nucleus
Markscheme
C
Examiners report
There were comments from some teachers about the electron micrograph used in this question. The mitochondrion that candidates had to identify has a sigmoid shape rather than the classic ovoid shape of a textbook diagram, but the internal structure is clearly the same as ovoid mitochondria elsewhere in the micrograph and cristae are visible, so there should not have been any confusion. Students should be able to recognise mitochondria in micrographs from the densely stained matrix and the invaginated inner membrane. The statistics show that some of the stronger candidates misidentified this organelle as a lysosome, but there are other single-membraned structures visible in micrograph that are more densely stained and nearly circular in outline and these are the lysosomes.
