The micrograph shows the structure of a testis undergoing spermatogenesis.

What is the structure labelled X?

A. Sperm
B. Sertoli cell
C. Leydig cell
D. Germinal epithelium cell

B

This attracted the most comments from teachers, with many saying that the quality of the micrograph was poor and that the Sertoli cell did not show clearly. The examining team reevaluated the micrograph, because the statistics for this question were very unusual, but it was decided that the Sertoli cell showed about as clearly as it they ever do. The cytoplasm does not usually stain densely so can appear as a gap between other cells rather than a strong feature itself. The possible answers to the question allowed candidates to identify the cell by eliminating the incorrect answers. The cell was clearly not a sperm or a Leydig cell, so two answers could easily be eliminated. The remaining answers were Sertoli cell and germinal epithelium. Although more candidates chose the former, large numbers of candidates decided that the cell was a germinal epithelium cell. This is not possible, because the cell is about half way through the wall of the seminiferous tubule, not in its outer layer of cells.  
Many of the stronger candidates thought that the cell was in the germinal epithelium and there was therefore a negative discrimination index. On average, weaker candidates answered the question slightly better than strong candidates. This is an area of the programme that should be emphasized more by teachers to ensure that candidates' knowledge is better. Perhaps as it comes at the end of the AHL it is sometimes neglected.