Question 21M.2.SL.TZ1.1d
| Date | May 2021 | Marks available | [Maximum mark: 1] | Reference code | 21M.2.SL.TZ1.1d |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Suggest | Question number | d | 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.]
Allium root tips continue to show some growth even at high concentrations of NVP. Suggest a possible reason for the growth seen in root tips with 800μmol NVP.
[1]
a. still some mitosis ✔
b. individual cells grow/elongate (expand by absorbing water) ✔
c. NVP is not 100 % effective / does not enter all of the cells / not all cells have come in contact with NVP ✔
d. roots have reached maximum saturation of NVP and are no longer functionally affected ✔
e. some cells are resistant to the drug ✔
Accept reasonable suggestions.
Most candidates earned this mark; some gave imaginative answers.
