Question 21M.2.SL.TZ1.c
| Date | May 2021 | Marks available | [Maximum mark: 2] | Reference code | 21M.2.SL.TZ1.c |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of 0μmol. In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.
[Source: Onwuamah CK, Ekama SO, Audu RA, Ezechi OC, Poirier MC, Odeigah PGC (2014) Exposure of Allium cepa Root Cells to Zidovudine or Nevirapine Induces Cytogenotoxic Changes. PLOS ONE 9(3): e90296. https://doi.org/10.1371/journal.pone.0090296 (CC0 1.0 - https://creativecommons.org/publicdomain/zero/1.0/).]
Both ZDV and NVP are believed to have a damaging effect on the process of mitosis but ZDV in particular is believed to block the formation of the spindle.
[Source: Medical Images / Carolina Biological.]
Based on the information, suggest with a reason which of the labelled cell types will become more common in Allium root tips treated with ZDV.
[2]
a. Y (will become more common) ✔
b. spindle not formed yet
OR
cells x and z have spindles ✔
c. cells in Y cannot progress (into Z/into metaphase) ✔
Many students correctly identified cell type Y but reasoning was less accurate.
